Lopez, L.; Chalopin, B.; Riviere de la Souchere, A.; Fabre, C.; Treps, N.; Maitre, A.
2009-10-15
We investigate the spatial quantum properties of the light emitted by a perfectly spatially degenerate optical parametric oscillator (self-imaging optical parametric oscillator). We show that this device produces local squeezing for areas bigger than a coherence area that depends on the crystal length and pump width. Furthermore, it generates local EPR beams in the far field. We show, calculating the eigenmodes of the system, that it is highly multimode for realistic experimental parameters.
Quantum teleportation of nonclassical wave packets: An effective multimode theory
Benichi, Hugo; Takeda, Shuntaro; Lee, Noriyuki; Furusawa, Akira
2011-07-15
We develop a simple and efficient theoretical model to understand the quantum properties of broadband continuous variable quantum teleportation. We show that, if stated properly, the problem of multimode teleportation can be simplified to teleportation of a single effective mode that describes the input state temporal characteristic. Using that model, we show how the finite bandwidth of squeezing and external noise in the classical channel affect the output teleported quantum field. We choose an approach that is especially relevant for the case of non-Gaussian nonclassical quantum states and we finally back-test our model with recent experimental results.
Multimode optomechanical system in the quantum regime.
Nielsen, William Hvidtfelt Padkær; Tsaturyan, Yeghishe; Møller, Christoffer Bo; Polzik, Eugene S; Schliesser, Albert
2017-01-03
We realize a simple and robust optomechanical system with a multitude of long-lived (Q > 10(7)) mechanical modes in a phononic-bandgap shielded membrane resonator. An optical mode of a compact Fabry-Perot resonator detects these modes' motion with a measurement rate (96 kHz) that exceeds the mechanical decoherence rates already at moderate cryogenic temperatures (10 K). Reaching this quantum regime entails, inter alia, quantum measurement backaction exceeding thermal forces and thus strong optomechanical quantum correlations. In particular, we observe ponderomotive squeezing of the output light mediated by a multitude of mechanical resonator modes, with quantum noise suppression up to -2.4 dB (-3.6 dB if corrected for detection losses) and bandwidths ≲90 kHz. The multimode nature of the membrane and Fabry-Perot resonators will allow multimode entanglement involving electromagnetic, mechanical, and spin degrees of freedom.
Multimode optomechanical system in the quantum regime
NASA Astrophysics Data System (ADS)
Hvidtfelt Padkær Nielsen, William; Tsaturyan, Yeghishe; Møller, Christoffer Bo; Polzik, Eugene S.; Schliesser, Albert
2017-01-01
We realize a simple and robust optomechanical system with a multitude of long-lived (Q > 107) mechanical modes in a phononic-bandgap shielded membrane resonator. An optical mode of a compact Fabry–Perot resonator detects these modes’ motion with a measurement rate (96 kHz) that exceeds the mechanical decoherence rates already at moderate cryogenic temperatures (10 K). Reaching this quantum regime entails, inter alia, quantum measurement backaction exceeding thermal forces and thus strong optomechanical quantum correlations. In particular, we observe ponderomotive squeezing of the output light mediated by a multitude of mechanical resonator modes, with quantum noise suppression up to ‑2.4 dB (‑3.6 dB if corrected for detection losses) and bandwidths ≲90 kHz. The multimode nature of the membrane and Fabry–Perot resonators will allow multimode entanglement involving electromagnetic, mechanical, and spin degrees of freedom.
Invariant measures on multimode quantum Gaussian states
Lupo, C.; Mancini, S.; De Pasquale, A.; Facchi, P.; Florio, G.; Pascazio, S.
2012-12-15
We derive the invariant measure on the manifold of multimode quantum Gaussian states, induced by the Haar measure on the group of Gaussian unitary transformations. To this end, by introducing a bipartition of the system in two disjoint subsystems, we use a parameterization highlighting the role of nonlocal degrees of freedom-the symplectic eigenvalues-which characterize quantum entanglement across the given bipartition. A finite measure is then obtained by imposing a physically motivated energy constraint. By averaging over the local degrees of freedom we finally derive the invariant distribution of the symplectic eigenvalues in some cases of particular interest for applications in quantum optics and quantum information.
Invariant measures on multimode quantum Gaussian states
NASA Astrophysics Data System (ADS)
Lupo, C.; Mancini, S.; De Pasquale, A.; Facchi, P.; Florio, G.; Pascazio, S.
2012-12-01
We derive the invariant measure on the manifold of multimode quantum Gaussian states, induced by the Haar measure on the group of Gaussian unitary transformations. To this end, by introducing a bipartition of the system in two disjoint subsystems, we use a parameterization highlighting the role of nonlocal degrees of freedom—the symplectic eigenvalues—which characterize quantum entanglement across the given bipartition. A finite measure is then obtained by imposing a physically motivated energy constraint. By averaging over the local degrees of freedom we finally derive the invariant distribution of the symplectic eigenvalues in some cases of particular interest for applications in quantum optics and quantum information.
A Single-Photon Subtractor for Multimode Quantum States
NASA Astrophysics Data System (ADS)
Ra, Young-Sik; Jacquard, Clément; Averchenko, Valentin; Roslund, Jonathan; Cai, Yin; Dufour, Adrien; Fabre, Claude; Treps, Nicolas
2016-05-01
In the last decade, single-photon subtraction has proved to be key operations in optical quantum information processing and quantum state engineering. Implementation of the photon subtraction has been based on linear optics and single-photon detection on single-mode resources. This technique, however, becomes unsuitable with multimode resources such as spectrally multimode squeezed states or continuous variables cluster states. We implement a single-photon subtractor for such multimode resources based on sum-frequency generation and single-photon detection. An input multimode quantum state interacts with a bright control beam whose spectrum has been engineered through ultrafast pulse-shaping. The multimode quantum state resulting from the single-photon subtractor is analyzed with multimode homodyne detection whose local oscillator spectrum is independently engineered. We characterize the single-photon subtractor via coherent-state quantum process tomography, which provides its mode-selectivity and subtraction modes. The ability to simultaneously control the state engineering and its detection ensures both flexibility and scalability in the production of highly entangled non-Gaussian quantum states.
Effect of multimode entanglement on lossy optical quantum metrology
NASA Astrophysics Data System (ADS)
Knott, P. A.; Proctor, T. J.; Nemoto, Kae; Dunningham, J. A.; Munro, W. J.
2014-09-01
In optical interferometry multimode entanglement is often assumed to be the driving force behind quantum enhanced measurements. Recent work has shown this assumption to be false: single-mode quantum states perform just as well as their multimode entangled counterparts. We go beyond this to show that when photon losses occur, an inevitability in any realistic system, multimode entanglement is actually detrimental to obtaining quantum enhanced measurements. We specifically apply this idea to a superposition of coherent states, demonstrating that these states show a robustness to loss that allows them to significantly outperform their competitors in realistic systems. A practically viable measurement scheme is then presented that allows measurements close to the theoretical bound, even with loss. These results promote an alternate way of approaching optical quantum metrology using single-mode states that we expect to have great implications for the future.
Two-photon quantum walk in a multimode fiber
Defienne, Hugo; Barbieri, Marco; Walmsley, Ian A.; Smith, Brian J.; Gigan, Sylvain
2016-01-01
Multiphoton propagation in connected structures—a quantum walk—offers the potential of simulating complex physical systems and provides a route to universal quantum computation. Increasing the complexity of quantum photonic networks where the walk occurs is essential for many applications. We implement a quantum walk of indistinguishable photon pairs in a multimode fiber supporting 380 modes. Using wavefront shaping, we control the propagation of the two-photon state through the fiber in which all modes are coupled. Excitation of arbitrary output modes of the system is realized by controlling classical and quantum interferences. This report demonstrates a highly multimode platform for multiphoton interference experiments and provides a powerful method to program a general high-dimensional multiport optical circuit. This work paves the way for the next generation of photonic devices for quantum simulation, computing, and communication. PMID:27152325
Two-photon quantum walk in a multimode fiber.
Defienne, Hugo; Barbieri, Marco; Walmsley, Ian A; Smith, Brian J; Gigan, Sylvain
2016-01-01
Multiphoton propagation in connected structures-a quantum walk-offers the potential of simulating complex physical systems and provides a route to universal quantum computation. Increasing the complexity of quantum photonic networks where the walk occurs is essential for many applications. We implement a quantum walk of indistinguishable photon pairs in a multimode fiber supporting 380 modes. Using wavefront shaping, we control the propagation of the two-photon state through the fiber in which all modes are coupled. Excitation of arbitrary output modes of the system is realized by controlling classical and quantum interferences. This report demonstrates a highly multimode platform for multiphoton interference experiments and provides a powerful method to program a general high-dimensional multiport optical circuit. This work paves the way for the next generation of photonic devices for quantum simulation, computing, and communication.
Multimode circuit quantum electrodynamics with hybrid metamaterial transmission lines.
Egger, D J; Wilhelm, F K
2013-10-18
Quantum transmission lines are central to superconducting and hybrid quantum computing. In this work we show how coupling them to a left-handed transmission line allows circuit QED to reach a new regime: multimode ultrastrong coupling. Out of the many potential applications of this novel device, we discuss the preparation of multipartite entangled states and the simulation of the spin-boson model where a quantum phase transition is reached up to finite size effects.
Quantum annealing with ultracold atoms in a multimode optical resonator
NASA Astrophysics Data System (ADS)
Torggler, Valentin; Krämer, Sebastian; Ritsch, Helmut
2017-03-01
A dilutely filled N -site optical lattice near zero temperature within a high-Q multimode cavity can be mapped to a spin ensemble with tailorable interactions at all length scales. The effective full site to site interaction matrix can be dynamically controlled by the application of up to N (N +1 )/2 laser beams of suitable geometry, frequency, and power, which allows for the implementation of quantum annealing dynamics relying on the all-to-all effective spin coupling controllable in real time. Via an adiabatic sweep starting from a superfluid initial state one can find the lowest-energy stationary state of this system. As the cavity modes are lossy, errors can be amended and the ground state can still be reached even from a finite temperature state via ground-state cavity cooling. The physical properties of the final atomic state can be directly and almost nondestructively read off from the cavity output fields. As an example we simulate a quantum Hopfield associative memory scheme.
Teleporting photonic qudits using multimode quantum scissors.
Goyal, Sandeep K; Konrad, Thomas
2013-12-19
Teleportation plays an important role in the communication of quantum information between the nodes of a quantum network and is viewed as an essential ingredient for long-distance Quantum Cryptography. We describe a method to teleport the quantum information carried by a photon in a superposition of a number d of light modes (a "qudit") by the help of d additional photons based on transcription. A qudit encoded into a single excitation of d light modes (in our case Laguerre-Gauss modes which carry orbital angular momentum) is transcribed to d single-rail photonic qubits, which are spatially separated. Each single-rail qubit consists of a superposition of vacuum and a single photon in each one of the modes. After successful teleportation of each of the d single-rail qubits by means of "quantum scissors" they are converted back into a qudit carried by a single photon which completes the teleportation scheme.
Multimode squeezing, biphotons and uncertainty relations in polarization quantum optics
NASA Technical Reports Server (NTRS)
Karassiov, V. P.
1994-01-01
The concept of squeezing and uncertainty relations are discussed for multimode quantum light with the consideration of polarization. Using the polarization gauge SU(2) invariance of free electromagnetic fields, we separate the polarization and biphoton degrees of freedom from other ones, and consider uncertainty relations characterizing polarization and biphoton observables. As a consequence, we obtain a new classification of states of unpolarized (and partially polarized) light within quantum optics. We also discuss briefly some interrelations of our analysis with experiments connected with solving some fundamental problems of physics.
Multimode circuit optomechanics near the quantum limit
Massel, Francesco; Cho, Sung Un; Pirkkalainen, Juha-Matti; Hakonen, Pertti J.; Heikkilä, Tero T.; Sillanpää, Mika A.
2012-01-01
The coupling of distinct systems underlies nearly all physical phenomena. A basic instance is that of interacting harmonic oscillators, giving rise to, for example, the phonon eigenmodes in a lattice. Of particular importance are the interactions in hybrid quantum systems, which can combine the benefits of each part in quantum technologies. Here we investigate a hybrid optomechanical system having three degrees of freedom, consisting of a microwave cavity and two micromechanical beams with closely spaced frequencies around 32 MHz and no direct interaction. We record the first evidence of tripartite optomechanical mixing, implying that the eigenmodes are combinations of one photonic and two phononic modes. We identify an asymmetric dark mode having a long lifetime. Simultaneously, we operate the nearly macroscopic mechanical modes close to the motional quantum ground state, down to 1.8 thermal quanta, achieved by back-action cooling. These results constitute an important advance towards engineering of entangled motional states. PMID:22871806
Multimode circuit optomechanics near the quantum limit.
Massel, Francesco; Cho, Sung Un; Pirkkalainen, Juha-Matti; Hakonen, Pertti J; Heikkilä, Tero T; Sillanpää, Mika A
2012-01-01
The coupling of distinct systems underlies nearly all physical phenomena. A basic instance is that of interacting harmonic oscillators, giving rise to, for example, the phonon eigenmodes in a lattice. Of particular importance are the interactions in hybrid quantum systems, which can combine the benefits of each part in quantum technologies. Here we investigate a hybrid optomechanical system having three degrees of freedom, consisting of a microwave cavity and two micromechanical beams with closely spaced frequencies around 32 MHz and no direct interaction. We record the first evidence of tripartite optomechanical mixing, implying that the eigenmodes are combinations of one photonic and two phononic modes. We identify an asymmetric dark mode having a long lifetime. Simultaneously, we operate the nearly macroscopic mechanical modes close to the motional quantum ground state, down to 1.8 thermal quanta, achieved by back-action cooling. These results constitute an important advance towards engineering of entangled motional states.
Near-field hyperspectral quantum probing of multimodal plasmonic resonators
NASA Astrophysics Data System (ADS)
Cuche, A.; Berthel, M.; Kumar, U.; Colas des Francs, G.; Huant, S.; Dujardin, E.; Girard, C.; Drezet, A.
2017-03-01
Quantum systems, excited by an external source of photons, display a photodynamics that is ruled by a subtle balance between radiative or nonradiative energy channels when interacting with metallic nanostructures. We apply and generalize this concept to achieve a quantum probing of multimodal plasmonic resonators by collecting and filtering the broad emission spectra generated by a nanodiamond (ND) hosting a small set of nitrogen-vacancy (NV) color centers attached at the apex of an optical tip. Spatially and spectrally resolved information on the photonic local density of states (ph-LDOS) can be recorded with this technique in the immediate vicinity of plasmonic resonators, paving the way for a complete near-field optical characterization of any kind of nanoresonators in the single photon regime.
Magnetically engineered semiconductor quantum dots as multimodal imaging probes.
Jing, Lihong; Ding, Ke; Kershaw, Stephen V; Kempson, Ivan M; Rogach, Andrey L; Gao, Mingyuan
2014-10-08
Light-emitting semiconductor quantum dots (QDs) combined with magnetic resonance imaging contrast agents within a single nanoparticle platform are considered to perform as multimodal imaging probes in biomedical research and related clinical applications. The principles of their rational design are outlined and contemporary synthetic strategies are reviewed (heterocrystalline growth; co-encapsulation or assembly of preformed QDs and magnetic nanoparticles; conjugation of magnetic chelates onto QDs; and doping of QDs with transition metal ions), identifying the strengths and weaknesses of different approaches. Some of the opportunities and benefits that arise through in vivo imaging using these dual-mode probes are highlighted where tumor location and delineation is demonstrated in both MRI and fluorescence modality. Work on the toxicological assessments of QD/magnetic nanoparticles is also reviewed, along with progress in reducing their toxicological side effects for eventual clinical use. The review concludes with an outlook for future biomedical imaging and the identification of key challenges in reaching clinical applications.
NASA Astrophysics Data System (ADS)
Dwivedi, A.; Mishra, Kavita; Rai, S. B.
2015-11-01
This work investigates the promising multi-modal luminescence (upconversion (UC), downshifting (DS) and quantum cutting (QC)) properties of RE3+ (Tm3+, Yb3+) and Bi3+ activated GdNbO4 phosphors synthesized using the well-known solid state reaction method. Structural characterization using x-ray diffraction measurements confirms the formation of the pure phase of the GdNbO4 host with no impurities. The optical band gap (E g) of GdNbO4 (with and without RE3+ ions) calculated from UV-Vis-near-infrared (NIR) measurements was found to be the same ~4.44 eV which indicates that GdNbO4 is a wide band gap material. Further, Bi3+ doping presents an interesting E g tuning of the GdNbO4 phosphor, i.e. E g increases up to 5.38 eV. In terms of luminescence, this material produces intense blue and NIR emission via multi-modal optical processes. On NIR excitation (λ exc = 980 nm), Gd0.94Tm0.01Yb0.05NbO4 produces intense upconverted blue and NIR and relatively weak red emission. In addition to the UC process, Gd0.94Tm0.01Yb0.05NbO4 also exhibits pump power dependent variation in fluorescence intensity ratio for I 472/I 477 showing the applicability of this material as an optical heater. On UV excitation (λ exc = 265 nm), Gd0.99Tm0.01NbO4 produces intense DS blue emission due to the Tm3+ ion, overlapped with the emission of the (NbO4)3- ion through strong energy transfer (ET) from (NbO4)3- to Tm3+ ions. Interestingly, NIR QC has also been successfully observed in Gd0.9Yb0.1NbO4, Gd0.89Bi0.01Yb0.1NbO4 and Gd0.79Tm0.01Yb0.2NbO4 phosphors through cooperative ET from the (NbO4)3- group to the Yb3+ ion, Bi(6s)-Nb(4d) to the Yb3+ ion and the Tm3+ ion to the Yb3+ ion, respectively. The mechanisms involved in these processes are explained in detail in this work. The QC efficiency in this work has been found to be ~177%. Thus, the multi-modal luminescence (UC, DS and QC) property of this material makes it a promising candidate for display devices, spectral
Tumor-Targeted Multimodal Optical Imaging with Versatile Cadmium-Free Quantum Dots
Liu, Xiangyou; Braun, Gary B.; Zhong, Haizheng; Hall, David J.; Han, Wenlong; Qin, Mingde; Zhao, Chuanzhen; Wang, Meina; She, Zhi-Gang; Cao, Chuanbao; Sailor, Michael J.; Stallcup, William B.; Ruoslahti, Erkki
2016-01-01
The rapid development of fluorescence imaging technologies requires concurrent improvements in the performance of fluorescent probes. Quantum dots have been extensively used as an imaging probe in various research areas because of their inherent advantages based on unique optical and electronic properties. However, their clinical translation has been limited by the potential toxicity especially from cadmium. Here, a versatile bioimaging probe is developed by using highly luminescent cadmium-free CuInSe2/ZnS core/shell quantum dots conjugated with CGKRK (Cys–Gly–Lys–Arg–Lys) tumor-targeting peptides. This probe exhibits excellent photostability, reasonably long circulation time, minimal toxicity, and strong tumor-specific homing property. The most important feature of this probe is that it shows distinctive versatility in tumor-targeted multimodal imaging including near-infrared, time-gated, and two-photon imaging in different tumor models. In a glioblastoma mouse model, the targeted probe clearly denotes tumor boundaries and positively labels a population of diffusely infiltrating tumor cells, suggesting its utility in precise tumor detection during surgery. This work lays a foundation for potential clinical translation of the probe. PMID:27441036
Energy exchange between modes in a multimode two-color quantum dot laser with optical feedback.
Virte, Martin; Pawlus, Robert; Sciamanna, Marc; Panajotov, Krassimir; Breuer, Stefan
2016-07-15
We investigate experimentally and theoretically the multimode dynamics of a two-color quantum dot laser subject to time-delayed optical feedback. We unveil energy exchanges between the longitudinal modes of the excited state triggered by variations of the feedback phase, and observe that the modal competition between longitudinal modes appears independently within the ground state and excited state emission. These features are accurately reproduced with a quantum dot laser model extended to take into account multiple modes for both ground and excited states. Finally, we discuss the significant impact of such behavior on feedback-based control of two-color quantum dot lasers.
Gold–silica quantum rattles for multimodal imaging and therapy
Hembury, Mathew; Chiappini, Ciro; Bertazzo, Sergio; Kalber, Tammy L.; Drisko, Glenna L.; Ogunlade, Olumide; Walker-Samuel, Simon; Krishna, Katla Sai; Jumeaux, Coline; Beard, Paul; Kumar, Challa S. S. R.; Porter, Alexandra E.; Lythgoe, Mark F.; Boissière, Cédric; Sanchez, Clément; Stevens, Molly M.
2015-01-01
Gold quantum dots exhibit distinctive optical and magnetic behaviors compared with larger gold nanoparticles. However, their unfavorable interaction with living systems and lack of stability in aqueous solvents has so far prevented their adoption in biology and medicine. Here, a simple synthetic pathway integrates gold quantum dots within a mesoporous silica shell, alongside larger gold nanoparticles within the shell’s central cavity. This “quantum rattle” structure is stable in aqueous solutions, does not elicit cell toxicity, preserves the attractive near-infrared photonics and paramagnetism of gold quantum dots, and enhances the drug-carrier performance of the silica shell. In vivo, the quantum rattles reduced tumor burden in a single course of photothermal therapy while coupling three complementary imaging modalities: near-infrared fluorescence, photoacoustic, and magnetic resonance imaging. The incorporation of gold within the quantum rattles significantly enhanced the drug-carrier performance of the silica shell. This innovative material design based on the mutually beneficial interaction of gold and silica introduces the use of gold quantum dots for imaging and therapeutic applications. PMID:25653336
Gold–silica quantum rattles for multimodal imaging and therapy
Hembury, Mathew; Chiappini, Ciro; Bertazzo, Sergio; ...
2015-02-04
Gold quantum dots exhibit distinctive optical and magnetic behaviors compared with larger gold nanoparticles. However, their unfavorable interaction with living systems and lack of stability in aqueous solvents has so far prevented their adoption in biology and medicine. In this paper, a simple synthetic pathway integrates gold quantum dots within a mesoporous silica shell, alongside larger gold nanoparticles within the shell’s central cavity. This “quantum rattle” structure is stable in aqueous solutions, does not elicit cell toxicity, preserves the attractive near-infrared photonics and paramagnetism of gold quantum dots, and enhances the drug-carrier performance of the silica shell. In vivo, themore » quantum rattles reduced tumor burden in a single course of photothermal therapy while coupling three complementary imaging modalities: near-infrared fluorescence, photoacoustic, and magnetic resonance imaging. The incorporation of gold within the quantum rattles significantly enhanced the drug-carrier performance of the silica shell. Finally, this innovative material design based on the mutually beneficial interaction of gold and silica introduces the use of gold quantum dots for imaging and therapeutic applications.« less
Gold–silica quantum rattles for multimodal imaging and therapy
Hembury, Mathew; Chiappini, Ciro; Bertazzo, Sergio; Kalber, Tammy L.; Drisko, Glenna L.; Ogunlade, Olumide; Walker-Samuel, Simon; Krishna, Katla Sai; Jumeaux, Coline; Beard, Paul; Kumar, Challa S. S. R.; Porter, Alexandra E.; Lythgoe, Mark F.; Boissière, Cédric; Sanchez, Clément; Stevens, Molly M.
2015-02-04
Gold quantum dots exhibit distinctive optical and magnetic behaviors compared with larger gold nanoparticles. However, their unfavorable interaction with living systems and lack of stability in aqueous solvents has so far prevented their adoption in biology and medicine. In this paper, a simple synthetic pathway integrates gold quantum dots within a mesoporous silica shell, alongside larger gold nanoparticles within the shell’s central cavity. This “quantum rattle” structure is stable in aqueous solutions, does not elicit cell toxicity, preserves the attractive near-infrared photonics and paramagnetism of gold quantum dots, and enhances the drug-carrier performance of the silica shell. In vivo, the quantum rattles reduced tumor burden in a single course of photothermal therapy while coupling three complementary imaging modalities: near-infrared fluorescence, photoacoustic, and magnetic resonance imaging. The incorporation of gold within the quantum rattles significantly enhanced the drug-carrier performance of the silica shell. Finally, this innovative material design based on the mutually beneficial interaction of gold and silica introduces the use of gold quantum dots for imaging and therapeutic applications.
Gold-silica quantum rattles for multimodal imaging and therapy.
Hembury, Mathew; Chiappini, Ciro; Bertazzo, Sergio; Kalber, Tammy L; Drisko, Glenna L; Ogunlade, Olumide; Walker-Samuel, Simon; Krishna, Katla Sai; Jumeaux, Coline; Beard, Paul; Kumar, Challa S S R; Porter, Alexandra E; Lythgoe, Mark F; Boissière, Cédric; Sanchez, Clément; Stevens, Molly M
2015-02-17
Gold quantum dots exhibit distinctive optical and magnetic behaviors compared with larger gold nanoparticles. However, their unfavorable interaction with living systems and lack of stability in aqueous solvents has so far prevented their adoption in biology and medicine. Here, a simple synthetic pathway integrates gold quantum dots within a mesoporous silica shell, alongside larger gold nanoparticles within the shell's central cavity. This "quantum rattle" structure is stable in aqueous solutions, does not elicit cell toxicity, preserves the attractive near-infrared photonics and paramagnetism of gold quantum dots, and enhances the drug-carrier performance of the silica shell. In vivo, the quantum rattles reduced tumor burden in a single course of photothermal therapy while coupling three complementary imaging modalities: near-infrared fluorescence, photoacoustic, and magnetic resonance imaging. The incorporation of gold within the quantum rattles significantly enhanced the drug-carrier performance of the silica shell. This innovative material design based on the mutually beneficial interaction of gold and silica introduces the use of gold quantum dots for imaging and therapeutic applications.
NASA Astrophysics Data System (ADS)
Parniak, Michał; Pęcak, Daniel; Wasilewski, Wojciech
2016-11-01
We analyse the properties of a Raman quantum light-atom interface in long atomic ensemble and its applications as a quantum memory or two-mode squeezed state generator. We consider the weak-coupling regime and include both Stokes and anti-Stokes scattering and the effects of Doppler broadening in buffer gas assuming frequent velocity-averaging collisions. We find the Green functions describing multimode transformation from input to output fields of photons and atomic excitations. Proper mode basis is found via singular value decomposition for short interaction times. It reveals that triples of modes are coupled by a transformation equivalent to a combination of two beamsplitters and a two-mode squeezing operation. We analyse the possible transformations on an example of warm rubidium-87 vapour. The model we present bridges the gap between the Stokes only and anti-Stokes only interactions providing simple, universal description in a temporally and longitudinally multimode situation. Our results also provide an easy way to find an evolution of the states in a Schrödinger picture thus facilitating understanding and design.
Quantum properties of exponential states
Luis, Alfredo
2007-05-15
The use of Renyi entropy as an uncertainty measure alternative to variance leads to the study of states with quantum fluctuations below the levels established by Gaussian states, which are the position-momentum minimum uncertainty states according to variance. We examine the quantum properties of states with exponential wave functions, which combine reduced fluctuations with practical feasibility.
Near-field optical properties of quantum dots, applications and perspectives.
Zora, A; Triberis, G P; Simserides, C
2011-11-01
Recent years have witnessed tremendous research in quantum dots as excellent models of quantum physics at the nanoscale and as excellent candidates for various applications based on their optoelectronic properties. This review intends to present theoretical and experimental investigations of the near-field optical properties of these structures, and their multimodal applications such as biosensors, biological labels, optical fibers, switches and sensors, visual displays, photovoltaic devices and related patents.
Multimodal imaging probes based on Gd-DOTA conjugated quantum dot nanomicelles.
Liu, Liwei; Law, Wing-Cheung; Yong, Ken-Tye; Roy, Indrajit; Ding, Hong; Erogbogbo, Folarin; Zhang, Xihe; Prasad, Paras N
2011-05-07
Recently, multimodal nanoparticles integrating dual- or tri-imaging modalities into a single hybrid nanosystem have attracted plenty of attention in biomedical research. Here, we report the fabrication of two types of multimodal micelle-encapsulated nanoparticles, which were systematically characterized and thoroughly evaluated in terms of their imaging potential and biocompatibility. Optical and magnetic resonance (MR) imaging probes were integrated by conjugating DOTA-gadolinium (Gd) derivative to quantum dot based nanomicelles. Two amphiphilic block copolymer micelles, amine-terminated mPEG-phospholipid and amine-modified Pluronic F127, were chosen as the capping agents because of their excellent biocompatibility and ability to prevent opsonization and prolong circulation time in vivo. Owing to their different hydrophobic-hydrophilic structure, the micellar aggregates exhibited different sizes and protection of core QDs. This work revealed the differences between these nanomicelles in terms of the stability over a wide range of pH, along with their cytotoxicity and the capacity for chelating gadolinium, thus providing a useful guideline for tailor-making multimodal nanoparticles for specific biomedical applications.
Mn-doped near-infrared quantum dots as multimodal targeted probes for pancreatic cancer imaging
NASA Astrophysics Data System (ADS)
Yong, Ken-Tye
2009-01-01
This work presents a novel approach to producing manganese (Mn)-doped quantum dots (Mnd-QDs) emitting in the near-infrared (NIR). Surface functionalization of Mnd-QDs with lysine makes them stably disperse in aqueous media and able to conjugate with targeting molecules. The nanoparticles were structurally and compositionally characterized and maintained a high photoluminescence quantum yield and displayed paramagnetism in water. The receptor-mediated delivery of bioconjugated Mnd-QDs into pancreatic cancer cells was demonstrated using the confocal microscopy technique. Cytotoxicity of Mnd-QDs on live cells has been evaluated. The NIR-emitting characteristic of the QDs has been exploited to acquire whole animal body imaging with high contrast signals. In addition, histological and blood analysis of mice have revealed that no long-term toxic effects arise from MnD-QDs. These studies suggest multimodal Mnd-QDs have the potentials as probes for early pancreatic cancer imaging and detection.
Multimode dynamics in quantum cascade lasers: From coherent instability to mode locking
NASA Astrophysics Data System (ADS)
Wang, Christine Yi-Ting
Quantum Cascade Lasers (QCLs) are unipolar semiconductor lasers based on intersubband transitions in quantum wells. Since their invention in 1994, these lasers have undergone tremendous improvement, and have become the most prominent coherent light source in the mid-infrared and terahertz spectral ranges. However, the understanding of multimode regimes in QCLs is still in its infancy, and there has not been much effort toward generating ultrafast pulses from QCLs. The recent development of low loss, high power QCLs enables the study of those previously under-investigated aspects. This thesis can be divided into two main parts. In the first part, we study the multimode regimes in QCLs. We find that QCLs, because of their extremely fast gain recovery time, differ from diode lasers in multimode operation. While a saturable absorber can often lead to self mode-locking in lasers with long gain recovery compared to the cavity round-trip time, in QCLs it lowers the threshold of a coherent multimode instability, which is driven by the same fundamental mechanism of Rabi oscillations as the elusive Risken-Nummedal-Graham-Haken (RNGH) instability predicted 40 years ago. The main experimental signature of RNGH instability is a splitting corresponding to twice the Rabi frequency in optical spectrum. In QCLs this coherent instability is enhanced due to the large Rabi frequency compared to the relaxation rates. We have also shown that spatial hole burning, which is not so readily observable in diode lasers, also plays an important role in QCLs. Both experimental data and simulations based on Maxwell-Bloch equations are presented. In the second part of this thesis, we demonstrate active mode-locking in QCLs. The stable mode-locked pulse train was generated by actively modulating the pumping current of a small section on a QCL. Stable mode locking was confirmed by second-order interferometric autocorrelation measurements, and a FWHM of 3 ps and about 0.5 pJ per pulse were deduced
NASA Astrophysics Data System (ADS)
Schneeweiss, Philipp; Zeiger, Sophie; Hoinkes, Thomas; Rauschenbeutel, Arno; Volz, Jürgen
2017-01-01
We experimentally realize an optical fiber ring resonator that includes a tapered section with subwavelength-diameter waist. In this section, the guided light exhibits a significant evanescent field which allows for efficient interfacing with optical emitters. A commercial tunable fiber beam splitter provides simple and robust coupling to the resonator. Key parameters of the resonator such as its out-coupling rate, free spectral range, and birefringence can be adjusted. Thanks to the low taper- and coupling-losses, the resonator exhibits an unloaded finesse of F=75+/-1, sufficient for reaching the regime of strong coupling for emitters placed in the evanescent field. The system is ideally suited for trapping ensembles of laser-cooled atoms along the nanofiber section. Based on measured parameters, we estimate that the system can serve as a platform for optical multimode strong coupling experiments. Finally, we discuss the possibilities of using the resonator for applications based on chiral quantum optics.
Schneeweiss, Philipp; Zeiger, Sophie; Hoinkes, Thomas; Rauschenbeutel, Arno; Volz, Jürgen
2017-01-01
We experimentally realize an optical fiber ring resonator that includes a tapered section with a subwavelength-diameter waist. In this section, the guided light exhibits a significant evanescent field which allows for efficient interfacing with optical emitters. A commercial tunable fiber beam splitter provides simple and robust coupling to the resonator. Key parameters of the resonator such as the out-coupling rate, free spectral range, and birefringence can be adjusted. Thanks to the low taper- and coupling-losses, the resonator exhibits an unloaded finesse of F=75±1, sufficient for reaching the regime of strong coupling for emitters placed in the evanescent field. The system is ideally suited for trapping ensembles of laser-cooled atoms along the nanofiber section. Based on measured parameters, we estimate that the system can serve as a platform for optical multimode strong coupling experiments. Finally, we discuss the possibilities of using the resonator for applications based on chiral quantum optics.
Multimodality and interactivity: connecting properties of serious games with educational outcomes.
Ritterfeld, Ute; Shen, Cuihua; Wang, Hua; Nocera, Luciano; Wong, Wee Ling
2009-12-01
Serious games have become an important genre of digital media and are often acclaimed for their potential to enhance deeper learning because of their unique technological properties. Yet the discourse has largely remained at a conceptual level. For an empirical evaluation of educational games, extra effort is needed to separate intertwined and confounding factors in order to manipulate and thus attribute the outcome to one property independent of another. This study represents one of the first attempts to empirically test the educational impact of two important properties of serious games, multimodality and interactivity, through a partial 2 x 3 (interactive, noninteractive by high, moderate, low in multimodality) factorial between-participants follow-up experiment. Results indicate that both multimodality and interactivity contribute to educational outcomes individually. Implications for educational strategies and future research directions are discussed.
Schindler, Torben; Walter, Johannes; Peukert, Wolfgang; Segets, Doris; Unruh, Tobias
2015-12-10
Properties of small semiconductor nanoparticles (NPs) are strongly governed by their size. Precise characterization is a key requirement for tailored dispersities and thus for high-quality devices. Results of a careful analysis of particle size distributions (PSDs) of ZnO are presented combining advantages of UV/vis absorption spectroscopy, analytical ultracentrifugation, and small-angle X-ray scattering (SAXS). Our study reveals that careful cross-validation of these different methods is mandatory to end up with reliable resolution. PSDs of ZnO NPs are multimodal on a size range of 2-8 nm, a finding that is not yet sufficiently addressed. In the second part of our work the evolution of PSDs was studied using in situ SAXS. General principles for the appearance of multimodalities covering a temperature range between 15 and 45 °C were found which are solely determined by the aging state indicated by the size of the medium-sized fraction. Whenever this fraction exceeds a critical diameter, a new multimodality is identified, independent of the particular time-temperature combination. A fraction of larger particles aggregates first before a fraction of smaller particles is detected. Fixed multimodalities have not yet been addressed adequately and could only be evidenced due to careful size analysis.
Center-of-mass motion as a sensitive convergence test for variational multimode quantum dynamics
NASA Astrophysics Data System (ADS)
Cosme, Jayson G.; Weiss, Christoph; Brand, Joachim
2016-10-01
Multimode expansions in computational quantum dynamics promise convergence toward exact results upon increasing the number of modes. Convergence is difficult to ascertain in practice due to the unfavorable scaling of required resources for many-particle problems and therefore a simplified criterion based on a threshold value for the least occupied mode function is often used. Here we show how the separable quantum motion of the center of mass can be used to sensitively detect unconverged numerical multiparticle dynamics in harmonic potentials. Based on an experimentally relevant example of attractively interacting bosons in one dimension, we demonstrate that the simplified convergence criterion fails to assure qualitatively correct results. Furthermore, the numerical evidence for the creation of two-hump fragmented bright soliton-like states presented by A. I. Streltsov et al. [Phys. Rev. Lett. 100, 130401 (2008), 10.1103/PhysRevLett.100.130401] is shown to be inconsistent with exact results. Implications for understanding dynamical fragmentation in attractive boson systems are briefly discussed.
Determining surface properties with bimodal and multimodal AFM.
Forchheimer, D; Borysov, Stanislav S; Platz, D; Haviland, David B
2014-12-05
Conventional dynamic atomic force microscopy (AFM) can be extended to bimodal and multimodal AFM in which the cantilever is simultaneously excited at two or more resonance frequencies. Such excitation schemes result in one additional amplitude and phase images for each driven resonance, and potentially convey more information about the surface under investigation. Here we present a theoretical basis for using this information to approximate the parameters of a tip-surface interaction model. The theory is verified by simulations with added noise corresponding to room-temperature measurements.
NASA Astrophysics Data System (ADS)
Bahadur, A.; Yadav, R. S.; Yadav, R. V.; Rai, S. B.
2017-02-01
This paper reports the optical properties of Tb3+/Yb3+ co-doped lithium borate (LB) glass prepared by melt quench method. The absorption spectrum of the Yb3+ doped LB glass contains intense NIR band centered at 976 nm due to 2F7/2→2F5/2 transition. The emission spectra of the prepared glasses have been monitored on excitation with 266, 355 and 976 nm. The Yb3+ doped glass emits a broad NIR band centered at 976 nm whereas the Tb3+ doped glass gives off visible bands on excitations with 266 and 355 nm. When the Tb3+ and Yb3+ ions are co-doped together, the emission intensity in the visible region decreases whereas it increases in the NIR region significantly. The increase in the emission intensity in the NIR region is due to efficient cooperative energy transfer (CET) from Tb3+ to Yb3+ ions. The quantum cutting efficiency for Tb3+/Yb3+ co-doped glass has been calculated and compared for 266 and 355 nm excitations. The quantum cutting efficiency is larger for 355 nm excitation (137%). The Tb3+/Yb3+ co-doped LB glass also emits upconverted visible bands on excitation with 976 nm. The mechanisms involved in the energy transfer have been discussed using schematic energy level diagram. The Tb3+/Yb3+ co-doped LB glass may be used in the optical devices and in solar cell for solar spectral conversion and behaves as a multi-modal photo-luminescent material.
Multimode analysis of highly tunable, quantum cascade powered, circular graphene spaser
Jayasekara, Charith Premaratne, Malin; Stockman, Mark I.; Gunapala, Sarath D.
2015-11-07
We carried out a detailed analysis of a circular graphene spaser made of a circular graphene flake and a quantum cascade well structure. Owing to unique properties of graphene and quantum cascade well structure, the proposed design shows high mechanical and thermal stability and low optical losses. Additionally, operation characteristics of the model are analysed and tunability of the device is demonstrated. Some advantages of the proposed design include compact size, lower power operation, and the ability to set the operating wavelength over a wide range from Mid-IR to Near-IR. Thus, it can have wide spread applications including designing of ultracompact and ultrafast devices, nanoscopy and biomedical applications.
NASA Astrophysics Data System (ADS)
Sitbon, Gary; Bouccara, Sophie; Tasso, Mariana; Francois, Aurélie; Bezdetnaya, Lina; Marchal, Frédéric; Beaumont, Marine; Pons, Thomas
2014-07-01
The development of sensitive multimodal contrast agents is a key issue to provide better global, multi-scale images for diagnostic or therapeutic purposes. Here we present the synthesis of Zn-Cu-In-(S, Se)/Zn1-xMnxS core-shell quantum dots (QDs) that can be used as markers for both near-infrared fluorescence imaging and magnetic resonance imaging (MRI). We first present the synthesis of Zn-Cu-In-(S, Se) cores coated with a thick ZnS shell doped with various proportions of Mn. Their emission wavelengths can be tuned over the NIR optical window suitable for deep tissue imaging. The incorporation of manganese ions (up to a few thousand ions per QD) confers them a paramagnetic character, as demonstrated by structural analysis and electron paramagnetic resonance spectroscopy. These QDs maintain their optical properties after transfer to water using ligand exchange. They exhibit T1-relaxivities up to 1400 mM-1 [QD] s-1 at 7 T and 300 K. We finally show that these QDs are suitable multimodal in vivo probes and demonstrate MRI and NIR fluorescence detection of regional lymph nodes in mice.The development of sensitive multimodal contrast agents is a key issue to provide better global, multi-scale images for diagnostic or therapeutic purposes. Here we present the synthesis of Zn-Cu-In-(S, Se)/Zn1-xMnxS core-shell quantum dots (QDs) that can be used as markers for both near-infrared fluorescence imaging and magnetic resonance imaging (MRI). We first present the synthesis of Zn-Cu-In-(S, Se) cores coated with a thick ZnS shell doped with various proportions of Mn. Their emission wavelengths can be tuned over the NIR optical window suitable for deep tissue imaging. The incorporation of manganese ions (up to a few thousand ions per QD) confers them a paramagnetic character, as demonstrated by structural analysis and electron paramagnetic resonance spectroscopy. These QDs maintain their optical properties after transfer to water using ligand exchange. They exhibit T1-relaxivities
Fractal properties of quantum spacetime.
Benedetti, Dario
2009-03-20
We show that, in general, a spacetime having a quantum group symmetry has also a scale-dependent fractal dimension which deviates from its classical value at short scales, a phenomenon that resembles what is observed in some approaches to quantum gravity. In particular, we analyze the cases of a quantum sphere and of kappa-Minkowski spacetime, the latter being relevant in the context of quantum gravity.
Electronic properties of aperiodic quantum dot chains
NASA Astrophysics Data System (ADS)
Korotaev, P. Yu.; Vekilov, Yu. Kh.; Kaputkina, N. E.
2012-04-01
The electronic spectral and transport properties of aperiodic quantum dot chains are investigated. The systems with singular continuous energy spectrum are considered: Thue-Morse chain, double-periodic chain, Rudin-Shapiro chain. The influence of electronic energy in quantum dot on the spectral properties, band structure, density of states and spectral resistivity, is discussed. Low resistivity regions correspond to delocalized states and these states could be current states. Also we discuss the magnetic field application as the way to tune electronic energy in quantum dot and to obtain metallic or insulating conducting states of the systems.
Quantum optical properties in plasmonic systems
NASA Astrophysics Data System (ADS)
Ooi, C. H. Raymond
2015-04-01
Plasmonic metallic particle (MP) can affect the optical properties of a quantum system (QS) in a remarkable way. We develop a general quantum nonlinear formalism with exact vectorial description for the scattered photons by the QS. The formalism enables us to study the variations of the dielectric function and photon spectrum of the QS with the particle distance between QS and MP, exciting laser direction, polarization and phase in the presence of surface plasmon resonance (SPR) in the MP. The quantum formalism also serves as a powerful tool for studying the effects of these parameters on the nonclassical properties of the scattered photons. The plasmonic effect of nanoparticles has promising possibilities as it provides a new way for manipulating quantum optical properties of light in nanophotonic systems.
Monogamy properties of quantum and classical correlations
Giorgi, Gian Luca
2011-11-15
In contrast with entanglement, as measured by concurrence, in general, quantum discord does not possess the property of monogamy; that is, there is no tradeoff between the quantum discord shared by a pair of subsystems and the quantum discord that both of them can share with a third party. Here, we show that, as far as monogamy is considered, quantum discord of pure states is equivalent to the entanglement of formation. This result allows one to analytically prove that none of the pure three-qubit states belonging to the subclass of W states is monogamous. A suitable physical interpretation of the meaning of the correlation information as a quantifier of monogamy for the total information is also given. Finally, we prove that, for rank 2 two-qubit states, discord and classical correlations are bounded from above by single-qubit von Neumann entropies.
NASA Astrophysics Data System (ADS)
Huang, H.; Arsenijević, D.; Schires, K.; Sadeev, T.; Bimberg, D.; Grillot, F.
2016-12-01
Quantum dot lasers are envisioned to be the next generation of optical transmitters used for short-reach communication links, owing to their low threshold current and high temperature operation. However, in a context of steady increase in both speed and reach, quantum dot lasers emitting on their upper energy levels have been recently of greater interest as they are touted for their faster modulation dynamics. This work aims at further evaluating the potential impact of such lasers in communication links by characterizing their long-delay optical feedback responses as well as the role of the lasing states on the multimode dynamics of InAs/GaAs quantum-dot Fabry-Perot devices sharing the same design. Results unveil that the excited-state laser shows a much larger sensitivity to optical feedback, with a more complex route to chaos, and a first destabilization point occurring at lower feedback strengths than for a comparable ground-state laser, which remains almost unaffected.
Koole, Rolf; van Schooneveld, Matti M; Hilhorst, Jan; Castermans, Karolien; Cormode, David P; Strijkers, Gustav J; de Mello Donegá, Celso; Vanmaekelbergh, Daniel; Griffioen, Arjan W; Nicolay, Klaas; Fayad, Zahi A; Meijerink, Andries; Mulder, Willem J M
2008-12-01
Silica particles as a nanoparticulate carrier material for contrast agents have received considerable attention the past few years, since the material holds great promise for biomedical applications. A key feature for successful application of this material in vivo is biocompatibility, which may be significantly improved by appropriate surface modification. In this study, we report a novel strategy to coat silica particles with a dense monolayer of paramagnetic and PEGylated lipids. The silica nanoparticles carry a quantum dot in their center and are made target-specific by the conjugation of multiple alphavbeta3-integrin-specific RGD-peptides. We demonstrate their specific uptake by endothelial cells in vitro using fluorescence microscopy, quantitative fluorescence imaging, and magnetic resonance imaging. The lipid-coated silica particles introduced here represent a new platform for nanoparticulate multimodality contrast agents.
Koole, Rolf; van Schooneveld, Matti M.; Hilhorst, Jan; Castermans, Karolien; Cormode, David P.; Strijkers, Gustav J.; de Mello Donegá, Celso; Vanmaekelbergh, Daniel; Griffioen, Arjan W.; Nicolay, Klaas; Fayad, Zahi A.; Meijerink, Andries; Mulder, Willem J. M.
2012-01-01
Silica particles as a nanoparticulate carrier material for contrast agents have received considerable attention the past few years, since the material holds great promise for biomedical applications. A key feature for successful application of this material in vivo is biocompatibility, which may be significantly improved by appropriate surface modification. In this study we report a novel strategy to coat silica particles with a dense monolayer of paramagnetic and PEGylated lipids. The silica nanoparticles carry a quantum dot in their centre and are made target-specific by the conjugation of multiple αvβ3-integrin-specifc RGD-peptides. We demonstrate their specific uptake by endothelial cells in vitro using fluorescence microscopy, quantitative fluorescence imaging and magnetic resonance imaging. The lipid coated silica particles introduced here represent a new platform for nanoparticulate multimodality contrast agents. PMID:19035793
Multi-mode of Four and Six Wave Parametric Amplified Process
Zhu, Dayu; Yang, Yiheng; Zhang, Da; Liu, Ruizhou; Ma, Danmeng; Li, Changbiao; Zhang, Yanpeng
2017-01-01
Multiple quantum modes in correlated fields are essential for future quantum information processing and quantum computing. Here we report the generation of multi-mode phenomenon through parametric amplified four- and six-wave mixing processes in a rubidium atomic ensemble. The multi-mode properties in both frequency and spatial domains are studied. On one hand, the multi-mode behavior is dominantly controlled by the intensity of external dressing effect, or nonlinear phase shift through internal dressing effect, in frequency domain; on the other hand, the multi-mode behavior is visually demonstrated from the images of the biphoton fields directly, in spatial domain. Besides, the correlation of the two output fields is also demonstrated in both domains. Our approach supports efficient applications for scalable quantum correlated imaging. PMID:28255163
Multi-mode of Four and Six Wave Parametric Amplified Process
NASA Astrophysics Data System (ADS)
Zhu, Dayu; Yang, Yiheng; Zhang, Da; Liu, Ruizhou; Ma, Danmeng; Li, Changbiao; Zhang, Yanpeng
2017-03-01
Multiple quantum modes in correlated fields are essential for future quantum information processing and quantum computing. Here we report the generation of multi-mode phenomenon through parametric amplified four- and six-wave mixing processes in a rubidium atomic ensemble. The multi-mode properties in both frequency and spatial domains are studied. On one hand, the multi-mode behavior is dominantly controlled by the intensity of external dressing effect, or nonlinear phase shift through internal dressing effect, in frequency domain; on the other hand, the multi-mode behavior is visually demonstrated from the images of the biphoton fields directly, in spatial domain. Besides, the correlation of the two output fields is also demonstrated in both domains. Our approach supports efficient applications for scalable quantum correlated imaging.
The lifetime and attenuation properties measurements of a US/MR multimodality molecular probe.
Liao, Ai-Ho; Shen, Che-Chou; Cheng, Chih-Hao; Chuang, Ho-Chiao; Lin, Chin-Hsiang
2013-01-01
In our previous studies we explored the potential of using a combined US/magnetic resonance (MR) multimodality contrast agent, albumin-gadolinium-diethylenetriaminepentacetate (Gd-DTPA) MBs, to induce BBB opening and for distinguishing between FUS-induced BBB opening and intracerebral hemorrhage in MR T1-weighted contrast imaging. According to the previous study in the literature, 1-2 µm bubbles have more pronounced acoustic activity at frequencies above 10 MHz. The present study developed a new targeted US/MR multimodality MB and the acoustic properties were compared with two commercial MBs, SonoVue and Targestar SA. The acoustic activities of these 1.15-2.78 µm MBs with different shells at 10 MHz were investigated. The feasibility of designing a new targeted US/MR multimodality MB was investigated. The lifetime (survival of MBs in the liquid suspension) and attenuation properties of lipid MBs (SonoVue and Targestar SA), albumin-(Gd-DTPA) MBs, and avidin-conjugated albumin (avidin-albumin)-(Gd-DTPA) MBs at 10 MHz were investigated with the pulse-echo substitution method. It was found that incorporating avidin into the albumin MBs and avidin-albumin-(Gd-DTPA) MBs affects the size distribution but does not affect the concentration of MBs produced. The avidin-albumin-shelled MBs had more significant nonlinear activity at 4-18 MHz (p=0.025), while the nonlinear activity of the other MBs peaked at 6-24 MHz (p=0.003-0.044). Moreover, the incorporation of paramagnetic metal ions into the MB shells increased their attenuation coefficients. With regard to the lifetime of these agents, the attenuations of the SonoVue and Targestar SA lipid MBs were 87.96% and 8.74%, respectively, while those of albumin MBs, avidin-albumin MBs, albumin-(Gd-DTPA) MBs, and avidin-albumin-(Gd-DTPA) MBs were 49.52%, 41.38%, 74.69%, and 100%, respectively. Avidin conjugation decreased the lifetime of the albumin MBs, but not that of the lipid MBs. The incorporation of paramagnetic metal ions
Contractivity properties of a quantum diffusion semigroup
NASA Astrophysics Data System (ADS)
Datta, Nilanjana; Pautrat, Yan; Rouzé, Cambyse
2017-01-01
We consider a quantum generalization of the classical heat equation and study contractivity properties of its associated semigroup. We prove a Nash inequality and a logarithmic Sobolev inequality. The former leads to an ultracontractivity result. This in turn implies that the largest eigenvalue and the purity of a state with positive Wigner function, evolving under the action of the semigroup, decrease at least inverse polynomially in time, while its entropy increases at least logarithmically in time.
Nonclassical properties and quantum resources of hierarchical photonic superposition states
Volkoff, T. J.
2015-11-15
We motivate and introduce a class of “hierarchical” quantum superposition states of N coupled quantum oscillators. Unlike other well-known multimode photonic Schrödinger-cat states such as entangled coherent states, the hierarchical superposition states are characterized as two-branch superpositions of tensor products of single-mode Schrödinger-cat states. In addition to analyzing the photon statistics and quasiprobability distributions of prominent examples of these nonclassical states, we consider their usefulness for highprecision quantum metrology of nonlinear optical Hamiltonians and quantify their mode entanglement. We propose two methods for generating hierarchical superpositions in N = 2 coupled microwave cavities, exploiting currently existing quantum optical technology for generating entanglement between spatially separated electromagnetic field modes.
NASA Astrophysics Data System (ADS)
Ji, Se-Wan; Kim, M. S.; Nha, Hyunchul
2015-04-01
It is a topic of fundamental and practical importance how a quantum correlated state can be reliably distributed through a noisy channel for quantum information processing. The concept of quantum steering recently defined in a rigorous manner is relevant to study it under certain circumstances and here we address quantum steerability of Gaussian states to this aim. In particular, we attempt to reformulate the criterion for Gaussian steering in terms of local and global purities and show that it is sufficient and necessary for the case of steering a 1-mode system by an N-mode system. It subsequently enables us to reinforce a strong monogamy relation under which only one party can steer a local system of 1-mode. Moreover, we show that only a negative partial-transpose state can manifest quantum steerability by Gaussian measurements in relation to the Peres conjecture. We also discuss our formulation for the case of distributing a two-mode squeezed state via one-way quantum channels making dissipation and amplification effects, respectively. Finally, we extend our approach to include non-Gaussian measurements, more precisely, all orders of higher-order squeezing measurements, and find that this broad set of non-Gaussian measurements is not useful to demonstrate steering for Gaussian states beyond Gaussian measurements.
Time-Dependent Properties of Multimodal Polyoxymethylene Based Binder for Powder Injection Molding
NASA Astrophysics Data System (ADS)
Gonzalez-Gutierrez, Joamin; Stringari, Gustavo Beulke; Zupancic, Barbara; Kubyshkina, Galina; Bernstorff, Bernd Von; Emri, Igor
Powder injection molding (PIM) is one of the most versatile methods for the manufacturing of small complex shaped components from metal, ceramic or cemented carbide powders for the use in many applications. PIM consists of mixing the powder and a polymeric binder, injecting this mixture in a mold, debinding and then sintering. Catalytic debinding of polyoxymethylene (POM) is attractive since it shows high debinding rates and low risk of cracking. This work examines the possibility of using POM with bimodal molecular mass distribution as the main component of the binding agent by studying its time-dependent properties and comparing them to monomodal POM. Furthermore, possible optimization of the binder formulation was investigated by the addition of shorter polymeric chains (wax) to bimodal POM, as to create a multimodal material. It was observed that the magnitude of the complex viscosity for the commercial bimodal material was more than 2 times lower than for the chemically identical monomodal POM within the investigated frequency range and temperature. Viscosity values were observed to drop as the content of wax was increased, without compromising the binders mechanical properties in solid state. A new formulation of bimodal POM plus 8 wt.% of added wax provided the most appropriate results from investigated combinations. This work has shown how the addition of short polymeric chains in POM influences its time-dependent properties in solid and molten state, which can be an important tool for the optimization of binders designed to be used in PIM technology.
Quantum chaos and electron transport properties in a quantum waveguide
NASA Astrophysics Data System (ADS)
Lee, Hoshik
We numerically investigate electron transport properties in an electron waveguide which can be constructed in 2DEG of the heterostructure of GaAs and AlGaAs. We apply R-matrix theory to solve a Schrodinger equation and construct a S-matrix, and we then calculate conductance of an electron waveguide. We study single impurity scattering in a waveguide. A delta-function model as a single impurity is very attractive, but it has been known that delta-function potential does not give a convergent result in two or higher space dimensions. However, we find that it can be used as a single impurity in a waveguide with the truncation of the number of modes. We also compute conductance for a finite size impurity by using R-matrix theory. We propose an appropriate criteria for determining the cut-off mode for a delta-function impurity that reproduces the conductance of a waveguide when a finite impurity presents. We find quantum scattering echoes in a ripple waveguide. A ripple waveguide (or cavity) is widely used for quantum chaos studies because it is easy to control a particle's dynamics. Moreover we can obtain an exact expression of Hamiltonian matrix with for the waveguide using a simple coordinate transformation. Having an exact Hamiltonian matrix reduces computation time significantly. It saves a lot of computational needs. We identify three families of resonance which correspond to three different classical phase space structures. Quasi bound states of one of those resonances reside on a hetero-clinic tangle formed by unstable manifolds and stable manifolds in the phase space of a corresponding classical system. Resonances due to these states appear in the conductance in a nearly periodic manner as a function of energy. Period from energy frequency gives a good agreement with a prediction of the classical theory. We also demonstrate wavepacket dynamics in a ripple waveguide. We find quantum echoes in the transmitted probability of a wavepacket. The period of echoes also
NASA Astrophysics Data System (ADS)
Ye, Yuanxin; Shen, Li
2016-06-01
Automatic matching of multi-modal remote sensing images (e.g., optical, LiDAR, SAR and maps) remains a challenging task in remote sensing image analysis due to significant non-linear radiometric differences between these images. This paper addresses this problem and proposes a novel similarity metric for multi-modal matching using geometric structural properties of images. We first extend the phase congruency model with illumination and contrast invariance, and then use the extended model to build a dense descriptor called the Histogram of Orientated Phase Congruency (HOPC) that captures geometric structure or shape features of images. Finally, HOPC is integrated as the similarity metric to detect tie-points between images by designing a fast template matching scheme. This novel metric aims to represent geometric structural similarities between multi-modal remote sensing datasets and is robust against significant non-linear radiometric changes. HOPC has been evaluated with a variety of multi-modal images including optical, LiDAR, SAR and map data. Experimental results show its superiority to the recent state-of-the-art similarity metrics (e.g., NCC, MI, etc.), and demonstrate its improved matching performance.
Truncated correlation hierarchy schemes for driven-dissipative multimode quantum systems
NASA Astrophysics Data System (ADS)
Casteels, W.; Finazzi, S.; Le Boité, A.; Storme, F.; Ciuti, C.
2016-09-01
We present a method to describe driven-dissipative multi-mode systems by considering a truncated hierarchy of equations for the correlation functions. We consider two hierarchy truncation schemes with a global cutoff on the correlation order, which is the sum of the exponents of the operators involved in the correlation functions: a ‘hard’ cutoff corresponding to an expansion around the vacuum, which applies to a regime where the number of excitations per site is small; a ‘soft’ cutoff which corresponds to an expansion around coherent states, which can be applied for large excitation numbers per site. This approach is applied to describe the bunching-antibunching crossover in the driven-dissipative Bose-Hubbard model for photonic systems. The results have been successfully benchmarked by comparison with calculations based on the corner-space renormalization method in 1D and 2D systems. The regime of validity and strengths of the present truncation methods are critically discussed.
Quantum properties of charged ferroelectric domain walls
NASA Astrophysics Data System (ADS)
Sturman, B.; Podivilov, E.; Stepanov, M.; Tagantsev, A.; Setter, N.
2015-12-01
We consider the properties of charged domain walls in ferroelectrics as a quantum problem. This includes determination of self-consistent attracting 1D potential for compensating charge carriers, the number and positions of discrete energy levels in this potential, dependencies on the ferroelectric characteristics, as well as the spatial structure and formation energy of the wall. Our description is based on the Hartree and Thomas-Fermi methods and Landau theory for the ferroelectric transitions. Changeover from a few to many quantum levels (with the electron binding energies ˜1 eV) is controlled by a single characteristic parameter. The quantum models well describe the core of the wall, whose width is typically ˜10 nm. Additionally, the walls possess pronounced long-range tails which are due to trap recharging. For the trap concentration Nt=(1017-1018) cm-3 , the tail length ℓ is of the μ m scale. On the distances much larger than ℓ the walls are electrically uncoupled from each other and the crystal faces.
NASA Astrophysics Data System (ADS)
Yadav, Ranvijay; Singh, S. K.; Verma, R. K.; Rai, S. B.
2014-04-01
Micro-crystalline Y2O3 phosphor co-doped with Yb3+/Tm3+ has been synthesized and characterized. The phosphor material gives efficient multimodal emission via downshifting (DS), upconversion (UC), and downconversion (DC)/quantum cutting (QC) luminescence processes. Cross relaxation and co-operative energy transfer (CET) have been ascribed as the possible mechanism for QC; as result of which a UV/blue photon absorbed by Tm3+ splits into two near infrared photons (wavelength range 950-1050 nm) emitted by Yb3+. The Yb3+ concentration dependent ET efficiency and QC efficiency has also been evaluated. Such multi-mode emitting phosphors could have potential applications in increasing the conversion efficiency of solar cells via spectral modification.
Structural properties of the human corpus callosum: Multimodal assessment and sex differences.
Björnholm, L; Nikkinen, J; Kiviniemi, V; Nordström, T; Niemelä, S; Drakesmith, M; Evans, J C; Pike, G B; Veijola, J; Paus, T
2017-02-22
A number of structural properties of white matter can be assessed in vivo using multimodal magnetic resonance imaging (MRI). We measured profiles of R1 and R2 relaxation rates, myelin water fraction (MWF) and diffusion tensor measures (fractional anisotropy [FA], mean diffusivity [MD]) across the mid-sagittal section of the corpus callosum in two samples of young individuals. In Part 1, we compared histology-derived axon diameter (Aboitiz et al., 1992) to MRI measures obtained in 402 young men (19.55 ± 0.84 years) recruited from the Avon Longitudinal Study on Parents and Children. In Part 2, we examined sex differences in FA, MD and magnetization transfer ratio (MTR) across the corpus callosum in 433 young (26.50 ± 0.51 years) men and women recruited from the Northern Finland Birth Cohort 1986. We found that R1, R2, and MWF follow the anterior-to-posterior profile of small-axon density. Sex differences in mean MTR were similar across the corpus callosum (males > females) while these in FA differed by the callosal segment (Body: M>F; Splenium: F>M). We suggest that the values of R1, R2 and MWF are driven by high surface area of myelin in regions with high density of "small axons".
Multimode mediated qubit-qubit coupling and dark-state symmetries in circuit quantum electrodynamics
Filipp, S.; Goeppl, M.; Fink, J. M.; Baur, M.; Bianchetti, R.; Steffen, L.; Wallraff, A.
2011-06-15
Microwave cavities with high quality factors enable coherent coupling of distant quantum systems. Virtual photons lead to a transverse interaction between qubits when they are nonresonant with the cavity but resonant with each other. We experimentally investigate the inverse scaling of the interqubit coupling with the detuning from a cavity mode and its proportionality to the qubit-cavity interaction strength. We demonstrate that the enhanced coupling at higher frequencies is mediated by multiple higher-harmonic cavity modes. Moreover, we observe dark states of the coupled qubit-qubit system and analyze their relation to the symmetry of the applied driving field at different frequencies.
Spectral Properties of Fractional Quantum Hall Hamiltonians
NASA Astrophysics Data System (ADS)
Weerasinghe, Amila
The fractional quantum Hall (FQH) effect plays a prominent role in the study of topological phases of matter and of strongly correlated electron systems in general. FQH systems have been demonstrated to show many interesting novel properties such as fractional charges, and are believed to harbor even more intriguing phenomena such as fractional statistics. However, there remain many interesting questions to be addressed in this regime. The work reported in this thesis aims to push the envelope of our understanding of the low-energy properties of FQH states using microscopic principles. In the first part of the thesis, we present a systematic perturbative approach to study excitations in the thin cylinder/torus limit of the quantum Hall states. The approach is applied to the Haldane-Rezayi and Gaffnian quantum Hall states, which are both expected to have gapless excitations in the usual two-dimensional thermodynamic limit. For the Haldane-Rezayi state, we confirm that gapless excitations are present also in the "one-dimensional" thermodynamic limit of an infinite thin cylinder, in agreement with earlier considerations based on the wave functions alone. In contrast, we identify the lowest excitations of the Gaffnian state in the thin cylinder limit, and conclude that they are gapped, using a combination of perturbative and numerical means. We discuss possible scenarios for the cross-over between the two-dimensional and the one-dimensional thermodynamic limit in this case. In the second part of the thesis, we study the low energy spectral properties of positive center-of-mass conserving two-body Hamiltonians as they arise in models of FQH states. Starting from the observation that positive many-body Hamiltonians must have ground state energies that increase monotonously in particle number, we explore what general additional constraints can be obtained for two-body interactions with "center-of-mass conservation" symmetry, both in the presence and absence of particle
Quantum algorithm for molecular properties and geometry optimization.
Kassal, Ivan; Aspuru-Guzik, Alán
2009-12-14
Quantum computers, if available, could substantially accelerate quantum simulations. We extend this result to show that the computation of molecular properties (energy derivatives) could also be sped up using quantum computers. We provide a quantum algorithm for the numerical evaluation of molecular properties, whose time cost is a constant multiple of the time needed to compute the molecular energy, regardless of the size of the system. Molecular properties computed with the proposed approach could also be used for the optimization of molecular geometries or other properties. For that purpose, we discuss the benefits of quantum techniques for Newton's method and Householder methods. Finally, global minima for the proposed optimizations can be found using the quantum basin hopper algorithm, which offers an additional quadratic reduction in cost over classical multi-start techniques.
NASA Astrophysics Data System (ADS)
Sin, Yongkun; Presser, Nathan; Foran, Brendan; Ives, Neil; Moss, Steven C.
2009-02-01
Extensive investigations by a number of groups have identified catastrophic sudden degradation as the main failure mode in both single-mode and multi-mode InGaAs-AlGaAs strained quantum well (QW) lasers. Significant progress made in performance characteristics of broad-area InGaAs strained QW single emitters in recent years has led to an optical output power of over 20W and a power conversion efficiency of over 70% under CW operation. However, unlike 980nm single-mode lasers that have shown high reliability operation under a high optical power density of ~50MW/cm2, broad-area lasers have not achieved the same level of reliability even under a much lower optical power density of ~5MW/cm2. This paper investigates possible mechanisms that prevent broad-area lasers from achieving high reliability operation by performing accelerated lifetests of these devices and in-depth failure mode analyses of degraded devices with various destructive and non-destructive techniques including EBIC, FIB, and HR-TEM techniques. The diode lasers that we have investigated are commercial MOCVD-grown broad-area strained InGaAs single QW lasers at ~975nm. Both passivated and unpassivated broad-area lasers were studied that yielded catastrophic failures at the front facet and also in the bulk. To investigate the role that generation and propagation of defects plays in degradation processes via recombination enhanced defect reaction (REDR), EBIC was employed to study dark line defects in degraded lasers, failed under different stress conditions, and the correlation between DLDs and stress levels is reported. FIB was then employed to prepare TEM samples from the DLD areas for cross-sectional HR-TEM analysis.
NASA Astrophysics Data System (ADS)
Dąbrowski, M.; Chrapkiewicz, R.; Wasilewski, W.
2016-11-01
Warm atomic vapor quantum memories are simple and robust, yet suffer from a number of parasitic processes which produce excess noise. For operating in a single-photon regime precise filtering of the output light is essential. Here, we report a combination of magnetically tuned absorption and Faraday filters, both light-direction insensitive, which stop the driving lasers and attenuate spurious fluorescence and four-wave mixing while transmitting narrowband Stokes and anti-Stokes photons generated in write-in and readout processes. We characterize both filters with respect to adjustable working parameters. We demonstrate a significant increase in the signal-to-noise ratio upon applying the filters seen qualitatively in measurements of correlation between the Raman scattered photons.
Optical properties of quantum-dot-doped liquid scintillators
Aberle, C.; Li, J.J.; Weiss, S.; Winslow, L.
2014-01-01
Semiconductor nanoparticles (quantum dots) were studied in the context of liquid scintillator development for upcoming neutrino experiments. The unique optical and chemical properties of quantum dots are particularly promising for the use in neutrinoless double-beta decay experiments. Liquid scintillators for large scale neutrino detectors have to meet specific requirements which are reviewed, highlighting the peculiarities of quantum-dot-doping. In this paper, we report results on laboratory-scale measurements of the attenuation length and the fluorescence properties of three commercial quantum dot samples. The results include absorbance and emission stability measurements, improvement in transparency due to filtering of the quantum dot samples, precipitation tests to isolate the quantum dots from solution and energy transfer studies with quantum dots and the fluorophore PPO. PMID:25392711
Optical properties of quantum-dot-doped liquid scintillators
NASA Astrophysics Data System (ADS)
Aberle, C.; Li, J. J.; Weiss, S.; Winslow, L.
2013-10-01
Semiconductor nanoparticles (quantum dots) were studied in the context of liquid scintillator development for upcoming neutrino experiments. The unique optical and chemical properties of quantum dots are particularly promising for the use in neutrinoless double-beta decay experiments. Liquid scintillators for large scale neutrino detectors have to meet specific requirements which are reviewed, highlighting the peculiarities of quantum-dot-doping. In this paper, we report results on laboratory-scale measurements of the attenuation length and the fluorescence properties of three commercial quantum dot samples. The results include absorbance and emission stability measurements, improvement in transparency due to filtering of the quantum dot samples, precipitation tests to isolate the quantum dots from solution and energy transfer studies with quantum dots and the fluorophore PPO.
Optical properties of quantum-dot-doped liquid scintillators.
Aberle, C; Li, J J; Weiss, S; Winslow, L
2013-10-14
Semiconductor nanoparticles (quantum dots) were studied in the context of liquid scintillator development for upcoming neutrino experiments. The unique optical and chemical properties of quantum dots are particularly promising for the use in neutrinoless double-beta decay experiments. Liquid scintillators for large scale neutrino detectors have to meet specific requirements which are reviewed, highlighting the peculiarities of quantum-dot-doping. In this paper, we report results on laboratory-scale measurements of the attenuation length and the fluorescence properties of three commercial quantum dot samples. The results include absorbance and emission stability measurements, improvement in transparency due to filtering of the quantum dot samples, precipitation tests to isolate the quantum dots from solution and energy transfer studies with quantum dots and the fluorophore PPO.
A family of generalized quantum entropies: definition and properties
NASA Astrophysics Data System (ADS)
Bosyk, G. M.; Zozor, S.; Holik, F.; Portesi, M.; Lamberti, P. W.
2016-08-01
We present a quantum version of the generalized (h,φ )-entropies, introduced by Salicrú et al. for the study of classical probability distributions. We establish their basic properties and show that already known quantum entropies such as von Neumann, and quantum versions of Rényi, Tsallis, and unified entropies, constitute particular classes of the present general quantum Salicrú form. We exhibit that majorization plays a key role in explaining most of their common features. We give a characterization of the quantum (h,φ )-entropies under the action of quantum operations and study their properties for composite systems. We apply these generalized entropies to the problem of detection of quantum entanglement and introduce a discussion on possible generalized conditional entropies as well.
Selenium quantum dots: Preparation, structure, and properties
NASA Astrophysics Data System (ADS)
Qian, Fuli; Li, Xueming; Tang, Libin; Lai, Sin Ki; Lu, Chaoyu; Lau, Shu Ping
2017-01-01
An interesting class of low-dimensional nanomaterials, namely, selenium quantum dots (SeQDs), which are composed of nano-sized selenium particles, is reported in this study. The SeQDs possess a hexagonal crystal structure. They can be synthesized in large quantity by ultrasound liquid-phase exfoliation using NbSe2 powders as the source material and N-Methyl-2-pyrrolidone (NMP) as the dispersant. During sonication, the Nb-Se bonds dissociate; the SeQDs are formed, while niobium is separated by centrifugation. The SeQDs have a narrow diameter distribution from 1.9 to 4.6 nm and can be dispersed with high stability in NMP without the need for passivating agents. They exhibit photoluminescence properties that are expected to find useful applications in bioimaging, optoelectronics, as well as nanocomposites.
Bushnell, M C; Duncan, G H; Tremblay, N
1993-03-01
1. The role of the thalamic ventroposterior medial (VPM) nucleus in the discriminative aspects of nociception and thermoreception was evaluated in alert, trained rhesus monkeys. Single-unit responses were recorded from VPM while the monkeys performed a battery of tasks involving noxious heat, innocuous cool, and air-puff stimuli presented to the face. The discriminative ability of the monkey was compared directly with the responses of single neurons, to determine whether the neuronal response could subserve the monkey's discriminative behavior. 2. Most thermally sensitive neurons exhibited multimodal properties. Only 18% responded exclusively to heat (HT-Heat neurons), whereas 27% responded to innocuous mechanical, as well as noxious mechanical and heat stimuli (WDR-Heat). Twenty-three percent responded to innocuous mechanical stimuli and innocuous skin cooling (Mechano-Cool), and 32% responded to mechanical, innocuous cool, and noxious heat stimuli (WDR-Heat-Cool). 3. Almost all mechanical receptive fields were confined to one division of the trigeminal nerve. This was true for all of the above categories of VPM neurons, even those showing highly convergent properties (WDR-Heat-Cool). 4. Heat-activated neurons produced graded responses to noxious skin heating in the 46 to 49 degrees C range. Stimulus-response functions of neurons that responded to both heat and cool did not differ from those of neurons that responded exclusively to skin heating. 5. When the monkeys were detecting small changes in the intensity of a noxious heat stimulus (e.g., from 47 to 47.1-47.8 degrees C), heat-activated neurons responded to the smallest temperature changes that could be detected by the monkeys. Further, there was a high correlation between the monkey's success in detecting the stimulus changes and the magnitude of the neuronal responses to those changes. 6. Although the responsiveness of VPM cool-activated neurons was not compared with the monkeys' threshold for detecting
Electronic properties of superlattices on quantum rings
NASA Astrophysics Data System (ADS)
da Costa, D. R.; Chaves, A.; Ferreira, W. P.; Farias, G. A.; Ferreira, R.
2017-04-01
We present a theoretical study of the one-electron states of a semiconductor-made quantum ring (QR) containing a series of piecewise-constant wells and barriers distributed along the ring circumference. The single quantum well and the superlattice cases are considered in detail. We also investigate how such confining potentials affect the Aharonov–Bohm like oscillations of the energy spectrum and current in the presence of a magnetic field. The model is simple enough so as to allow obtaining various analytical or quasi-analytical results. We show that the well-in-a-ring structure presents enhanced localization features, as well as specific geometrical resonances in its above-barrier spectrum. We stress that the superlattice-in-a-ring structure allows giving a physical meaning to the often used but usually artificial Born–von-Karman periodic conditions, and discuss in detail the formation of energy minibands and minigaps for the circumferential motion, as well as several properties of the superlattice eigenstates in the presence of the magnetic field. We obtain that the Aharonov–Bohm oscillations of below-barrier miniband states are reinforced, owing to the important tunnel coupling between neighbour wells of the superlattice, which permits the electron to move in the ring. Additionally, we analysis a superlattice-like structure made of a regular distribution of ionized impurities placed around the QR, a system that may implement the superlattice in a ring idea. Finally, we consider several random disorder models, in order to study roughness disorder and to tackle the robustness of some results against deviations from the ideally nanostructured ring system.
Luminescent properties of cadmium selenide quantum dots in fluorophosphate glasses
NASA Astrophysics Data System (ADS)
Lipatova, Zh. O.; Kolobkova, E. V.; Babkina, A. N.
2016-11-01
The optical properties of fluorophosphate glasses with CdSe quantum dots are studied. Secondary heat treatment at a temperature exceeding the glass transition temperature resulted in the formation of quantum dots with sizes of 3.7-6.2 nm. The influence of the semiconductor component concentration on the spectral-luminescent characteristics of glasses is shown. It is experimentally demonstrated that glasses with a lower CdSe concentration have a higher absolute luminescence quantum yield.
NASA Astrophysics Data System (ADS)
Sin, Yongkun; Presser, Nathan; Mason, Maribeth; Moss, Steven C.
2006-02-01
High-power multi-mode broad area InGaAs strained quantum well (QW) single emitters (λ ~ 920-980nm) have been mainly used for industrial applications. Recently, these broad area lasers with CW output powers >5W have also found applications in communications as pump lasers for Er-Yb co-doped fiber amplifiers. This application requires very demanding characteristics including higher reliability than industrial applications. In contrast to 980nm single mode InGaAs strained QW lasers that are widely employed in both terrestrial and submarine applications, the fact that multimode lasers have never been used in optical communications necessitates careful study of these lasers. We report investigations of performance characteristics, reliability, and failure modes of high-power multi-mode single emitters. The lasers studied were broad area strained InGaAs-GaAs single QW lasers grown either by MOCVD or MBE. Typical apertures were around 100μm wide and cavity lengths were <=4.2mm. AR-HR coated laser diode chips were mounted on carriers with junction down configuration to reduce thermal impedance. Laser thresholds were <=453mA at RT. At 6A injection current typical CW output powers were over 5W at 25°C with wall-plug efficiency of ~60%. Characteristics measured included thermal impedance and optical beam profiles that are critical in understanding performance and reliability. Automatic current control burn-in tests with different stress conditions were performed and log (I)-V characteristics were measured at RT to correlate degradation in optical output power and an increase in trap density estimated from the 2κ•T term in bulk recombination current. We also report initial analysis of lifetest results and failure modes from these lasers.
Wo, Fangjie; Xu, Rujiao; Shao, Yuxiang; Zhang, Zheyu; Chu, Maoquan; Shi, Donglu; Liu, Shupeng
2016-01-01
In this study, a multimodal therapeutic system was shown to be much more lethal in cancer cell killing compared to a single means of nano therapy, be it photothermal or photodynamic. Hollow magnetic nanospheres (HMNSs) were designed and synthesized for the synergistic effects of both magneto-mechanical and photothermal cancer therapy. By these combined stimuli, the cancer cells were structurally and physically destroyed with the morphological characteristics distinctively different from those by other therapeutics. HMNSs were also coated with the silica shells and conjugated with carboxylated graphene quantum dots (GQDs) as a core-shell composite: HMNS/SiO2/GQDs. The composite was further loaded with an anticancer drug doxorubicin (DOX) and stabilized with liposomes. The multimodal system was able to kill cancer cells with four different therapeutic mechanisms in a synergetic and multilateral fashion, namely, the magnetic field-mediated mechanical stimulation, photothermal damage, photodynamic toxicity, and chemotherapy. The unique nanocomposites with combined mechanical, chemo, and physical effects will provide an alternative strategy for highly improved cancer therapy efficiency. PMID:26941842
Wo, Fangjie; Xu, Rujiao; Shao, Yuxiang; Zhang, Zheyu; Chu, Maoquan; Shi, Donglu; Liu, Shupeng
2016-01-01
In this study, a multimodal therapeutic system was shown to be much more lethal in cancer cell killing compared to a single means of nano therapy, be it photothermal or photodynamic. Hollow magnetic nanospheres (HMNSs) were designed and synthesized for the synergistic effects of both magneto-mechanical and photothermal cancer therapy. By these combined stimuli, the cancer cells were structurally and physically destroyed with the morphological characteristics distinctively different from those by other therapeutics. HMNSs were also coated with the silica shells and conjugated with carboxylated graphene quantum dots (GQDs) as a core-shell composite: HMNS/SiO2/GQDs. The composite was further loaded with an anticancer drug doxorubicin (DOX) and stabilized with liposomes. The multimodal system was able to kill cancer cells with four different therapeutic mechanisms in a synergetic and multilateral fashion, namely, the magnetic field-mediated mechanical stimulation, photothermal damage, photodynamic toxicity, and chemotherapy. The unique nanocomposites with combined mechanical, chemo, and physical effects will provide an alternative strategy for highly improved cancer therapy efficiency.
Cheng, Yuanbing; Wu, Jian; Zhao, Lingjuan; Luo, Xianshu; Wang, Qi Jie
2015-01-01
We have designed and demonstrated InAs/GaAs quantum dots-in-a-well laser diodes for short cavities with transverse fundamental mode operation by using an active multimode interferometer (MMI) structure for the first time to the best of our knowledge. Room-temperature continuous-wave ground-state lasing at 1280 nm has been achieved with an output power of 116 mW per facet, which is 2.4 times higher than that of the conventional ridge laser diodes. By using the MMI structures, the excited-state (ES) lasing is effectively suppressed with no ES lasing, even at a high injection current of 400 mA. This device has great potential for high-power single-mode laser emission with low electric power consumption and simple fabrication processes.
Wu, Qi; Sun, Yaming; Zhang, Xiaoli; Zhang, Xia; Dong, Shuqing; Qiu, Hongdeng; Wang, Litao; Zhao, Liang
2017-04-07
Graphene quantum dots (GQDs), which possess hydrophobic, hydrophilic, π-π stacking and hydrogen bonding properties, have great prospect in HPLC. In this study, a novel GQDs bonded silica stationary phase was prepared and applied in multiple separation modes including normal phase, reversed phase and hydrophilic chromatography mode. Alkaloids, nucleosides and nucleobases were chosen as test compounds to evaluate the separation performance of this column in hydrophilic chromatographic mode. The tested polar compounds achieved baseline separation and the resolutions reached 2.32, 4.62, 7.79, 1.68 for thymidine, uridine, adenosine, cytidine and guanosine. This new column showed satisfactory chromatographic performance for anilines, phenols and polycyclic aromatic hydrocarbons in normal and reversed phase mode. Five anilines were completely separated within 10min under the condition of mobile phase containing only 10% methanol. The effect of water content, buffer concentration and pH on chromatographic separation was further investigated, founding that this new stationary phase showed a complex retention mechanism of partitioning, adsorption and electrostatic interaction in hydrophilic chromatography mode, and the multiple retention interactions such as π-π stacking and π-π electron-donor-acceptor interaction played an important role during the separation process. This GQDs bonded column, which allows us to adjust appropriate chromatography mode according to the properties of analytes, has possibility in actual application after further research.
Nakamura, Michihiro; Hayashi, Koichiro; Kubo, Hitoshi; Kanadani, Takafumi; Harada, Masafumi; Yogo, Toshinobu
2017-04-15
Multimodal imaging using novel multifunctional nanoparticles provides a new approach for the biomedical field. Thiol-organosilica nanoparticles containing iron oxide magnetic nanoparticles (MNPs) as the core and rhodamine B in the thiol-organosilica layer (thiol OS-MNP/Rho) were synthesized in a one-pot process. The thiol OS-MNP/Rho showed enhanced magnetic resonance imaging (MRI) contrast and high fluorescence intensity. The relaxometry of thiol OS-MNP/Rho revealed a novel coating effect of the organosilica layer to the MNPs. The organosilica layer shortened the T2 relaxation time but not the T1 relaxation time of the MNPs. We injected thiol-OS-MNP/Rho into normal mice intravenously. Injected mice revealed an alteration of the liver contrast in the MRI and a fluorescent pattern based on the liver histological structure at the level between macroscopic and microscopic fluorescent imaging (mesoscopic FI). In addition, the labeled macrophages were observed at the single cell level histologically. We demonstrated a new approach to evaluate the liver at the macroscopic, microscopic level as well as the mesoscopic level using multimodal imaging.
Optical properties of few layered graphene quantum dots
NASA Astrophysics Data System (ADS)
Pratap Choudhary, Raghvendra; Shukla, Shobha; Vaibhav, Kumar; Bhagwan Pawar, Pranav; Saxena, Sumit
2015-09-01
Quantum dots provide a unique opportunity to study the confinement effects of electronic wave function on the properties of materials. We have investigated the optical properties of graphene quantum dots synthesized using ultra-fast light-matter interactions followed by one step reduction process. Atomic-scale morphological information suggests the presence of both zigzag and armchair edges in these quantum dots. Optical characterizations were performed using absorption, photoluminescence, and infrared spectroscopy. A shift in the emission spectrum and disappearance of n → π* transition in the absorption spectrum on reduction of the ablated samples confirmed the formation of graphene quantum dots. First principles calculations are in good agreement with the experimentally reported infrared data.
NASA Astrophysics Data System (ADS)
Montón, Helena; Parolo, Claudio; Aranda-Ramos, Antonio; Merkoçi, Arben; Nogués, Carme
2015-02-01
There is a great demand to develop novel techniques that allow useful and complete monitoring of apoptosis, which is a key factor of several diseases and a target for drug development. Here, we present the use of a novel dual electrochemical/optical label for the detection and study of apoptosis. We combined the specificity of Annexin-V for phosphatidylserine, a phospholipid expressed in the outer membrane of apoptotic cells, with the optical and electrochemical properties of quantum dots to create a more efficient label. Using this conjugate we addressed three important issues: (i) we made the labeling of apoptotic cells faster (30 min) and easier; (ii) we fully characterized the samples by common cell biological techniques (confocal laser scanning microscopy, scanning electron microscopy and flow cytometry); and (iii) we developed a fast, cheap and quantitative electrochemical detection method for apoptotic cells with results in full agreement with those obtained by flow cytometry.There is a great demand to develop novel techniques that allow useful and complete monitoring of apoptosis, which is a key factor of several diseases and a target for drug development. Here, we present the use of a novel dual electrochemical/optical label for the detection and study of apoptosis. We combined the specificity of Annexin-V for phosphatidylserine, a phospholipid expressed in the outer membrane of apoptotic cells, with the optical and electrochemical properties of quantum dots to create a more efficient label. Using this conjugate we addressed three important issues: (i) we made the labeling of apoptotic cells faster (30 min) and easier; (ii) we fully characterized the samples by common cell biological techniques (confocal laser scanning microscopy, scanning electron microscopy and flow cytometry); and (iii) we developed a fast, cheap and quantitative electrochemical detection method for apoptotic cells with results in full agreement with those obtained by flow cytometry
Optical properties of dielectric thin films including quantum dots
NASA Astrophysics Data System (ADS)
Flory, F.; Chen, Y. J.; Lee, C. C.; Escoubas, L.; Simon, J. J.; Torchio, P.; Le Rouzo, J.; Vedraine, S.; Derbal-Habak, Hassina; Ackermann, Jorg; Shupyk, Ivan; Didane, Yahia
2010-08-01
Depending on the minimum size of their micro/nano structure, thin films can exhibit very different behaviors and optical properties. From optical waveguides down to artificial anisotropy, through diffractive optics and photonic crystals, the application changes when decreasing the minimum feature size. Rigorous electromagnetic theory can be used to model most of the components but when the size is of a few nanometers, quantum theory has also to be used. These materials including quantum structures are of particular interest for other applications, in particular for solar cells, because of their luminescent and electronic properties. We show that the properties of electrons in multiple quantum wells can be easily modeled with a formalism similar to that used for multilayer waveguides. The effects of different parameters, in particular coupling between wells and well thickness dispersion, on possible discrete energy levels or energy band of electrons and on electron wave functions is given. When such quantum confinement appears the spectral absorption and the extinction coefficient dispersion with wavelength is modified. The dispersion of the real part of the refractive index can then be deduced from the Kramers- Krönig relations. Associated with homogenization theory this approach gives a new model of refractive index for thin films including quantum dots. Absorption spectra of samples composed of ZnO quantum dots in PMMA layers are in preparation are given.
Interaction of a quantum well with squeezed light: Quantum-statistical properties
Sete, Eyob A.; Eleuch, H.
2010-10-15
We investigate the quantum statistical properties of the light emitted by a quantum well interacting with squeezed light from a degenerate subthreshold optical parametric oscillator. We obtain analytical solutions for the pertinent quantum Langevin equations in the strong-coupling and low-excitation regimes. Using these solutions we calculate the intensity spectrum, autocorrelation function, and quadrature squeezing for the fluorescent light. We show that the fluorescent light exhibits bunching and quadrature squeezing. We also show that the squeezed light leads to narrowing of the width of the spectrum of the fluorescent light.
Optical, magnetic and electronic properties of graphene quantum dots
NASA Astrophysics Data System (ADS)
Guclu, A. Devrim
2011-03-01
We present a theory of optical, magnetic and electronic properties of graphene quantum dots. We demonstrate that there exists a class of triangular graphene quantum dots with zigzag edges [1-8] which combines magnetic, optical and transport properties in a single-material structure. These dots exhibit robust magnetic moment and optical transitions simultaneously in the THz, visible and UV spectral ranges due to the existence of a band of degenerate states lying at the Fermi level in the middle of the energy gap [1-6]. The magnetic and optical properties[5,7] are determined by strong electron-electron and excitonic interactions in the degenerate band, treated exactly using numerical techniques combining tight-binding, DFT, Hartree-Fock and configuration interactions methods. We show that the spin polarized degenerate band leads to quenching of the absorption spectrum at half-filling, while addition of a single electron fully depolarizes all electron spins and turns the absorption on. It is thus possible to design gate and size tunable graphene quantum dots with desired optical and magnetic properties for optoelectronic and photo-voltaic applications. Collaborators: P. Potasz, O. Voznyy, M. Korkusinski, and P. Hawrylak. The author thanks NRC-CNRS CRP, Canadian Institute for Advanced Research, Institute for Microstructural Sciences, and QuantumWorks for support.
Critical properties of dissipative quantum spin systems in finite dimensions
NASA Astrophysics Data System (ADS)
Takada, Kabuki; Nishimori, Hidetoshi
2016-10-01
We study the critical properties of finite-dimensional dissipative quantum spin systems with uniform ferromagnetic interactions. Starting from the transverse field Ising model coupled to a bath of harmonic oscillators with Ohmic spectral density, we generalize its classical representation to classical spin systems with O(n) symmetry and then take the large-n limit to reduce the system to a spherical model. The exact solution to the resulting spherical model with long-range interactions along the imaginary time axis shows a phase transition with static critical exponents coinciding with those of the conventional short-range spherical model in d+2 dimensions, where d is the spatial dimensionality of the original quantum system. This implies that the dynamical exponent is z = 2. These conclusions are consistent with the results of Monte Carlo simulations and renormalization group calculations for dissipative transverse field Ising and O(n) models in one and two dimensions. The present approach therefore serves as a useful tool for analytically investigating the properties of quantum phase transitions of the dissipative transverse field Ising and other related models. Our method may also offer a platform to study more complex phase transitions in dissipative finite-dimensional quantum spin systems, which have recently received renewed interest in the context of quantum annealing in a noisy environment.
Comparison of dynamic properties of InP/InAs quantum-dot and quantum-dash lasers
NASA Astrophysics Data System (ADS)
Sadeev, T.; Arsenijević, D.; Bimberg, D.
2016-10-01
The dynamic properties of MOVPE grown InP/InAs quantum-dot and quantum-dash lasers, showing identical structural design, emitting in the C-band are investigated and compared to each other. Based on the small-signal measurements, we show the impact of the density of states function on the cut-off frequency, being larger for quantum dots at low currents, and reaching similar values for quantum dashes only at higher currents. The large-signal measurements show error-free data transmission at 22.5 and 17.5 Gbit/s for the quantum-dot and quantum-dash lasers.
Quantum mechanical properties of graphene nano-flakes and quantum dots.
Shi, Hongqing; Barnard, Amanda S; Snook, Ian K
2012-11-07
In recent years considerable attention has been given to methods for modifying and controlling the electronic and quantum mechanical properties of graphene quantum dots. However, as these types of properties are indirect consequences of the wavefunction of the material, a more efficient way of determining properties may be to engineer the wavefunction directly. One way of doing this may be via deliberate structural modifications, such as producing graphene nanostructures with specific sizes and shapes. In this paper we use quantum mechanical simulations to determine whether the wavefunction, quantified via the distribution of the highest occupied molecular orbital, has a direct and reliable relationship to the physical structure, and whether structural modifications can be useful for wavefunction engineering. We find that the wavefunction of small molecular graphene structures can be different from those of larger nanoscale counterparts, and the distribution of the highest occupied molecular orbital is strongly affected by the geometric shape (but only weakly by edge and corner terminations). This indicates that both size and shape may be more useful parameters in determining quantum mechanical and electronic properties, which should then be reasonably robust against variations in the chemical passivation or functionalisation around the circumference.
Thermodynamical properties of Strunz’s quantum dissipative models
Zen, Freddy P.; Sulaiman, A.
2015-09-30
The existence of the negative of specific heat from quantum dissipative theory is investigated. Strunz’s quantum dissipative model will be used in this studies. The thermodynamical properties will be studied starts out from the thermo-dynamic partition function of the dissipative system. The path integral technique is used to calculate the partition function under consideration. The results shows that the specific heat can be negative if the damping parameter more than a half the oscillator frequency and also occur at low temperatures. For damping factor greater than the frequency of harmonic oscillator then specific heat will oscillate at low temperatures and approaching normal conditions at a high temperature.
Quantum-walk transport properties on graphene structures
NASA Astrophysics Data System (ADS)
Bougroura, Hamza; Aissaoui, Habib; Chancellor, Nicholas; Kendon, Viv
2016-12-01
We present numerical studies of quantum walks on C60 and related graphene structures to investigate their transport properties. Also known as a honeycomb lattice, the lattice formed by carbon atoms in the graphene phase can be rolled up to form nanotubes of various dimensions. Graphene nanotubes have many important applications, some of which rely on their unusual electrical conductivity and related properties. Quantum walks on graphs provide an abstract setting in which to study such transport properties independent of the other chemical and physical properties of a physical substance. They can thus be used to further the understanding of mechanisms behind such properties. We find that nanotube structures are significantly more efficient in transporting a quantum walk than cycles of equivalent size, provided the symmetry of the structure is respected in how they are used. We find faster transport on zigzag nanotubes compared to armchair nanotubes, which is unexpected given that for the actual materials the armchair nanotube is metallic, while the zigzag is semiconducting.
Highly sensitive humidity sensing properties of carbon quantum dots films
Zhang, Xing; Ming, Hai; Liu, Ruihua; Han, Xiao; Kang, Zhenhui; Liu, Yang; Zhang, Yonglai
2013-02-15
Graphical abstract: Display Omitted Highlights: ► A humidity sensing device was fabricated based on carbon quantum dots (CQDs) films. ► The conductivity of the CQDs films shows a linear and rapid response to atmosphere humidity. ► The humidity sensing property was due to the hydrogen bonds between the functional groups on CQDs. -- Abstract: We reported the fabrication of a humidity sensing device based on carbon quantum dots (CQDs) film. The conductivity of the CQDs film has a linear and rapid response to relative humidity, providing the opportunity for the fabrication of humidity sensing devices. The mechanism of our humidity sensor was proposed to be the formation of hydrogen bonds between carbon quantum dots and water molecules in the humidity environment, which significantly promote the electrons migration. In a control experiment, this hypothesis was confirmed by comparing the humidity sensitivity of candle soot (i.e. carbon nanoparticles) with and without oxygen containing groups on the surfaces.
Lopez, L.; Gigan, S.; Treps, N.; Maitre, A.; Fabre, C.; Gatti, A.
2005-07-15
Up to now, transverse quantum effects (usually labeled as 'quantum imaging' effects) which are generated by nonlinear devices inserted in resonant optical cavities have been calculated using the 'thin-crystal approximation', i.e., taking into account the effect of diffraction only inside the empty part of the cavity, and neglecting its effect in the nonlinear propagation inside the nonlinear crystal. We introduce in the present paper a theoretical method which is not restricted by this approximation. It allows us in particular to treat configurations closer to the actual experimental ones, where the crystal length is comparable to the Rayleigh length of the cavity mode. We use this method in the case of the confocal optical parametric oscillator, where the thin-crystal approximation predicts perfect squeezing on any area of the transverse plane, whatever its size and shape. We find that there exists in this case a 'coherence length' which gives the minimum size of a detector on which perfect squeezing can be observed, and which gives therefore a limit to the improvement of optical resolution that can be obtained using such devices.
Optical properties of GaN wurtzite quantum wires
NASA Astrophysics Data System (ADS)
Zhang, X. W.; Xia, J. B.
2006-03-01
The electronic structure and optical properties of freestanding GaN wurtzite quantum wires are studied in the framework of six-band effective-mass envelope function theory. It is found that the electron states are either twofold or fourfold degenerate. There is a dark exciton effect when the radius R of GaN wurtzite quantum wires is in the range of [0.7, 10.9] nm. The linear polarization factors are calculated in three cases, the quantum confinement effect (finite long wire), the dielectric effect and both effects (infinitely long wire). It is found that the linear polarization factor of a finite long wire whose length is much less than the electromagnetic wavelength decreases as R increases, is very close to unity (0.979) at R = 1 nm, and changes from a positive value to a negative value around R = 4.1 nm. The linear polarization factor of the dielectric effect is 0.934, independent of radius, as long as the radius remains much less than the electromagnetic wavelength. The result for the two effects shows that the quantum confinement effect gives a correction to the dielectric effect result. It is found that the linear polarization factor of very long (treated approximately as infinitely long) quantum wires is in the range of [0.8, 1]. The linear polarization factors of the quantum confinement effect of CdSe wurtzite quantum wires are calculated for comparison. In the CdSe case, the linear polarization factor of R = 1 nm is 0.857, in agreement with the experimental results (Hu et al 2001 Science 292 2060). This value is much smaller than unity, unlike 0.979 in the GaN case, mainly due to the big spin-orbit splitting energy Δso of CdSe material with wurtzite structure.
Tuning quantum properties in bilayer ruthenates
NASA Astrophysics Data System (ADS)
Ke, Xianglin
The mutual coupling among spin, charge, lattice and orbital degrees of freedom in transition-metal oxide materials often leads to the competition of various types of energetic states. This makes such materials dramatically susceptible to external parameters, giving rise to novel physical properties and rich phase diagrams. In this talk, I shall use a bilayer ruthenate, Ca3Ru2O7, as an example to discuss the emergent phenomena achieved by systematically tuning materials magnetic and electronic properties via chemical doping, magnetic field, and pressure. I shall show that this system provides a rare opportunity to investigate the interplay between correlated metal and Mott insulator. This work was done in collaboration with M. Zhu, T. Tao, S. D. Mahanti, Z. Q. Mao, J. Peng, T. Hong, W. Tian, H. Cao, C. R. dela Cruz, D. Singh, and K. Prokes.
Quantum chemistry structures and properties of 134 kilo molecules.
Ramakrishnan, Raghunathan; Dral, Pavlo O; Rupp, Matthias; von Lilienfeld, O Anatole
2014-01-01
Computational de novo design of new drugs and materials requires rigorous and unbiased exploration of chemical compound space. However, large uncharted territories persist due to its size scaling combinatorially with molecular size. We report computed geometric, energetic, electronic, and thermodynamic properties for 134k stable small organic molecules made up of CHONF. These molecules correspond to the subset of all 133,885 species with up to nine heavy atoms (CONF) out of the GDB-17 chemical universe of 166 billion organic molecules. We report geometries minimal in energy, corresponding harmonic frequencies, dipole moments, polarizabilities, along with energies, enthalpies, and free energies of atomization. All properties were calculated at the B3LYP/6-31G(2df,p) level of quantum chemistry. Furthermore, for the predominant stoichiometry, C7H10O2, there are 6,095 constitutional isomers among the 134k molecules. We report energies, enthalpies, and free energies of atomization at the more accurate G4MP2 level of theory for all of them. As such, this data set provides quantum chemical properties for a relevant, consistent, and comprehensive chemical space of small organic molecules. This database may serve the benchmarking of existing methods, development of new methods, such as hybrid quantum mechanics/machine learning, and systematic identification of structure-property relationships.
Optical properties of transition metal oxide quantum wells
Lin, Chungwei; Posadas, Agham; Choi, Miri; Demkov, Alexander A.
2015-01-21
Fabrication of a quantum well, a structure that confines the electron motion along one or more spatial directions, is a powerful method of controlling the electronic structure and corresponding optical response of a material. For example, semiconductor quantum wells are used to enhance optical properties of laser diodes. The ability to control the growth of transition metal oxide films to atomic precision opens an exciting opportunity of engineering quantum wells in these materials. The wide range of transition metal oxide band gaps offers unprecedented control of confinement while the strong correlation of d-electrons allows for various cooperative phenomena to come into play. Here, we combine density functional theory and tight-binding model Hamiltonian analysis to provide a simple physical picture of transition metal oxide quantum well states using a SrO/SrTiO{sub 3}/SrO heterostructure as an example. The optical properties of the well are investigated by computing the frequency-dependent dielectric functions. The effect of an external electric field, which is essential for electro-optical devices, is also considered.
Optical properties of transition metal oxide quantum wells
NASA Astrophysics Data System (ADS)
Lin, Chungwei; Posadas, Agham; Choi, Miri; Demkov, Alexander A.
2015-01-01
Fabrication of a quantum well, a structure that confines the electron motion along one or more spatial directions, is a powerful method of controlling the electronic structure and corresponding optical response of a material. For example, semiconductor quantum wells are used to enhance optical properties of laser diodes. The ability to control the growth of transition metal oxide films to atomic precision opens an exciting opportunity of engineering quantum wells in these materials. The wide range of transition metal oxide band gaps offers unprecedented control of confinement while the strong correlation of d-electrons allows for various cooperative phenomena to come into play. Here, we combine density functional theory and tight-binding model Hamiltonian analysis to provide a simple physical picture of transition metal oxide quantum well states using a SrO/SrTiO3/SrO heterostructure as an example. The optical properties of the well are investigated by computing the frequency-dependent dielectric functions. The effect of an external electric field, which is essential for electro-optical devices, is also considered.
Analysis of dynamic, modulation, and output power properties of self-assembled quantum dot lasers
NASA Astrophysics Data System (ADS)
Ghodsi Nahri, D.
2012-09-01
Dynamic, modulation, and output power (OP) characteristics of In(Ga)As/GaAs self-assembled quantum-dot lasers (SAQDLs) using multi-mode and multi-population rate equations analysis considering nonlinear material gain and thermal carrier escape pathways to both wetting layer and barriers are presented. I show that despite of significant effect of nonlinear material gain on time evolution of photon population, it does not affect 3-dB modulation bandwidth (MB). Thermal carrier escape processes have minor declining effects on modulation properties at around room-temperature (RT) operation and higher. Although turn-on delay increases with enhancement of temperature, in some bias currents, there is a reverse jump which is due to thermal carrier escape to barriers. In addition, it is indicated that optimum bias current to maximize MB increases as temperature enhances and that more disk-like SAQDs may provide higher MBs. Variations of some key parameters, bias current or mean quantum-dot (QD) radius, provide similar changing patterns for both MB and OP. While altering most of key parameters, average QD height, QD coverage, stripe width of the laser cavity, and temperature, leads to a tradeoff between MB and OP for a specific interval of those parameters. I show that considering our purpose, which is the highest OP or MB, we can achieve maximum possible output designing key parameters. For the present device, optimizing structural parameters, MB about 14 GHz is achieved at around RT operation under the moderate bias current 10 mA, which can be improved up to 30 GHz with decreasing carrier capture time. The results presented here may be used for designing QD lasers suitable for optical telecommunication.
Coherent Optical Propagation Properties Based on a Generalized Multi-Mode Optomechanical System
NASA Astrophysics Data System (ADS)
Chen, Hua-Jun; Fang, Xian-Wen; Chen, Chang-Zhao; Li, Yang; Tang, Xu-Dong
2017-03-01
A generalized three-modes optomechanical system is presented where two cavity modes driven by two-tone fields are coupled to a mechanical resonator. We find that two input probe lasers can be entirely absorbed by the mechanical resonator without inducing any energy output from any of the cavity modes termed as coherent perfect absorption. Furthermore, the input probe laser will transmit from one cavity to the other cavity without undergoing any energy loss which is termed as coherent perfect transmission under different parameter regimes. The origin and conditions that enable the phenomena to achieve are analysed, and potential applications in quantum information may be realized in all-optical domain based on these phenomena.
Cadmium-containing quantum dots: properties, applications, and toxicity.
Mo, Dan; Hu, Liang; Zeng, Guangming; Chen, Guiqiu; Wan, Jia; Yu, Zhigang; Huang, Zhenzhen; He, Kai; Zhang, Chen; Cheng, Min
2017-04-01
The marriage of biology with nanomaterials has significantly accelerated advancement of biological techniques, profoundly facilitating practical applications in biomedical fields. With unique optical properties (e.g., tunable broad excitation, narrow emission spectra, robust photostability, and high quantum yield), fluorescent quantum dots (QDs) have been reasonably functionalized with controllable interfaces and extensively used as a new class of optical probe in biological researches. In this review, we summarize the recent progress in synthesis and properties of QDs. Moreover, we provide an overview of the outstanding potential of QDs for biomedical research and innovative methods of drug delivery. Specifically, the applications of QDs as novel fluorescent nanomaterials for biomedical sensing and imaging have been detailedly highlighted and discussed. In addition, recent concerns on potential toxicity of QDs are also introduced, ranging from cell researches to animal models.
Properties of long quantum walks in one and two dimensions
NASA Astrophysics Data System (ADS)
Luo, Hao; Xue, Peng
2015-12-01
The quantum walk (QW) is the term given to a family of algorithms governing the evolution of a discrete quantum system and as such has a founding role in the study of quantum computation. We contribute to the investigation of QW phenomena by performing a detailed numerical study of discrete-time quantum walks. In one dimension (1D), we compute the structure of the probability distribution, which is not a smooth curve but shows oscillatory features on all length scales. By analyzing walks up to N = 1,000,000 steps, we discuss the scaling characteristics and limiting forms of the QW in both real and Fourier space. In 2D, with a view to ready experimental realization, we consider two types of QW, one based on a four-faced coin and the other on sequential flipping of a single two-faced coin. Both QWs may be generated using two two-faced coins, which in the first case are completely unentangled and in the second are maximally entangled. We draw on our 1D results to characterize the properties of both walks, demonstrating maximal speed-up and emerging semi-classical behavior in the maximally entangled QW.
Equilibration properties of a disordered interacting open quantum system
NASA Astrophysics Data System (ADS)
van Nieuwenburg, Evert; Huber, Sebastian
The central question in the field of many body localization is if a closed interacting quantum system effectively thermalizes in the presence of disorder. However, any experimental test necessarily involves the opening of the ideally closed quantum system. Both from a fundamental point of view as well as for concrete experimental investigations of many body localization phenomena, a solid understanding of the effect of an attached bath is of significant importance. We study the equilibration properties of disordered interacting open quantum systems. On the one hand we consider the equilibration of such a many body localized system by coupling baths to the ends of a 1D spin chain. We find non-monotonous behaviour of the slowest relaxation time towards equilibrium. On the other hand, we take the bath itself to be a disordered interacting open quantum system and investigate the dephasing of a single qubit coupled to it. The model for the bath has a many body localization transition, affecting the dephasing of the single qubit.
NASA Astrophysics Data System (ADS)
Kónya, G.; Szirmai, G.; Domokos, P.
2011-11-01
We develop a mean-field model describing the Hamiltonian interaction of ultracold atoms and the optical field in a cavity. The Bose-Einstein condensate is properly defined by means of a grand-canonical approach. The model is efficient because only the relevant excitation modes are taken into account. However, the model goes beyond the two-mode subspace necessary to describe the self-organization quantum phase transition observed recently. We calculate all the second-order correlations of the coupled atom field and radiation field hybrid bosonic system, including the entanglement between the two types of fields.
NASA Astrophysics Data System (ADS)
Claus, D.; Schumacher, P. M.; Labitzke, T.; Mlikota, M.; Weber, U.; Schmauder, S.; Schierbaum, N.; Schäffer, T. E.; WittmüÎ², P.; Teutsch, T.; Tarin, C.; Hoffmann, S.; Taran, F. A.; Brucker, S.; Mischinger, J.; Stenzel, A.; Osten, W.
2015-07-01
During minimally invasive surgery the visual (3 dimensional) and mechanical (haptic) feedback is restricted or even non-existing, which imposes a serious loss of important information for decision making. Information about the mechanical properties of the biological tissue helps the surgeon to localize tissue abnormalities (benign vs. malign tissue). The work described here is directed towards assisting the surgeon during minimally invasive surgery, which in particular relates to the segmentation and navigation based on the recovery of mechanical properties. Besides the development of noninvasive elastographic measurement techniques, a reliable constitutive FE-model of the organ (describing its mechanical properties) is generated resulting in a further improvement of the segmentation and localization process. At first silicon phantoms, with and without foreign bodies have been generated for the purpose of testing the transfer of information (delivery and processing of data). The stress-strain curve was recorded and embedded in the FE-model (Arruda-Boyce). Two dimensional (2D) displacement maps have experimentally been obtained from the phantom, which were in good agreement with the FE simulation.
Adali, Tülay; Levin-Schwartz, Yuri; Calhoun, Vince D.
2015-01-01
Fusion of information from multiple sets of data in order to extract a set of features that are most useful and relevant for the given task is inherent to many problems we deal with today. Since, usually, very little is known about the actual interaction among the datasets, it is highly desirable to minimize the underlying assumptions. This has been the main reason for the growing importance of data-driven methods, and in particular of independent component analysis (ICA) as it provides useful decompositions with a simple generative model and using only the assumption of statistical independence. A recent extension of ICA, independent vector analysis (IVA) generalizes ICA to multiple datasets by exploiting the statistical dependence across the datasets, and hence, as we discuss in this paper, provides an attractive solution to fusion of data from multiple datasets along with ICA. In this paper, we focus on two multivariate solutions for multi-modal data fusion that let multiple modalities fully interact for the estimation of underlying features that jointly report on all modalities. One solution is the Joint ICA model that has found wide application in medical imaging, and the second one is the the Transposed IVA model introduced here as a generalization of an approach based on multi-set canonical correlation analysis. In the discussion, we emphasize the role of diversity in the decompositions achieved by these two models, present their properties and implementation details to enable the user make informed decisions on the selection of a model along with its associated parameters. Discussions are supported by simulation results to help highlight the main issues in the implementation of these methods. PMID:26525830
Adali, Tülay; Levin-Schwartz, Yuri; Calhoun, Vince D
2015-09-01
Fusion of information from multiple sets of data in order to extract a set of features that are most useful and relevant for the given task is inherent to many problems we deal with today. Since, usually, very little is known about the actual interaction among the datasets, it is highly desirable to minimize the underlying assumptions. This has been the main reason for the growing importance of data-driven methods, and in particular of independent component analysis (ICA) as it provides useful decompositions with a simple generative model and using only the assumption of statistical independence. A recent extension of ICA, independent vector analysis (IVA) generalizes ICA to multiple datasets by exploiting the statistical dependence across the datasets, and hence, as we discuss in this paper, provides an attractive solution to fusion of data from multiple datasets along with ICA. In this paper, we focus on two multivariate solutions for multi-modal data fusion that let multiple modalities fully interact for the estimation of underlying features that jointly report on all modalities. One solution is the Joint ICA model that has found wide application in medical imaging, and the second one is the the Transposed IVA model introduced here as a generalization of an approach based on multi-set canonical correlation analysis. In the discussion, we emphasize the role of diversity in the decompositions achieved by these two models, present their properties and implementation details to enable the user make informed decisions on the selection of a model along with its associated parameters. Discussions are supported by simulation results to help highlight the main issues in the implementation of these methods.
Superposition states for quantum nanoelectronic circuits and their nonclassical properties
NASA Astrophysics Data System (ADS)
Choi, Jeong Ryeol
2016-09-01
Quantum properties of a superposition state for a series RLC nanoelectronic circuit are investigated. Two displaced number states of the same amplitude but with opposite phases are considered as components of the superposition state. We have assumed that the capacitance of the system varies with time and a time-dependent power source is exerted on the system. The effects of displacement and a sinusoidal power source on the characteristics of the state are addressed in detail. Depending on the magnitude of the sinusoidal power source, the wave packets that propagate in charge(q)-space are more or less distorted. Provided that the displacement is sufficiently high, distinct interference structures appear in the plot of the time behavior of the probability density whenever the two components of the wave packet meet together. This is strong evidence for the advent of nonclassical properties in the system, that cannot be interpretable by the classical theory. Nonclassicality of a quantum system is not only a beneficial topic for academic interest in itself, but its results can be useful resources for quantum information and computation as well.
NASA Astrophysics Data System (ADS)
Claus, D.; Schumacher, P. M.; Wilke, M.; Mlikota, M.; Weber, U.; Schmauder, S.; Schierbaum, N.; Schäffer, T. E.; Wittmüß, P.; Teutsch, T.; Tarin, C.; Hoffmann, S.; Brucker, S.; Mischinger, J.; Schwentner, C.; Stenzl, A.; Osten, W.
2015-03-01
Besides the many advantages minimally invasive surgery offers, the surgeon suffers from the loss of information, visual and mechanical (haptic feedback). The latter is an important tool, which helps the surgeon to localize tissue abnormalities (benign vs. malign tissue). We are aiming to generate a reliable constitutive FE model of the organ describing its mechanical properties by employing multiple elastographic measurement techniques at different scales (cell, tissue, and organ). A silicon phantom has been generated for the purpose of testing the transfer of information (delivery and processing of data). The stress-strain curve was recorded and embedded in the FE Model (Arruda-Boyce). A 2D displacement map was experimentally obtained from the phantom, which was in good agreement with the FE simulation.
Optimal error intervals for properties of the quantum state
NASA Astrophysics Data System (ADS)
Li, Xikun; Shang, Jiangwei; Ng, Hui Khoon; Englert, Berthold-Georg
2016-12-01
Quantum state estimation aims at determining the quantum state from observed data. Estimating the full state can require considerable efforts, but one is often only interested in a few properties of the state, such as the fidelity with a target state, or the degree of correlation for a specified bipartite structure. Rather than first estimating the state, one can, and should, estimate those quantities of interest directly from the data. We propose the use of optimal error intervals as a meaningful way of stating the accuracy of the estimated property values. Optimal error intervals are analogs of the optimal error regions for state estimation [New J. Phys. 15, 123026 (2013), 10.1088/1367-2630/15/12/123026]. They are optimal in two ways: They have the largest likelihood for the observed data and the prechosen size, and they are the smallest for the prechosen probability of containing the true value. As in the state situation, such optimal error intervals admit a simple description in terms of the marginal likelihood for the data for the properties of interest. Here, we present the concept and construction of optimal error intervals, report on an iterative algorithm for reliable computation of the marginal likelihood (a quantity difficult to calculate reliably), explain how plausible intervals—a notion of evidence provided by the data—are related to our optimal error intervals, and illustrate our methods with single-qubit and two-qubit examples.
Properties of the magnetopolaron in a triangular quantum well
NASA Astrophysics Data System (ADS)
Yali, Li; Shuping, Shan
2015-08-01
We study the properties of the magnetopolaron in a triangular quantum well within LLP variational method. At different electron-phonon coupling strength, we derive the relations between the ground state energy, the ground state binding energy with the electron areal density and the cyclotron frequency of magnetic field, respectively. Our numerical results show that the ground state energy is an increasing function of the electron areal density and the cyclotron frequency of the magnetic field. However, the ground state binding energy is a decreasing function of those.
Low-Energy Properties of Aperiodic Quantum Spin Chains
NASA Astrophysics Data System (ADS)
Vieira, André P.
2005-02-01
We investigate the low-energy properties of antiferromagnetic quantum XXZ spin chains with couplings following two-letter aperiodic sequences, by an adaptation of the Ma-Dasgupta-Hu renormalization-group method. For a given aperiodic sequence, we argue that, in the easy-plane anisotropy regime, intermediate between the XX and Heisenberg limits, the general scaling form of the thermodynamic properties is essentially given by the exactly known XX behavior, providing a classification of the effects of aperiodicity on XXZ chains. As representative illustrations, we present analytical and numerical results for the low-temperature thermodynamics and the ground-state correlations for couplings following the Fibonacci quasiperiodic structure and a binary Rudin-Shapiro sequence, whose geometrical fluctuations are similar to those induced by randomness.
Low-energy properties of aperiodic quantum spin chains.
Vieira, André P
2005-02-25
We investigate the low-energy properties of antiferromagnetic quantum XXZ spin chains with couplings following two-letter aperiodic sequences, by an adaptation of the Ma-Dasgupta-Hu renormalization-group method. For a given aperiodic sequence, we argue that, in the easy-plane anisotropy regime, intermediate between the XX and Heisenberg limits, the general scaling form of the thermodynamic properties is essentially given by the exactly known XX behavior, providing a classification of the effects of aperiodicity on XXZ chains. As representative illustrations, we present analytical and numerical results for the low-temperature thermodynamics and the ground-state correlations for couplings following the Fibonacci quasiperiodic structure and a binary Rudin-Shapiro sequence, whose geometrical fluctuations are similar to those induced by randomness.
Topological phases and transport properties of screened interacting quantum wires
NASA Astrophysics Data System (ADS)
Xu, Hengyi; Xiong, Ye; Wang, Jun
2016-10-01
We study theoretically the effects of long-range and on-site Coulomb interactions on the topological phases and transport properties of spin-orbit-coupled quasi-one-dimensional quantum wires imposed on a s-wave superconductor. The distributions of the electrostatic potential and charge density are calculated self-consistently within the Hartree approximation. Due to the finite width of the wires and charge repulsion, the potential and density distribute inhomogeneously in the transverse direction and tend to accumulate along the lateral edges where the hard-wall confinement is assumed. This result has profound effects on the topological phases and the differential conductance of the interacting quantum wires and their hybrid junctions with superconductors. Coulomb interactions renormalize the gate voltage and alter the topological phases strongly by enhancing the topological regimes and producing jagged boundaries. Moreover, the multicritical points connecting different topological phases are modified remarkably in striking contrast to the predictions of the two-band model. We further suggest the possible non-magnetic topological phase transitions manipulated externally with the aid of long-range interactions. Finally, the transport properties of normal-superconductor junctions are further examined, in particular, the impacts of Coulomb interactions on the zero-bias peaks related to the Majorana fermions and near zero-energy peaks.
Properties of reactive oxygen species by quantum Monte Carlo.
Zen, Andrea; Trout, Bernhardt L; Guidoni, Leonardo
2014-07-07
The electronic properties of the oxygen molecule, in its singlet and triplet states, and of many small oxygen-containing radicals and anions have important roles in different fields of chemistry, biology, and atmospheric science. Nevertheless, the electronic structure of such species is a challenge for ab initio computational approaches because of the difficulties to correctly describe the statical and dynamical correlation effects in presence of one or more unpaired electrons. Only the highest-level quantum chemical approaches can yield reliable characterizations of their molecular properties, such as binding energies, equilibrium structures, molecular vibrations, charge distribution, and polarizabilities. In this work we use the variational Monte Carlo (VMC) and the lattice regularized Monte Carlo (LRDMC) methods to investigate the equilibrium geometries and molecular properties of oxygen and oxygen reactive species. Quantum Monte Carlo methods are used in combination with the Jastrow Antisymmetrized Geminal Power (JAGP) wave function ansatz, which has been recently shown to effectively describe the statical and dynamical correlation of different molecular systems. In particular, we have studied the oxygen molecule, the superoxide anion, the nitric oxide radical and anion, the hydroxyl and hydroperoxyl radicals and their corresponding anions, and the hydrotrioxyl radical. Overall, the methodology was able to correctly describe the geometrical and electronic properties of these systems, through compact but fully-optimised basis sets and with a computational cost which scales as N(3) - N(4), where N is the number of electrons. This work is therefore opening the way to the accurate study of the energetics and of the reactivity of large and complex oxygen species by first principles.
Properties of reactive oxygen species by quantum Monte Carlo
NASA Astrophysics Data System (ADS)
Zen, Andrea; Trout, Bernhardt L.; Guidoni, Leonardo
2014-07-01
The electronic properties of the oxygen molecule, in its singlet and triplet states, and of many small oxygen-containing radicals and anions have important roles in different fields of chemistry, biology, and atmospheric science. Nevertheless, the electronic structure of such species is a challenge for ab initio computational approaches because of the difficulties to correctly describe the statical and dynamical correlation effects in presence of one or more unpaired electrons. Only the highest-level quantum chemical approaches can yield reliable characterizations of their molecular properties, such as binding energies, equilibrium structures, molecular vibrations, charge distribution, and polarizabilities. In this work we use the variational Monte Carlo (VMC) and the lattice regularized Monte Carlo (LRDMC) methods to investigate the equilibrium geometries and molecular properties of oxygen and oxygen reactive species. Quantum Monte Carlo methods are used in combination with the Jastrow Antisymmetrized Geminal Power (JAGP) wave function ansatz, which has been recently shown to effectively describe the statical and dynamical correlation of different molecular systems. In particular, we have studied the oxygen molecule, the superoxide anion, the nitric oxide radical and anion, the hydroxyl and hydroperoxyl radicals and their corresponding anions, and the hydrotrioxyl radical. Overall, the methodology was able to correctly describe the geometrical and electronic properties of these systems, through compact but fully-optimised basis sets and with a computational cost which scales as N3 - N4, where N is the number of electrons. This work is therefore opening the way to the accurate study of the energetics and of the reactivity of large and complex oxygen species by first principles.
Properties of reactive oxygen species by quantum Monte Carlo
Zen, Andrea; Trout, Bernhardt L.; Guidoni, Leonardo
2014-07-07
The electronic properties of the oxygen molecule, in its singlet and triplet states, and of many small oxygen-containing radicals and anions have important roles in different fields of chemistry, biology, and atmospheric science. Nevertheless, the electronic structure of such species is a challenge for ab initio computational approaches because of the difficulties to correctly describe the statical and dynamical correlation effects in presence of one or more unpaired electrons. Only the highest-level quantum chemical approaches can yield reliable characterizations of their molecular properties, such as binding energies, equilibrium structures, molecular vibrations, charge distribution, and polarizabilities. In this work we use the variational Monte Carlo (VMC) and the lattice regularized Monte Carlo (LRDMC) methods to investigate the equilibrium geometries and molecular properties of oxygen and oxygen reactive species. Quantum Monte Carlo methods are used in combination with the Jastrow Antisymmetrized Geminal Power (JAGP) wave function ansatz, which has been recently shown to effectively describe the statical and dynamical correlation of different molecular systems. In particular, we have studied the oxygen molecule, the superoxide anion, the nitric oxide radical and anion, the hydroxyl and hydroperoxyl radicals and their corresponding anions, and the hydrotrioxyl radical. Overall, the methodology was able to correctly describe the geometrical and electronic properties of these systems, through compact but fully-optimised basis sets and with a computational cost which scales as N{sup 3} − N{sup 4}, where N is the number of electrons. This work is therefore opening the way to the accurate study of the energetics and of the reactivity of large and complex oxygen species by first principles.
Super quantum measures on effect algebras with the Riesz decomposition properties
Xie, Yongjian Ren, Fang; Yang, Aili
2015-10-15
We give one basis of the space of super quantum measures on finite effect algebras with the Riesz decomposition properties (RDP for short). Then we prove that the super quantum measures and quantum interference functions on finite effect algebras with the RDP are determined each other. At last, we investigate the relationships between the super quantum measures and the diagonally positive signed measures on finite effect algebras with the RDP in detail.
NASA Astrophysics Data System (ADS)
Sin, Yongkun; Presser, Nathan; Lingley, Zachary; Brodie, Miles; Foran, Brendan; Moss, Steven C.
2016-03-01
High power single-mode (SM) and multi-mode (MM) InGaAs-AlGaAs strained quantum well (QW) lasers are critical components for both telecommunications and potential space satellite communications systems. However, little has been reported on failure modes of state-of-the-art SM InGaAs-AlGaAs strained QW lasers although it is crucial to understand failure modes and underlying degradation mechanisms in developing these lasers that meet lifetime requirements for space satellite systems, where extremely high reliability of these lasers is required. Our present study addresses the aforementioned issues by performing long-term life tests under different test conditions followed by failure mode analysis (FMA) and physics of failure investigation. We performed long-term accelerated life-tests on state-of-the-art SM and MM InGaAs-AlGaAs strained QW lasers under ACC (automatic current control) mode. Our life-tests have accumulated over 25,000 test hours for SM lasers and over 35,000 test hours for MM lasers. FMA was performed on failed SM lasers using electron beam induced current (EBIC). This technique allowed us to identify failure types by observing dark line defects. All the SM failures we studied showed catastrophic and sudden degradation and all of these failures were bulk failures. Our group previously reported that bulk failure or COBD (catastrophic optical bulk damage) is the dominant failure mode of MM InGaAs-AlGaAs strained QW lasers. To the best of our knowledge, this is the first report demonstrating that the dominant failure mode of both SM and MM InGaAs-AlGaAs strained QW lasers is the bulk failure. Since degradation mechanisms responsible for COBD are still not well understood, we also employed other techniques including focused ion beam (FIB) processing and high-resolution TEM to further study dark line defects and dislocations in post-aged SM and MM lasers. Our long-term life test results and FMA results are reported.
NASA Astrophysics Data System (ADS)
O'Brien, Jeremy
2013-03-01
Of the approaches to quantum computing, photons are appealing for their low-noise properties and ease of manipulation, and relevance to other quantum technologies, including communication, metrology and measurement. We report an integrated waveguide approach to photonic quantum circuits for high performance, miniaturization and scalability [6-10]. We address the challenges of scaling up quantum circuits using new insights into how controlled operations can be efficiently realised, demonstrating Shor's algorithm with consecutive CNOT gates and the iterative phase estimation algorithm. We have shown how quantum circuits can be reconfigured, using thermo-optic phase shifters to realise a highly reconfigurable quantum circuit, and electro-optic phase shifters in lithium niobate to rapidly manipulate the path and polarisation of telecomm wavelength single photons. We have addressed miniaturisation using multimode interference architectures to directly implement NxN Hadamard operations, and by using high refractive index contrast materials such as SiOxNy, in which we have implemented quantum walks of correlated photons, and Si, in which we have demonstrated generation of orbital angular momentum states of light. We have incorporated microfluidic channels for the delivery of samples to measure the concentration of a blood protein with entangled states of light. We have begun to address the integration of superconducting single photon detectors and diamond and non-linear single photon sources. Finally, we give an overview of recent work on fundamental aspects of quantum measurement, including a quantum version of Wheeler's delayed choice experiment.
Quantum properties of light emitted by dipole nano-laser
NASA Astrophysics Data System (ADS)
Ghannam, Talal
Recent technological advances allow entire optical systems to be lithographically implanted on small silicon chips. These systems include tiny semiconductor lasers that function as light sources for digital optical signals. Future advances will rely on even smaller components. At the theoretical limit of this process, the smallest lasers will have an active medium consisting of a single atom (natural or artificial). Several suggestions for how this can be accomplished have already been published, such as nano-lasers based on photonic crystals and nano wires. In particular, the "dipole nanolaser" consists of a single quantum dot functioning as the active medium. It is optically coupled to a metal nanoparticles that form a resonant cavity. Laser light is generated from the near-field optical signal. The proposed work is a theoretical exploration of the nature of the resulting laser light. The dynamics of the system will be studied and relevant time scales described. These will form the basis for a set of operator equations describing the quantum properties of the emitted light. The dynamics will be studied in both density matrix and quantum Langevin formulations, with attention directed to noise sources. The equations will be linearized and solved using standard techniques. The result of the study will be a set of predicted noise spectra describing the statistics of the emitted light. The goal will be to identify the major noise contributions and suggest methods for suppressing them. This will be done by studying the probability of getting squeezed light from the nanoparticle for the certain scheme of parameters.
Physical Properties as Modal Operators in the Topos Approach to Quantum Mechanics
NASA Astrophysics Data System (ADS)
Freytes, H.; Domenech, G.; de Ronde, C.
2014-12-01
In the framework of the topos approach to quantum mechanics we give a representation of physical properties in terms of modal operators on Heyting algebras. It allows us to introduce a classical type study of the mentioned properties.
Chlorine doped graphene quantum dots: Preparation, properties, and photovoltaic detectors
Zhao, Jianhong; Xiang, Jinzhong; Tang, Libin Ji, Rongbin Yuan, Jun; Zhao, Jun; Yu, Ruiyun; Tai, Yunjian; Song, Liyuan
2014-09-15
Graphene quantum dots (GQDs) are becoming one of the hottest advanced functional materials because of the opening of the bandgap due to quantum confinement effect, which shows unique optical and electrical properties. The chlorine doped GQDs (Cl-GQDs) have been fabricated by chemical exfoliation of HCl treated carbon fibers (CFs), which were prepared from degreasing cotton through an annealing process at 1000 °C for 30 min. Raman study shows that both G and 2D peaks of GQDs may be redshifted (softened) by chlorine doping, leading to an n-type doping. The first vertical (Cl)-GQDs based photovoltaic detectors have been demonstrated, both the light absorbing and electron-accepting roles for (Cl)-GQDs in photodetection have been found, resulting in an exceptionally big ratio of photocurrent to dark current as high as ∼10{sup 5} at room temperature using a 405 nm laser irradiation under the reverse bias voltage. The study expands the application of (Cl)-GQDs to the important optoelectronic detection devices.
Optical properties of transition metal oxide quantum wells
NASA Astrophysics Data System (ADS)
Demkov, Alexander; Choi, Miri; Butcher, Matthew; Rodriguez, Cesar; He, Qian; Posadas, Agham; Borisevich, Albina; Zollner, Stefan; Lin, Chungwei; Ortmann, Elliott
2015-03-01
We report on the investigation of SrTiO3/LaAlO3 quantum wells (QWs) grown by molecular beam epitaxy (MBE) on LaAlO3 substrate. Structures with different QW thicknesses ranging from two to ten unit cells were grown and characterized using x-ray photoemission spectroscopy, reflection high-energy electron diffraction (RHEED), scanning transmission electron microscopy (STEM). Optical properties (complex dielectric function) were measured by spectroscopic ellipsometry (SE) in the range of 1.0 eV to 6.0 eV at room temperature. We observed that the absorption edge was blue-shifted by approximately 0.39 eV as the STO quantum well thickness was reduced to two unit cells (uc). Density functional theory and tight-binding are used to model the optical response of these heterostructures. Our results demonstrate that the energy level of the first sub-band can be controlled by the QW thickness in a complex oxide material. We acknowledge support from Air Force Office of Scientific Research (FA9550-12-10494).
Nuclear Quantum Effects on Aqueous Electron Attachment and Redox Properties.
Rybkin, Vladimir V; VandeVondele, Joost
2017-04-06
Nuclear quantum effects (NQEs) on the reduction and oxidation properties of small aqueous species (CO2, HO2, and O2) are quantified and rationalized by first-principles molecular dynamics and thermodynamic integration. Vertical electron attachment, or electron affinity, and detachment energies (VEA and VDE) are strongly affected by NQEs, decreasing in absolute value by 0.3 eV going from a classical to a quantum description of the nuclei. The effect is attributed to NQEs that lessen the solvent response upon oxidation/reduction. The reduction of solvent reorganization energy is expected to be general for small solutes in water. In the thermodynamic integral that yields the free energy of oxidation/reduction, these large changes enter with opposite sign, and only a small net effect (0.1 eV) remains. This is not obvious for CO2, where the integrand is strongly influenced by NQEs due to the onset of interaction of the reduced orbital with the conduction band of the liquid during thermodynamic integration. We conclude that NQEs might not have to be included in the computation of redox potentials, unless high accuracy is needed, but are important for VEA and VDE calculations.
Fundamental Entangling Operators in Quantum Mechanics and Their Properties
NASA Astrophysics Data System (ADS)
Dao-Ming, Lu
2016-07-01
For the first time, we introduce so-called fundamental entangling operators e^{iQ1 P2} and e^{iP1 Q2 } for composing bipartite entangled states of continuum variables, where Q i and P i ( i = 1, 2) are coordinate and momentum operator, respectively. We then analyze how these entangling operators naturally appear in the quantum image of classical quadratic coordinate transformation ( q 1, q 2) → ( A q 1 + B q 2, C q 1 + D q 2), where A D- B C = 1, which means even the basic coordinate transformation ( Q 1, Q 2) → ( A Q 1 + B Q 2, C Q 1 + D Q 2) involves entangling mechanism. We also analyse their Lie algebraic properties and use the integration technique within an ordered product of operators to show they are also one- and two- mode combinatorial squeezing operators.
Optical properties of geometrically optimized graphene quantum dots
NASA Astrophysics Data System (ADS)
Bugajny, Paweł; Szulakowska, Ludmiła; Jaworowski, Błazej; Potasz, Paweł
2017-01-01
We derive effective tight-binding model for geometrically optimized graphene quantum dots and based on it we investigate corresponding changes in their optical properties in comparison to ideal structures. We consider hexagonal and triangular dots with zigzag and armchair edges. Using density functional theory methods we show that displacement of lattice sites leads to changes in atomic distances and in consequence modifies their energy spectrum. We derive appropriate model within tight-binding method with edge-modified hopping integrals. Using group theoretical analysis, we determine allowed optical transitions and investigate oscillatory strength between bulk-bulk, bulk-edge and edge-edge transitions. We compare optical joint density of states for ideal and geometry optimized structures. We also investigate an enhanced effect of sites displacement which can be designed in artificial graphene-like nanostructures. A shift of absorption peaks is found for small structures, vanishing with increasing system size.
Biju, Vasudevanpillai; Itoh, Tamitake; Ishikawa, Mitsuru
2010-08-01
Bioconjugated nanomaterials offer endless opportunities to advance both nanobiotechnology and biomedical technology. In this regard, semiconductor nanoparticles, also called quantum dots, are of particular interest for multimodal, multifunctional and multiplexed imaging of biomolecules, cells, tissues and animals. The unique optical properties, such as size-dependent tunable absorption and emission in the visible and NIR regions, narrow emission and broad absorption bands, high photoluminescence quantum yields, large one- and multi-photon absorption cross-sections, and exceptional photostability are the advantages of quantum dots. Multimodal imaging probes are developed by interfacing the unique optical properties of quantum dots with magnetic or radioactive materials. Besides, crystalline structure of quantum dots adds scope for high-contrast X-ray and TEM imaging. Yet another unique feature of a quantum dot is its spacious and flexible surface which is promising to integrate multiple ligands and antibodies and construct multi-functional probes for bioimaging. In this critical review, we will summarize recent advancements in the preparation of biocompatible quantum dots, bioconjugation of quantum dots, and applications of quantum dots and their bioconjugates for targeted and nonspecific imaging of extracellular and intracellular proteins, organelles and functions (181 references).
Quantum nonlocal effects on optical properties of spherical nanoparticles
Moradi, Afshin
2015-02-15
To study the scattering of electromagnetic radiation by a spherical metallic nanoparticle with quantum spatial dispersion, we develop the standard nonlocal Mie theory by allowing for the excitation of the quantum longitudinal plasmon modes. To describe the quantum nonlocal effects, we use the quantum longitudinal dielectric function of the system. As in the standard Mie theory, the electromagnetic fields are expanded in terms of spherical vector wavefunctions. Then, the usual Maxwell boundary conditions are imposed plus the appropriate additional boundary conditions. Examples of calculated extinction spectra are presented, and it is found that the frequencies of the subsidiary peaks, due to quantum bulk plasmon excitations exhibit strong dependence on the quantum spatial dispersion.
ERIC Educational Resources Information Center
Gunel, Murat; Hand, Brian; Gunduz, Sevket
2006-01-01
Physics as a subject for school students requires an understanding and ability to move between different modes of representation for the concepts under review. However, the inability of students to have a multimodal understanding of the concepts is seen as restricting their understandings of the concepts. The aim of this study was to explore the…
Passive interferometric symmetries of multimode Gaussian pure states
NASA Astrophysics Data System (ADS)
Gabay, Natasha; Menicucci, Nicolas C.
2016-05-01
As large-scale multimode Gaussian states begin to become accessible in the laboratory, their representation and analysis become a useful topic of research in their own right. The graphical calculus for Gaussian pure states provides powerful tools for their representation, while this work presents a useful tool for their analysis: passive interferometric (i.e., number-conserving) symmetries. Here we show that these symmetries of multimode Gaussian states simplify calculations in measurement-based quantum computing and provide constructive tools for engineering large-scale harmonic systems with specific physical properties, and we provide a general mathematical framework for deriving them. Such symmetries are generated by linear combinations of operators expressed in the Schwinger representation of U (2 ) , called nullifiers because the Gaussian state in question is a zero eigenstate of them. This general framework is shown to have applications in the noise analysis of continuous-various cluster states and is expected to have additional applications in future work with large-scale multimode Gaussian states.
Quantum memory for images: A quantum hologram
Vasilyev, Denis V.; Sokolov, Ivan V.; Polzik, Eugene S.
2008-02-15
Matter-light quantum interface and quantum memory for light are important ingredients of quantum information protocols, such as quantum networks, distributed quantum computation, etc. [P. Zoller et al., Eur. Phys. J. D 36, 203 (2005)]. In this paper we present a spatially multimode scheme for quantum memory for light, which we call a quantum hologram. Our approach uses a multiatom ensemble which has been shown to be efficient for a single spatial mode quantum memory. Due to the multiatom nature of the ensemble and to the optical parallelism it is capable of storing many spatial modes, a feature critical for the present proposal. A quantum hologram with the fidelity exceeding that of classical hologram will be able to store quantum features of an image, such as multimode superposition and entangled quantum states, something that a standard hologram is unable to achieve.
Quantum Chemical Study of the Thermochemical Properties of Organophosphorous Compounds.
Khalfa, A; Ferrari, M; Fournet, R; Sirjean, B; Verdier, L; Glaude, P A
2015-10-22
Organophosphorous compounds are involved in many toxic compounds such as fungicides, pesticides, or chemical warfare nerve agents. The understanding of the decomposition chemistry of these compounds in the environment is largely limited by the scarcity of thermochemical data. Because of the high toxicity of many of these molecules, experimental determination of their thermochemical properties is very difficult. In this work, standard gas-phase thermodynamic data, i.e., enthalpies of formation (ΔfH298°), standard entropies (S298°), and heat capacities (Cp°(T)), were determined using quantum chemical calculations and more specifically the CBS-QB3 composite method, which was found to be the best compromise between precision and calculation time among high accuracy composite methods. A large number of molecules was theoretically investigated, involving trivalent and pentavalent phosphorus atoms, and C, H, O, N, S, and F atoms. These data were used to propose 83 original groups, used in the semiempirical group contribution method proposed by Benson. Thanks to these latter group values, thermochemical properties of several nerve agents, common pesticides and herbicides have been evaluated. Bond dissociations energies (BDE), useful for the analysis the thermal stability of the compounds, were also determined in several molecules of interest.
Local field-induced optical properties of Ag-coated CdS quantum dots.
Je, Koo-Chul; Ju, Honglyoul; Treguer, Mona; Cardinal, Thierry; Park, Seung-Han
2006-08-21
Local field-induced optical properties of Ag-coated CdS quantum dot structures are investigated. We experimentally observe a clear exciton peak due to the quantum confinement effect in uncoated CdS quantum dots, and surface plasmon resonance and red-shifted exciton peak in Ag-coated CdS composite quantum dot structures. We have calculated the Stark shift of the exciton peak as a function of the local field for different silver thicknesses and various sizes of quantum dots based on the effective-mass Hamiltonian using the numerical-matrix-diagonalization method. Our theoretical calculations strongly indicate that the exciton peak is red-shifted in the metal-semiconductor composite quantum dots due to a strong local field, i.e., the quantum confined Stark effect.
Radiolabeled Nanoparticles for Multimodality Tumor Imaging
Xing, Yan; Zhao, Jinhua; Conti, Peter S.; Chen, Kai
2014-01-01
Each imaging modality has its own unique strengths. Multimodality imaging, taking advantages of strengths from two or more imaging modalities, can provide overall structural, functional, and molecular information, offering the prospect of improved diagnostic and therapeutic monitoring abilities. The devices of molecular imaging with multimodality and multifunction are of great value for cancer diagnosis and treatment, and greatly accelerate the development of radionuclide-based multimodal molecular imaging. Radiolabeled nanoparticles bearing intrinsic properties have gained great interest in multimodality tumor imaging over the past decade. Significant breakthrough has been made toward the development of various radiolabeled nanoparticles, which can be used as novel cancer diagnostic tools in multimodality imaging systems. It is expected that quantitative multimodality imaging with multifunctional radiolabeled nanoparticles will afford accurate and precise assessment of biological signatures in cancer in a real-time manner and thus, pave the path towards personalized cancer medicine. This review addresses advantages and challenges in developing multimodality imaging probes by using different types of nanoparticles, and summarizes the recent advances in the applications of radiolabeled nanoparticles for multimodal imaging of tumor. The key issues involved in the translation of radiolabeled nanoparticles to the clinic are also discussed. PMID:24505237
Potestio, R; Delle Site, L
2012-02-07
Parahydrogen is the spin-zero singlet state of molecular hydrogen, which at low temperature (between 14 and 25 K) is in a fluid state. A classical treatment of the system leads to unphysical freezing, and the inclusion of quantum delocalization of the molecule is then required to obtain a realistic description of its equilibrium properties. In the present work, we employ the classical-quantum adaptive resolution method AdResS to investigate the spatial extension of quantum delocalization effects in the bulk fluid at low temperature. Specifically, we simulate a small, spherical region of the system in full quantum detail: this region is coupled to a bulk of coarse-grained particles with classical, quantum-derived effective interactions obtained from quantum simulations. The two regions are interfaced through open boundaries and in conditions of thermodynamic equilibrium. Structural properties of the fluid, namely, pair distribution functions, are measured for different sizes of the quantum region. The results of this work show that, for the thermodynamic conditions corresponding to the range of temperature between 14 and 25 K, the bead-based, quantum structural properties of low-temperature parahydrogen are deemed local and do not require the support of an explicit quantum bulk.
Spectroscopic properties of colloidal indium phosphide quantum wires
Wang, Lin-Wang; Wang, Fudong; Yu, Heng; Li, Jingbo; Hang, Qingling; Zemlyanov, Dmitry; Gibbons, Patrick C.; Wang, Lin-Wang; Janes, David B.; Buhro, William E.
2008-07-11
Colloidal InP quantum wires are grown by the solution-liquid-solid (SLS) method, and passivated with the traditional quantum dots surfactants 1-hexadecylamine and tri-n-octylphosphine oxide. The size dependence of the band gaps in the wires are determined from the absorption spectra, and compared to other experimental results for InP quantum dots and wires, and to the predictions of theory. The photoluminescence behavior of the wires is also investigated. Efforts to enhance photoluminescence efficiencies through photochemical etching in the presence of HF result only in photochemical thinning or photo-oxidation, without a significant influence on quantum-wire photoluminescence. However, photo-oxidation produces residual dot and rod domains within the wires, which are luminescent. The results establish that the quantum-wire band gaps are weakly influenced by the nature of the surface passivation, and that colloidal quantum wires have intrinsically low photoluminescence efficiencies.
Niebuhr, Nina I. Johnen, Wibke; Güldaglar, Timur; Runz, Armin; Echner, Gernot; Mann, Philipp; Möhler, Christian; Pfaffenberger, Asja; Greilich, Steffen; Jäkel, Oliver
2016-02-15
Purpose: Phantom surrogates were developed to allow multimodal [computed tomography (CT), magnetic resonance imaging (MRI), and teletherapy] and anthropomorphic tissue simulation as well as materials and methods to construct deformable organ shapes and anthropomorphic bone models. Methods: Agarose gels of variable concentrations and loadings were investigated to simulate various soft tissue types. Oils, fats, and Vaseline were investigated as surrogates for adipose tissue and bone marrow. Anthropomorphic shapes of bone and organs were realized using 3D-printing techniques based on segmentations of patient CT-scans. All materials were characterized in dual energy CT and MRI to adapt CT numbers, electron density, effective atomic number, as well as T1- and T2-relaxation times to patient and literature values. Results: Soft tissue simulation could be achieved with agarose gels in combination with a gadolinium-based contrast agent and NaF to simulate muscle, prostate, and tumor tissues. Vegetable oils were shown to be a good representation for adipose tissue in all modalities. Inner bone was realized using a mixture of Vaseline and K{sub 2}HPO{sub 4}, resulting in both a fatty bone marrow signal in MRI and inhomogeneous areas of low and high attenuation in CT. The high attenuation of outer bone was additionally adapted by applying gypsum bandages to the 3D-printed hollow bone case with values up to 1200 HU. Deformable hollow organs were manufactured using silicone. Signal loss in the MR images based on the conductivity of the gels needs to be further investigated. Conclusions: The presented surrogates and techniques allow the customized construction of multimodality, anthropomorphic, and deformable phantoms as exemplarily shown for a pelvic phantom, which is intended to study adaptive treatment scenarios in MR-guided radiation therapy.
Nonlinear optical properties and supercontinuum spectrum of titania-modified carbon quantum dots
NASA Astrophysics Data System (ADS)
Kulchin, Yu N.; Mayor, A. Yu; Proschenko, D. Yu; Postnova, I. V.; Shchipunov, Yu A.
2016-04-01
We have studied the nonlinear optical properties and supercontinuum spectrum of solutions of carbon quantum dots prepared by a hydrothermal process from chitin and then coated with titania. The titania coating has been shown to have an activating effect on the carbon quantum dots, enhancing supercontinuum generation in the blue-violet spectral region and enabling their nonlinear optical characteristics to be varied.
Photoluminescence Properties Research on Graphene Quantum Dots/Silver Composites.
Wang, Jun; Li, Yan; Zhang, Bo-Ping; Xie, Dan-Dan; Ge, Juan; Liu, Hui
2016-04-01
Graphene quantum dots (GQDs) possess unique properties of graphene and exhibit a series of new phenomena of 0 dimension (D) carbon materials. Thus, GQDs have attracted much attention from researchers and have shown great promise for many applications. Recently, many works focus on GQDs-metal ions and metal nanoparticles (NPs). Although, many researches point out that metal ions and metal NPs have significant effect on photoluminescence (PL) feature of GQDs, mainly focus on PL intensity. Here, for the first time, we reported that metal NPs also affected PL peak position which was dependent on the mix mechanism of metal and GQDs. When GQDs-silver (Ag) composite mixed by physical method and excited at a wavelength of 320 nm, PL peak position of composites first showed blue-shifted then red-shifted with increasing of Ag content. However, if GQDs-Ag composite prepared by chemical method, PL peak position of the composites blue-shifted. Furthermore, the shift of PL peak position of GQDs-Ag prepared both for physical and chemical method displayed excitation-dependent feature. When the excitation wavelength approached to Ag SPR peaks, no obvious PL shift was observed. The mechanism for different PL shifts and the phenomenon of excitation-dependent PL shift as well as the formation mechanism of GQDs-Ag composite by chemical method are discussed in detail in this paper.
Experiments on the thermoelectric properties of quantum dots
NASA Astrophysics Data System (ADS)
Svilans, Artis; Leijnse, Martin; Linke, Heiner
2016-12-01
Quantum dots (QDs) are good model systems for fundamental studies of mesoscopic transport phenomena using thermoelectric effects because of their small size, electrostatically tunable properties and thermoelectric response characteristics that are very sensitive to small thermal biases. Here we provide a review of experimental studies on thermoelectric properties of single QDs realized in two-dimensional electron gases, single-walled carbon nanotubes and semiconductor nanowires. A key requirement for such experiments is to have some methods for nanoscale thermal biasing at one's disposal. We briefly review the main techniques used in the field, namely, heating of the QD contacts, side heating and top heating, and touch upon their relative advantages. The thermoelectric response of a QD as a function of gate potential has a characteristic oscillatory behavior with the same period as is observed for conductance peaks. Much of the existing literature focuses on the agreement between experiments and theory, particularly for amplitude and line-shape of the thermovoltage Vth. A general observation is that the widely used single-electron tunneling approximation for QDs has limited success in reproducing measured Vth. Landauer-type calculations are often found to describe measurement results better, despite the large electron-electron interactions in QDs. More recently, nonlinear thermoelectric effects have moved into the focus of attention, and we offer a brief overview of the experiments done so far. We conclude by discussing open questions and avenues for future work, including the role of asymmetries in tunnel- and capacitive couplings in the thermoelectric behavior of QDs. xml:lang="fr"
Tailoring the physical properties of thiol-capped PbS quantum dots by thermal annealing.
Turyanska, L; Elfurawi, U; Li, M; Fay, M W; Thomas, N R; Mann, S; Blokland, J H; Christianen, P C M; Patanè, A
2009-08-05
We show that the thermal annealing of thiol-capped PbS colloidal quantum dots provides a means of narrowing the nanoparticle size distribution, increasing the size of the quantum dots and facilitating their coalescence preferentially along the 100 crystallographic axes. We exploit these phenomena to tune the photoluminescence emission of an ensemble of dots and to narrow the optical linewidth to values that compare with those reported at room temperature for single PbS quantum dots. We probe the influence of annealing on the electronic properties of the quantum dots by temperature dependent studies of the photoluminescence and magneto-photoluminescence.
Laser Optical Biasing of the Quantum Transport Properties of n-InSb.
1976-10-01
of the SdH oscillations. The research being done is directed at obtaining fundamental information concerning the effects of CO and CO2 laser radiation on the quantum transport properties on n-InSb. (Author)
Novel Quantum States with Exotic Spin Properties - Unconventional Generalization of Magnetism
2011-12-30
REPORT Novel quantum states with exotic spin properties- -Unconventional generalization of magnetism 14. ABSTRACT 16. SECURITY CLASSIFICATION OF: My...interference (QPI) spectroscopy of the STM measurement, which is in nice agreement with the 1. REPORT DATE ( DD -MM-YYYY) 4. TITLE AND SUBTITLE 30-12...ANSI Std. Z39.18 - 30-Sep-2011 Novel quantum states with exotic spin properties- -Unconventional generalization of magnetism Report Title ABSTRACT My
Density functional calculation of the structural and electronic properties of germanium quantum dots
Anas, M. M.; Gopir, G.
2015-04-24
We apply first principles density functional computational methods to study the structures, densities of states (DOS), and higher occupied molecular orbital (HOMO) – lowest unoccupied molecular orbital (LUMO) gaps of selected free-standing Ge semiconductor quantum dots up to 1.8nm. Our calculations are performed using numerical atomic orbital approach where linear combination of atomic orbital was applied. The surfaces of the quantum dots was passivized by hydrogen atoms. We find that surface passivation does affect the electronic properties associated with the changes of surface state, electron localization, and the energy gaps of germanium nanocrystals as well as the confinement of electrons inside the quantum dots (QDs). Our study shows that the energy gaps of germanium quantum dots decreases with the increasing dot diameter. The size-dependent variations of the computed HOMO-LUMO gaps in our quantum dots model were found to be consistent with the effects of quantum confinement reported in others theoretical and experimental calculation.
Density functional calculation of the structural and electronic properties of germanium quantum dots
NASA Astrophysics Data System (ADS)
Anas, M. M.; Gopir, G.
2015-04-01
We apply first principles density functional computational methods to study the structures, densities of states (DOS), and higher occupied molecular orbital (HOMO) - lowest unoccupied molecular orbital (LUMO) gaps of selected free-standing Ge semiconductor quantum dots up to 1.8nm. Our calculations are performed using numerical atomic orbital approach where linear combination of atomic orbital was applied. The surfaces of the quantum dots was passivized by hydrogen atoms. We find that surface passivation does affect the electronic properties associated with the changes of surface state, electron localization, and the energy gaps of germanium nanocrystals as well as the confinement of electrons inside the quantum dots (QDs). Our study shows that the energy gaps of germanium quantum dots decreases with the increasing dot diameter. The size-dependent variations of the computed HOMO-LUMO gaps in our quantum dots model were found to be consistent with the effects of quantum confinement reported in others theoretical and experimental calculation.
Can observations inside the Solar System reveal the gravitational properties of the quantum vacuum?
NASA Astrophysics Data System (ADS)
Hajdukovic, Dragan Slavkov
2013-02-01
The understanding of the gravitational properties of the quantum vacuum might be the next scientific revolution. It was recently proposed that the quantum vacuum contains the virtual gravitational dipoles; we argue that this hypothesis might be tested within the Solar System. The key point is that the quantum vacuum ("enriched" with the gravitational dipoles) induces a retrograde precession of the perihelion. It is obvious that this phenomenon might eventually be revealed by more accurate studies of orbits of planets and orbits of the artificial Earth satellites. However, we suggest that potentially the best "laboratory" for the study of the gravitational properties of the quantum vacuum is the recently discovered dwarf planet Eris with its satellite named Dysnomia; the distance of nearly 100 AU from the Sun makes it the unique system in which the precession of the perihelion of Dysnomia (around Eris) is strongly dominated by the quantum vacuum.
Spectral properties of a strongly coupled quantum-dot-metal-nanoparticle system
NASA Astrophysics Data System (ADS)
Hakami, Jabir; Wang, Ligang; Zubairy, M. Suhail
2014-05-01
We investigate the coherent control of the quantum optical properties of a quantum dot coupled to a metallic nanoparticle using a photon Green's function method, which is based on the exact quantization of the electromagnetic fields in a dissipative medium. The properties of the spontaneous emission spectra of such a system are studied in detail with and without involving the coherent field. The Rabi splitting effect in the spectrum emitted by the quantum dot under particular conditions is predicted for different sizes of the metal nanoparticles. We show that the spontaneous emission spectra of the transition coupled to surface plasmons may be further modified by adjusting the external coherent control on the adjacent transitions. Furthermore, the pronounced oscillatory behavior for the quantum-dot dynamics is demonstrated with the presence of the metal nanoparticle by the non-Markovian treatment. Our results may have potential applications in plasmonic-based quantum manipulation.
Nonlinear thermoelectric response due to energy-dependent transport properties of a quantum dot
NASA Astrophysics Data System (ADS)
Svilans, Artis; Burke, Adam M.; Svensson, Sofia Fahlvik; Leijnse, Martin; Linke, Heiner
2016-08-01
Quantum dots are useful model systems for studying quantum thermoelectric behavior because of their highly energy-dependent electron transport properties, which are tunable by electrostatic gating. As a result of this strong energy dependence, the thermoelectric response of quantum dots is expected to be nonlinear with respect to an applied thermal bias. However, until now this effect has been challenging to observe because, first, it is experimentally difficult to apply a sufficiently large thermal bias at the nanoscale and, second, it is difficult to distinguish thermal bias effects from purely temperature-dependent effects due to overall heating of a device. Here we take advantage of a novel thermal biasing technique and demonstrate a nonlinear thermoelectric response in a quantum dot which is defined in a heterostructured semiconductor nanowire. We also show that a theoretical model based on the Master equations fully explains the observed nonlinear thermoelectric response given the energy-dependent transport properties of the quantum dot.
NASA Astrophysics Data System (ADS)
Gutierrez, Rafael M.; Castañeda, Arcesio
2009-08-01
Quantum mechanics explains the existence and properties of the chemical bond responsible for the formation of molecules from isolated atoms. In this work we study quantum states of Double Quantum Wells, DQW, formed from isolated Single Quantum Wells, SQWs, that can be considered metamaterials. Using the quantum chemistry definition of the covalent bond, we discuss molecular states in DQW as a kind of nanochemistry of metamaterials with new properties, in particular new optical properties. An important particularity of such nanochemistry, is the possible experimental control of the geometrical parameters and effective masses characterizing the semiconductor heterostructures represented by the corresponding DQW. This implies a great potential for new applications of the controlled optical properties of the metamaterials. The use of ab initio methods of intensive numerical calculations permits to obtain macroscopic optical properties of the metamaterials from the fundamental components: the spatial distribution of the atoms and molecules constituting the semiconductor layers. The metamaterial new optical properties emerge from the coexistence of many body processes at atomic and molecular level and complex quantum phenomena such as covalent-like bonds at nanometric dimensions.
Investigation of Laser Optical Biasing on the Quantum Transport Properties of n-InSb.
1979-10-01
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Goldmann, E. Jahnke, F.; Lorke, M.; Frauenheim, T.
2014-06-16
The saturation behaviour of optical gain with increasing excitation density is an important factor for laser device performance. For active materials based on self-organized InGaAs/GaAs quantum dots, we study the interplay between structural properties of the quantum dots and many-body effects of excited carriers in the optical properties via a combination of tight-binding and quantum-kinetic calculations. We identify regimes where either phase-space filling or excitation-induced dephasing dominates the saturation behavior of the optical gain. The latter can lead to the emergence of a negative differential material gain.
The Intersection of Multimodality and Critical Perspective: Multimodality as Subversion
ERIC Educational Resources Information Center
Huang, Shin-ying
2015-01-01
This study explores the relevance of multimodality to critical media literacy. It is based on the understanding that communication is intrinsically multimodal and multimodal communication is inherently social and ideological. By analysing two English-language learners' multimodal ensembles, the study reports on how multimodality contributes to a…
Quantum Monte Carlo methods and lithium cluster properties
Owen, R.K.
1990-12-01
Properties of small lithium clusters with sizes ranging from n = 1 to 5 atoms were investigated using quantum Monte Carlo (QMC) methods. Cluster geometries were found from complete active space self consistent field (CASSCF) calculations. A detailed development of the QMC method leading to the variational QMC (V-QMC) and diffusion QMC (D-QMC) methods is shown. The many-body aspect of electron correlation is introduced into the QMC importance sampling electron-electron correlation functions by using density dependent parameters, and are shown to increase the amount of correlation energy obtained in V-QMC calculations. A detailed analysis of D-QMC time-step bias is made and is found to be at least linear with respect to the time-step. The D-QMC calculations determined the lithium cluster ionization potentials to be 0.1982(14) [0.1981], 0.1895(9) [0.1874(4)], 0.1530(34) [0.1599(73)], 0.1664(37) [0.1724(110)], 0.1613(43) [0.1675(110)] Hartrees for lithium clusters n = 1 through 5, respectively; in good agreement with experimental results shown in the brackets. Also, the binding energies per atom was computed to be 0.0177(8) [0.0203(12)], 0.0188(10) [0.0220(21)], 0.0247(8) [0.0310(12)], 0.0253(8) [0.0351(8)] Hartrees for lithium clusters n = 2 through 5, respectively. The lithium cluster one-electron density is shown to have charge concentrations corresponding to nonnuclear attractors. The overall shape of the electronic charge density also bears a remarkable similarity with the anisotropic harmonic oscillator model shape for the given number of valence electrons.
Quantum Monte Carlo methods and lithium cluster properties. [Atomic clusters
Owen, R.K.
1990-12-01
Properties of small lithium clusters with sizes ranging from n = 1 to 5 atoms were investigated using quantum Monte Carlo (QMC) methods. Cluster geometries were found from complete active space self consistent field (CASSCF) calculations. A detailed development of the QMC method leading to the variational QMC (V-QMC) and diffusion QMC (D-QMC) methods is shown. The many-body aspect of electron correlation is introduced into the QMC importance sampling electron-electron correlation functions by using density dependent parameters, and are shown to increase the amount of correlation energy obtained in V-QMC calculations. A detailed analysis of D-QMC time-step bias is made and is found to be at least linear with respect to the time-step. The D-QMC calculations determined the lithium cluster ionization potentials to be 0.1982(14) (0.1981), 0.1895(9) (0.1874(4)), 0.1530(34) (0.1599(73)), 0.1664(37) (0.1724(110)), 0.1613(43) (0.1675(110)) Hartrees for lithium clusters n = 1 through 5, respectively; in good agreement with experimental results shown in the brackets. Also, the binding energies per atom was computed to be 0.0177(8) (0.0203(12)), 0.0188(10) (0.0220(21)), 0.0247(8) (0.0310(12)), 0.0253(8) (0.0351(8)) Hartrees for lithium clusters n = 2 through 5, respectively. The lithium cluster one-electron density is shown to have charge concentrations corresponding to nonnuclear attractors. The overall shape of the electronic charge density also bears a remarkable similarity with the anisotropic harmonic oscillator model shape for the given number of valence electrons.
Ultrafast optical properties of lithographically defined quantum dot amplifiers
Miaja-Avila, L.; Verma, V. B.; Mirin, R. P.; Silverman, K. L.; Coleman, J. J.
2014-02-10
We measure the ultrafast optical response of lithographically defined quantum dot amplifiers at 40 K. Recovery of the gain mostly occurs in less than 1 picosecond, with some longer-term transients attributable to carrier heating. Recovery of the absorption proceeds on a much longer timescale, representative of relaxation between quantum dot levels and carrier recombination. We also measure transparency current-density in these devices.
Properties of minimum spanning trees and fractional quantum Hall states
NASA Astrophysics Data System (ADS)
Jackson, Thomas Sundal
This dissertation consists of work done on two disjoint problems. In the first two chapters I discuss fractal properties of average-case solutions to the random minimal spanning tree (MST) problem: given a graph with costs on the edges, the MST is the spanning tree minimizing the sum of the total cost of the chosen edges. In the random version the costs are quenched random variables. I solve the random MST problem on the Bethe lattice with appropriate boundary conditions and use the results to infer fractal dimensions in the mean-field approximation. I find that connected components of the MST in a window have dimension D=6, which establishes the upper critical dimension dc=6. This contradicts a value dc=8 proposed previously in the literature; I correct the argument that led to this value. I then develop an exact low-density expansion for the random MST on a finite graph and use it to develop an expansion for the MST on critical percolation clusters. I prove this perturbation expansion is renormalizable around dc=6. Using a renormalization-group approach, I calculate the fractal dimension Dp of paths on the latter MST to first order in epsilon=6-d for d≤6, with the result Dp˜2-epsilon/7. In the final chapter, I investigate the correspondence between wavefunctions in the fractional quantum Hall effect obtained as blocks of a conformal field theory (CFT) versus those defined as zero-energy eigenstates of projection Hamiltonians, specifically one which forbids three particles to come together in one of two linearly-independent states of relative angular momentum six and all states of lesser relative angular momentum. I construct zero-energy states from amplitudes of superconformal currents using a result due to Simon. The counting of edge excitations of these states agrees with the character formula for the superconformal Kac vacuum module at generic central charge c, which implies this Hamiltonian is gapless for all c. I attempt to obtain a rational theory by
Optical Properties of Quantum Vacuum. Space-Time Engineering
Gevorkyan, A. S.; Gevorkyan, A. A.
2011-03-28
The propagation of electromagnetic waves in the vacuum is considered taking into account quantum fluctuations in the limits of Maxwell-Langevin (ML) type stochastic differential equations. For a model of fluctuations, type of 'white noise', using ML equations a partial differential equation of second order is obtained which describes the quantum distribution of virtual particles in vacuum. It is proved that in order to satisfy observed facts, the Lamb Shift etc, the virtual particles should be quantized in unperturbed vacuum. It is shown that the quantized virtual particles in toto (approximately 86 percent) are condensed on the 'ground state' energy level. It is proved that the extension of Maxwell electrodynamics with inclusion of quantum vacuum fluctuations may be constructed on a 6D space-time continuum, where 4D is Minkowski space-time and 2D is a compactified subspace. In detail is studied of vacuum's refraction indexes under the influence of external electromagnetic fields.
Tuning the optical properties of dilute nitride site controlled quantum dots
Juska, G.; Dimastrodonato, V.; Mereni, L. O.; Gocalinska, A.; Pelucchi, E.
2013-12-04
We show that deterministic control of the properties of pyramidal site-controlled quantum dots (QD) could be achieved by exposing the QD layer to nitrogen precursor unsymmetrical dimethylhydrazine (UDMHy). The properties that could be tuned include an expected emission reduction in dilute nitride materials, excitonic pattern (biexciton binding energy) and improved carrier confinement potential symmetry (reduced fine-structure splitting)
Emergence of equilibrium thermodynamic properties in quantum pure states. I. Theory
Fresch, Barbara; Moro, Giorgio J.
2010-07-21
Investigation on foundational aspects of quantum statistical mechanics recently entered a renaissance period due to novel intuitions from quantum information theory and to increasing attention on the dynamical aspects of single quantum systems. In the present contribution a simple but effective theoretical framework is introduced to clarify the connections between a purely mechanical description and the thermodynamic characterization of the equilibrium state of an isolated quantum system. A salient feature of our approach is the very transparent distinction between the statistical aspects and the dynamical aspects in the description of isolated quantum systems. Like in the classical statistical mechanics, the equilibrium distribution of any property is identified on the basis of the time evolution of the considered system. As a consequence equilibrium properties of quantum system appear to depend on the details of the initial state due to the abundance of constants of the motion in the Schroedinger dynamics. On the other hand the study of the probability distributions of some functions, such as the entropy or the equilibrium state of a subsystem, in statistical ensembles of pure states reveals the crucial role of typicality as the bridge between macroscopic thermodynamics and microscopic quantum dynamics. We shall consider two particular ensembles: the random pure state ensemble and the fixed expectation energy ensemble. The relation between the introduced ensembles, the properties of a given isolated system, and the standard quantum statistical description are discussed throughout the presentation. Finally we point out the conditions which should be satisfied by an ensemble in order to get meaningful thermodynamical characterization of an isolated quantum system.
Shen, Yi; Tan, Rui; Gee, Megan Y; Greytak, Andrew B
2015-03-24
This article describes an experiment designed to identify the role of specific molecular ligands in maintaining the high photoluminescence (PL) quantum yield (QY) observed in as-synthesized CdSe/CdZnS and CdSe/CdS quantum dots (QDs). Although it has been possible for many years to prepare core/shell quantum dots with near-unity quantum yield through high-temperature colloidal synthesis, purification of such colloidal particles is frequently accompanied by a reduction in quantum yield. Here, a recently established gel permeation chromatography (GPC) technique is used to remove weakly associated ligands without a change in solvent: a decrease in ensemble QY and average PL lifetime is observed. Minor components of the initial mixture that were removed by GPC are then added separately to purified QD samples to determine whether reintroduction of these components can restore the photophysical properties of the initial sample. We show that among these putative ligands trioctylphosphine and cadmium oleate can regenerate the initial high QY of all samples, but only the "L-type" ligands (trioctyphosphine and oleylamine) can restore the QY without changing the shapes of the optical spectra. On the basis of the PL decay analysis, we confirm that quenching in GPC-purified samples and regeneration in ligand-introduced samples are associated chiefly with changes in the relative population fraction of QDs with different decay rates. The reversibility of the QY regeneration process has also been studied; the introduction and removal of trioctylphosphine and oleylamine tend to be reversible, while cadmium oleate is not. Finally, isothermal titration calorimetry has been used to study the relationship between the binding strength of the neutral ligands to the surface and photophysical property changes in QD samples to which they are added.
Linear and nonlinear optical properties of anisotropic quantum dots in a magnetic field
NASA Astrophysics Data System (ADS)
Xie, Wenfang
2013-05-01
We have investigated the linear and nonlinear optical properties of a two-dimensional anisotropic quantum dot in a magnetic field. Based on the computed energies and wave functions, the linear, third-order nonlinear and total optical absorption coefficients as well as the refractive index changes have been examined. The results are presented as a function of the incident photon energy for the different cases of anisotropy, dot size and external magnetic field. The results show that the linear and nonlinear optical properties of anisotropic quantum dots are strongly affected by the degree of anisotropy, the dot size, the external magnetic field and the polarized direction of the incident electromagnetic wave. The result also shows that the size effect of anisotropy quantum dots on the optical absorptions is different from that of isotropic quantum dots.
Bound state properties of ABC-stacked trilayer graphene quantum dots.
Xiong, Haonan; Jiang, Wentao; Song, Yipu; Duan, Luming
2017-04-03
The few-layer graphene quantum dot provides a promising platform for quantum computing with both spin and valley degrees of freedom. Gate-defined quantum dots in particular can avoid noise from edge disorders. In connection with the recent experimental efforts [Y. Song et al., Nano Lett. 16, 6245 (2016)], we investigate the bound state properties of trilayer graphene (TLG) quantum dots (QDs) through numerical simulations. We show that the valley degeneracy can be lifted by breaking the time reversal symmetry through the application of a perpendicular magnetic field. The spectrum under such a potential exhibits a transition from one group of Landau levels to the other group, which can be understood analytically through perturbation theory. Our results provide insight to the transport property of TLG QDs, with possible applications to study of spin qubits and valleytronics in TLG QDs.
On quantum Rényi entropies: A new generalization and some properties
Müller-Lennert, Martin; Dupuis, Frédéric; Szehr, Oleg; Fehr, Serge; Tomamichel, Marco
2013-12-15
The Rényi entropies constitute a family of information measures that generalizes the well-known Shannon entropy, inheriting many of its properties. They appear in the form of unconditional and conditional entropies, relative entropies, or mutual information, and have found many applications in information theory and beyond. Various generalizations of Rényi entropies to the quantum setting have been proposed, most prominently Petz's quasi-entropies and Renner's conditional min-, max-, and collision entropy. However, these quantum extensions are incompatible and thus unsatisfactory. We propose a new quantum generalization of the family of Rényi entropies that contains the von Neumann entropy, min-entropy, collision entropy, and the max-entropy as special cases, thus encompassing most quantum entropies in use today. We show several natural properties for this definition, including data-processing inequalities, a duality relation, and an entropic uncertainty relation.
Quantum Optical Lattices for Emergent Many-Body Phases of Ultracold Atoms
NASA Astrophysics Data System (ADS)
Caballero-Benitez, Santiago F.; Mekhov, Igor B.
2015-12-01
Confining ultracold gases in cavities creates a paradigm of quantum trapping potentials. We show that this allows us to bridge models with global collective and short-range interactions as novel quantum phases possess properties of both. Some phases appear solely due to quantum light-matter correlations. Because of a global, but spatially structured, interaction, the competition between quantum matter and light waves leads to multimode structures even in single-mode cavities, including delocalized dimers of matter-field coherences (bonds), beyond density orders as supersolids and density waves.
The properties of Q-deformed hyperbolic and trigonometric functions in quantum deformation
Deta, U. A. E-mail: utamadeta@unesa.ac.id; Suparmi
2015-09-30
Quantum deformation has been studied due to its relation with applications in nuclear physics, conformal field theory, and statistical-quantum theory. The q-deformation of hyperbolic function was introduced by Arai. The application of q-deformed functions has been widely used in quantum mechanics. The properties of this two kinds of system explained in this paper including their derivative. The graph of q-deformed functions presented using Matlab. The special case is given for modified Poschl-Teller plus q-deformed Scarf II trigonometry potentials.
Markov property and strong additivity of von Neumann entropy for graded quantum systems
Moriya, Hajime
2006-03-15
The quantum Markov property is equivalent to the strong additivity of von Neumann entropy for graded quantum systems. The additivity of von Neumann entropy for bipartite graded systems implies the statistical independence of states. However, the structure of Markov states for graded systems is different from that for tensor-product systems which have trivial grading. For three-composed graded systems we have U(1)-gauge invariant Markov states whose restriction to the marginal pair of subsystems is nonseparable.
Erogbogbo, Folarin; Yong, Ken-Tye; Hu, Rui; Law, Wing-Cheung; Ding, Hong; Chang, Ching-Wen; Prasad, Paras N; Swihart, Mark T
2010-09-28
Luminescent silicon quantum dots (SiQDs) are gaining momentum in bioimaging applications, based on their unique combination of optical properties and biocompatibility. Here, we report the development of a multimodal probe that combines the optical properties of silicon quantum dots with the superparamagnetic properties of iron oxide nanoparticles to create biocompatible magnetofluorescent nanoprobes. Multiple nanoparticles of each type are coencapsulated within the hydrophobic core of biocompatible phospholipid-polyethyleneglycol (DSPE-PEG) micelles. The size distribution and composition of the magnetofluorescent nanoprobes were characterized by transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). Enhanced cellular uptake of these probes in the presence of a magnetic field was demonstrated in vitro. Their luminescence stability in a prostate cancer tumor model microenvironment was demonstrated in vivo. This paves the way for multimodal silicon quantum-dot-based nanoplatforms for a variety of imaging and delivery applications.
Optical and electronic properties of quantum dots with magnetic impurities
NASA Astrophysics Data System (ADS)
Govorov, Alexander O.
2008-10-01
The article discusses some of the recent results on semiconductor quantum dots with magnetic impurities. A single Mn impurity incorporated in a quantum dot strongly changes the optical response of a quantum-dot system. A character of Mn-carrier interaction is very different for II-VI and III-V quantum dots (QDs). In the II-VI QDs, a Mn impurity influences mostly the spin-structure of an exciton. In the III-V dots, a spatial localization of hole by a Mn impurity can be very important, and ultimately yields a totally different spin structure. A Mn-doped QD with a variable number of mobile carriers represents an artificial magnetic atom. Due to the Mn-carrier interaction, the order of filling of electronic shells in the magnetic QDs can be very different to the case of the real atoms. The "periodic" table of the artificial magnetic atoms can be realized in voltage-tunable transistor structures. For the electron numbers corresponding to the regime of Hund's rule, the magnetic Mn-carrier coupling is especially strong and the magnetic-polaron states are very robust. Magnetic QD molecules are also very different to the real molecules. QD molecules can demonstrate spontaneous breaking of symmetry and phase transitions. Single QDs and QD molecules can be viewed as voltage-tunable nanoscale memory cells where information is stored in the form of robust magnetic-polaron states. To cite this article: A.O. Govorov, C. R. Physique 9 (2008).
Temporal Multimode Storage of Entangled Photon Pairs
NASA Astrophysics Data System (ADS)
Tiranov, Alexey; Strassmann, Peter C.; Lavoie, Jonathan; Brunner, Nicolas; Huber, Marcus; Verma, Varun B.; Nam, Sae Woo; Mirin, Richard P.; Lita, Adriana E.; Marsili, Francesco; Afzelius, Mikael; Bussières, Félix; Gisin, Nicolas
2016-12-01
Multiplexed quantum memories capable of storing and processing entangled photons are essential for the development of quantum networks. In this context, we demonstrate and certify the simultaneous storage and retrieval of two entangled photons inside a solid-state quantum memory and measure a temporal multimode capacity of ten modes. This is achieved by producing two polarization-entangled pairs from parametric down-conversion and mapping one photon of each pair onto a rare-earth-ion-doped (REID) crystal using the atomic frequency comb (AFC) protocol. We develop a concept of indirect entanglement witnesses, which can be used as Schmidt number witnesses, and we use it to experimentally certify the presence of more than one entangled pair retrieved from the quantum memory. Our work puts forward REID-AFC as a platform compatible with temporal multiplexing of several entangled photon pairs along with a new entanglement certification method, useful for the characterization of multiplexed quantum memories.
NASA Astrophysics Data System (ADS)
Chen, Roland K.; Shih, A. J.
2013-08-01
This study develops a new class of gellan gum-based tissue-mimicking phantom material and a model to predict and control the elastic modulus, thermal conductivity, and electrical conductivity by adjusting the mass fractions of gellan gum, propylene glycol, and sodium chloride, respectively. One of the advantages of gellan gum is its gelling efficiency allowing highly regulable mechanical properties (elastic modulus, toughness, etc). An experiment was performed on 16 gellan gum-based tissue-mimicking phantoms and a regression model was fit to quantitatively predict three material properties (elastic modulus, thermal conductivity, and electrical conductivity) based on the phantom material's composition. Based on these material properties and the regression model developed, tissue-mimicking phantoms of porcine spinal cord and liver were formulated. These gellan gum tissue-mimicking phantoms have the mechanical, thermal, and electrical properties approximately equivalent to those of the spinal cord and the liver.
Quantum-Theoretical Methods and Studies Relating to Properties of Materials
1989-12-19
V. B.; Halow, I.; Bailey, S. M.; Schumm, R. H. Selected Values of Chemical Thermodynamic Properties , NBS Technical Note 270-3, Nat]. Bur. Stands... Thermodynamic Properties of Individual Substances (in Russian); Glyshko, W. P., Ed.; Science: Moscow, 1982. (14) Shimanouchi, T. J. Phys. Chem. Ref. Data...Theoretical Methods and Studies Relating to Properties of Materials. -’This research concerned-the development of new ab initio nonempirical quantum
ERIC Educational Resources Information Center
Casey, Heather
2012-01-01
Multimodal learning clubs link principles of motivation and engagement with 21st century technological tools and texts to support content area learning. The author describes how a sixth grade health teacher and his class incorporated multimodal learning clubs into a unit of study on human body systems. The students worked collaboratively online…
Dispersion properties of compressional electromagnetic waves in quantum dusty magnetoplasmas
Ali, S.; Shukla, P.K.
2006-05-15
A new dispersion relation for low-frequency compressional electromagnetic waves is derived by employing quantum magnetohydrodynamic model and Maxwell equations in cold quantum dusty magnetoplasmas. The latter is composed of inertialess electrons, mobile ions, and immobile charged dust particulates. The dispersion relation for the low-frequency compressional electromagnetic modes is further analyzed for the waves propagating parallel, perpendicular, and oblique to the external magnetic field direction. It is found theoretically and numerically that the quantum parameter {alpha}{sub q}=(n{sub i0}/n{sub e0})({Dirac_h}/2{pi}){sup 2}/(4m{sub e}m{sub i}) affects the real angular frequencies and the phase speeds of the compressional electromagnetic modes. Here, n{sub i0} (n{sub e0}) is the equilibrium number density of the ions (electrons), m{sub e} (m{sub i}) is the electron (ion) mass, and ({Dirac_h}/2{pi}) is the Plank constant divided by 2{pi}.
Properties of classical and quantum Jensen-Shannon divergence
Brieet, Jop; Harremoees, Peter
2009-05-15
Jensen-Shannon divergence (JD) is a symmetrized and smoothed version of the most important divergence measure of information theory, Kullback divergence. As opposed to Kullback divergence it determines in a very direct way a metric; indeed, it is the square of a metric. We consider a family of divergence measures (JD{sub {alpha}} for {alpha}>0), the Jensen divergences of order {alpha}, which generalize JD as JD{sub 1}=JD. Using a result of Schoenberg, we prove that JD{sub {alpha}} is the square of a metric for {alpha} is an element of (0,2], and that the resulting metric space of probability distributions can be isometrically embedded in a real Hilbert space. Quantum Jensen-Shannon divergence (QJD) is a symmetrized and smoothed version of quantum relative entropy and can be extended to a family of quantum Jensen divergences of order {alpha} (QJD{sub {alpha}}). We strengthen results by Lamberti and co-workers by proving that for qubits and pure states, QJD{sub {alpha}}{sup 1/2} is a metric space which can be isometrically embedded in a real Hilbert space when {alpha} is an element of (0,2]. In analogy with Burbea and Rao's generalization of JD, we also define general QJD by associating a Jensen-type quantity to any weighted family of states. Appropriate interpretations of quantities introduced are discussed and bounds are derived in terms of the total variation and trace distance.
Quantum Monte Carlo Calculations of Nanostructure Optical Properties
NASA Astrophysics Data System (ADS)
Williamson, Andrew
2003-03-01
Near linear scaling Quantum Monte Carlo (QMC) calculations[1] are used to calculate the optical gaps, electron affinities, and ionization potentials of silicon and germanium quantum dots ranging in size from 0 to 2 nm[2]. These QMC results are used to examine the accuracy of semi-empirical and density functional (DFT) calculations. We find optical gaps are underestimated by DFT by 1-2 eV depending on choice of functional. Corrections introduced by the time dependent formalisms are found to be minimal in these systems. Our results also show that quantum confinement in germanium is significantly greater than in silicon leading to a crossover of their optical gaps in dots between 2 and 3 nm in size, verifying recent experiment observations. [1] A. J. Williamson, R.Q. Hood and J.C. Grossman, Phys. Rev. Lett. 87, 246406-1 (2001). [2] A.J. Williamson J.C. Grossman, R.Q. Hood, A. Puzder and Giulia Galli, Phys. Rev. Lett, 89, 196803 (2002).
Synthesis, properties and biomedical applications of carbon-based quantum dots: An updated review.
Namdari, Pooria; Negahdari, Babak; Eatemadi, Ali
2017-03-01
Carbon-based quantum dots (CQDs) are a newly developed class of carbon nano-materials that have attracted much interest and attention as promising competitors to already available semiconductor quantum dots owing to their un-comparable and unique properties. In addition, controllability of CQDs unique physiochemical properties is as a result of their surface passivation and functionalization. This is an update article (between 2013 and 2016) on the recent progress, characteristics and synthesis methods of CQDs and different advantages in varieties of applications.
NASA Astrophysics Data System (ADS)
Jha, Pradip Kumar; Kumar, Manoj; Lahon, Siddhartha; Gumber, Sukirti; Mohan, Man
2014-01-01
Here we have investigated the influence of external magnetic field on the optical absorption and refractive index changes of a parabolically confined quantum dot in the presence of Rashba spin orbit interaction. We have used density matrix formulation for obtaining optical properties within the effective mass approximation. The results are presented as a function of quantum confinement potential, magnetic field, Rashba spin orbit interaction strength and photon energy. Our results indicate the important influence of magnetic field on the peak positions of absorption coefficient and refractive index changes. The role of confinement strength and spin orbit interaction strength as control parameters on the linear and nonlinear properties have been demonstrated.
Wei, Wei; Dai, Ying; Niu, Chengwang; Huang, Baibiao
2015-01-01
In-plane transition-metal dichalcogenides (TMDs) quantum wells have been studied on the basis of first-principles density functional calculations to reveal how to control the electronic structures and the properties. In collection of quantum confinement, strain and intrinsic electric field, TMD quantum wells offer a diverse of exciting new physics. The band gap can be continuously reduced ascribed to the potential drop over the embedded TMD and the strain substantially affects the band gap nature. The true type-II alignment forms due to the coherent lattice and strong interface coupling suggesting the effective separation and collection of excitons. Interestingly, two-dimensional quantum wells of in-plane TMD can enrich the photoluminescence properties of TMD materials. The intrinsic electric polarization enhances the spin-orbital coupling and demonstrates the possibility to achieve topological insulator state and valleytronics in TMD quantum wells. In-plane TMD quantum wells have opened up new possibilities of applications in next-generation devices at nanoscale. PMID:26616013
Specific features of photoluminescence properties of copper-doped cadmium selenide quantum dots
Tselikov, G. I.; Dorofeev, S. G.; Tananaev, P. N.; Timoshenko, V. Yu.
2011-09-15
The effect of doping with copper on the photoluminescence properties of cadmium selenide quantum dots 4 nm in dimension is studied. The quenching of the excitonic photoluminescence band related to the quantum dots and the appearance of an impurity photoluminescence band in the near-infrared region are observed after doping of the quantum dots with copper. It is established that, on doping of the quantum dots, the photoluminescence kinetics undergoes substantial changes. The photoluminescence kinetics of the undoped quantum dots is adequately described by a sum of exponential relaxation relations, whereas the photoluminescence kinetics experimentally observed in the region of the impurity band of the copper-doped samples follows stretched exponential decay, with the average lifetimes 0.3-0.6 {mu}s at the photon energies in the range of 1.47-1.82 eV. The experimentally observed changes in the photoluminescence properties are attributed to transformation of radiative centers in the quantum dots when doped with copper atoms.
Pinto, S.; Roldan Gutierrez, Manuel A; Ramos, M. M.D.; Gomes, M.J.M.; Molina, S. I.; Pennycook, Stephen J; Varela del Arco, Maria; Buljan, M.; Barradas, N.; Alves, E.; Chahboun, A.; Bernstorff, S.
2012-01-01
In this work, we investigate the structural properties of Ge quantum dot lattices in amorphous silica matrix, prepared by low-temperature magnetron sputtering deposition of (Ge+SiO{sub 2})/SiO{sub 2} multilayers. The dependence of quantum dot shape, size, separation, and arrangement type on the Ge-rich (Ge + SiO{sub 2}) layer thickness is studied. We show that the quantum dots are elongated along the growth direction, perpendicular to the multilayer surface. The size of the quantum dots and their separation along the growth direction can be tuned by changing the Ge-rich layer thickness. The average value of the quantum dots size along the lateral (in-plane) direction along with their lateral separation is not affected by the thickness of the Ge-rich layer. However, the thickness of the Ge-rich layer significantly affects the quantum dot ordering. In addition, we investigate the dependence of the multilayer average atomic composition and also the quantum dot crystalline quality on the deposition parameters.
Pinto, S. R. C.; Ramos, M. M. D.; Gomes, M. J. M.; Buljan, M.; Chahboun, A.; Roldan, M. A.; Molina, S. I.; Bernstorff, S.; Varela, M.; Pennycook, S. J.; Barradas, N. P.; Alves, E.
2012-04-01
In this work, we investigate the structural properties of Ge quantum dot lattices in amorphous silica matrix, prepared by low-temperature magnetron sputtering deposition of (Ge+SiO{sub 2})/SiO{sub 2} multilayers. The dependence of quantum dot shape, size, separation, and arrangement type on the Ge-rich (Ge + SiO{sub 2}) layer thickness is studied. We show that the quantum dots are elongated along the growth direction, perpendicular to the multilayer surface. The size of the quantum dots and their separation along the growth direction can be tuned by changing the Ge-rich layer thickness. The average value of the quantum dots size along the lateral (in-plane) direction along with their lateral separation is not affected by the thickness of the Ge-rich layer. However, the thickness of the Ge-rich layer significantly affects the quantum dot ordering. In addition, we investigate the dependence of the multilayer average atomic composition and also the quantum dot crystalline quality on the deposition parameters.
Realistic Many-Body Quantum Systems vs. Full Random Matrices: Static and Dynamical Properties
NASA Astrophysics Data System (ADS)
Torres-Herrera, Eduardo; Karp, Jonathan; Távora, Marco; Santos, Lea
2016-10-01
We study the static and dynamical properties of isolated many-body quantum systems and compare them with the results for full random matrices. In doing so, we link concepts from quantum information theory with those from quantum chaos. In particular, we relate the von Neumann entanglement entropy with the Shannon information entropy and discuss their relevance for the analysis of the degree of complexity of the eigenstates, the behavior of the system at different time scales and the conditions for thermalization. A main advantage of full random matrices is that they enable the derivation of analytical expressions that agree extremely well with the numerics and provide bounds for realistic many-body quantum systems.
Homayoon, Zahra
2014-09-28
A new, full (nine)-dimensional potential energy surface and dipole moment surface to describe the NO{sup +}(H{sub 2}O) cluster is reported. The PES is based on fitting of roughly 32 000 CCSD(T)-F12/aug-cc-pVTZ electronic energies. The surface is a linear least-squares fit using a permutationally invariant basis with Morse-type variables. The PES is used in a Diffusion Monte Carlo study of the zero-point energy and wavefunction of the NO{sup +}(H{sub 2}O) and NO{sup +}(D{sub 2}O) complexes. Using the calculated ZPE the dissociation energies of the clusters are reported. Vibrational configuration interaction calculations of NO{sup +}(H{sub 2}O) and NO{sup +}(D{sub 2}O) using the MULTIMODE program are performed. The fundamental, a number of overtone, and combination states of the clusters are reported. The IR spectrum of the NO{sup +}(H{sub 2}O) cluster is calculated using 4, 5, 7, and 8 modes VSCF/CI calculations. The anharmonic, coupled vibrational calculations, and IR spectrum show very good agreement with experiment. Mode coupling of the water “antisymmetric” stretching mode with the low-frequency intermolecular modes results in intensity borrowing.
NASA Astrophysics Data System (ADS)
Panda, Debiprasad; Ahmad, Aijaz; Adhikary, Sourav; Ghadi, Hemant; Chakrabarti, Subhananda
2016-09-01
In this paper, we have proposed a technique to maintain the constant overgrowth percentage of quantum dots (QDs) in all layers of a multistacked heterostructure and hence the dot size uniformity is achieved. Two samples have been grown and compared in terms of their optical properties. Post growth annealing was carried out to observe the variation in their properties. The active layer of sample A is composed of 2.7 monolayer (ML) InAs QDs and the QD deposition amount is same for all the stacks. For the proposed sample B, 8ML In(Ga)As QDs were grown as seed layer, and the subsequent QD deposition is kept constant at 5ML. The overgrowth percentage in all QD layers were constant ( 40%) for this sample. Monomodal photoluminescence (PL) emission spectra was observed for the proposed sample B, whereas sample A has multimodal spectra. The samples were subjected to post growth annealing in argon atmosphere for 650, 700, 750, 800, 850, and 900°C. A negligible shift in the PL peak was observed for sample B up to 750°C, which confirms better thermal stability. The PL activation energy variation with respect to the annealed temperature was negligible for the proposed sample B ( 165 meV up to 750 °C). Hence the proposed growth mode of In(Ga)As multistacked QD heterostructure has better optical characteristics than the conventional structure in terms of PL spectra, FWHM, and also activation energy.
Negative circular polarization as a universal property of quantum dots
Taylor, Matthew W.; Spencer, Peter; Murray, Ray
2015-03-23
This paper shows that negative circular polarization, a spin flip of polarized carriers resulting in emission of opposite helicity, can be observed in undoped, n-doped, and p-doped InAs/GaAs quantum dots. These results contradict the usual interpretation of the effect. We show using power dependent and time resolved spectroscopy that the generation of negative circular polarization correlates with excited state emission. Furthermore, a longer spin lifetime of negatively polarized excitons is observed where emission is largely ground state in character.
Some Properties of Generalized Connections in Quantum Gravity
NASA Astrophysics Data System (ADS)
Velhinho, J. M.
2002-12-01
Theories of connections play an important role in fundamental interactions, including Yang-Mills theories and gravity in the Ashtekar formulation. Typically in such cases, the classical configuration space {A}/ {G} of connections modulo gauge transformations is an infinite dimensional non-linear space of great complexity. Having in mind a rigorous quantization procedure, methods of functional calculus in an extension of {A}/ {G} have been developed. For a compact gauge group G, the compact space /line { {A}{ {/}} {G}} ( ⊃ {A}/ {G}) introduced by Ashtekar and Isham using C*-algebraic methods is a natural candidate to replace {A}/ {G} in the quantum context, 1 allowing the construction of diffeomorphism invariant measures. 2,3,4 Equally important is the space of generalized connections bar {A} introduced in a similar way by Baez. 5 bar {A} is particularly useful for the definition of vector fields in /line { {A}{ {/}} {G}} , fundamental in the construction of quantum observables. 6 These works crucially depend on the use of (generalized) Wilson variables associated to certain types of curves. We will consider the case of piecewise analytic curves, 1,2,5 althought most of the arguments apply equally to the piecewise smooth case. 7,8...
Seo, Joobeom; Sakamoto, Hirotoshi; Matsuda, Ryotaro; Kitagawa, Susumu
2010-01-01
Remarkable advances in the recent development of porous coordination polymers (PCPs) or metal organic frameworks (MOFs) have paved the way toward functional chemistry having potential application such as molecular storage, separation, and catalysis. Moreover flexible PCPs, which are structurally transformable depending upon guest molecules adsorption/desorption, have received much attention because they provide unique properties, dissimilar to those of zeolites. PCPs can be categorized into structurally monomodal and multimodal classes. Monomodal PCPs possess single uniform pores in the framework. In contrast, multimodal PCPs have more than two types of pores in the framework. Interpenetrated PCPs can possess more than two types of pores with different sizes and shapes in the same framework depending on relative position of individual motifs, resulting in multimodal PCPs. Moreover, interpenetrated PCPs have several advantages, such as high thermal stability, flexibility, and ultramicropore for effective adsorption. In this review, chemistry of PCPs based on monomodal and multimodal PCPs are summarized and discussed.
Overy, Catherine; Blunt, N. S.; Shepherd, James J.; Booth, George H.; Cleland, Deidre; Alavi, Ali
2014-12-28
Properties that are necessarily formulated within pure (symmetric) expectation values are difficult to calculate for projector quantum Monte Carlo approaches, but are critical in order to compute many of the important observable properties of electronic systems. Here, we investigate an approach for the sampling of unbiased reduced density matrices within the full configuration interaction quantum Monte Carlo dynamic, which requires only small computational overheads. This is achieved via an independent replica population of walkers in the dynamic, sampled alongside the original population. The resulting reduced density matrices are free from systematic error (beyond those present via constraints on the dynamic itself) and can be used to compute a variety of expectation values and properties, with rapid convergence to an exact limit. A quasi-variational energy estimate derived from these density matrices is proposed as an accurate alternative to the projected estimator for multiconfigurational wavefunctions, while its variational property could potentially lend itself to accurate extrapolation approaches in larger systems.
Overy, Catherine; Booth, George H; Blunt, N S; Shepherd, James J; Cleland, Deidre; Alavi, Ali
2014-12-28
Properties that are necessarily formulated within pure (symmetric) expectation values are difficult to calculate for projector quantum Monte Carlo approaches, but are critical in order to compute many of the important observable properties of electronic systems. Here, we investigate an approach for the sampling of unbiased reduced density matrices within the full configuration interaction quantum Monte Carlo dynamic, which requires only small computational overheads. This is achieved via an independent replica population of walkers in the dynamic, sampled alongside the original population. The resulting reduced density matrices are free from systematic error (beyond those present via constraints on the dynamic itself) and can be used to compute a variety of expectation values and properties, with rapid convergence to an exact limit. A quasi-variational energy estimate derived from these density matrices is proposed as an accurate alternative to the projected estimator for multiconfigurational wavefunctions, while its variational property could potentially lend itself to accurate extrapolation approaches in larger systems.
Optical Properties of Fluorescent Mixtures: Comparing Quantum Dots to Organic Dyes
ERIC Educational Resources Information Center
Hutchins, Benjamin M.; Morgan, Thomas T.; Ucak-Astarlioglu, Mine G.; Wlilliams, Mary Elizabeth
2007-01-01
The study describes and compares the size-dependent optical properties of organic dyes with those of semiconductor nanocrystals or quantum dots (QDs). The analysis shows that mixtures of QDs contain emission colors that are sum of the individual QD components.
Matsuura, Motoharu; Ohta, Hiroaki; Seki, Ryota
2015-03-15
We experimentally show the dynamic frequency chirp properties induced by signal amplification in a quantum-dot semiconductor optical amplifier (QD-SOA) for the first time. We also compare the red and blue chirp peak values and temporal chirp changes while changing the gain and injected signal powers of the QD-SOA with those of a common SOA.
Sobotta, B; Söhn, M; Shaw, W; Alber, M
2011-05-21
Frequently, radiotherapy treatments are comprised of several dose distributions computed or optimized in different patient geometries. Therefore, the need arises to compute the comprehensive biological effect or physical figure of merit of the combined dose of a number of distinct geometry instances. For that purpose the dose is typically accumulated in a reference geometry through deformation fields obtained from deformable image registration. However, it is difficult to establish precise voxel-by-voxel relationships between different anatomical images in many cases. In this work, the mathematical properties of commonly used score functions are exploited to derive an upper boundary for the maximum effect for normal tissue and a lower boundary for the minimum effect for the target of accumulated doses on multiple geometry instances.
NASA Astrophysics Data System (ADS)
Dorofeeva, O. V.; Ryzhova, O. N.; Moiseeva, N. F.
2008-06-01
The enthalpies of formation, entropies, and heat capacities of 95 organophosphorus derivatives calculated by nonempirical quantum-chemical methods were used to develop the additive method for estimating the thermodynamic properties of these compounds. 86 group contribution values were obtained for estimating the thermodynamic properties of diverse organic derivatives of phosphorus in the oxidation states 3 and 5 (three-and four-coordinate phosphorus atoms).
Optical properties of individual site-controlled Ge quantum dots
Grydlik, Martyna E-mail: martyna.grydlik@jku.at; Brehm, Moritz E-mail: martyna.grydlik@jku.at; Tayagaki, Takeshi; Langer, Gregor; Schäffler, Friedrich; Schmidt, Oliver G.
2015-06-22
We report photoluminescence (PL) experiments on individual SiGe quantum dots (QDs) that were epitaxially grown in a site-controlled fashion on pre-patterned Si(001) substrates. We demonstrate that the PL line-widths of single QDs decrease with excitation power to about 16 meV, a value that is much narrower than any of the previously reported PL signals in the SiGe/Si heterosystem. At low temperatures, the PL-intensity becomes limited by a 25 meV high potential-barrier between the QDs and the surrounding Ge wetting layer (WL). This barrier impedes QD filling from the WL which collects and traps most of the optically excited holes in this type-II heterosystem.
Lanthanide macrocyclic complexes, 'quantum dyes': optical properties and significance
NASA Astrophysics Data System (ADS)
Vallarino, Lidia M.; Harlow, Patrick M.; Leif, Robert C.
1993-05-01
Macrocylic complexes of the lanthanide (III) ions were functionalized to permit their attachment to antibodies, nucleic acid probes, and any other species capable of specific binding. The Eu(III) complex was found to possess a combination of properties (water solubility, inertness to metal release, ligand-sensitized luminescence, reactive peripheral functionalities) that make it suitable as a luminescent marker for bio-substrates. Its coupling to avidin was achieved, and the properties of the resulting conjugate were investigated.
NASA Astrophysics Data System (ADS)
Cheung, Carling L.; Looi, Thomas; Drake, James; Kim, Peter C. W.
2012-02-01
The development of image guided robotic and mechatronic platforms for medical applications requires a phantom model for initial testing. Finding an appropriate phantom becomes challenging when the targeted patient population is pediatrics, particularly infants, neonates or fetuses. Our group is currently developing a pediatricsized surgical robot that operates under fused MRI and laparoscopic video guidance. To support this work, we describe a method for designing and manufacturing silicone rubber organ phantoms for the purpose of testing the robotics and the image fusion system. A surface model of the organ is obtained and converted into a mold that is then rapid-prototyped using a 3D printer. The mold is filled with a solution containing a particular ratio of silicone rubber to slacker additive to achieve a specific set of tactile and imaging characteristics in the phantom. The expected MRI relaxation times of different ratios of silicone rubber to slacker additive are experimentally quantified so that the imaging properties of the phantom can be matched to those of the organ that it represents. Samples of silicone rubber and slacker additive mixed in ratios ranging from 1:0 to 1:1.5 were prepared and scanned using inversion recovery and spin echo sequences with varying TI and TE, respectively, in order to fit curves to calculate the expected T1 and T2 relaxation times of each ratio. A set of infantsized abdominal organs was prepared, which were successfully sutured by the robot and imaged using different modalities.
Synthesis and quantum transport properties of Bi₂Se₃ topological insulator nanostructures.
Yan, Yuan; Liao, Zhi-Min; Zhou, Yang-Bo; Wu, Han-Chun; Bie, Ya-Qing; Chen, Jing-Jing; Meng, Jie; Wu, Xiao-Song; Yu, Da-Peng
2013-01-01
Bi₂Se₃ nanocrystals with various morphologies, including nanotower, nanoplate, nanoflake, nanobeam and nanowire, have been synthesized. Well-distinguished Shubnikov-de Haas (SdH) oscillations were observed in Bi₂Se₃ nanoplates and nanobeams. Careful analysis of the SdH oscillations suggests the existence of Berry's phase π, which confirms the quantum transport of the surface Dirac fermions in both Bi₂Se₃ nanoplates and nanobeams without intended doping. The observation of the singular quantum transport of the topological surface states implies that the high-quality Bi₂Se₃ nanostructures have superiorities for investigating the novel physical properties and developing the potential applications.
Electronic and dielectric properties of vacancy clusters as quantum dot in silicane
Mohan, Brij Sharma, Munish; Ahluwalia, P. K.; Kumar, Ashok
2015-06-24
First principal study of electronic and dielectric properties of a silicane nanostructure containing cluster of vacancies as quantum dot (QD) has been investigated within density functional theory (DFT). Electronic band structure and corresponding density of states show the decrease in band gap with increasing size of quantum dot. A band gap of 0.38 eV has been achieved for silicane containing 3QD. Electron energy loss spectra (EEL) function shows additional plasmonic features for QD containing silicane in visible region, which may have potential applications in optoelectronic devices.
Electronic and dielectric properties of vacancy clusters as quantum dot in silicane
NASA Astrophysics Data System (ADS)
Mohan, Brij; Sharma, Munish; Kumar, Ashok; Ahluwalia, P. K.
2015-06-01
First principal study of electronic and dielectric properties of a silicane nanostructure containing cluster of vacancies as quantum dot (QD) has been investigated within density functional theory (DFT). Electronic band structure and corresponding density of states show the decrease in band gap with increasing size of quantum dot. A band gap of 0.38 eV has been achieved for silicane containing 3QD. Electron energy loss spectra (EEL) function shows additional plasmonic features for QD containing silicane in visible region, which may have potential applications in optoelectronic devices.
Unique properties of graphene quantum dots and their applications in photonic/electronic devices
NASA Astrophysics Data System (ADS)
Choi, Suk-Ho
2017-03-01
In recent years, graphene quantum dots (GQDs) have been recognized as an attractive building block for electronic, photonic, and bio-molecular device applications. This paper reports the current status of studies on the novel properties of GQDs and their hybrids with conventional and low-dimensional materials for device applications. In this review, more emphasis is placed on the structural, electronic, and optical properties of GQDs, and device structures based on the combination of GQDs with various semiconducting/insulating materials such as graphene, silicon dioxide, Si quantum dots, silica nanoparticles, organic materials, and so on. Because of GQDs’ unique properties, their hybrid structures are employed in high-efficiency devices, including photodetectors, solar cells, light-emitting diodes, flash memory, and sensors.
Dielectric and Thermal Properties of Transformer Oil Modified by Semiconductive CdS Quantum Dots
NASA Astrophysics Data System (ADS)
Abd-Elhady, Amr M.; Ibrahim, Mohamed E.; Taha, T. A.; Izzularab, Mohamed A.
2016-10-01
In this paper, modified transformer oil semiconductor quantum dots (QDs) are presented. Cadmium sulfide (CdS) quantum dots of radius 4.5 nm with a hexagonal crystal structure are added to transformer oil to improve its dielectric and thermal properties. CdS QDs modified oil is prepared considering different filler loading levels. Alternating current breakdown voltages of the transformer oil samples before and after the modification are measured based on American Society for Testing and Materials D1816 standard. The relative permittivity and dissipation factor are measured for all samples. Also, thermal properties of the oil samples are experimentally evaluated according to the temperature change measurement considering heating and cooling processes. The results show significant improvements in dielectric and thermal properties of the modified transformer oil, as well as an increase in the breakdown strength by about 81% in comparison to the base transformer oil.
CheckDen, a program to compute quantum molecular properties on spatial grids.
Pacios, Luis F; Fernandez, Alberto
2009-09-01
CheckDen, a program to compute quantum molecular properties on a variety of spatial grids is presented. The program reads as unique input wavefunction files written by standard quantum packages and calculates the electron density rho(r), promolecule and density difference function, gradient of rho(r), Laplacian of rho(r), information entropy, electrostatic potential, kinetic energy densities G(r) and K(r), electron localization function (ELF), and localized orbital locator (LOL) function. These properties can be calculated on a wide range of one-, two-, and three-dimensional grids that can be processed by widely used graphics programs to render high-resolution images. CheckDen offers also other options as extracting separate atom contributions to the property computed, converting grid output data into CUBE and OpenDX volumetric data formats, and perform arithmetic combinations with grid files in all the recognized formats.
Emission and Propagation Properties of Midinfrared Quantum Cascade Lasers
Krishnaswami, Kannan; Bernacki, Bruce E.; Cannon, Bret D.; Ho, Nicolas; Anheier, Norman C.
2008-02-15
We report divergence, astigmatism and M^{2} measurements of quantum cascade lasers (QCL) with an emission wavelength of 8.77 mum. Emission profiles from the QCL facet showed divergence angles of 62° and 32° FWHM ± 2° for the fast and slow axes, respectively. The observation of far field structure superimposed on the fast axes profiles was attributed to the position of the QCL die with respect to the edge of the laser submount, emphasizing the need for careful placement. Two diffraction-limited Germanium aspheric microlenses were designed and fabricated to efficiently collect, collimate, and focus QCL emission. A confocal system comprised of these lenses was used to measure the beam propagation figure of merit (M2) yielding 1.8 and 1.2 for the fast and slow axes, respectively. Astigmatism at the exit facet was calculated to be about 3.4 mum, or less than half a wave. To the best of our knowledge, this is the first experimental measurement of astigmatism and M^{2} reported for mid-IR QCLs.
Optical Properties of Active Regions in Terahertz Quantum Cascade Lasers
NASA Astrophysics Data System (ADS)
Dyksik, M.; Motyka, M.; Rudno-Rudziński, W.; Sęk, G.; Misiewicz, J.; Pucicki, D.; Kosiel, K.; Sankowska, I.; Kubacka-Traczyk, J.; Bugajski, M.
2016-07-01
In this work, AlGaAs/GaAs superlattice, with layers' sequence and compositions imitating the active and injector regions of a quantum cascade laser designed for emission in the terahertz spectral range, was investigated. Three independent absorption-like optical spectroscopy techniques were employed in order to study the band structure of the minibands formed within the conduction band. Photoreflectance measurements provided information about interband transitions in the investigated system. Common transmission spectra revealed, in the target range of intraband transitions, mainly a number of lines associated with the phonon-related processes, including two-phonon absorption. In contrast, differential transmittance realized by means of Fourier-transform spectroscopy was utilized to probe the confined states of the conduction band. The obtained energy separation between the second and third confined electron levels, expected to be predominantly contributing to the lasing, was found to be ~9 meV. The optical spectroscopy measurements were supported by numerical calculations performed in the effective mass approximation and XRD measurements for layers' width verification. The calculated energy spacings are in a good agreement with the experimental values.
New quantum properties of phonons and their detection
NASA Technical Reports Server (NTRS)
Artoni, Maurizo; Birman, Joseph L.
1994-01-01
We present a theoretical investigation on new and interesting properties of the phonon polarization field in solids. In particular, non-classical aspects of the phonon population and an experimental scheme that would enable one to detect them will be discussed.
Multimode Strong Coupling in Circuit QED
NASA Astrophysics Data System (ADS)
Sundaresan, Neereja; Liu, Yanbing; Sadri, Darius; Szocs, Laszlo; Underwood, Devin; Malekakhlagh, Moein; Tureci, Hakan; Houck, Andrew
We present experimental and theoretical studies in the multimode strong coupling (MMSC) regime of cavity quantum electrodynamics (QED). In MMSC, a single atom is simultaneously coupled to a large, but discrete, number of cavity harmonics, with atom-mode coupling strengths comparable to the free spectral range (FSR). This regime is readily accessible in circuit QED, by strongly coupling a transmon qubit to a low fundamental frequency microwave cavity. We present some key results from our original experiment (PRX 5, 021035, 2015), in which a transmon qubit, resonant with the 75th harmonic of a 90 MHz cavity, reached qubit-mode coupling strengths exceeding 30MHz. When this system is coherently driven, we observed complex multimode fluorescence, with the notable formation of ultra-narrow linewidths. To better understand these unique features of multimode resonance fluorescence we developed a quantum formalism, which attributes the spectral linewidth narrowing to the correlated spontaneous emission of doubly dressed states. Finally we will share preliminary experimental results from our continuing study of MMSC, this time from a system where qubit-mode coupling strengths approach and even exceed the FSR.
Effect of surface ligands on the optical properties of aqueous soluble CdTe quantum dots
2012-01-01
We investigate systematically the influence of the nature of thiol-type capping ligands on the optical and structural properties of highly luminescent CdTe quantum dots synthesized in aqueous media, comparing mercaptopropionic acid (MPA), thioglycolic acid (TGA), 1-thioglycerol (TGH), and glutathione (GSH). The growth rate, size distribution, and quantum yield strongly depend on the type of surface ligand used. While TGH binds too strongly to the nanocrystal surface inhibiting growth, the use of GSH results in the fastest growth kinetics. TGA and MPA show intermediate growth kinetics, but MPA yields a much lower initial size distribution than TGA. The obtained fluorescence quantum yields range from 38% to 73%. XPS studies unambiguously put into evidence the formation of a CdS shell on the CdTe core due to the thermal decomposition of the capping ligands. This shell is thicker when GSH is used as ligand, as compared with TGA ligands. PMID:23017183
NASA Technical Reports Server (NTRS)
Danilowicz, R.
1973-01-01
Ground-state properties of quantum crystals have received considerable attention from both theorists and experimentalists. The theoretical results have varied widely with the Monte Carlo calculations being the most successful. The molecular field approximation yields ground-state properties which agree closely with the Monte Carlo results. This approach evaluates the dynamical behavior of each pair of molecules in the molecular field of the other N-2 molecules. In addition to predicting ground-state properties that agree well with experiment, this approach yields data on the relative importance of interactions of different nearest neighbor pairs.
NASA Astrophysics Data System (ADS)
Singh, Gautam; Fisch, Michael; Kumar, Satyendra
2016-05-01
Investigations of the mixtures of semiconducting quantum scale particles in anisotropic liquid crystal (LC) medium have become a vibrant area of research primarily due to their very interesting phenomenology. The results of these investigations fall into four groups: (i) Photoluminescent emissive properties of the quantum particles ordinarily depend on the size, shape, and chemical nature of the particles. These undergo important changes in their spectrum, polarization, and isotropy of emission when dissolved in an anisotropic LC phase. Moreover, their response to external stimuli such as mechanical, optical, or electric fields is altered in important ways; (ii) physical properties of LCs such as viscosity, dielectric relaxation, etc are modified by the addition of quantum particles. Their presence in ferroelectric smectic LC is known to give rise to an antiferro- to ferri-electric phase transition and suppresses the paraelectric phase; (iii) switching characteristics of LC devices are altered in important ways by the addition of quantum particles. Their threshold voltage is usually lowered, contrast ratio, and switching speed of nematic, ferroelectric, and cholesteric devices may increase or decrease depending on the concentration, applied field, and particle anisotropy; and (iv) controlled aggregation of quantum particles at the interface between isotropic and LC domains, near added polystyrene beads, and in the vicinity of point defects gives rise to interesting photonic structures, enables studies of photon antibunching and single photon sources. Clearly, there is a need to understand the basic and applied aspects of these systems and find routes to their technological applications including sensors, electrooptical devices, and solar energy harvesting. This review provides an overview of recent work involving liquid crystals and a variety of quantum particles.
Multimode model for projective photon-counting measurements
Tualle-Brouri, Rosa; Ourjoumtsev, Alexei; Dantan, Aurelien; Grangier, Philippe; Wubs, Martijn; Soerensen, Anders S.
2009-07-15
We present a general model to account for the multimode nature of the quantum electromagnetic field in projective photon-counting measurements. We focus on photon-subtraction experiments, where non-Gaussian states are produced conditionally. These are useful states for continuous-variable quantum-information processing. We present a general method called mode reduction that reduces the multimode model to an effective two-mode problem. We apply this method to a multimode model describing broadband parametric down-conversion, thereby improving the analysis of existing experimental results. The main improvement is that spatial and frequency filters before the photon detector are taken into account explicitly. We find excellent agreement with previously published experimental results, using fewer free parameters than before, and discuss the implications of our analysis for the optimized production of states with negative Wigner functions.
Measuring Gaussian Quantum Information and Correlations Using the Rényi Entropy of Order 2
NASA Astrophysics Data System (ADS)
Adesso, Gerardo; Girolami, Davide; Serafini, Alessio
2012-11-01
We demonstrate that the Rényi-2 entropy provides a natural measure of information for any multimode Gaussian state of quantum harmonic systems, operationally linked to the phase-space Shannon sampling entropy of the Wigner distribution of the state. We prove that, in the Gaussian scenario, such an entropy satisfies the strong subadditivity inequality, a key requirement for quantum information theory. This allows us to define and analyze measures of Gaussian entanglement and more general quantum correlations based on such an entropy, which are shown to satisfy relevant properties such as monogamy.
Do the cations in clay and the polymer matrix affect quantum dot fluorescent properties?
Wei, Wenjun; Liu, Cui; Liu, Jiyan; Liu, Xueqing; Zou, Linling; Cai, Shaojun; Shi, Hong; Cao, Yuan-Cheng
2016-06-01
This paper studied the effects of cations and polymer matrix on the fluorescent properties of quantum dots (QDs). The results indicated that temperature has a greater impact on fluorescence intensity than clay cations (mainly K(+) and Na(+) ). Combined fluorescence lifetime and steady-state spectrometer tests showed that QD lifetimes all decreased when the cation concentration was increased, but the quantum yields were steady at various cation concentrations of 0, 0.05, 0.5 and 1 M. Poly(ethylene oxide) (PEO), poly(vinyl alcohol) (PVA) and diepoxy resin were used to study the effects of polymers on QD lifetime and quantum yield. The results showed that the lifetime for QDs 550 nm in PEO and PVA was 17.33 and 17.12 ns, respectively; for the epoxy resin, the lifetime was 0.74 ns, a sharp decrease from 24.47 ns. The quantum yield for QDs 550 nm changed from 34.22% to 7.45% and 7.81% in PEO and PVA, respectively; for the epoxy resin the quantum yield was 2.25%. QDs 580 nm and 620 nm showed the same results as QDs 550 nm. This study provides useful information on the design, synthesis and application of QDs-polymer luminescent materials. Copyright © 2015 John Wiley & Sons, Ltd.
NASA Astrophysics Data System (ADS)
Goswami, Mrinmoy; Ghosh, Ranajit; Maruyama, Takahiro; Meikap, Ajit Kumar
2016-02-01
A new kind of polyaniline/carbon nanotube/CdS quantum dot composites have been developed via in-situ polymerization of aniline monomer in the presence of dispersed CdS quantum dots (size: 2.7-4.8 nm) and multi-walled carbon nanotubes (CNT), which exhibits enhanced optical and electrical properties. The existences of 1st order, 2nd order, and 3rd order longitudinal optical phonon modes, strongly indicate the high quality of synthesized CdS quantum dots. The occurrence of red shift of free exciton energy in photoluminescence is due to size dependent quantum confinement effect of CdS. The conductivity of the composites (for example PANI/CNT/CdS (2 wt.% CdS)) is increased by about 7 of magnitude compared to that of pure PANI indicating a charge transfer between CNT and polymer via CdS quantum dots. This advanced material has a great potential for high-performance of electro-optical applications.
Tselikov, G. I. Timoshenko, V. Yu.; Plenge, J.; Ruehl, E.; Shatalova, A. M.; Shandryuk, G. A.; Merekalov, A. S.; Tal'roze, R. V.
2013-05-15
The photoluminescence properties of cadmium-selenide (CdSe) quantum dots with an average size of {approx}3 nm, embedded in a liquid-crystal polymer matrix are studied. It was found that an increase in the quantum-dot concentration results in modification of the intrinsic (exciton) photoluminescence spectrum in the range 500-600 nm and a nonmonotonic change in its intensity. Time-resolved measurements show the biexponential decay of the photoluminescence intensity with various ratios of fast and slow components depending on the quantum-dot concentration. In this case, the characteristic lifetimes of exciton photoluminescence are 5-10 and 35-50 ns for the fast and slow components, respectively, which is much shorter than the times for colloidal CdSe quantum dots of the same size. The observed features of the photoluminescence spectra and kinetics are explained by the effects of light reabsorption, energy transfer from quantum dots to the liquid-crystal polymer matrix, and the effect of the electronic states at the CdSe/(liquid crystal) interface.
Manifestation of magnetic quantum fluctuations in the dielectric properties of a multiferroic.
Kim, Jae Wook; Khim, Seunghyun; Chun, Sae Hwan; Jo, Y; Balicas, L; Yi, H T; Cheong, S-W; Harrison, N; Batista, C D; Han, Jung Hoon; Kim, Kee Hoon
2014-07-29
Insulating magnets can display novel signatures of quantum fluctuations as similar to the case of metallic magnets. However, their weak spin-lattice coupling has made such observations challenging. Here we find that antiferromagnetic (AF) quantum fluctuations manifest in the dielectric properties of multiferroic Ba2CoGe2O7, where a ferroelectric polarization develops concomitant to an AF ordering. Upon application of a magnetic field (H), dielectric constant shows a characteristic power-law dependence near absolute zero temperature and close to the critical field Hc=37.1 T due to enhanced AF quantum fluctuations. When H>Hc, the dielectric constant shows the temperature-dependent anomalies that reflect a crossover from a field-tuned quantum critical to a gapped spin-polarized state. We uncover theoretically that a linear relation between AF susceptibility and dielectric constant stems from the generic magnetoelectric coupling and directly explains the experimental findings, opening a new pathway for studying quantum criticality in condensed matter.
NASA Astrophysics Data System (ADS)
Carmeli, Benny; Metiu, Horia
1987-02-01
We calculate the equilibrium properties of a system consisting of two strongly interacting quantum and classical subsystems, by using a fast Fourier transform method to evaluate the quantum contribution and a Monte Carlo method to evaluate the contribution of the classical part. The method is applied to a model relevant to tunneling problems.
Alimohammadi, Mohammad; Xu, Yang; Wang, Daoyuan; Biris, Alexandru S; Khodakovskaya, Mariya V
2011-07-22
Plant seedlings were exposed to single-walled carbon nanotube-quantum dot conjugates (SWCNT-QD) mixed in the growth medium in order to understand the interactions between these multicomponent nanosystems and plants. A combination of fluorescent and Raman-scattering 2D mapping analysis was used to clearly monitor the presence of the SWCNT-QD conjugates in various parts of the tomato seedlings. We found that the addition of QDs to SWCNTs dramatically changed the biological viability of the tomato plants by significantly accelerating leaf senescence and inhibiting root formation. Although the exposure of SWCNTs only to the plants induced positive effects, the chlorophyll content decreased by 1.5-fold in leaves, and the total weight of the root system decreased four times for the tomato plants exposed to SWCNT-QDs (50 µg ml(-1)) compared to plants grown on regular medium as controls. Our results clearly indicate that the exposure of plants to multicomponent nanomaterials is highly influenced by the presence and bioactivity of each component, individually. Such studies could be the foundation for understanding how complex nanosized systems affect the activity of various biological systems with a major impact on ecotoxicology.
NASA Astrophysics Data System (ADS)
Alimohammadi, Mohammad; Xu, Yang; Wang, Daoyuan; Biris, Alexandru S.; Khodakovskaya, Mariya V.
2011-07-01
Plant seedlings were exposed to single-walled carbon nanotube-quantum dot conjugates (SWCNT-QD) mixed in the growth medium in order to understand the interactions between these multicomponent nanosystems and plants. A combination of fluorescent and Raman-scattering 2D mapping analysis was used to clearly monitor the presence of the SWCNT-QD conjugates in various parts of the tomato seedlings. We found that the addition of QDs to SWCNTs dramatically changed the biological viability of the tomato plants by significantly accelerating leaf senescence and inhibiting root formation. Although the exposure of SWCNTs only to the plants induced positive effects, the chlorophyll content decreased by 1.5-fold in leaves, and the total weight of the root system decreased four times for the tomato plants exposed to SWCNT-QDs (50 µg ml - 1) compared to plants grown on regular medium as controls. Our results clearly indicate that the exposure of plants to multicomponent nanomaterials is highly influenced by the presence and bioactivity of each component, individually. Such studies could be the foundation for understanding how complex nanosized systems affect the activity of various biological systems with a major impact on ecotoxicology.
Quantum transport properties of the three-dimensional Dirac semimetal Cd3As2 single crystals
NASA Astrophysics Data System (ADS)
He, Lan-Po; Li, Shi-Yan
2016-11-01
The discovery of the three-dimensional Dirac semimetals have expanded the family of topological materials, and attracted massive attentions in recent few years. In this short review, we briefly overview the quantum transport properties of a well-studied three-dimensional Dirac semimetal, Cd3As2. These unusual transport phenomena include the unexpected ultra-high charge mobility, large linear magnetoresistivity, remarkable Shubnikov-de Hass oscillations, and the evolution of the nontrivial Berry’s phase. These quantum transport properties not only reflect the novel electronic structure of Dirac semimetals, but also give the possibilities for their future device applications. Project supported by the National Basic Research Program of China (Grant Nos. 2012CB821402 and 2015CB921401), the National Natural Science Foundation of China, the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning, and STCSM of China (Grant No. 15XD1500200).
Synthesis and Optical Properties of Si and Ge Nanocrystals in the Quantum Confinement Regime*
NASA Astrophysics Data System (ADS)
Wilcoxon, J. P.; Newcomer, P. P.; Samara, G. A.
1997-03-01
Size-selected, crystalline nanoclusters of Si and Ge down to about 2 nm in size were grown in solution inside inverse micellar cages, purified using high pressure liquid chromatography and their optical properties studied. These properties, which reflect the effects of quantum confinement, differ considerably from those obtained on Si and Ge clusters prepared by other methods. Tailorable, visible (red to blue) room temperature photoluminescence due to both near band edge recombination and surface recombination is observed. The optical absorption spectra of the smaller clusters exhibit structure which provides insight into the electronic structure of these clusters. The present results will be compared with results on Si and Ge clusters in glass matrices and on porous Si and will be discussed in terms of recent models of quantum confinement for these materials *This work was supported by the United States Department of Energy under Contract DE-AC04-94Al85000.
Lasing properties of non-resonant single quantum dot-cavity system under incoherent excitation.
Guan, Huan; Yao, Peijun; Yu, Wenhai; Wang, Pei; Ming, Hai
2012-12-17
Single quantum dot laser has earned extensive interest due to its peculiar properties, however, most of works are focused on the resonant case. In this paper, the lasing oscillation based on off-resonant quantum dot (QD)-cavity system is investigated detailedly through two-electrons QD model. By gradually increasing the pump rate, the typical lasing signatures are shown with and without detuning, include the spectral transition from multiple peaks to single peak, and antibunching to Poissonian distribution. It is also demonstrated how detuning factor strongly influence photon statistics and emission properties, specially, the side peak of spectra induced by the exchange energy (named "sub-peak") will go across the main peak from left to right when the detuning is gradually increased, and, furthermore, we find the "sub-peak cross of spectra" will facilitate the lasing oscillation because of the existence of exchange energy.
A computational study of the quantum transport properties of a Cu-CNT composite.
Ghorbani-Asl, Mahdi; Bristowe, Paul D; Koziol, Krzysztof
2015-07-28
The quantum transport properties of a Cu-CNT composite are studied using a non-equilibrium Green's function approach combined with the self-consistent-charge density-functional tight-binding method. The results show that the electrical conductance of the composite depends strongly on CNT density and alignment but more weakly on chirality. Alignment with the applied bias is preferred and the conductance of the composite increases as its mass density increases.
Wu, Jiang; Wang, Zhiming M; Dorogan, Vitaliy G; Li, Shibin; Lee, Jihoon; Mazur, Yuriy I; Kim, Eun Soo; Salamo, Gregory J
2013-01-02
Strain-free GaAs/Al0.33Ga0.67As quantum rings are fabricated by droplet epitaxy. Both photoresponse and photoluminescence spectra confirm optical transitions in quantum rings, suggesting that droplet epitaxial nanomaterials are applicable to intermediate band solar cells. The effects of post-growth annealing on the quantum ring solar cells are investigated, and the optical properties of the solar cells with and without thermal treatment are characterized by photoluminescence technique. Rapid thermal annealing treatment has resulted in the significant improvement of material quality, which can be served as a standard process for quantum structure solar cells grown by droplet epitaxy.
Alibolandi, Mona; Abnous, Khalil; Sadeghi, Fatemeh; Hosseinkhani, Hossein; Ramezani, Mohammad; Hadizadeh, Farzin
2016-03-16
In this study, we report the design and delivery of tumor-targeted, quantum dot (QD) and doxorubicin (DOX)-encapsulated PEG-PLGA nanopolymersomes (NPs) for the imaging and chemotherapy of breast cancer. To achieve active cancer targeting, QD and DOX-encapsulated NPs were conjugated with folate for folate-binding protein receptor-guided delivery, which overexpressed in many cancer cells. Hydrophobic DOX and hydrophilic MSA-capped QD were encapsulated in the bilayer and core of the PEG-PLGA nanopolymersomes, respectively. The data show that the formulated NPs sustained DOX release for a period of 12 days. Fluorescence microscopy and MTT assay demonstrated that the developed folate-targeted DOX-QD NPs had higher cytotoxicity than non-targeted NPs and the free form of the drug; moreover, they preferentially accumulated in 4T1 and MCF-7 cells in vitro. In vivo experiments including whole organ tissue-homogenate analysis and organ fluorescence microscopy imaging of BALB/c mice bearing 4T1 breast adenocarcinoma showed that the folate receptor-targeted QD encapsulated NPs accumulate at tumor sites 6h following intravenous injection. Acute toxicity studies of the prepared targeted QD-loaded NPs showed no evidence of long-term harmful histopathological and physiological effects on the treated animals. The in vivo tumor inhibitory effect of folic acid (FA)-QD-DOX NPs demonstrated an augmented therapeutic efficacy of targeted formulation over the non-targeted and free drug. The data obtained illustrate a high potential of the prepared targeted theranostic nanoplatform in the treatment and imaging of breast cancer. This study may open new directions for preparation of QD-based theranostic polymersomes for clinical application.
NASA Astrophysics Data System (ADS)
Sin, Yongkun; Lingley, Zachary; Brodie, Miles; Huang, Michael; Bushmaker, Adam; Theiss, Jesse; Presser, Nathan; Foran, Brendan; Moss, Steven C.
2016-03-01
Remarkable progress made in vertical cavity surface emitting lasers (VCSELs) emitting at 850 and 980 nm has led them to find an increasing number of applications in high speed data communications as well as in potential space satellite systems. However, little has been reported on reliability and failure modes of InGaAs VCSELs emitting at ~980 nm although it is crucial to understand failure modes and underlying degradation mechanisms in developing these VCSELs that exceed lifetime requirements for space missions. The active layer of commercial VCSELs that we studied consisted of two or three InGaAs quantum wells. The laser structures were fabricated into deep mesas followed by a steam oxidation process to form oxide-apertures for current and optical confinements. Our multi- mode VCSELs showed a laser threshold of ~ 0.5 mA at RT. Failures were generated via accelerated life-testing of VCSELs. For the present study, we report on failure mode analysis of degraded oxide-VCSELs using various techniques. We employed nondestructive techniques including electroluminescence (EL), optical beam induced current (OBIC), and electron beam induced current (EBIC) techniques as well as destructive techniques including focused ion beam (FIB) and high-resolution TEM techniques to study VCSELs that showed different degradation behaviors. Especially, we employed FIB systems to locally remove a portion of top-DBR mirrors of degraded VCSELs, which made it possible for our subsequent EBIC and OBIC techniques to locate damaged areas that were generated as a result of degradation processes and also for our HR-TEM technique to prepare TEM cross sections from damaged areas. Our nondestructive and destructive physical analysis results are reported including defect and structural analysis results from pre-aged VCSELs as well as from degraded VCSELs life-tested under different test conditions.
Kemény, Ferenc; Meier, Beat
2016-02-01
While sequence learning research models complex phenomena, previous studies have mostly focused on unimodal sequences. The goal of the current experiment is to put implicit sequence learning into a multimodal context: to test whether it can operate across different modalities. We used the Task Sequence Learning paradigm to test whether sequence learning varies across modalities, and whether participants are able to learn multimodal sequences. Our results show that implicit sequence learning is very similar regardless of the source modality. However, the presence of correlated task and response sequences was required for learning to take place. The experiment provides new evidence for implicit sequence learning of abstract conceptual representations. In general, the results suggest that correlated sequences are necessary for implicit sequence learning to occur. Moreover, they show that elements from different modalities can be automatically integrated into one unitary multimodal sequence.
NASA Astrophysics Data System (ADS)
Naumova, N. L.; Vasilyeva, I. A.
2015-09-01
The spectral-luminescent properties of some dyes of substituted arylpolyenes and cross-conjugated ketones class in Shpolsky matrices, promising for using in solving quantum optics and nanophotonics, were studied.
Process-Dependent Properties in Colloidally Synthesized “Giant” Core/Shell Nanocrystal Quantum Dots
Hollingsworth, Jennifer A.; Ghosh, Yagnaseni; Dennis, Allison M.; Mangum, Benjamin D.; Park, Young-Shin; Kundu, Janardan; Htoon, Han
2012-06-07
Due to their characteristic bright and stable photoluminescence, semiconductor nanocrystal quantum dots (NQDs) have attracted much interest as efficient light emitters for applications from single-particle tracking to solid-state lighting. Despite their numerous enabling traits, however, NQD optical properties are frustratingly sensitive to their chemical environment, exhibit fluorescence intermittency ('blinking'), and are susceptible to Auger recombination, an efficient nonradiative decay process. Previously, we showed for the first time that colloidal CdSe/CdS core/shell nanocrystal quantum dots (NQDs) comprising ultrathick shells (number of shell monolayers, n, > 10) grown by protracted successive ionic layer adsorption and reaction (SILAR) leads to remarkable photostability and significantly suppressed blinking behavior as a function of increasing shell thickness. We have also shown that these so-called 'giant' NQDs (g-NQDs) afford nearly complete suppression of non-radiative Auger recombination, revealed in our studies as long biexciton lifetimes and efficient multiexciton emission. The unique behavior of this core/shell system prompted us to assess correlations between specific physicochemical properties - beyond shell thickness - and functionality. Here, we demonstrate the ability of particle shape/faceting, crystalline phase, and core size to determine ensemble and single-particle optical properties (quantum yield/brightness, blinking, radiative lifetimes). Significantly, we show how reaction process parameters (surface-stabilizing ligands, ligand:NQD ratio, choice of 'inert' solvent, and modifications to the SILAR method itself) can be tuned to modify these function-dictating NQD physical properties, ultimately leading to an optimized synthetic approach that results in the complete suppression of blinking. We find that the resulting 'guiding principles' can be applied to other NQD compositions, allowing us to achieve non-blinking behavior in the near
Strain induced novel quantum magnetotransport properties of topological insulators
NASA Astrophysics Data System (ADS)
Ma, Ning; Zhang, Shengli; Liu, Daqing
2016-12-01
Recent theoretical and experimental researches have revealed that the strained bulk HgTe can be regarded as a three-dimensional topological insulator (TI). Motivated by this, we explore the strain effects on the transport properties of the HgTe surface states, which are modulated by a weak 1D in-plane electrostatic periodic potential in the presence of a perpendicular magnetic field. We analytically derive the zero frequency (dc) diffusion conductivity for the case of quasielastic scattering in the Kubo formalism, and find that, in strong magnetic field regime, the Shubnikov-de Haas oscillations are superimposed on top of the Weiss oscillations due to the electric modulation for null and finite strain. Furthermore, the strain is shown to remove the degeneracy in inversion symmetric Dirac cones on the top and bottom surfaces. This accordingly gives rise to the splitting and mixture of Landau levels, and the asymmetric spectrum of the dc conductivity. These phenomena, not known in a conventional 2D electron gas and even in a strainless TI and graphene, are a consequence of the anomalous spectrum of surface states in a fully stained TI. These results should be valuable for electronic and spintronic applications of TIs, and thus we fully expect to see them in the further experiment.
Metal colloids and quantum dots: linear and nonlinear optical properties
Henderson, Don O.
1997-05-12
Nanophase materials have found a wide application in a variety of technological areas which include ultrafast optical switching high density information storage and retrieval, electronics, and catalysts, to mention a few. Nanocrystal science has also drawn considerable interest from the fundamental perspective engaging physicists, chemists, and material scientists into this area of rapidly expanding and challenging research. Basic questions concerning how matter evolves from atomic like behavior to molecular and onto bulk lie at the center nanocrystal research. In addition, because of the high surface to volume ratio of the nanocrystals, the interaction potential between a nanocrystal and its surrounding environment becomes an important issue in determining its properties. While significant progress has been made in nanocrystal research, there are many problems concerned with their fabrication. In particular, the difficulty of incorporating nanocrystals into a matrix that is appropriate for ultimate device development has hindered some aspects of nanocrystal research. Ion implantation is a method that is now established as a technique for fabricating metal and semiconductor nanocrystals. It is highly versatile in that one may select nearly any host material for incorporating the nanocrystals of interest. The flexibility of being able to select the host matrix is also interesting from the point of view that it opens the opportunity to investigate matrix-nanocrystal interactions. We summarize in the following sections results on metal and semiconductor nanocrystals formed by ion implantation into dielectric hosts.
Transport Properties of a Nonequilibrium Quantum Dot Connected to Ferromagnetic Leads
NASA Astrophysics Data System (ADS)
Yongmei, Zhang
2017-03-01
In this paper, transmission resonance and conductance properties of nonequilibrium quantum dot connected by ferromagnetic leads are investigated. Thermoelectric properties are also studied. Using the tight-binding formalism and numerically solving the Schrodinger equation, spin-dependent transmissions are obtained and plotted as a function of incoming electron energy. Transmissions of spin up and spin down electrons change in different ways as voltage bias and tilt angle change. Current spin polarization can be sensitively tuned by adjusting voltage bias. These research indicates the possible methods to modulate tilt angle or the bias voltage to obtain spin-dependent transmission, spin polarized current and effective Seebeck coefficients.
Modeling on the size dependent properties of InP quantum dots: a hybrid functional study.
Cho, Eunseog; Jang, Hyosook; Lee, Junho; Jang, Eunjoo
2013-05-31
Theoretical calculations based on density functional theory were performed to provide better understanding of the size dependent electronic properties of InP quantum dots (QDs). Using a hybrid functional approach, we suggest a reliable analytical equation to describe the change of energy band gap as a function of size. Synthesizing colloidal InP QDs with 2-4 nm diameter and measuring their optical properties was also carried out. It was found that the theoretical band gaps showed a linear dependence on the inverse size of QDs and gave energy band gaps almost identical to the experimental values.
A quantum model for bending vibrations and thermodynamic properties of C3.
NASA Technical Reports Server (NTRS)
Hansen, C. F.; Pearson, W. E.
1973-01-01
The investigation reported was conducted to clarify the thermodynamic properties of C3 by further developing the limit to the partition function suggested by Strauss and Thiele (1967). A quantum solution for the energy levels of a quadratically perturbed square well potential is presented and the consistency of this limit with observed energy levels is established. In the process a more complete physical picture of the bending C3 molecules emerges. The values of entropy deduced from various measurements of graphite pressure are compared with this limit, and the thermodynamic properties predicted for the limiting case are evaluated.
NASA Astrophysics Data System (ADS)
Sin, Yongkun; LaLumondiere, Stephen; DeIonno, Erica; Foran, Brendan; Presser, Nathan; Lotshaw, William; Moss, Steven C.
2014-03-01
A number of groups have studied reliability and degradation processes in GaAs-based lasers, but none of these studies have yielded a reliability model based on the physics of failure. Unsuccessful development of this model originates from the facts that: (i) defects related phenomena responsible for degradation in GaAs-based lasers are difficult to study due to the lack of suitable non-destructive techniques and (ii) degradation process occurs extremely fast after a long period of latency. Therefore, most of laser diode manufacturers perform accelerated multi-cell lifetests to estimate lifetimes of lasers using an empirical model, but this approach is a concern especially for satellite communication systems where high reliability is required of lasers for long-term duration in the space environment. Since it is a challenge to control defects introduced during the growth of laser structures, we studied degradation processes in broad-area InGaAs-AlGaAs strained quantum well (QW) lasers with intrinsic defects as well as those with defects introduced via proton irradiation. For the present study, we investigated the root causes of catastrophic degradation processes in MOCVD-grown broad-area InGaAs-AlGaAs strained QW lasers using various failure mode analysis techniques. A number of lasers were proton irradiated with different energies and fluences. We also studied GaAs double heterostructure (DH) test samples with different amounts of intrinsic defects introduced during MOCVD growth. These samples were proton irradiated as well to introduce additional defects. Deep level transient spectroscopy (DLTS) and time resolved photoluminescence (TR-PL) techniques were employed to study traps (due to point defects) and non-radiative recombination centers (NRCs) in pre- and poststressed lasers, respectively. These characteristics were compared with those in pre- and post-proton irradiated lasers and DHs to study the role that defects and NRCs play in catastrophic degradation
NASA Astrophysics Data System (ADS)
Chen, Y.; Maharjan, N.; Liu, Z.; Nakarmi, M. L.; Chaldyshev, V. V.; Kundelev, E. V.; Poddubny, A. N.; Vasil'ev, A. P.; Yagovkina, M. A.; Shakya, N. M.
2017-03-01
An AlGaAs/GaAs multiple-quantum-well based resonant Bragg structure was designed to match the optical Bragg resonance with the exciton-polariton resonance at the second quantum state in the GaAs quantum wells. The sample structure with 60 periods of AlGaAs/GaAs quantum wells was grown on a semi-insulating GaAs substrate by molecular beam epitaxy. Angle- and temperature-dependent photoluminescence, optical reflectance, and electro-reflectance spectroscopies were employed to study the resonant optical properties of the Bragg structure. Broad and enhanced optical and electro-reflectance features were observed when the Bragg resonance was tuned to the second quantum state of the GaAs quantum well excitons, manifesting a strong light-matter interaction. From the electro-optical experiments, we found the electro-reflectance features related to the transitions of x(e2-hh2) and x(e2-hh1) excitons. The excitonic transition x(e2-hh1), which is prohibited at zero electric field, was allowed by a DC bias due to the brake of symmetry and increased overlap of the electron and hole wave functions caused by the electric field. By tuning the Bragg resonance frequency, we have observed the electro-reflectance feature related to the second quantum state up to room temperature, which evidences a robust light-matter interaction in the resonant Bragg structure.
Effect of gamma-ray irradiation on the size and properties of CdS quantum dots in reverse micelles
NASA Astrophysics Data System (ADS)
Bekasova, O. D.; Revina, A. A.; Rusanov, A. L.; Kornienko, E. S.; Kurganov, B. I.
2013-11-01
Cadmium sulfide quantum dots 1.3-5.6 nm in size have been synthesized in sodium bis(2-ethylhexy1)sulfosuccinate (AOT)-water-isooctane micellar solutions with various [H2O]/[AOT] molar ratios (w=2.5, 5.0 or 10). Gamma irradiation method has been used to change the size and optical properties of quantum dots. It has been found that γ-irradiation reduces the size polydispersity of quantum dots in the micellar system and alters their fluorescent properties. Fluorescence intensity is enhanced after γ-irradiation. The average fluorescence lifetime of single quantum dots sized 5.2±0.4 nm increases from 5.14 to 6.39 ns after γ-irradiation at a dose of 7.9 kGy. To the best of our knowledge, this is the first report on fluorescence lifetime of single CdS quantum dots in micellar solution.
NASA Astrophysics Data System (ADS)
Nagashima, Hiroki; Tsuda, Shin-ichi; Tsuboi, Nobuyuki; Koshi, Mitsuo; Hayashi, A. Koichi; Tokumasu, Takashi
2014-03-01
In this paper, we have analysed an effect of quantum nature of the hydrogen molecule on its thermodynamic and transport properties using molecular dynamics (MD) method based on the path integral method. We performed NVE constant MD simulation and the quantum effect on the molecular mechanism was analysed. The simulation results were compared with experimental data. As a result, we clarified that the quantum nature makes the virial pressure larger than in classical mechanics and taking account the quantum nature makes smaller intermolecular interaction energy and larger repulsive force than classical representation. Besides, we have confirmed that the path-integral-based MD method well reproduces the thermal conductivity and quantum effect on the transport properties is also large.
Structure and transport properties of Ge quantum dots in a SiO2 matrix
NASA Astrophysics Data System (ADS)
Slunjski, R.; Dubček, P.; Radić, N.; Bernstorff, S.; Pivac, B.
2015-06-01
Germanium (Ge) nanoparticles or quantum dots (QDs) embedded in a transparent dielectric matrix have properties radically different from the bulk semiconductor and present a great potential for application in electronic and optoelectronic devices. Due to quantum confinement properties, the optical bandgap of QD-based materials can be tuned by varying the nanoparticle size. These properties may be exploited for the fabrication of nanoscale electronic devices or advanced solar cells. In this work we explored structural and transport properties of QD based superstructures for advanced solar cells. Magnetron cosputtering was used for deposition and upon suitable thermal treatment a superstructure of QDs was formed. Transport properties were explored by I-V measurement in the dark together with a C-V characterization. The obtained results were modeled with the known transport mechanisms for QDs containing materials. A special emphasis is given to trap controlled space charge limited current and hopping conductivity mechanism. We have shown that in our samples a significant charge is stored in the SiO2 layers with embedded Ge QDs. That charge is predominantly stored into traps at or close to the Ge(QDs)/SiO2 interface.
Self-consistent calculations of optical properties of type I and type II quantum heterostructures
NASA Astrophysics Data System (ADS)
Shuvayev, Vladimir A.
In this Thesis the self-consistent computational methods are applied to the study of the optical properties of semiconductor nanostructures with one- and two-dimensional quantum confinements. At first, the self-consistent Schrodinger-Poisson system of equations is applied to the cylindrical core-shell structure with type II band alignment without direct Coulomb interaction between carriers. The electron and hole states and confining potential are obtained from a numerical solution of this system. The photoluminescence kinetics is theoretically analyzed, with the nanostructure size dispersion taken into account. The results are applied to the radiative recombination in the system of ZnTe/ZnSe stacked quantum dots. A good agreement with both continuous wave and time-resolved experimental observations is found. It is shown that size distribution results in the photoluminescence decay that has essentially non-exponential behavior even at the tail of the decay where the carrier lifetime is almost the same due to slowly changing overlap of the electron and hole wavefunctions. Also, a model situation applicable to colloidal core-shell nanowires is investigated and discussed. With respect to the excitons in type I quantum wells, a new computationally efficient and flexible approach of calculating the characteristics of excitons, based on a self-consistent variational treatment of the electron-hole Coulomb interaction, is developed. In this approach, a system of self-consistent equations describing the motion of an electron-hole pair is derived. The motion in the growth direction of the quantum well is separated from the in-plane motion, but each of them occurs in modified potentials found self-consistently. This approach is applied to a shallow quantum well with the delta-potential profile, for which analytical expressions for the exciton binding energy and the ground state eigenfunctions are obtained, and to the quantum well with the square potential profile with several
NASA Astrophysics Data System (ADS)
Yuan, Jian-Hui; Chen, Ni; Zhang, Yan; Mo, Hua; Zhang, Zhi-Hai
2016-03-01
Electric field effect on the second-order nonlinear optical properties in semiparabolic quantum wells are studied theoretically. Both the second-harmonic generation susceptibility and nonlinear optical rectification depend dramatically on the direction and the strength of the electric field. Numerical results show that both the second-harmonic generation susceptibility and nonlinear optical rectification are always weakened as the electric field increases where the direction of the electric field is along the growth direction of the quantum wells, which is in contrast to the conventional case. However, the second-harmonic generation susceptibility is weakened, but the nonlinear optical rectification is strengthened as the electric field increases where the direction of the electric field is against the growth direction of the quantum wells. Also it is the blue (or red) shift of the resonance that is induced by increasing of the electric field when the direction of the electric field is along (or against) the growth direction of the quantum wells. Finally, the resonant peak and its corresponding to the resonant energy are also taken into account.
Xu, Xianmei; Wang, Yilin; Gule, Teri; Luo, Qiang; Zhou, Liya; Gong, Fuzhong
2013-03-15
Highlights: ► Stable CdSe QDs were synthesized by the one-step and two-level process respectively. ► The fabricated white LEDs show good white balance. ► CdSe QDs present well green to yellow band luminescence. ► CdSe QDs displayed a broad excitation band. - Abstract: Yellow light-emitting cadmium selenide quantum dots were synthesized using one-step and two-step methods in an aqueous medium. The structural luminescent properties of these quantum dots were investigated. The obtained cadmium selenide quantum dots displayed a broad excitation band suitable for blue or near-ultraviolet light-emitting diode applications. White light-emitting diodes were fabricated by coating the cadmium selenide samples onto a 460 nm-emitting indium gallium nitrite chip. Both samples exhibited good white balance. Under a 20 mA working current, the white light-emitting diode fabricated via the one-step and two-step methods showed Commission Internationale de l’Éclairage coordinates at (0.27, 0.23) and (0.27, 0.33), respectively, and a color rendering index equal to 41 and 37, respectively. The one-step approach was simpler, greener, and more effective than the two-step approach. The one-step approach can be enhanced by combining cadmium selenide quantum dots with proper phosphors.
NASA Astrophysics Data System (ADS)
Desgranges, C.; Anderson, P. W.; Delhommelle, J.
2017-02-01
Using molecular simulation, we determine the critical properties of Si as well as the loci for several remarkable thermodynamic contours spanning the supercritical region of the phase diagram. We consider a classical three-body potential as well as a quantum (tight-binding) many-body model, and determine the loci for the ideality contours, including the Zeno line and the H line of ideal enthalpy. The two strategies (classical or quantum) lead to strongly asymmetric binodals and to critical properties in good agreement with each other. The Zeno and H lines are found to remain linear over a wide temperature interval, despite the changes in electronic structure undergone by the fluid along these contours. We also show that the classical and quantum model yield markedly different results for the parameters defining the H line, the exponents for the power-laws underlying the line of minima for the isothermal enthalpy and for the density required to achieve ideal behavior, most notably for the enthalpy.
Desgranges, C; Anderson, P W; Delhommelle, J
2017-02-01
Using molecular simulation, we determine the critical properties of Si as well as the loci for several remarkable thermodynamic contours spanning the supercritical region of the phase diagram. We consider a classical three-body potential as well as a quantum (tight-binding) many-body model, and determine the loci for the ideality contours, including the Zeno line and the H line of ideal enthalpy. The two strategies (classical or quantum) lead to strongly asymmetric binodals and to critical properties in good agreement with each other. The Zeno and H lines are found to remain linear over a wide temperature interval, despite the changes in electronic structure undergone by the fluid along these contours. We also show that the classical and quantum model yield markedly different results for the parameters defining the H line, the exponents for the power-laws underlying the line of minima for the isothermal enthalpy and for the density required to achieve ideal behavior, most notably for the enthalpy.
Multimodal Information Exploration.
ERIC Educational Resources Information Center
Stock, Oliviero; Zancanaro, Massimo; Strapparava, Carlo
1997-01-01
Discussion of information exploration and software design in computer-based educational systems focuses on the integration of hypermedia and natural language dialog. AlFRESCO is described, an interactive natural language-centered multimodal system that was developed for users interested in frescoes and paintings. (LRW)
Bigot-Astruc, Marianne; Molin, Denis; Sillard, Pierre
2014-11-04
A depressed graded-index multimode optical fiber includes a central core, an inner depressed cladding, a depressed trench, an outer depressed cladding, and an outer cladding. The central core has an alpha-index profile. The depressed claddings limit the impact of leaky modes on optical-fiber performance characteristics (e.g., bandwidth, core size, and/or numerical aperture).
Generating Multimodal References
ERIC Educational Resources Information Center
van der Sluis, Ielka; Krahmer, Emiel
2007-01-01
This article presents a new computational model for the generation of multimodal referring expressions (REs), based on observations in human communication. The algorithm is an extension of the graph-based algorithm proposed by Krahmer, van Erk, and Verleg (2003) and makes use of a so-called Flashlight Model for pointing. The Flashlight Model…
Díaz, Natalia; Suárez, Dimas; Sordo, Tomás L
2003-11-30
Herein, we present theoretical results on the conformational properties of benzylpenicillin, which are characterized by means of quantum chemical calculations (MP2/6-31G* and B3LYP/6-31G*) and classical molecular dynamics simulations (5 ns) both in the gas phase and in aqueous solution. In the gas phase, the benzylpenicillin conformer in which the thiazolidine ring has the carboxylate group oriented axially is the most favored one. Both intramolecular CH. O and dispersion interactions contribute to stabilize the axial conformer with respect to the equatorial one. In aqueous solution, a molecular dynamics simulation predicts a relative population of the axial:equatorial conformers of 0.70:0.30 in consonance with NMR experimental data. Overall, the quantum chemical calculations as well as the simulations give insight into substituent effects, the conformational dynamics of benzylpenicillin, the frequency of ring-puckering motions, and the correlation of side chain and ring-puckering motions.
Impact of strain on the electronic properties of InAs/GaSb quantum well systems
NASA Astrophysics Data System (ADS)
Tiemann, L.; Mueller, S.; Wu, Q.-S.; Tschirky, T.; Ensslin, K.; Wegscheider, W.; Troyer, M.; Soluyanov, A. A.; Ihn, T.
2017-03-01
Electron-hole hybridization in InAs/GaSb double quantum well structures leads to the formation of a mini-band-gap. We experimentally and theoretically studied the impact of strain on the transport properties of this material system. Thinned samples were mounted to piezoelectric elements to exert strain along the [011] and [001] crystal directions. When the Fermi energy is tuned through the minigap, the resistivity at the charge neutrality point is found to be susceptible to external strain. In the electron and hole regimes, strain influences the Landau level structure. By analyzing the intrinsic strain from the epitaxial growth and the external strain from the piezo elements and combining our experimental results with numerical simulations of strained and unstrained quantum wells, we can illustrate why the InAs/GaSb material system is regularly found to be semimetallic.
Oura, Makoto; Yamamoto, Johtaro; Jin, Takashi; Kinjo, Masataka
2017-01-23
Quantum dot (QD) and quantum rod (QR) nanocrystals are widely used non-organic nanocrystals. Their strong fluorescence and photostability make them suitable for biomedical imaging applications. However, their pH-dependence and antibunching properties have not been studied much, especially in aqueous conditions. In this report, we used fluorescence correlation spectroscopy (FCS) with high temporal resolution to demonstrate that the fluorescent blinking and antibunching of QDs/QRs can be changed by varying the pH of their solutions. Furthermore, herein, we reported the relationship between the aggregation and antibunching relaxation time of QDs/QRs for the first time. The findings of this study suggest that FCS can be used to discover novel environmental indicators via observing nanosecond and microsecond phenomena.
Donchev, A. G.; Galkin, N. G.; Illarionov, A. A.; Khoruzhii, O. V.; Olevanov, M. A.; Ozrin, V. D.; Subbotin, M. V.; Tarasov, V. I.
2006-01-01
We have recently introduced a quantum mechanical polarizable force field (QMPFF) fitted solely to high-level quantum mechanical data for simulations of biomolecular systems. Here, we present an improved form of the force field, QMPFF2, and apply it to simulations of liquid water. The results of the simulations show excellent agreement with a variety of experimental thermodynamic and structural data, as good or better than that provided by specialized water potentials. In particular, QMPFF2 is the only ab initio force field to accurately reproduce the anomalous temperature dependence of water density to our knowledge. The ability of the same force field to successfully simulate the properties of both organic molecules and water suggests it will be useful for simulations of proteins and protein–ligand interactions in the aqueous environment. PMID:16723394
Optical properties and aging of PbS quantum dots embedded in a porous matrix
NASA Astrophysics Data System (ADS)
Litvin, Aleksandr P.; Parfenov, Peter S.; Ushakova, Elena V.; Fedorov, Anatoly V.; Artemyev, Mikhail V.; Prudnikau, Anatoly V.; Rukhlenko, Ivan D.; Baranov, Alexander V.
2013-09-01
PbS quantum dots (QDs) with diameter of 2.9-7.4 nm were embedded into a porous matrix. The samples prepared by developed low-cost effortless method demonstrate linear dependencies of optical density and luminescence intensity on the QDs concentration and perfect homogeneity. Optical properties of quantum dots in the matrix were studied using absorption and steady-state and time-resolved photoluminescence spectroscopy. Luminescence lifetimes were found to be size-dependent and increase with decreasing of QDs size. The aging behavior of PbS QDs in a porous matrix was explored for a variety of QDs sizes. The energy transfer process in quasi-monodispersed PbS QDs ensemble was discovered.
Chen, Wei; Li, Fushan Wu, Chaoxing; Guo, Tailiang
2014-02-10
Graphene quantum dots (GQDs), which are edge-bound nanometer-size graphene pieces, have fascinating electronic and optical properties due to their quantum confinement and edge effect. In this paper, GQDs were synthesized by using acid treatment and chemical exfoliation of multi-walled carbon nanotubes (MWCNTs). The structure of the GQDs was investigated by transmission electron microscope. The GQDs have a uniform size distribution, zigzag edge structure and two-dimensional morphology. The results indicated that the GQDs have bright blue emission upon UV excitation. The highly fluorescent GQDs exhibited high water solubility and good stability. It is shown that the acid treatment of MWCNTs leads to the formation of the functional group in zigzag sites, which results in the pH-dependent fluorescence of the GQDs.
NASA Astrophysics Data System (ADS)
Li, L. L.; Moldovan, D.; Xu, W.; Peeters, F. M.
2017-02-01
Recently, black phosphorus quantum dots were fabricated experimentally. Motivated by these experiments, we theoretically investigate the electronic and optical properties of rectangular phosphorene quantum dots (RPQDs) in the presence of an in-plane electric field and a perpendicular magnetic field. The energy spectra and wave functions of RPQDs are obtained numerically using the tight-binding approach. We find edge states within the band gap of the RPQD which are well separated from the bulk states. In an undoped RPQD and for in-plane polarized light, due to the presence of well-defined edge states, we find three types of optical transitions which are between the bulk states, between the edge and bulk states, and between the edge states. The electric and magnetic fields influence the bulk-to-bulk, edge-to-bulk, and edge-to-edge transitions differently due to the different responses of bulk and edge states to these fields.
NASA Astrophysics Data System (ADS)
Brogi, Bharat Bhushan; Chand, Shyam; Ahluwalia, P. K.
2015-06-01
Theoretical study of the Coulomb blockade effect on transport properties (Transmission Probability and I-V characteristics) for varied configuration of coupled quantum dot system has been studied by using Non Equilibrium Green Function(NEGF) formalism and Equation of Motion(EOM) method in the presence of magnetic flux. The self consistent approach and intra-dot Coulomb interaction is being taken into account. As the key parameters of the coupled quantum dot system such as dot-lead coupling, inter-dot tunneling and magnetic flux threading through the system can be tuned, the effect of asymmetry parameter and magnetic flux on this tuning is being explored in Coulomb blockade regime. The presence of the Coulomb blockade due to on-dot Coulomb interaction decreases the width of transmission peak at energy level ɛ + U and by adjusting the magnetic flux the swapping effect in the Fano peaks in asymmetric and symmetric parallel configuration sustains despite strong Coulomb blockade effect.
Li, L L; Moldovan, D; Xu, W; Peeters, F M
2017-02-24
Recently, black phosphorus quantum dots were fabricated experimentally. Motivated by these experiments, we theoretically investigate the electronic and optical properties of rectangular phosphorene quantum dots (RPQDs) in the presence of an in-plane electric field and a perpendicular magnetic field. The energy spectra and wave functions of RPQDs are obtained numerically using the tight-binding approach. We find edge states within the band gap of the RPQD which are well separated from the bulk states. In an undoped RPQD and for in-plane polarized light, due to the presence of well-defined edge states, we find three types of optical transitions which are between the bulk states, between the edge and bulk states, and between the edge states. The electric and magnetic fields influence the bulk-to-bulk, edge-to-bulk, and edge-to-edge transitions differently due to the different responses of bulk and edge states to these fields.
Generation and characterization of discrete spatial entanglement in multimode nonlinear waveguides
NASA Astrophysics Data System (ADS)
Jachura, Michał; Karpiński, Michał; Banaszek, Konrad; Bharadwaj, Divya; Lugani, Jasleen; Thyagarajan, K.
2017-03-01
We analyze theoretically spontaneous parametric down-conversion in a multimode nonlinear waveguide as a source of entangled pairs of spatial qubits, realized as superpositions of a photon in two orthogonal transverse modes of the waveguide. It is shown that, by exploiting intermodal dispersion, down-conversion into the relevant pairs of spatial modes can be selected by spectral filtering, which also provides means to fine tune the properties of the generated entangled state. We also discuss an inverting interferometer detecting the spatial parity of the input beam as a versatile tool to characterize properties of the generated state. A single-photon Wigner function obtained by a scan of the displaced parity can be used to identify the basis modes of a spatial qubit, whereas correlations between displaced parity measurements on two photons can directly verify quantum entanglement through a violation of Bell's inequalities.
Trung, Nguyen Ngoc; Luu, Quynh-Phuong; Son, Bui Thanh; Sinh, Le Hoang; Bae, Jin-Young
2013-01-01
Our research focused on the morphological and optical properties of core/shell cadmium selenide/zinc sulfide (CdSe/ZnS) quantum dots incorporated in silicone resin. After dispersing ligand-coated quantum dots into Dow Corning two-component silicone resins (OE6630A and OE6630B at 1:4 mixing ratio by weight), the resins were cured at 150 degrees C for 1.5 hours to produce the quantum dot-silicone resin nanocomposites. The optical, morphological and thermal properties of the quantum dot incorporated in silicone resin were investigated by ultraviolet-visible, fluorescence, atomic force microscopy, field emission scanning electron microscopy, differential scanning calorimetry and thermogravimetric analysis. When the quantum dots, originally coated with trioctylamine ligand, were transferred from a chloroform solvent to methyl phenyl silicone oil and silicone resins of high viscosity, the quantum dots showed increased turbidity and lowered fluorescence intensity. Fluorescence enhancement was investigated by using various functional ligands such as poly(1, 1-dimethyl silazane) (multi-silazane), hexamethylenediamine (diamine), cysteamine (amino-thiol), triethylsilane (reactive hydrosilane), hexamethyldisilazane, nonamethyltrisilazane, octamethylcyclotetrasilazane (reactive amines). The results showed that the reactive amines were good additive ligands for enhancing the fluorescence of CdSe/ZnS quantum dots dispersed in the silicone resins, providing 1.2-2.48 Im/W and 4.2-5.56% higher luminous efficiency and photoluminescence conversion efficiency, respectively. We speculate that these reactive amines donate electrons to the surface electron traps, thereby reducing charge recombination. In addition, quantum dots aggregate to form quantum dot clusters with a relatively homogeneously dispersed in the silicone resin matrices, showing good emission properties due to surface passivation and good colloidal stability with the addition of silazane compounds to the resin
Nanoparticles in Higher-Order Multimodal Imaging
NASA Astrophysics Data System (ADS)
Rieffel, James Ki
Imaging procedures are a cornerstone in our current medical infrastructure. In everything from screening, diagnostics, and treatment, medical imaging is perhaps our greatest tool in evaluating individual health. Recently, there has been tremendous increase in the development of multimodal systems that combine the strengths of complimentary imaging technologies to overcome their independent weaknesses. Clinically, this has manifested in the virtually universal manufacture of combined PET-CT scanners. With this push toward more integrated imaging, new contrast agents with multimodal functionality are needed. Nanoparticle-based systems are ideal candidates based on their unique size, properties, and diversity. In chapter 1, an extensive background on recent multimodal imaging agents capable of enhancing signal or contrast in three or more modalities is presented. Chapter 2 discusses the development and characterization of a nanoparticulate probe with hexamodal imaging functionality. It is my hope that the information contained in this thesis will demonstrate the many benefits of nanoparticles in multimodal imaging, and provide insight into the potential of fully integrated imaging.
Quantum Correlation Properties in Two Qubits One-axis Spin Squeezing Model
NASA Astrophysics Data System (ADS)
Guo-Hui, Yang
2017-02-01
Using the concurrence (C) and quantum discord (QD) criterions, the quantum correlation properties in two qubits one-axis spin squeezing model with an external magnetic field are investigated. It is found that one obvious difference in the limit case T → 0 (ground state) is the sudden disappearance phenomenon (SDP) occured in the behavior of C, while not in QD. In order to further explain the SDP, we obtain the analytic expressions of ground state C and QD which reveal that the SDP is not really "entanglement sudden disappeared", it is decayed to zero very quickly. Proper tuning the parameters μ(the spin squeezing interaction in x direction) and Ω(the external magnetic field in z direction) not only can obviously broaden the scope of ground state C exists but also can enhance the value of ground state QD. For the finite temperature case, one evident difference is that the sudden birth phenomenon (SBP) is appeared in the evolution of C, while not in QD, and decreasing the coupling parameters μ or Ω can obviously prolong the time interval before entanglement sudden birth. The value of C and QD are both enhanced by increasing the parameters μ or Ω in finite temperature case. In addition, through investigating the effects of temperature T on the quantum correlation properties with the variation of Ω and μ, one can find that the temperature scope of C and QD exists are broadened with increasing the parameters μ or Ω, and one can obtain the quantum correlation at higher temperature through changing these parameters.
Thermoelectric properties of Mg2X (X = Si, Ge) based bulk and quantum well systems
NASA Astrophysics Data System (ADS)
Yelgel, Övgü Ceyda
2017-01-01
Mg2X (X = Si, Ge) compounds are promising thermoelectric materials for middle temperature applications due to good thermoelectric properties, nontoxicity, and abundantly available constituent elements. So far, these materials used in applications have all been in bulk form. Herein we report a full theory of thermoelectric transport properties of 3D bulk and 2D quantum well systems. The main aim of this present work is to show the effect of quantum confinement on the enhancement of the thermoelectric figure of merit theoretically. Results are given for n-type Mg2 Si0.5 Ge0.5 solid solutions and n-type Mg2Si/Mg2Ge/Mg2Si quantum well systems where the values of well widths are taken as 10 nm, 15 nm, and 20 nm, respectively. The n-type doping is made by using Sb- and La-elements as dopants. Experimental results for solid solutions are included to provide demonstration of proof of principle for the theoretical model applied for 3D bulk structures. The maximum thermoelectric figure of merits of Lax Mg2 -x Si0.49 Ge0.5 Sb0.01 solid solutions are obtained to be 0.64 and 0.56 at 800 K for x = 0 and x = 0.01 sample, respectively. While, at the same temperature, due to the relatively low phonon thermal conductivity the state-of-the-art ZT values of 2.41 and 2.26 have been attained in the Mg2Si/Mg2Ge/Mg2Si quantum well samples with 0.01 wt. % Sb-doped and 0.01 wt. % Sb- and 0.01 wt. % La-doped, respectively.
Dwyer, Donard S
2005-01-01
Background Electronic properties of amino acid side chains such as inductive and field effects have not been characterized in any detail. Quantum mechanics (QM) calculations and fundamental equations that account for substituent effects may provide insight into these important properties. PM3 analysis of electron distribution and polarizability was used to derive quantitative scales that describe steric factors, inductive effects, resonance effects, and field effects of amino acid side chains. Results These studies revealed that: (1) different semiempirical QM methods yield similar results for the electronic effects of side chain groups, (2) polarizability, which reflects molecular deformability, represents steric factors in electronic terms, and (3) inductive effects contribute to the propensity of an amino acid for α-helices. Conclusion The data provide initial characterization of the substituent effects of amino acid side chains and suggest that these properties affect electron density along the peptide backbone. PMID:16078995
Greiff, Kirsti; Mathiassen, John Reidar; Misimi, Ekrem; Hersleth, Margrethe; Aursand, Ida G.
2015-01-01
The European diet today generally contains too much sodium (Na+). A partial substitution of NaCl by KCl has shown to be a promising method for reducing sodium content. The aim of this work was to investigate the sensorial changes of cooked ham with reduced sodium content. Traditional sensorial evaluation and objective multimodal machine vision were used. The salt content in the hams was decreased from 3.4% to 1.4%, and 25% of the Na+ was replaced by K+. The salt reduction had highest influence on the sensory attributes salty taste, after taste, tenderness, hardness and color hue. The multimodal machine vision system showed changes in lightness, as a function of reduced salt content. Compared to the reference ham (3.4% salt), a replacement of Na+-ions by K+-ions of 25% gave no significant changes in WHC, moisture, pH, expressed moisture, the sensory profile attributes or the surface lightness and shininess. A further reduction of salt down to 1.7–1.4% salt, led to a decrease in WHC and an increase in expressible moisture. PMID:26422367
Greiff, Kirsti; Mathiassen, John Reidar; Misimi, Ekrem; Hersleth, Margrethe; Aursand, Ida G
2015-01-01
The European diet today generally contains too much sodium (Na(+)). A partial substitution of NaCl by KCl has shown to be a promising method for reducing sodium content. The aim of this work was to investigate the sensorial changes of cooked ham with reduced sodium content. Traditional sensorial evaluation and objective multimodal machine vision were used. The salt content in the hams was decreased from 3.4% to 1.4%, and 25% of the Na(+) was replaced by K(+). The salt reduction had highest influence on the sensory attributes salty taste, after taste, tenderness, hardness and color hue. The multimodal machine vision system showed changes in lightness, as a function of reduced salt content. Compared to the reference ham (3.4% salt), a replacement of Na(+)-ions by K(+)-ions of 25% gave no significant changes in WHC, moisture, pH, expressed moisture, the sensory profile attributes or the surface lightness and shininess. A further reduction of salt down to 1.7-1.4% salt, led to a decrease in WHC and an increase in expressible moisture.
NASA Astrophysics Data System (ADS)
Han, Yu; Gong, Wei-Jiang; Wei, Guo-Zhu
2009-12-01
Electron transport properties of a triple-terminal Aharonov-Bohm interferometer are theoretically studied. By applying a Rashba spin-orbit coupling to a quantum dot locally, we find that remarkable spin polarization comes about in the electron transport process with tuning the structure parameters, i.e., the magnetic flux or quantum dot levels. When the quantum dot levels are aligned with the Fermi level, there only appear spin polarization in this structure by the presence of an appropriate magnetic flux. However, in absence of magnetic flux spin polarization and spin separation can be simultaneously realized with the adjustment of quantum dot levels, namely, an incident electron from one terminal can select a specific terminal to depart from the quantum dots according to its spin state.
Ab initio quantum Monte Carlo calculations of ground-state properties of manganese's oxides
NASA Astrophysics Data System (ADS)
Sharma, Vinit; Krogel, Jaron T.; Kent, P. R. C.; Reboredo, Fernando A.
One of the critical scientific challenges of contemporary research is to obtain an accurate theoretical description of the electronic properties of strongly correlated systems such as transition metal oxides and rare-earth compounds, since state-of-art ab-initio methods based on approximate density functionals are not always sufficiently accurate. Quantum Monte Carlo (QMC) methods, which use statistical sampling to evaluate many-body wave functions, have the potential to answer this challenge. Owing to the few fundamental approximations made and the direct treatment of electron correlation, QMC methods are among the most accurate electronic structure methods available to date. We assess the accuracy of the diffusion Monte Carlo method in the case of rocksalt manganese oxide (MnO). We study the electronic properties of this strongly-correlated oxide, which has been identified as a suitable candidate for many applications ranging from catalysts to electronic devices. ``This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.'' Ab initio quantum Monte Carlo calculations of ground-state properties of manganese's oxides.
NASA Astrophysics Data System (ADS)
Koc, Fatih; Sahin, Mehmet
2014-05-01
In this study, a detailed investigation of the electronic and optical properties (i.e., binding energies, absorption wavelength, overlap of the electron-hole wave functions, recombination oscillator strength, etc.) of an exciton and a biexciton in CdTe/CdSe core/shell type-II quantum dot heterostructures has been carried out in the frame of the single band effective mass approximation. In order to determine the electronic properties, we have self-consistently solved the Poisson-Schrödinger equations in the Hartree approximation. We have considered all probable Coulomb interaction effects on both energy levels and also on the corresponding wave functions for both single exciton and biexciton. In addition, we have taken into account the quantum mechanical exchange-correlation effects in the local density approximation between same kinds of particles for biexciton. Also, we have examined the effect of the ligands and dielectric mismatch on the electronic and optical properties. We have used a different approximation proposed by Sahin and Koc [Appl. Phys. Lett. 102, 183103 (2013)] for the recombination oscillator strength of the biexciton for bound and unbound cases. The results obtained have been presented comparatively as a function of the shell thicknesses and probable physical reasons in behind of the results have been discussed in a detail.
Usman, Muhammad; Tasco, Vittorianna; Todaro, Maria Teresa; De Giorgi, Milena; O'Reilly, Eoin P; Klimeck, Gerhard; Passaseo, Adriana
2012-04-27
III-V growth and surface conditions strongly influence the physical structure and resulting optical properties of self-assembled quantum dots (QDs). Beyond the design of a desired active optical wavelength, the polarization response of QDs is of particular interest for optical communications and quantum information science. Previous theoretical studies based on a pure InAs QD model failed to reproduce experimentally observed polarization properties. In this work, multi-million atom simulations are performed in an effort to understand the correlation between chemical composition and polarization properties of QDs. A systematic analysis of QD structural parameters leads us to propose a two-layer composition model, mimicking In segregation and In-Ga intermixing effects. This model, consistent with mostly accepted compositional findings, allows us to accurately fit the experimental PL spectra. The detailed study of QD morphology parameters presented here serves as a tool for using growth dynamics to engineer the strain field inside and around the QD structures, allowing tuning of the polarization response.
Quantum and Thermodynamic Properties of Spontaneous and Low-Energy Induced Fission of Nuclei
Kadmensky, S.G.
2005-12-01
It is shown that A. Bohr's concept of transition fission states can be matched with the properties of Coriolis interaction if an axisymmetric fissile nucleus near the scission point remains cold despite a nonadiabatic character of nuclear collective deformation motion. The quantum and thermodynamic properties of various stages of binary and ternary fission after the descent of a fissile nucleus from the outer saddle point are studied within quantum-mechanical fission theory. It is shown that two-particle nucleon-nucleon correlations--in particular, superfluid correlations--play an important role in the formation of fission products and in the classification of fission transitions. The distributions of thermalized primary fission fragments with respect to spins and their projections onto the symmetry axis of the fissile nucleus and fission fragments are constructed, these distributions determining the properties of prompt neutrons and gamma rays emitted by these fragments. A new nonevaporation mechanism of third-particle production in ternary fission is proposed. This mechanism involves transitions of third particles from the cluster states of the fissile-nucleus neck to high-energy states under effects of the shake-off type that are due to the nonadiabatic character of nuclear collective deformation motion.
Koc, Fatih; Sahin, Mehmet E-mail: mehsahin@gmail.com
2014-05-21
In this study, a detailed investigation of the electronic and optical properties (i.e., binding energies, absorption wavelength, overlap of the electron-hole wave functions, recombination oscillator strength, etc.) of an exciton and a biexciton in CdTe/CdSe core/shell type-II quantum dot heterostructures has been carried out in the frame of the single band effective mass approximation. In order to determine the electronic properties, we have self-consistently solved the Poisson-Schrödinger equations in the Hartree approximation. We have considered all probable Coulomb interaction effects on both energy levels and also on the corresponding wave functions for both single exciton and biexciton. In addition, we have taken into account the quantum mechanical exchange-correlation effects in the local density approximation between same kinds of particles for biexciton. Also, we have examined the effect of the ligands and dielectric mismatch on the electronic and optical properties. We have used a different approximation proposed by Sahin and Koc [Appl. Phys. Lett. 102, 183103 (2013)] for the recombination oscillator strength of the biexciton for bound and unbound cases. The results obtained have been presented comparatively as a function of the shell thicknesses and probable physical reasons in behind of the results have been discussed in a detail.
Quantum statistics of optical parametric processes with squeezed reservoirs
NASA Astrophysics Data System (ADS)
Peřina, Jan; Křepelka, Jaromír
2013-11-01
Quantum statistics including joint photon-number and integrated-intensity probability distributions are derived in time evolution of general optical parametric process involving processes of frequency conversion, parametric amplification and subharmonic generation taking into account losses and noise described by squeezed reservoirs. Using these tools quantum entanglement of modes is considered and the other nonclassical properties of the process under discussion are demonstrated by means of conditional probability distributions and their Fano factors, difference-number probability distributions, quantum oscillations, squeezing of vacuum fluctuations and negative values of the joint and difference wave probability quasidistributions. Nonclassical properties are illustrated for spontaneous process as well as stimulated process by means of chaotic light and squeezed vacuum field. Multimode processes are investigated in the spirit of the Mandel-Rice photocount formula.
Advanced Technology for Improved Quantum Device Properties Using Highly Strained Materials
1991-03-01
Improved Quantum PE 61153N Device Properties Using Highly Strained Materials PE 1401N~R&T 414s 001-02 IN G. AUTHOR(S) (William J. Schaff , S.D. Offsey and...DECEMBER 15, 1989 CORNELL UNIVERSITY.......................... ITHACA, NY 14853-5401 PREPARED BY: WJ. Schaff ........ S.D. Offsey I - L.F. Eastman D ’’. i...Mandeville, R. Saito, P.J. Tasker, W.J. Schaff and L.F. Eastman, 12th IEEE/Comell Conference on’Advanced Concepts in High Speed Semiconductor Devices
Relativistic (SR-ZORA) quantum theory of atoms in molecules properties.
Anderson, James S M; Rodríguez, Juan I; Ayers, Paul W; Götz, Andreas W
2017-01-15
The Quantum Theory of Atoms in Molecules (QTAIM) is used to elucidate the effects of relativity on chemical systems. To do this, molecules are studied using density-functional theory at both the nonrelativistic level and using the scalar relativistic zeroth-order regular approximation. Relativistic effects on the QTAIM properties and topology of the electron density can be significant for chemical systems with heavy atoms. It is important, therefore, to use the appropriate relativistic treatment of QTAIM (Anderson and Ayers, J. Phys. Chem. 2009, 115, 13001) when treating systems with heavy atoms. © 2016 Wiley Periodicals, Inc.
Liu, Chunyu; Chang, Kaiwen; Guo, Wenbin E-mail: chenwy@jlu.edu.cn Li, Hao; Shen, Liang; Chen, Weiyou E-mail: chenwy@jlu.edu.cn; Yan, Dawei E-mail: chenwy@jlu.edu.cn
2014-08-18
Carbon quantum dots (Cdots) are synthesized by a simple method and introduced into active layer of polymer solar cells (PSCs). The performance of doped devices was apparently improved, and the highest power conversion efficiency of 7.05% was obtained, corresponding to a 28.2% enhancement compared with that of the contrast device. The charge transport properties, resistance, impedance, and transient absorption spectrum are systematically investigated to explore how the Cdots affect on PSCs performance. This study reveals the importance of Cdots in enhancing the efficiency of PSCs and gives insight into the mechanism of charge transport improvement.
Optical Properties of a Quantum Dot-Ring System Grown Using Droplet Epitaxy.
Linares-García, Gabriel; Meza-Montes, Lilia; Stinaff, Eric; Alsolamy, S M; Ware, M E; Mazur, Y I; Wang, Z M; Lee, Jihoon; Salamo, G J
2016-12-01
Electronic and optical properties of InAs/GaAs nanostructures grown by the droplet epitaxy method are studied. Carrier states were determined by k · p theory including effects of strain and In gradient concentration for a model geometry. Wavefunctions are highly localized in the dots. Coulomb and exchange interactions are studied and we found the system is in the strong confinement regime. Microphotoluminescence spectra and lifetimes were calculated and compared with measurements performed on a set of quantum rings in a single sample. Some features of spectra are in good agreement.
Spectral properties of a double-quantum-dot structure: A causal Green's function approach
NASA Astrophysics Data System (ADS)
You, J. Q.; Zheng, Hou-Zhi
1999-09-01
Spectral properties of a double quantum dot (QD) structure are studied by a causal Green's function (GF) approach. The double QD system is modeled by an Anderson-type Hamiltonian in which both the intra- and interdot Coulomb interactions are taken into account. The GF's are derived by an equation-of-motion method and the real-space renormalization-group technique. The numerical results show that the average occupation number of electrons in the QD exhibits staircase features and the local density of states depends appreciably on the electron occupation of the dot.
Cosmin Obreja, Alexandru; Cristea, Dana; Radoi, Antonio; Gavrila, Raluca; Comanescu, Florin; Kusko, Cristian; Mihalache, Iuliana
2014-08-25
We show that graphene quantum dots (GQD) embedded in a semiconducting poly(3-hexylthiophene) polymeric matrix act as charge trapping nanomaterials. In plane current-voltage (I-V) measurements of thin films realized from this nanocomposite deposited on gold interdigitated electrodes revealed that the GQD enhanced dramatically the hole transport. I-V characteristics exhibited a strong nonlinear behavior and a pinched hysteresis loop, a signature of a memristive response. The transport properties of this nanocomposite were explained in terms of a trap controlled space charge limited current mechanism.
The electronic properties of concentric double quantum ring and possibility designing XOR gate
NASA Astrophysics Data System (ADS)
AL-Badry, Lafy. F.
2017-03-01
In this paper I have investigated the Aharonov-Bohm oscillation in concentric double quantum ring. The outer ring attached to leads while the inner ring only tunnel-coupled to the outer ring. The effect of inner ring on electron transport properties through outer ring studied and found that the conductance spectrum consists of two types of oscillations. One is the normal Aharonov-Bohm oscillation, and other is a small oscillations superposed above AB oscillation. The AB oscillation utilized to designing nanoscale XOR gate by choosing the magnetic flux and tuning the gate voltages which realization XOR gate action.
NASA Astrophysics Data System (ADS)
Eftekhari, F.; Tavassoly, M. K.
In this paper, we will present a general formalism for constructing the nonlinear charge coherent states which in special case lead to the standard charge coherent states. The suQ(1, 1) algebra as a nonlinear deformed algebra realization of the introduced states is established. In addition, the corresponding even and odd nonlinear charge coherent states have also been introduced. The formalism has the potentiality to be applied to systems either with known "nonlinearity function" f(n) or solvable quantum system with known "discrete nondegenerate spectrum" en. As some physical appearances, a few known physical systems in the two mentioned categories have been considered. Finally, since the construction of nonclassical states is a central topic of quantum optics, nonclassical features and quantum statistical properties of the introduced states have been investigated by evaluating single- and two-mode squeezing, su(1, 1)-squeezing, Mandel parameter and antibunching effect (via g-correlation function) as well as some of their generalized forms we have introduced in the present paper.
Growth and properties of Hg-based quantum well structures and superlattices
NASA Technical Reports Server (NTRS)
Schetzina, J. F.
1990-01-01
An overview of the properties of HgTe-CdTe quantum well structures and superlattices (SL) is presented. These new quantum structures are candidates for use as new long wavelength infrared (LWIR) and very long wavelength infrared (VLWIR) detectors, as well as for other optoelectronic applications. Much has been learned within the past two years about the physics of such structures. The valence band offset has been determined to be approx. 350 meV, independent of temperature. The occurrence of electron and hole mobilities in excess of 10(exp 5)cm(exp 2)/V center dot s is now understood on the basis of SL band structure calculations. The in-plane and out-of-plane electron and hole effective masses have been measured and interpreted theoretically for HgTe-CdTe superlattices. Controlled substitutional doping of superlattices has recently been achieved at North Carolina State University (NCSU), and modulation-doped SLs have now been successfully grown and studied. Most recently, a dramatic lowering of the growth temperature of Hg-based quantum well structure and SLs (to approx. 100 C) has been achieved by means of photoassisted molecular beam epitaxy (MBE) at NCSU. A number of new devices have been fabricated from these doped multilayers.
Multifunctional nanostructured materials for multimodal cancer imaging and therapy.
Liao, Jinfeng; Qi, Tingting; Chu, Bingyang; Peng, Jinrong; Luo, Feng; Qian, Zhiyong
2014-01-01
This paper reviews the recent research and development of multifunctional nanostructured materials for multimodal imaging and therapy. The biomedical applications for multifunctional imaging, diagnosis and therapy are discussed for several nanostructured materials such as polymeric nanoparticles, magnetic nanoparticles, gold nanomaterials, carbon materials, quantum dots and silica nanoparticles. Due to the unique features of nanostructured materials including the large surface area, structural diversity, multifunctionality, and long circulation time in blood, these materials have emerged as attractive preferences for optimized therapy. Multimodal imaging can be introduced to nanostructured materials for precise and fast diagnosis of cancer, which overcomes the shortcoming of single-imaging modality. Meanwhile, nanostructured materials can be also used to deliver therapeutic agents to the disease site in order to accomplish multimodal imaging and simultaneous diagnosis and therapy.
NASA Astrophysics Data System (ADS)
Zhou, Zhi; Du, Yingzi; Thomas, N. L.; Delp, Edward J., III
2010-04-01
Multimodal biometrics use more than one means of biometric identification to achieve higher recognition accuracy, since sometimes a unimodal biometric is not good enough used to do identification and classification. In this paper, we proposed a multimodal eye recognition system, which can obtain both iris and sclera patterns from one color eye image. Gabor filter and 1-D Log-Gabor filter algorithms have been applied as the iris recognition algorithms. In sclera recognition, we introduced automatic sclera segmentation, sclera pattern enhancement, sclera pattern template generation, and sclera pattern matching. We applied kernelbased matching score fusion to improve the performance of the eye recognition system. The experimental results show that the proposed eye recognition method can achieve better performance compared to unimodal biometric identification, and the accuracy of our proposed kernel-based matching score fusion method is higher than two classic linear matching score fusion methods: Principal Component Analysis (PCA) and Linear Discriminant Analysis (LDA).
Steinke, S. K.; Meystre, P.
2011-08-15
We analyze a detailed model of a Bose-Einstein condensate (BEC) trapped in a ring optical resonator and contrast its classical and quantum properties to those of a Fabry-Perot geometry. The inclusion of two counterpropagating light fields and three matter field modes leads to important differences between the two situations. Specifically, we identify an experimentally realizable region where the system's behavior differs strongly from that of a BEC in a Fabry-Perot cavity, and also where quantum corrections become significant. The classical dynamics are rich, and near bifurcation points in the mean-field classical system, the quantum fluctuations have a major impact on the system's dynamics.
Properties of the Katugampola fractional derivative with potential application in quantum mechanics
NASA Astrophysics Data System (ADS)
Anderson, Douglas R.; Ulness, Darin J.
2015-06-01
Katugampola [e-print arXiv:1410.6535] recently introduced a limit based fractional derivative, Dα (referred to in this work as the Katugampola fractional derivative) that maintains many of the familiar properties of standard derivatives such as the product, quotient, and chain rules. Typically, fractional derivatives are handled using an integral representation and, as such, are non-local in character. The current work starts with a key property of the Katugampola fractional derivative, D α [ y ] = t 1 - α /d y d t , and the associated differential operator, Dα = t1-αD1. These operators, their inverses, commutators, anti-commutators, and several important differential equations are studied. The anti-commutator serves as a basis for the development of a self-adjoint operator which could potentially be useful in quantum mechanics. A Hamiltonian is constructed from this operator and applied to the particle in a box model.
Quantum Monte Carlo study of the electric properties of a ferroelectric superlattice
NASA Astrophysics Data System (ADS)
Feraoun, A.; Zaim, A.; Kerouad, M.
2016-12-01
By using quantum Monte Carlo (MC) simulation, the electric properties of an Ising spin superlattice formed by two ferroelectric slabs A and B with an antiferroelectric interfacial coupling was studied within the framework of the Transverse Ising Model (TIM). We have examined the effects of the temperature T and the transverse field Ω on the polarization properties. We have also examined the effects of the interfacial coupling JAB, T, and Ω on the hysteresis behavior. Our results are in good agreement with the previous theoretical results; we have found that the critical temperature Tc and the critical transverse field Ωc decrease with the increase of Ω and T respectively. In addition one or triple hysteresis loops can appear in the present system.
Tuning optical properties of water-soluble CdTe quantum dots for biological applications
NASA Astrophysics Data System (ADS)
Schulze, Anne S.; Tavernaro, Isabella; Machka, Friederike; Dakischew, Olga; Lips, Katrin S.; Wickleder, Mathias S.
2017-02-01
In this study, two different synthetic methods in aqueous solution are presented to tune the optical properties of CdTe and CdSe semiconductor nanoparticles. Additionally, the influence of different temperatures, pressures, precursor ratios, surface ligands, bases, and core components in the synthesis was investigated with regard to the particle sizes and optical properties. As a result, a red shift of the emission and absorption maxima with increasing reaction temperature (100 to 220°C), pressure (1 to 25 bar), and different ratios of core components of alloyed semiconductor nanoparticles could be observed without a change of the particle size. An increase in particle size from 2.5 to 5 nm was only achieved by variation of the mercaptocarboxylic acid ligands in combination with the reaction time and used base. To get a first hint on the cytotoxic effects and cell uptake of the synthesized quantum dots, in vitro tests mesenchymal stem cells (MSCs) were carried out.
Electrical properties of individual self-assembled GeSi quantum rings
NASA Astrophysics Data System (ADS)
Zhang, Shengli; Lv, Yi; Jiang, Zuimin; Yang, Xinju
2011-11-01
The nanoscale electrical properties of self-assembled GeSi quantum rings (QRs) were investigated by conductive scanning probe microscopy at room temperature. The current distribution of individual GeSi QRs measured by conductive atomic force microscopy (CAFM) shows a low conductivity at the central hole as compared to the rim; however, the QRs' composition distribution obtained by selective chemical etching combined with AFM observation reveals that within the QRs' central holes, the Ge content is high, which should lead to a high conductivity instead of a low one as observed. Together with the results obtained by scanning capacitance microscopy (SCM) and electrostatic force microscopy (EFM), it is supposed that the GeSi QRs' electrical properties are mainly determined by the ring-shaped topography, rather than by the complete oxidation of the QRs' central hole or their composition distributions.
High-contrast qubit interactions using multimode cavity QED.
McKay, David C; Naik, Ravi; Reinhold, Philip; Bishop, Lev S; Schuster, David I
2015-02-27
We introduce a new multimode cavity QED architecture for superconducting circuits that can be used to implement photonic memories, more efficient Purcell filters, and quantum simulations of photonic materials. We show that qubit interactions mediated by multimode cavities can have exponentially improved contrast for two qubit gates without sacrificing gate speed. Using two qubits coupled via a three-mode cavity system we spectroscopically observe multimode strong couplings up to 102 MHz and demonstrate suppressed interactions off resonance of 10 kHz when the qubits are ≈600 MHz detuned from the cavity resonance. We study Landau-Zener transitions in our multimode systems and demonstrate quasiadiabatic loading of single photons into the multimode cavity in 25 ns. We introduce an adiabatic gate protocol to realize a controlled-Z gate between the qubits in 95 ns and create a Bell state with 94.7% fidelity. This corresponds to an on/off ratio (gate contrast) of 1000.
Growth and Optical Properties of Al rich AlN/AlGaN Quantum Wells
NASA Astrophysics Data System (ADS)
Tahtamouni, T. M. Al; Nepal, N.; Nakarmi, M. L.; Lin, J. Y.; Jiang, H. X.
2006-03-01
Al rich AlGaN alloys are promising materials for the applications in the optoelectronic devices such as deep ultraviolet (UV) emitters and detectors in the spectral range down to 200 nm. AlGaN based UV emitters (λ<340nm) has applications in bio-chemical agent detection and medical research/ health care. To realize deep UV emission (λ< 280 nm) Al rich AlGaN based quantum wells (QWs) are required. We report here the growth of AlN/AlxGa1-xNQWs (x>0.65) on AlN/sapphire templates by metalorganic chemical vapor deposition (MOCVD). Deep UV photoluminescence (PL) was employed to study the optical properties of the QWs. Well width (Al composition) dependence was studied by varying the QW thickness (Al composition) with fixed x ˜ 0.65 (well width at 3 nm). Optical properties of these QWs such as the effects of alloy fluctuation, temperature, strain and piezoelectric field, carrier and exciton localizations on the quantum efficiency have been studied. Carrier and exciton dynamics were probed. Implications of our findings on the applications of Al rich AlN/AlGaN QWs for UV emitters and detectors will also be discussed.
NASA Astrophysics Data System (ADS)
Bejan, D.
2017-02-01
The effects of exciton and electric field on the nonlinear optical properties, such as refraction index change, optical absorption coefficient and optical rectification of semiparabolic one-dimensional quantum dot, were theoretically investigated. The energy eigenvalues and eigenfunctions are calculated numerically within the effective mass approximation for a typical GaAs/ Al0.3Ga0.7 As quantum dot, for the cases where there is an exciton or a single electron/hole in the structure. Optical properties are obtained using the compact density matrix approach and steady state solutions. Our results show that: i) if the increasing electric field is oriented along the growth direction, the refractive index change structure and the resonance peaks of the absorption coefficient and optical rectification present a blue shift and are weakened for exciton and electron systems but have a red shift and are strengthened for the hole system; ii) when the field, oriented against the growth direction, augments, the above optical parameters present a red shift and are increased for exciton and electron systems but have a blue shift and are lowered for the hole system; iii) the exciton presence in the structure enhances the amplitude of the resonant peaks of all optical parameters even at zero electric field.
The effect of Coulomb interactions on thermoelectric properties of quantum dots
NASA Astrophysics Data System (ADS)
Zimbovskaya, Natalya; Kuzmin, Valery
2014-03-01
Thermoelectric effects in a quantum dot coupled to the source and drain charge reservoirs are explored using a nonequilibrium Green's functions formalism beyond the Hartree-Fock approxomation. We concentrate on theoretical analysis of the influence of Coulomb interactions on thermopower and the figure of merit ZT . Obtained results show that Coulomb interactions between charge carriers on the dot significantly contribute to its thermoelectric properties. In the present work, we trace the transition from the Coulomb blockade regime to Kondo regime in the thermoelectric properties of the quantum dot which occurs when we gradually strengthen the coupling of the dot to the charge reservoirs. We show that within the Coulomb blockade regime (when the coupling of the dot to the leads is weak compared to the characteristic strength of the charge carriers interactions) thermoelectric characteristics of the dot display distinct features caused by Coulomb interactions. These features indicate possibilities of enhancement of thermoelectric efficiency of the considered systems. Within the Kondo regime, when the couplings of the dot to the leads became stronger, the influence of Coulomb interactions declines bringing a decrease in the the thermoelectric efficiency.
Observation of the quantum paradox of separation of a single photon from one of its properties
NASA Astrophysics Data System (ADS)
Ashby, James M.; Schwarz, Peter D.; Schlosshauer, Maximilian
2016-07-01
We report an experimental realization of the quantum paradox of the separation of a single photon from one of its properties (the so-called "quantum Cheshire cat"). We use a modified Sagnac interferometer with displaced paths to produce appropriately pre- and postselected states of heralded single photons. Weak measurements of photon presence and circular polarization are performed in each arm of the interferometer by introducing weak absorbers and small polarization rotations and analyzing changes in the postselected signal. The absorber is found to have an appreciable effect only in one arm of the interferometer, while the polarization rotation significantly affects the signal only when performed in the other arm. We carry out both sequential and simultaneous weak measurements and find good agreement between measured and predicted weak values. In the language of Aharonov et al. and in the sense of the ensemble averages described by weak values, the experiment establishes the separation of a particle from one its properties during the passage through the interferometer.
Photo-physical properties enhancement of bare and core-shell quantum dots
NASA Astrophysics Data System (ADS)
Mumin, Md Abdul; Akhter, Kazi Farida; Charpentier, Paul A.
2014-03-01
Semiconductor nanocrystals (NCs) (also known as quantum dots, QDs) have attracted immense attention for their size-tunable optical properties that makes them impressive candidates for solar cells, light emitting devices, lasers, as well as biomedical imaging. However monodispersity, high and consistent photoluminescence, photostability, and biocompatibility are still major challenges. This work focuses on optimizing the photophysical properties and biocompatibility of QDs by forming core-shell nanostructures and their encapsulation by a carrier. Highly luminescent CdS and CdS-ZnS core-shell QDs with 5 nm sizes were synthesized using a facile approach based on pyrolysis of the single molecule precursors. After capping the CdS QDs with a thin layer of ZnS to reduce toxicity, the photoluminescence and photostability of the core-shell QDs was significantly enhanced. To make both the bare and core/shell structure QDs more resistant against photochemical reactions, a mesoporous silica layer was grown on the QDs through a reverse microemulsion technique based on hydrophobic interaction. This encapsulation enhanced the quantum yield and photostability compared to the bare QDs by providing much stronger resistance to oxidation and Oswald ripening of QDs. Encapsulation also improved biocompatibility of QDs that was evaluated with human umbilical vein endothelial cell lines (HUVEC).
Photo-physical properties enhancement of bare and core-shell quantum dots
Mumin, Md Abdul Akhter, Kazi Farida Charpentier, Paul A.
2014-03-31
Semiconductor nanocrystals (NCs) (also known as quantum dots, QDs) have attracted immense attention for their size-tunable optical properties that makes them impressive candidates for solar cells, light emitting devices, lasers, as well as biomedical imaging. However monodispersity, high and consistent photoluminescence, photostability, and biocompatibility are still major challenges. This work focuses on optimizing the photophysical properties and biocompatibility of QDs by forming core-shell nanostructures and their encapsulation by a carrier. Highly luminescent CdS and CdS-ZnS core-shell QDs with 5 nm sizes were synthesized using a facile approach based on pyrolysis of the single molecule precursors. After capping the CdS QDs with a thin layer of ZnS to reduce toxicity, the photoluminescence and photostability of the core-shell QDs was significantly enhanced. To make both the bare and core/shell structure QDs more resistant against photochemical reactions, a mesoporous silica layer was grown on the QDs through a reverse microemulsion technique based on hydrophobic interaction. This encapsulation enhanced the quantum yield and photostability compared to the bare QDs by providing much stronger resistance to oxidation and Oswald ripening of QDs. Encapsulation also improved biocompatibility of QDs that was evaluated with human umbilical vein endothelial cell lines (HUVEC)
Quantum simulation of structure, transport properties, and melting in dense hydrogen
NASA Astrophysics Data System (ADS)
Kang, Dongdong; Dai, Jiayu; Yuan, Jianmin
2016-10-01
Due to the low mass, hydrogen exhibits significant nuclear quantum effects (NQEs), especially under low temperatures and high pressures. NQEs on structure and transport properties of dense liquid hydrogen under extreme conditions are investigated using the improved centroid path integral molecular dynamics (PIMD) simulations. The results show that with the inclusion of NQEs, the radial distribution functions are obviously broadened. The self-diffusion is largely higher while the shear viscosity is notably lower than the results of without the inclusion of NQEs due to the lower collision cross sections even when the NQEs have little effects on the static structures. The electrical conductivity is also significantly affected by NQEs. Quantum nuclear character induces complex behaviors for ionic transport properties of dense liquid hydrogen. In addition, the melting temperature of dense hydrogen is also investigated using the two-phase approach based on the PIMD with the Yukawa potential describing the interaction between ions. The results show that the NQEs have a significant impact on the melting of dense hydrogen, which largely lower the melting temperature by 10% at the density range of 10-1000 g/cm3.
Quantum computation for quantum chemistry
NASA Astrophysics Data System (ADS)
Aspuru-Guzik, Alan
2010-03-01
Numerically exact simulation of quantum systems on classical computers is in general, an intractable computational problem. Computational chemists have made progress in the development of approximate methods to tackle complex chemical problems. The downside of these approximate methods is that their failure for certain important cases such as long-range charge transfer states in the case of traditional density functional theory. In 1982, Richard Feynman suggested that a quantum device should be able to simulate quantum systems (in our case, molecules) exactly using quantum computers in a tractable fashion. Our group has been working in the development of quantum chemistry algorithms for quantum devices. In this talk, I will describe how quantum computers can be employed to carry out numerically exact quantum chemistry and chemical reaction dynamics calculations, as well as molecular properties. Finally, I will describe our recent experimental quantum computation of the energy of the hydrogen molecule using an optical quantum computer.
Multimodal mechanisms of food creaminess sensation.
Chen, Jianshe; Eaton, Louise
2012-12-01
In this work, the sensory creaminess of a set of four viscosity-matched fluid foods (single cream, evaporated milk, corn starch solution, and corn starch solution containing long chain free fatty acids) was tested by a panel of 16 assessors via controlled sensation mechanisms of smell only, taste only, taste and tactile, and integrated multimodal. It was found that all sensation channels were able to discriminate between creamy and non-creamy foods, but only the multimodal method gave creaminess ratings in agreement with the samples' fat content. Results from this study show that the presence of long chain free fatty acids has no influence on creaminess perception. It is certain that food creaminess is not a primary sensory property but an integrated sensory perception (or sensory experience) derived from combined sensations of visual, olfactory, gustatory, and tactile cues. Creamy colour, milky flavour, and smooth texture are probably the most important sensory features of food creaminess.
Multimodality imaging in nanomedicine and nanotheranostics
Li, Xue; Zhang, Xue-Ning; Li, Xiao-Dong; Chang, Jin
2016-01-01
Accurate diagnosis of tumors needs much detailed information. However, available single imaging modality cannot provide complete or comprehensive data. Nanomedicine is the application of nanotechnology to medicine, and multimodality imaging based on nanoparticles has been receiving extensive attention. This new hybrid imaging technology could provide complementary information from different imaging modalities using only a single injection of contrast agent. In this review, we introduce recent developments in multifunctional nanoparticles and their biomedical applications to multimodal imaging and theragnosis as nanomedicine. Most of the reviewed studies are based on the intrinsic properties of nanoparticles and their application in clinical imaging technology. The imaging techniques include positron emission tomography, single-photon emission computed tomography, computerized tomography, magnetic resonance imaging, optical imaging, and ultrasound imaging. PMID:27807501
Solomon, Justin; Samei, Ehsan
2014-09-15
Purpose: Quantum noise properties of CT images are generally assessed using simple geometric phantoms with uniform backgrounds. Such phantoms may be inadequate when assessing nonlinear reconstruction or postprocessing algorithms. The purpose of this study was to design anatomically informed textured phantoms and use the phantoms to assess quantum noise properties across two clinically available reconstruction algorithms, filtered back projection (FBP) and sinogram affirmed iterative reconstruction (SAFIRE). Methods: Two phantoms were designed to represent lung and soft-tissue textures. The lung phantom included intricate vessel-like structures along with embedded nodules (spherical, lobulated, and spiculated). The soft tissue phantom was designed based on a three-dimensional clustered lumpy background with included low-contrast lesions (spherical and anthropomorphic). The phantoms were built using rapid prototyping (3D printing) technology and, along with a uniform phantom of similar size, were imaged on a Siemens SOMATOM Definition Flash CT scanner and reconstructed with FBP and SAFIRE. Fifty repeated acquisitions were acquired for each background type and noise was assessed by estimating pixel-value statistics, such as standard deviation (i.e., noise magnitude), autocorrelation, and noise power spectrum. Noise stationarity was also assessed by examining the spatial distribution of noise magnitude. The noise properties were compared across background types and between the two reconstruction algorithms. Results: In FBP and SAFIRE images, noise was globally nonstationary for all phantoms. In FBP images of all phantoms, and in SAFIRE images of the uniform phantom, noise appeared to be locally stationary (within a reasonably small region of interest). Noise was locally nonstationary in SAFIRE images of the textured phantoms with edge pixels showing higher noise magnitude compared to pixels in more homogenous regions. For pixels in uniform regions, noise magnitude was
Dikareva, N. V. Vikhrova, O. V.; Zvonkov, B. N.; Malekhonova, N. V.; Nekorkin, S. M.; Pirogov, A. V.; Pavlov, D. A.
2015-01-15
Heterostructures containing single GaAsSb/GaAs quantum wells and bilayer GaAsSb/InGaAs quantum wells are produced by metal-organic vapor-phase epitaxy at atmospheric pressure. The growth temperature of the quantum-confined layers is 500–570°C. The structural quality of the samples and the quality of heterointerfaces of the quantum wells are studied by the high-resolution transmission electron microscopy of cross sections. The emission properties of the heterostructures are studied by photoluminescence measurements. The structures are subjected to thermal annealing under conditions chosen in accordance with the temperature and time of growth of the upper cladding p-InGaP layer during the formation of GaAs/InGaP laser structures with an active region containing quantum-confined GaAsSb layers. It is found that such heat treatment can have a profound effect on the emission properties of the active region, only if a bilayer GaAsSb/InGaAs quantum well is formed.
Linear-optics realization of channels for single-photon multimode qudits
Piani, Marco; Pitkanen, David; Luetkenhaus, Norbert; Kaltenbaek, Rainer
2011-09-15
We propose and theoretically study a method for the stochastic realization of arbitrary quantum channels on multimode single-photon qudits. In order for our method to be undemanding in its implementation, we restrict our analysis to linear-optical techniques, vacuum ancillary states, and nonadaptive schemes, but we allow for random switching between different optical networks. With our method it is possible to deterministically implement random-unitary channels and to stochastically implement general channels. We provide an expression for the optimal probability of success of our scheme and calculate this quantity for specific examples such as the qubit amplitude-damping channel. The success probability is shown to be related to the entanglement properties of the Choi-Jamiolkowski state isomorphic to the channel.
Patty, Kira; Campbell, Quinn; Hamilton, Nathan; West, Robert G.; Sadeghi, Seyed M.; Mao, Chuanbin
2014-09-21
We used photoactive substrates consisting of about 1 nm coating of a metal oxide on glass substrates to investigate the impact of the structures of colloidal quantum dots on their photophysical and photochemical properties. We showed during irradiation these substrates can interact uniquely with such quantum dots, inducing distinct forms of photo-induced processes when they have different cores, shells, or ligands. In particular, our results showed that for certain types of core-shell quantum dot structures an ultrathin layer of a metal oxide can reduce suppression of quantum efficiency of the quantum dots happening when they undergo extensive photo-oxidation. This suggests the possibility of shrinking the sizes of quantum dots without significant enhancement of their non-radiative decay rates. We show that such quantum dots are not influenced significantly by Coulomb blockade or photoionization, while those without a shell can undergo a large amount of photo-induced fluorescence enhancement via such blockade when they are in touch with the metal oxide.
NASA Astrophysics Data System (ADS)
Patty, Kira; Sadeghi, Seyed M.; Campbell, Quinn; Hamilton, Nathan; West, Robert G.; Mao, Chuanbin
2014-09-01
We used photoactive substrates consisting of about 1 nm coating of a metal oxide on glass substrates to investigate the impact of the structures of colloidal quantum dots on their photophysical and photochemical properties. We showed during irradiation these substrates can interact uniquely with such quantum dots, inducing distinct forms of photo-induced processes when they have different cores, shells, or ligands. In particular, our results showed that for certain types of core-shell quantum dot structures an ultrathin layer of a metal oxide can reduce suppression of quantum efficiency of the quantum dots happening when they undergo extensive photo-oxidation. This suggests the possibility of shrinking the sizes of quantum dots without significant enhancement of their non-radiative decay rates. We show that such quantum dots are not influenced significantly by Coulomb blockade or photoionization, while those without a shell can undergo a large amount of photo-induced fluorescence enhancement via such blockade when they are in touch with the metal oxide.
Diffusive and quantum effects of water properties in different states of matter
Yeh, Kuan-Yu; Huang, Shao-Nung; Chen, Li-Jen E-mail: stlin@ntu.edu.tw; Lin, Shiang-Tai E-mail: stlin@ntu.edu.tw
2014-07-28
The enthalpy, entropy, and free energy of water are important physical quantities for understanding many interesting phenomena in biological systems. However, conventional approaches require different treatments to incorporate quantum and diffusive effects of water in different states of matter. In this work, we demonstrate the use of the two-phase thermodynamic (2PT) model as a unified approach to obtain the properties of water over the whole phase region of water from short (∼20 ps) classical molecular dynamics trajectories. The 2PT model provides an effective way to separate the diffusive modes (gas-like component) from the harmonic vibrational modes (solid-like component) in the vibrational density of states (DoS). Therefore, both diffusive and quantum effect can be properly accounted for water by applying suitable statistical mechanical weighting functions to the DoS components. We applied the 2PT model to systematically examine the enthalpy, entropy, and their temperature dependence of five commonly used rigid water models. The 2PT results are found to be consistent with those obtained from more sophisticated calculations. While the thermodynamic properties determined from different water models are largely similar, the phase boundary determined from the equality of free energy is very sensitive to the small inaccuracy in the values of enthalpy and absolute entropy. The enthalpy, entropy, and diffusivity of water are strongly interrelated, which challenge further improvement of rigid water model via parameter fitting. Our results show that the 2PT is an efficient method for studying the properties of water under various chemical and biological environments.
Reddy, V Sivaranjana; Camacho, Cristopher; Xia, Jianlong; Jasti, Ramesh; Irle, Stephan
2014-09-09
The size-dependent ultraviolet/visible photophysical property trends of [n]cycloparaphenylenes ([n]CPPs, n = 6, 8, and 10) are theoretically investigated using quantum dynamics simulations. For geometry optimizations on the ground- and excited-state Born-Oppenheimer potential energy surfaces (PESs), we employ density functional theory (DFT) and time-dependent DFT calculations. Harmonic normal-mode analyses are carried out for the electronic ground state at Franck-Condon geometries. A diabatic Hamiltonian, comprising four low-lying singlet excited electronic states and 26 vibrational degrees of freedom of CPP, is constructed within the linear vibronic coupling (VC) model to elucidate the absorption spectral features in the range of 300-500 nm. Quantum nuclear dynamics is simulated within the multiconfiguration time-dependent Hartree approach to calculate the vibronic structure of the excited electronic states. The symmetry-forbidden S0 → S1 transition appears in the longer wavelength region of the spectrum with weak intensity due to VC. It is found that the Jahn-Teller and pseudo-Jahn-Teller effects in the doubly degenerate S2 and S3 electronic states are essential in the quantitative interpretation of the experimental observation of a broad absorption peak around 340 nm. The vibronic mixing of the S1 state with higher electronic states is responsible for the efficient photoluminescence from the S1 state. The fluorescence properties are characterized on the basis of the stationary points of the excited-state PESs. The findings reveal that vibronic effects become important in determining the photophysical properties of CPPs with increased ring size.
Diffusive and quantum effects of water properties in different states of matter.
Yeh, Kuan-Yu; Huang, Shao-Nung; Chen, Li-Jen; Lin, Shiang-Tai
2014-07-28
The enthalpy, entropy, and free energy of water are important physical quantities for understanding many interesting phenomena in biological systems. However, conventional approaches require different treatments to incorporate quantum and diffusive effects of water in different states of matter. In this work, we demonstrate the use of the two-phase thermodynamic (2PT) model as a unified approach to obtain the properties of water over the whole phase region of water from short (∼20 ps) classical molecular dynamics trajectories. The 2PT model provides an effective way to separate the diffusive modes (gas-like component) from the harmonic vibrational modes (solid-like component) in the vibrational density of states (DoS). Therefore, both diffusive and quantum effect can be properly accounted for water by applying suitable statistical mechanical weighting functions to the DoS components. We applied the 2PT model to systematically examine the enthalpy, entropy, and their temperature dependence of five commonly used rigid water models. The 2PT results are found to be consistent with those obtained from more sophisticated calculations. While the thermodynamic properties determined from different water models are largely similar, the phase boundary determined from the equality of free energy is very sensitive to the small inaccuracy in the values of enthalpy and absolute entropy. The enthalpy, entropy, and diffusivity of water are strongly interrelated, which challenge further improvement of rigid water model via parameter fitting. Our results show that the 2PT is an efficient method for studying the properties of water under various chemical and biological environments.
NASA Astrophysics Data System (ADS)
Ye, Hui; Yang, Ligong; Gu, Peifu
2002-09-01
Semiconducting ferroelectric antimony sulphoiodide (SbSI) microcrystallite doped organically modified TiO2 thin films were successfully fabricated with the sol-gel process. Ferroelectric SbSI crystallites have some attractive properties, including high dielectric permittivity, high electro-optical coefficient and high photoconductivity. SbSI is also an intrinsic semiconductor with a relatively narrow eneryg gap. The Bohr radius of the SbSI crystal was calculated larger than other semiconductors due to its large dielectric constant. If the crystal size is smaller than its Bohr radius and the microcrystallite are dispersed in a suitable matrix, a dramatic improvement of the nonlinear three-order nonlinearity will be achieved due to the quantum confinement effect. The SbSI quantum dot composites were proved to be good candidates for nonlinear and electro-optical devices. Glycidopropyltrimetroxysilane modified TiO2 was chosen as the matrix and SbSI was synthesized in situ by using SbI3, SC(NH2)2. The materials in thin film were heat-treated in different conditions and the size of the microcrystallite was characterized by the XRD. A value of 3.5pm/V of effective transverse electro-optical coefficient reff for the nano-composite containing 8 wt percent of antimony sulfide iodide was measured. The third-order nonlinear optical susceptibility of the SbSI quantum dot thin film was measured by degenerate four-wave mixing at 532nm using a frequency double Nd:YAG laser beams with a pulse width of around 10ns, the x(3) value of 3 μm sample was measured to be 6 × 10-11 esu.
NASA Astrophysics Data System (ADS)
Taherian, M.; Sabbagh Alvani, A. A.; Shokrgozar, M. A.; Salimi, R.; Moosakhani, S.; Sameie, H.; Tabatabaee, F.
2014-03-01
In the present study, the ZnS semiconductor quantum dots were successfully synthesized via an aqueous method utilizing glutathione (GSH), thioglycolic acid (TGA) and polyvinyl pyrrolidone (PVP) as capping agents. The structural, morphological and photo-physical properties and biocompatibility were investigated using comprehensive characterization techniques such as x-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), dynamic light scattering (DLS), Fourier transform infrared spectrometry (FT-IR), UV-Vis optical absorption, photoluminescence (PL) spectrometer and MTT assay. The XRD patterns showed a cubic zinc blende crystal structure and a crystallite size of about 2-3 nm using Scherrer's equation confirmed by the electron micrographs and Effective Mass Approximation (EMA). The DLS and zeta-potential results revealed that GSH capped ZnS nanoparticles have the narrowest size distribution with an average size of 27 nm and relatively good colloidal stability. Also, the FT-IR spectrum confirmed the interaction of the capping agent groups with ZnS nanoparticles. According to the UV-Vis absorption results, optical bandgap of the spherical capped nanoparticles is higher compared to the uncapped sample and could be wider than 3.67 eV (corresponding to the bulk ZnS), which is due to the quantum confinement effect. From photoluminescence spectra, it was found that the emission becomes more intensive and shifts towards the shorter wavelengths in the presence of the capping agent. Moreover, the emission mechanism of uncapped and capped ZnS was discussed in detail. Finally, the MTT results revealed the satisfactory (>94%) biocompatibility of GSH capped ZnS quantum dots which would be a promising candidate applicable in fluorescent biological labels.
NASA Astrophysics Data System (ADS)
Rogacheva, E. I.; Budnik, A. V.; Sipatov, A. Yu.; Nashchekina, O. N.; Dresselhaus, M. S.
2015-02-01
The dependences of the electrical conductivity, the Hall coefficient, and the Seebeck coefficient on the layer thickness d (d = 18-600 nm) of p-type topological insulator Bi2Te3 thin films grown by thermal evaporation in vacuum on glass substrates were obtained at room temperature. In the thickness range of d = 18-100 nm, sustained oscillations with a substantial amplitude were revealed. The observed oscillations are well approximated by a harmonic function with a period Δd = (9.5 ± 0.5) nm. At d > 100 nm, the transport coefficients practically do not change as d is increased. The oscillations of the kinetic properties are attributed to the quantum size effects due to the hole confinement in the Bi2Te3 quantum wells. The results of the theoretical calculations of Δd within the framework of a model of an infinitely deep potential well are in good agreement with the experimental results. It is suggested that the substantial amplitude of the oscillations and their sustained character as a function of d are connected with the topologically protected gapless surface states of Bi2Te3 and are inherent to topological insulators.
Vidanović, Ivana; Bogojević, Aleksandar; Belić, Aleksandar
2009-12-01
We analyze the method for calculation of properties of nonrelativistic quantum systems based on exact diagonalization of space-discretized short-time evolution operators. In this paper we present a detailed analysis of the errors associated with space discretization. Approaches using direct diagonalization of real-space discretized Hamiltonians lead to polynomial errors in discretization spacing Delta . Here we show that the method based on the diagonalization of the short-time evolution operators leads to substantially smaller discretization errors, vanishing exponentially with 1/Delta(2). As a result, the presented calculation scheme is particularly well suited for numerical studies of few-body quantum systems. The analytically derived discretization errors estimates are numerically shown to hold for several models. In the follow up paper [I. Vidanović, A. Bogojević, A. Balaz, and A. Belić, Phys. Rev. E 80, 066706 (2009)] we present and analyze substantial improvements that result from the merger of this approach with the recently introduced effective-action scheme for high-precision calculation of short-time propagation.
Photoluminescence properties of hybrid SiO2-coated CdTe/CdSe quantum dots.
Liu, Ning; Yang, Ping
2014-09-01
Hybrid SiO2-coated CdTe/CdSe quantum dots (QDs) were prepared using CdTe/CdSe QDs prepared by hydrothermal synthesis. A CdSe interlayer made CdTe/CdSe cores with unique type II heterostructures. The hybrid SiO2-coated CdTe/CdSe QDs revealed excellent photoluminescence (PL) properties compared with hybrid SiO2-coated CdTe QDs. Because of the existence of spatial separations of carriers in the type II CdTe/CdSe core/shell QDs, the hybrid QDs had a relatively extended PL lifetime and high stability in phosphate-buffered saline buffer solutions. This is ascribed to the unique components and stable surface state of hybrid SiO2-coated CdTe/CdSe QDs. During the stabilization test in phosphate-buffered saline buffer solutions, both static and dynamic quenching occurred. The quenching mechanism of the hybrid QDs was not suited with the Stern–Volmer equation. However, the relative stable surface of CdTe/CdSe QDs resulted in lower degradation and relative high PL quantum yields compared with hybrid SiO2-coated CdTe QDs. As a result, hybrid SiO2-coated CdTe/CdSe QDs can be used in bioapplications.
NASA Astrophysics Data System (ADS)
Chernyavskiy, Andrey; Khamitov, Kamil; Teplov, Alexey; Voevodin, Vadim; Voevodin, Vladimir
2016-10-01
In recent years, quantum information technologies (QIT) showed great development, although, the way of the implementation of QIT faces the serious difficulties, some of which are challenging computational tasks. This work is devoted to the deep and broad analysis of the parallel algorithmic properties of such tasks. As an example we take one- and two-qubit transformations of a many-qubit quantum state, which are the most critical kernels of many important QIT applications. The analysis of the algorithms uses the methodology of the AlgoWiki project (algowiki-project.org) and consists of two parts: theoretical and experimental. Theoretical part includes features like sequential and parallel complexity, macro structure, and visual information graph. Experimental part was made by using the petascale Lomonosov supercomputer (Moscow State University, Russia) and includes the analysis of locality and memory access, scalability and the set of more specific dynamic characteristics of realization. This approach allowed us to obtain bottlenecks and generate ideas of efficiency improvement.
Size dependent magnetic and optical properties in diamond shaped graphene quantum dots: A DFT study
NASA Astrophysics Data System (ADS)
Das, Ritwika; Dhar, Namrata; Bandyopadhyay, Arka; Jana, Debnarayan
2016-12-01
The magnetic and optical properties of diamond shaped graphene quantum dots (DSGQDs) have been investigated by varying their sizes with the help of density functional theory (DFT). The study of density of states (DOS) has revealed that the Fermi energy decreases with increase in sizes (number of carbon atoms). The intermediate structure with 30 carbon atoms shows the highest magnetic moment (8 μB, μB being the Bohr magneton). The shifting of optical transitions to higher energy in smallest DSGQD (16 carbon atoms) bears the signature of stronger quantum confinement. However, for the largest structure (48 carbon atoms) multiple broad peaks appear in case of parallel polarization and in this case electron energy loss spectra (EELS) peak (in the energy range 0-5 eV) is sharp in nature (compared to high energy peak). This may be attributed to π plasmon and the broad peak (in the range 10-16 eV) corresponds to π + σ plasmon. A detail calculation of the Raman spectra has indicated some prominent mode of vibrations which can be used to characterize these structures (with hydrogen terminated dangling bonds). We think that these theoretical observations can be utilized for novel device designs involving DSGQDs.
Quantum properties of a binary bosonic mixture in a double well
NASA Astrophysics Data System (ADS)
Mujal, Pere; Juliá-Díaz, Bruno; Polls, Artur
2016-04-01
This work contains a detailed analysis of the properties of the ground state of a two-component two-site Bose-Hubbard model, which captures the physics of a binary mixture of Bose-Einstein condensates trapped in a double-well potential. The atom-atom interactions within each species and among the two species are taken as variable parameters, while the hopping terms are kept fixed. To characterize the ground state, we use observables such as the imbalance of population and its quantum uncertainty. The quantum many-body correlations present in the system are further quantified by studying the degree of condensation of each species, the entanglement between the two sites, and the entanglement between the two species. The latter is measured by means of the Schmidt gap, the von Neumann entropy, or the purity obtained after tracing out a part of the system. A number of relevant states are identified, e.g., Schrödinger catlike many-body states, in which the outcome of the population imbalance of both components is completely correlated, and other states with even larger von Neumann entropy which have a large spread in Fock space.
Quantum robots and quantum computers
Benioff, P.
1998-07-01
Validation of a presumably universal theory, such as quantum mechanics, requires a quantum mechanical description of systems that carry out theoretical calculations and systems that carry out experiments. The description of quantum computers is under active development. No description of systems to carry out experiments has been given. A small step in this direction is taken here by giving a description of quantum robots as mobile systems with on board quantum computers that interact with different environments. Some properties of these systems are discussed. A specific model based on the literature descriptions of quantum Turing machines is presented.
Learning multimodal latent attributes.
Fu, Yanwei; Hospedales, Timothy M; Xiang, Tao; Gong, Shaogang
2014-02-01
The rapid development of social media sharing has created a huge demand for automatic media classification and annotation techniques. Attribute learning has emerged as a promising paradigm for bridging the semantic gap and addressing data sparsity via transferring attribute knowledge in object recognition and relatively simple action classification. In this paper, we address the task of attribute learning for understanding multimedia data with sparse and incomplete labels. In particular, we focus on videos of social group activities, which are particularly challenging and topical examples of this task because of their multimodal content and complex and unstructured nature relative to the density of annotations. To solve this problem, we 1) introduce a concept of semilatent attribute space, expressing user-defined and latent attributes in a unified framework, and 2) propose a novel scalable probabilistic topic model for learning multimodal semilatent attributes, which dramatically reduces requirements for an exhaustive accurate attribute ontology and expensive annotation effort. We show that our framework is able to exploit latent attributes to outperform contemporary approaches for addressing a variety of realistic multimedia sparse data learning tasks including: multitask learning, learning with label noise, N-shot transfer learning, and importantly zero-shot learning.
Electronic and Quantum Transport Properties of Atomically Identified Si Point Defects in Graphene.
Lopez-Bezanilla, Alejandro; Zhou, Wu; Idrobo, Juan-Carlos
2014-05-15
We report high-resolution scanning transmission electron microscopy images displaying a range of inclusions of isolated silicon atoms at the edges and inner zones of graphene layers. Whereas the incorporation of Si atoms to a graphene armchair edge involves no reconstruction of the neighboring carbon atoms, the inclusion of a Si atom to a zigzag graphene edge entails the formation of five-membered carbon rings. In all the observed atomic edge terminations, a Si atom is found bridging two C atoms in a 2-fold coordinated configuration. The atomic-scale observations are underpinned by first-principles calculations of the electronic and quantum transport properties of the structural anomalies. Experimental estimations of Si-doped graphene band gaps realized by means of transport measurements may be affected by a low doping rate of 2-fold coordinated Si atoms at the graphene edges, and 4-fold coordinated at inner zones due to the apparition of mobility gaps.
Kang, Hyeong-Gon; Tokumasu, Fuyuki; Clarke, Matthew; Zhou, Zhenping; Tang, Jianyong; Nguyen, Tinh; Hwang, Jeeseong
2010-01-01
We present results on the dynamic fluorescence properties of bioconjugated nanocrystals or quantum dots (QDs) in different chemical and physical environments. A variety of QD samples was prepared and compared: isolated individual QDs, QD aggregates, and QDs conjugated to other nanoscale materials, such as single-wall carbon nanotubes (SWCNTs) and human erythrocyte plasma membrane proteins. We discuss plausible scenarios to explain the results obtained for the fluorescence characteristics of QDs in these samples, especially for the excitation time-dependent fluorescence emission from clustered QDs. We also qualitatively demonstrate enhanced fluorescence emission signals from clustered QDs and deduce that the band 3 membrane proteins in erythrocytes are clustered. This approach is promising for the development of QD-based quantitative molecular imaging techniques for biomedical studies involving biomolecule clustering.
Polarization quantum properties in a type-II optical parametric oscillator below threshold
Zambrini, Roberta; Miguel, Maxi San; Gatti, Alessandra; Lugiato, Luigi
2003-12-01
We study the far-field spatial distribution of the quantum fluctuations in the transverse profile of the output light beam generated by a type-II optical parametric oscillator below threshold, including the effects of transverse walk-off. We study how quadrature field correlations depend on the polarization. We find spatial Einstein-Podolsky-Rosen entanglement in quadrature-polarization components. For the far-field points not affected by walk-off there is almost complete noise suppression in the proper quadratures difference of any orthogonal polarization components. We show the entanglement of the state of symmetric, intense, or macroscopic, spatial light modes. We also investigate nonclassical polarization properties in terms of the Stokes operators. We find perfect correlations in all Stokes parameters measured in opposite far-field points in the direction orthogonal to the walk-off, while locally the field is unpolarized and we find no polarization squeezing.
Structure and properties of InAs/AlAs quantum dots for broadband emission
NASA Astrophysics Data System (ADS)
Meng, X. Q.; Jin, P.; Liang, Z. M.; Liu, F. Q.; Wang, Z. G.; Zhang, Z. Y.
2010-11-01
The InAs quantum dots (QDs) on an AlAs layer are grown on GaAs substrates by molecular beam epitaxy technique. The properties of materials and optics of such QD structures have been investigated by cross sectional transmission electron microscopy and photoluminescence (PL) techniques. It is discovered that the inhomogeneous strain filed mainly exists below InAs QDs layers in the case of no wetting layer. The full width at half maximums (FWHMs) and intensities of PL emission peaks of InAs QDs are found to be closely related to the thickness of the thin AlAs layers. The InAs QDs on an eight monolayer AlAs layer, with wide FWHMs and large integral intensity of PL emission peaks, are favorable for producing broadband QD superluminescent diodes, external-cavity QD laser with large tuning range.
NASA Astrophysics Data System (ADS)
Bakanov, A. G.; Toropov, N. A.; Vartanyan, T. A.
2016-03-01
The optical properties of a composite material consisting of a thin polymer film, which is activated by semiconductor CdSe/ZnS quantum dots (QDs) and silver nanoparticles, on a transparent dielectric substrate have been investigated. It is revealed that the presence of silver nanoparticles leads to an increase in the QD absorption (by a factor of 4) and in the fluorescence intensity (by a factor of 10), whereas the fluorescence time drops by a factor of about 10. Excitation of the composite medium by a pulsed laser is found to result in narrowing of the fluorescence band and a sublinear dependence of its intensity on the pulse energy. In the absence of silver nanoparticles, the fluorescence spectrum of QDs is independent of the excitation-pulse energy density, and the fluorescence intensity depends linearly on the pulse energy in the entire range of energy densities, up to 75 mJ/cm2.
NASA Astrophysics Data System (ADS)
Ding, Xiaobin; Sun, Rui; Koike, Fumihiro; Kato, Daiji; Murakami, Izumi; Sakaue, Hiroyuki A.; Dong, Chenzhong
2017-03-01
The electron correlation effects and Breit interaction as well as Quantum Electro-Dynamics (QED) effects were expected to have important contribution to the energy level and transition properties of heavy highly charged ions. The ground states [Ne]3 s 23 p 63 d 2 and first excited states [Ne]3 s 23 p 53 d 3 of W54+ ion have been studied by using Multi-Configuration Dirac-Fock method with the implementation of Grasp2K package. A restricted active space method was employed to investigate the correlation contribution from different models. The Breit interaction and QED effects were taken into account in the relativistic configuration interaction calculation with the converged wavefunction. It is found that the correlation contribution from 3 s and 3 p orbital have important contribution to the energy level, transition wavelength and probability of the ground and the first excited state of W54+ ion.
NASA Astrophysics Data System (ADS)
Silva, A. A. P.; Vasconcellos, Áurea. R.; Luzzi, Roberto; Meneses, E. A.; Laureto, E.
2009-10-01
Systems in which one or more directions are in the nanometric space scale exhibit significantly some peculiar phenomena and processes. We consider here the case of nanometric quantum wells with complex structure, displaying fractal-like characteristics, which are part of semiconductor heterostructures. An extensive theoretical study of the optical properties of photoluminescence and excited photoluminescence, and then involving absorption and the question of emergence of the so-called Stokes shift that is observed in some cases are performed. The results are compared with some experimental data. This is of relevance for opening up the possibility to use optical measurements to perform a (nondestructive) quality control of samples grown under different methods and protocols.
Jackson, Robert L.; Crandall, Erika R.; Bozack, Michael J.
2015-05-21
The objective of this work is to evaluate the effect of scale dependent mechanical and electrical properties on electrical contact resistance (ECR) between rough surfaces. This work attempts to build on existing ECR models that neglect potentially important quantum- and size-dependent contact and electrical conduction mechanisms present due to the asperity sizes on typical surfaces. The electrical conductance at small scales can quantize or show a stepping trend as the contact area is varied in the range of the free electron Fermi wavelength squared. This work then evaluates if these effects remain important for the interface between rough surfaces, which may include many small scale contacts of varying sizes. The results suggest that these effects may be significant in some cases, while insignificant for others. It depends on the load and the multiscale structure of the surface roughness.
NASA Astrophysics Data System (ADS)
Crespi, Vincent H.; Han, J. E.
2001-03-01
We describe a new class of nanoscale structured metals wherein the effects of quantum confinement are combined with dispersive metallic electronic states to induce modifications to the fundamental low-energy microscopic properties of a three-dimensional metal: the density of states, the distribution of Fermi velocities, and the collective electronic response (J. E. Han and Vincent H. Crespi, to appear in Phys. Rev. Lett.). The metalattice, metal-infiltrated colloidal lattice, possesses two very different length scales, lattice constants of metal atoms and of colloidal spheres. We compute the electronic properties of the metalattice using an empirical tight-binding method. As a result of the hierarchy in the two length scales, electronic states bifurcate into two classes with weak and strong dispersion. The dispersive states reflect the symmetry of the colloidal lattice and have major contribution to the transport properties such as inversion of Fermi velocity and optical response. We also discuss the magnetic structure of the metalattice with magnetic infiltrants such as Pd and Rh.
Luminescence Properties of Sm3+/Eu3+ Co-Doped ZnO Quantum Dots.
Liu, Fengyi; Li, Hong; Hu, Yajing; Na, Jin; Mou, Yun; Yang, Kun; Ye, Zuhu; Li, Mingyue; Xie, Ya-Hong
2016-04-01
In order to improve luminescence properties of semiconductor ZnO quantum dots (QDs), Sm3+/Eu3+ co-doped ZnO QDs have been controllably synthesized by sol-gel method in this paper. ZnO QDs have a spherical shape with mean diameter at about 5-6 nm, which was characterized by high-resolution transmission electron microscopy (HRTEM). ZnO QDs have hexagonal wurtzite structure with parts of Sm3+ and Eu3+ incorporated into the lattice, which was demonstrated by X-ray Diffraction (XRD). Luminescence properties at room temperature (RT) of different amount of Sm3+ and 2 mol% Eu3+ doped ZnO QDs were examined in-depth by optical spectra. In contrast to the Pr3+/Eu3+ co-doped fluorescent performance researched in our previous study, the photoluminescence (PL) spectra indicates the unique luminescence properties of Sm3+/Eu3+ co-doped ZnO QDs. In addition, fluorescence lifetimes were obtained to illustrate the luminous mechanism.
The Optical Properties of CdSe Quantum Dots by Using Spray-Atomization Method
NASA Astrophysics Data System (ADS)
Rosmani, C. H.; Abdullah, S.; Rusop, M.
2013-06-01
Cadmium Selenide (CdSe) quantum dots (QDs) is inorganic material by using spray-atomization method which is the novelty to find out the optical properties for the CdSe QDs. The Selenium (Se) precursor and Cadmium (Cd) precursor were prepared first. Se precursor by using sodium sulfite aqueous was mixed with selenium (Se) powder. For Cd precursor was used cadmium chloride (CdCI) as the Cd precursor. From previous research, CdSe QDs was obtained by using capping agent such as tri-n-octylphosphine oxide (TOPO) and trioctylphosphine (TOP). These capping agent are hazardous to environment and human. By using spray-atomization method it is more safe and economically. The photoluminescence (PL) was used to investigate the optical properties and to investigate the energy band gap from PL result. The field emission scanning electron microscopy (FESEM) was used to know the surface morphology of CdSe QDs. By PL result, the energy band gap was calculate and the comparison was investigate between the size of particle and the energy band gap. This important in this paper is to investigate the optical properties of CdSe QDs by using sprays-atomization method and to relate with the particle size.
Karkov, Hanne Sophie; Krogh, Berit Olsen; Woo, James; Parimal, Siddharth; Ahmadian, Haleh; Cramer, Steven M
2015-11-01
In this study, a unique set of antibody Fab fragments was designed in silico and produced to examine the relationship between protein surface properties and selectivity in multimodal chromatographic systems. We hypothesized that multimodal ligands containing both hydrophobic and charged moieties would interact strongly with protein surface regions where charged groups and hydrophobic patches were in close spatial proximity. Protein surface property characterization tools were employed to identify the potential multimodal ligand binding regions on the Fab fragment of a humanized antibody and to evaluate the impact of mutations on surface charge and hydrophobicity. Twenty Fab variants were generated by site-directed mutagenesis, recombinant expression, and affinity purification. Column gradient experiments were carried out with the Fab variants in multimodal, cation-exchange, and hydrophobic interaction chromatographic systems. The results clearly indicated that selectivity in the multimodal system was different from the other chromatographic modes examined. Column retention data for the reduced charge Fab variants identified a binding site comprising light chain CDR1 as the main electrostatic interaction site for the multimodal and cation-exchange ligands. Furthermore, the multimodal ligand binding was enhanced by additional hydrophobic contributions as evident from the results obtained with hydrophobic Fab variants. The use of in silico protein surface property analyses combined with molecular biology techniques, protein expression, and chromatographic evaluations represents a previously undescribed and powerful approach for investigating multimodal selectivity with complex biomolecules.
Fabrication and Transport Properties of Quantum Nanotransistors Coupled with Nanogap Electrodes
NASA Astrophysics Data System (ADS)
Hirakawa, Kazuhiko; Shibata, Kenji; Umeno, Akinori
Electrical manipulation and read-out of quantum mechanical states in single quantum dots and molecules by nanogap metal electrodes is expected to bring about great innovation in ICT (information-communication technology) devices. We have been working on technologies of accessing to single molecules and quantum dots by nanogap electrodes and exploring device applications of novel physics manifested in such nanotransistors.
Ground state properties of quantum Kagomé ice hardcore bosons
NASA Astrophysics Data System (ADS)
Owerre, S. A.
2016-11-01
We study the quantum Kagomé ice hardcore bosons, which correspond to the XY limit of the quantum spin ice Hamiltonian. We estimate the values of their zero-temperature thermodynamic quantities using the large-S expansion. We show that our semiclassical analysis is consistent with the finite temperature quantum Monte Carlo estimates.
Vinyltrimethoxysilane-modified zinc oxide quantum dots with tuned optical properties
NASA Astrophysics Data System (ADS)
Tăbăcaru, Aurel; Muşat, Viorica; Ţigău, Nicolae; Vasile, Bogdan Ştefan; Surdu, Vasile-Adrian
2015-12-01
Surface modification of zinc oxide nanoparticles (ZnO NPs) with covalently attachable organosilane species is a promising route for the preparation of hybrid nanomaterials in which optical and physico-chemical properties can be easily tuned. As a continuation of our ongoing studies regarding the surface modification of ZnO NPs with adjustable optical properties, we here report a novel series of hybrid zinc oxide quantum dots (ZnO QDs) modified with vinyltrimethoxysilane (VTMS). The modified ZnO QDs, with sizes spanning the range 3-4 nm, were obtained through a simple and low-cost precipitation method. They were morpho-structurally characterized by means of X-ray diffraction, high-resolution transmission electron microscopy and Fourier transform infrared spectroscopy, while their optical properties were studied by UV-vis spectroscopy. When applied as thin films on glass substrate, the obtained ZnO QDs showed excellent optical transmittance between 85 and 90%, and low reflectance in the visible domain. The photoluminescence spectra showed a significant blue-shift of the emission bands, from 578 nm for unmodified ZnO to 540 nm for ZnO modified with 10% VTMS. A new opposite trend of band gap variation from 3.494 eV for unmodified ZnO to 3.32 eV for ZnO modified with 10% VTMS was detected, while an organosilane loading higher than 10% was found to reincrease both nanoparticles size and band gap energy. These results highlighted the better ability of VTMS to attain a higher degree of nanoparticles size reduction, along with the tuning of the optical properties, with respect to the previously reported ZnO-MPS series.
Optimisation of optical properties of a long-wavelength GaInNAs quantum-well laser diode
Alias, M S; Maskuriy, F; Faiz, F; Mitani, S M; AL-Omari, A N
2013-11-30
We report optimisation of optical properties of a strained GaInNAs/GaAs quantum-well laser, by taking into account the many-body effect theory and the bowing parameter. The theoretical transition energies and the GaInNAs bowing parameter are fitted into the photoluminescence spectrum of the GaInNAs quantum well, obtained in the experiment. The theoretical results for the photoluminescence spectrum and laser characteristics (light, current and voltage) exhibits a high degree of agreement with the experimental results. (lasers)
Ananthanarayanan, Arundithi; Wang, Yue; Routh, Parimal; Sk, Mahasin Alam; Than, Aung; Lin, Ming; Zhang, Jie; Chen, Jie; Sun, Handong; Chen, Peng
2015-05-07
Graphene quantum dots (GQDs) are emerging zero-dimensional materials promising a wide spectrum of applications, particularly, as superior fluorescent reporters for bio-imaging and optical sensing. Heteroatom doping can endow GQDs with new or improved photoluminescence properties. Here, we demonstrate a simple strategy for the synthesis of nitrogen and phosphorus co-doped GQDs from a single biomolecule precursor (adenosine triphosphate - ATP). Such ATP-GQDs exhibit high fluorescence quantum yield, strong two-photon upconversion, small molecular weight, high photostability, and good biocompatibility. Furthermore, transferrin conjugated ATP-GQDs have been used for imaging and real-time tracking of transferrin receptors in live cells.
Measure of the non-Gaussian character of a quantum state
Genoni, Marco G.; Paris, Matteo G. A.; Banaszek, Konrad
2007-10-15
We address the issue of quantifying the non-Gaussian character of a bosonic quantum state and introduce a non-Gaussianity measure based on the Hilbert-Schmidt distance between the state under examination and a reference Gaussian state. We analyze in detail the properties of the proposed measure and exploit it to evaluate the non-Gaussianity of some relevant single-mode and multimode quantum states. The evolution of non-Gaussianity is also analyzed for quantum states undergoing the processes of Gaussification by loss and de-Gaussification by photon-subtraction. The suggested measure is easily computable for any state of a bosonic system and allows one to define a corresponding measure for the non-Gaussian character of a quantum operation.
Physical properties of the candidate quantum spin-ice system Pr2Hf2O7
NASA Astrophysics Data System (ADS)
Anand, V. K.; Opherden, L.; Xu, J.; Adroja, D. T.; Islam, A. T. M. N.; Herrmannsdörfer, T.; Hornung, J.; Schönemann, R.; Uhlarz, M.; Walker, H. C.; Casati, N.; Lake, B.
2016-10-01
Physical properties of a pyrohafnate compound Pr2Hf2O7 have been investigated by ac magnetic susceptibility χac(T ) , dc magnetic susceptibility χ (T ) , isothermal magnetization M (H ) , and heat-capacity Cp(T ) measurements on polycrystalline as well as single-crystal samples combined with high-resolution synchrotron x-ray diffraction (XRD) for structural characterization and inelastic neutron scattering (INS) to determine the crystal-field energy-level scheme and wave functions. Synchrotron XRD data confirm the ordered cubic pyrochlore (F d 3 ¯m ) structure without any noticeable site mixing or oxygen deficiency. No clear evidence of long-range magnetic ordering is observed down to 90 mK, however the χac(T ) evinces slow spin dynamics revealed by a frequency dependent broad peak associated with spin freezing. The INS data reveal the expected five well-defined magnetic excitations due to crystal-field splitting of the J =4 ground-state multiplet of the Pr3 +. The crystal-field parameters and ground-state wave function of Pr3 + have been determined. The Ising anisotropic nature of the magnetic ground state is inferred from the INS as well as χ (T ) and M (H ) data. Together these properties make Pr2Hf2O7 a candidate compound for quantum spin-ice behavior.
Properties of the Katugampola fractional derivative with potential application in quantum mechanics
Anderson, Douglas R.; Ulness, Darin J.
2015-06-15
Katugampola [e-print http://arxiv.org/abs/1410.6535 ] recently introduced a limit based fractional derivative, D{sup α} (referred to in this work as the Katugampola fractional derivative) that maintains many of the familiar properties of standard derivatives such as the product, quotient, and chain rules. Typically, fractional derivatives are handled using an integral representation and, as such, are non-local in character. The current work starts with a key property of the Katugampola fractional derivative, D{sup α}[y]=t{sup 1−α}(dy)/(dt) , and the associated differential operator, D{sup α} = t{sup 1−α}D{sup 1}. These operators, their inverses, commutators, anti-commutators, and several important differential equations are studied. The anti-commutator serves as a basis for the development of a self-adjoint operator which could potentially be useful in quantum mechanics. A Hamiltonian is constructed from this operator and applied to the particle in a box model.
Metal colloids and semiconductor quantum dots: Linear and nonlinear optical properties
NASA Technical Reports Server (NTRS)
Henderson, D. O.; My, R.; Tung, Y.; Ueda, A.; Zhu, J.; Collins, W. E.; Hall, Christopher
1995-01-01
One aspect of this project involves a collaborative effort with the Solid State Division of ORNL. The thrust behind this research is to develop ion implantion for synthesizing novel materials (quantum dots wires and wells, and metal colloids) for applications in all optical switching devices, up conversion, and the synthesis of novel refractory materials. In general the host material is typically a glass such as optical grade silica. The ions of interest are Au, Ag, Cd, Se, In, P, Sb, Ga and As. An emphasis is placed on host guest interactions between the matrix and the implanted ion and how the matrix effects and implantation parameters can be used to obtain designer level optical devices tailored for specific applications. The specific materials of interest are: CdSe, CdTe, InAs, GaAs, InP, GaP, InSb, GaSb and InGaAs. A second aspect of this research program involves using porous glass (25-200 A) for fabricating materials of finite size. In this part of the program, we are particularly interested in characterizing the thermodynamic and optical properties of these non-composite materials. We also address how phase diagram of the confined material is altered by the interfacial properties between the confined material and the pore wall.
Shape Engineered InAs Quantum Dots with Stabilized Electronic Properties
NASA Astrophysics Data System (ADS)
Tokranov, Vadim E.; Yakimov, Michael; Katsnelson, Alex; Lamberti, Matthew; Oktyabrsky, Serge
2003-07-01
We have studied the influence of overgrowth procedure and a few monolayer-thick AlAs capping layers on the properties of self-assembled InAs quantum dots (QDs) using transmission electron microscopy (TEM), scanning electron microscopy, and photoluminescence (PL). PL spectroscopy was used to study and optimize optical properties of the QDs by shape engineering (QD truncation) through adjustment of the thickness of overlayers and temperature of the subsequent heating. QDs with 6 nm-thick overlayer with heating step at 560°C was found to have the highest PL intensity at room temperature and the lowest FWHM, 29 meV. Ground state energy of the truncated QDs is very stable against variations of growth parameters. TEM measurements show that the capping AlAs layer covers the QDs entirely even though the dots are truncated by the heating step. 1.22 μm edge-emitting laser with triple-layer truncated QD gain medium demonstrated room temperature minimum threshold current density, 56 A/cm2, and high saturated modal gain, 16 cm-1. Extremely high characteristic temperature, To = 304 K in the 20 - 60°C interval, and maximum lasing temperature of 219°C were measured for this laser diode.
First principles calculation of thermo-mechanical properties of thoria using Quantum ESPRESSO
NASA Astrophysics Data System (ADS)
Malakkal, Linu; Szpunar, Barbara; Zuniga, Juan Carlos; Siripurapu, Ravi Kiran; Szpunar, Jerzy A.
2016-05-01
In this work, we have used Quantum ESPRESSO (QE), an open source first principles code, based on density-functional theory, plane waves, and pseudopotentials, along with quasi-harmonic approximation (QHA) to calculate the thermo-mechanical properties of thorium dioxide (ThO2). Using Python programming language, our group developed qe-nipy-advanced, an interface to QE, which can evaluate the structural and thermo-mechanical properties of materials. We predicted the phonon contribution to thermal conductivity (kL) using the Slack model. We performed the calculations within local density approximation (LDA) and generalized gradient approximation (GGA) with the recently proposed version for solids (PBEsol). We employed a Monkhorst-Pack 5 × 5 × 5 k-points mesh in reciprocal space with a plane wave cut-off energy of 150 Ry to obtain the convergence of the structure. We calculated the dynamical matrices of the lattice on a 4 × 4 × 4 mesh. We have predicted the heat capacity, thermal expansion and the phonon contribution to thermal conductivity, as a function of temperature up to 1400K, and compared them with the previous work and known experimental results.
Storage of multiple single-photon pulses emitted from a quantum dot in a solid-state quantum memory
Tang, Jian-Shun; Zhou, Zong-Quan; Wang, Yi-Tao; Li, Yu-Long; Liu, Xiao; Hua, Yi-Lin; Zou, Yang; Wang, Shuang; He, De-Yong; Chen, Geng; Sun, Yong-Nan; Yu, Ying; Li, Mi-Feng; Zha, Guo-Wei; Ni, Hai-Qiao; Niu, Zhi-Chuan; Li, Chuan-Feng; Guo, Guang-Can
2015-01-01
Quantum repeaters are critical components for distributing entanglement over long distances in presence of unavoidable optical losses during transmission. Stimulated by the Duan–Lukin–Cirac–Zoller protocol, many improved quantum repeater protocols based on quantum memories have been proposed, which commonly focus on the entanglement-distribution rate. Among these protocols, the elimination of multiple photons (or multiple photon-pairs) and the use of multimode quantum memory are demonstrated to have the ability to greatly improve the entanglement-distribution rate. Here, we demonstrate the storage of deterministic single photons emitted from a quantum dot in a polarization-maintaining solid-state quantum memory; in addition, multi-temporal-mode memory with 1, 20 and 100 narrow single-photon pulses is also demonstrated. Multi-photons are eliminated, and only one photon at most is contained in each pulse. Moreover, the solid-state properties of both sub-systems make this configuration more stable and easier to be scalable. Our work will be helpful in the construction of efficient quantum repeaters based on all-solid-state devices. PMID:26468996
Storage of multiple single-photon pulses emitted from a quantum dot in a solid-state quantum memory.
Tang, Jian-Shun; Zhou, Zong-Quan; Wang, Yi-Tao; Li, Yu-Long; Liu, Xiao; Hua, Yi-Lin; Zou, Yang; Wang, Shuang; He, De-Yong; Chen, Geng; Sun, Yong-Nan; Yu, Ying; Li, Mi-Feng; Zha, Guo-Wei; Ni, Hai-Qiao; Niu, Zhi-Chuan; Li, Chuan-Feng; Guo, Guang-Can
2015-10-15
Quantum repeaters are critical components for distributing entanglement over long distances in presence of unavoidable optical losses during transmission. Stimulated by the Duan-Lukin-Cirac-Zoller protocol, many improved quantum repeater protocols based on quantum memories have been proposed, which commonly focus on the entanglement-distribution rate. Among these protocols, the elimination of multiple photons (or multiple photon-pairs) and the use of multimode quantum memory are demonstrated to have the ability to greatly improve the entanglement-distribution rate. Here, we demonstrate the storage of deterministic single photons emitted from a quantum dot in a polarization-maintaining solid-state quantum memory; in addition, multi-temporal-mode memory with 1, 20 and 100 narrow single-photon pulses is also demonstrated. Multi-photons are eliminated, and only one photon at most is contained in each pulse. Moreover, the solid-state properties of both sub-systems make this configuration more stable and easier to be scalable. Our work will be helpful in the construction of efficient quantum repeaters based on all-solid-state devices.
Charge Transfer as a Probe for the Interfacial Properties of Quantum Dot-Ligand Complexes
NASA Astrophysics Data System (ADS)
Weinberg, David Joseph
This dissertation describes the study of charge transfer interactions between colloidal quantum dots (QDs) and molecular redox partners in the context of both fundamental investigations of charge recombination mechanisms in nanocrystal-molecule systems, and as a technique to probe the properties of the QD ligand shell. Charge separation in a system of CdS nanocrystals and organic hole acceptors results in the formation of a spin-correlated radical ion pair. Interrogating this photogenerated species with EPR and magnetic field effect transient absorption techniques reveals that the charge recombination dynamics of this donor-acceptor system are dictated by the radical pair intersystem crossing mechanism on the nanosecond timescale. These experiments also indicate that the photoinjected electron localizes at a CdS QD surface trap state, and the coupling between the electron and hole in this spin-correlated system is low. Additional studies involving the CdS QDs and organic hole acceptors are proposed which would investigate the exchange of charge and energy within the nanocrystal organic adlayer. Collisional charge transfer interactions between substituted benzoquinone molecules and PbS QDs coated with mixed monolayers of oleic acid and perfluorodecanethiol are monitored via photoluminescence and transient absorption spectroscopies. These experiments reveal that partially fluorinated ligand shells are less permeable to solution phase molecules and offer greater protection of the nanocrystal surface than their aliphatic counterparts. Only a small amount of fluorinated surfactant ( 20% surface coverage) is necessary to profoundly change the permeability of the ligand shell, and the protective nature of these fluorinated molecules is likely a combination of the molecular volume and oleophobicity of these ligands. Follow up work is discussed which would elucidate the influence of solvent and extent of surfactant fluorination on the permeability of these ligand shells, as
NASA Astrophysics Data System (ADS)
Hur, Gwang-Ok
The -kicked rotor is a paradigm of quantum chaos. Its realisation with clouds of cold atoms in pulsed optical lattices demonstrated the well-known quantum chaos phenomenon of 'dynamical localisation'. In those experi ments by several groups world-wide, the £-kicks were applied at equal time intervals. However, recent theoretical and experimental work by the cold atom group at UCL Monteiro et al 2002, Jonckheere et al 2003, Jones et al 2004 showed that novel quantum and classical dynamics arises if the atomic cloud is pulsed with repeating sequences of unequally spaced kicks. In Mon teiro et al 2002 it was found that the energy absorption rates depend on the momentum of the atoms relative to the optical lattice hence a type of chaotic ratchet was proposed. In Jonckheere et al and Jones et al, a possible mechanism for selecting atoms according to their momenta (velocity filter) was investigated. The aim of this thesis was to study the properties of the underlying eigen values and eigenstates. Despite the unequally-spaced kicks, these systems are still time-periodic, so we in fact investigated the Floquet states, which are eigenstates of U(T), the one-period time evolution operator. The Floquet states and corresponding eigenvalues were obtained by diagonalising a ma trix representation of the operator U(T). It was found that the form of the eigenstates enables us to analyse qual itatively the atomic momentum probability distributions, N(p) measured experimentally. In particular, the momentum width of the individual eigen states varies strongly with < p > as expected from the theoretical and ex- perimental results obtained previously. In addition, at specific < p > close to values which in the experiment yield directed motion (ratchet transport), the probability distribution of the individual Floquet states is asymmetric, mirroring the asymmetric N(p) measured in clouds of cesium atoms. In the penultimate chapter, the spectral fluctuations (eigenvalue statis tics) are
Notes on Translational and Rotational Properties of Tensor Fields in Relativistic Quantum Mechanics
NASA Astrophysics Data System (ADS)
Dvoeglazov, V. V.
Recently, several discussions on the possible observability of 4-vector fields have been published in literature. Furthermore, several authors recently claimed existence of the helicity=0 fundamental field. We re-examine the theory of antisymmetric tensor fields and 4-vector potentials. We study the massless limits. In fact, a theoretical motivation for this venture is the old papers of Ogievetskiĭ and Polubarinov, Hayashi, and Kalb and Ramond. Ogievetskiĭ and Polubarinov proposed the concept of the notoph, whose helicity properties are complementary to those of the photon. We analyze the quantum field theory with taking into account mass dimensions of the notoph and the photon. It appears to be possible to describe both photon and notoph degrees of freedom on the basis of the modified Bargmann-Wigner formalism for the symmetric second-rank spinor. Next, we proceed to derive equations for the symmetric tensor of the second rank on the basis of the Bargmann-Wigner formalism in a straightforward way. The symmetric multispinor of the fourth rank is used. Due to serious problems with the interpretation of the results obtained on using the standard procedure we generalize it and obtain the spin-2 relativistic equations, which are consistent with the general relativity. Thus, in fact we deduced the gravitational field equations from relativistic quantum mechanics. The relations of this theory with the scalar-tensor theories of gravitation and f(R) are discussed. Particular attention has been paid to the correct definitions of the energy-momentum tensor and other Nöther currents in the electromagnetic theory, the relativistic theory of gravitation, the general relativity, and their generalizations. We estimate possible interactions, fermion-notoph, graviton-notoph, photon-notoph, and we conclude that they can probably be seen in experiments in the next few years.
Multimode fiber optic wavelength division multiplexing
NASA Technical Reports Server (NTRS)
Spencer, J. L.
1982-01-01
Optical wavelength division multiplexing (WDM) systems, with signals transmitted on different wavelengths through a single optical fiber, can have increased bandwidth and fault isolation properties over single wavelength optical systems. Two WDM system designs that might be used with multimode fibers are considered and a general description of the components which could be used to implement the system are given. The components described are sources, multiplexers, demultiplexers, and detectors. Emphasis is given to the demultiplexer technique which is the major developmental component in the WDM system.
NASA Astrophysics Data System (ADS)
Altıntaş, A.; ćakmak, K. E.; Güçlü, A. D.
2017-01-01
We theoretically investigate the effects of long-range disorder and electron-electron interactions on the optical properties of hexagonal armchair graphene quantum dots consisting of up to 10 806 atoms. The numerical calculations are performed using a combination of tight-binding, mean-field Hubbard, and configuration interaction methods. Imperfections in the graphene quantum dots are modeled as a long-range random potential landscape, giving rise to electron-hole puddles. We show that, when the electron-hole puddles are present, the tight-binding method gives a poor description of the low-energy absorption spectra compared to mean-field and configuration interaction calculation results. As the size of the graphene quantum dot is increased, the universal optical conductivity limit can be observed in the absorption spectrum. When disorder is present, the calculated absorption spectrum approaches the experimental results for isolated monolayers of graphene sheets.
NASA Astrophysics Data System (ADS)
Yamijala, Sharma S. R. K. C.; Bandyopadhyay, Arkamita; Pati, Swapan K.
2014-05-01
Spin-polarized density functional theory calculations have been performed on armchair graphene quantum dots and boron-nitride quantum dots (AG/BNQDs) and the effect of carbon/boron-nitride substitution on the electronic properties of these AG/BNQDs has been investigated. As a first step to consider more realistic quantum dots, quantum dots which are a combination of zigzag QDs and armchair QDs have been considered. Effect of substitution on these hybrid quantum dots has been explored for both GQDs and BNQDs and such results have been compared and contrasted with the results of substituted AG/BNQDs and their zigzag analogs. Our work suggests that the edge substitution can play an important tool while tuning the electronic properties of quantum dots.
Toward quantum plasmonic networks
Holtfrerich, M. W.; Dowran, M.; Davidson, R.; Lawrie, B. J.; Pooser, R. C.; Marino, A. M.
2016-08-30
Here, we demonstrate the transduction of macroscopic quantum entanglement by independent, distant plasmonic structures embedded in separate thin silver films. In particular, we show that the plasmon-mediated transmission through each film conserves spatially dependent, entangled quantum images, opening the door for the implementation of parallel quantum protocols, super-resolution imaging, and quantum plasmonic sensing geometries at the nanoscale level. The conservation of quantum information by the transduction process shows that continuous variable multi-mode entanglement is momentarily transferred from entangled beams of light to the space-like separated, completely independent plasmonic structures, thus providing a first important step toward establishing a multichannel quantum network across separate solid-state substrates.
Towards prediction of correlated material properties using quantum Monte Carlo methods
NASA Astrophysics Data System (ADS)
Wagner, Lucas
Correlated electron systems offer a richness of physics far beyond noninteracting systems. If we would like to pursue the dream of designer correlated materials, or, even to set a more modest goal, to explain in detail the properties and effective physics of known materials, then accurate simulation methods are required. Using modern computational resources, quantum Monte Carlo (QMC) techniques offer a way to directly simulate electron correlations. I will show some recent results on a few extremely challenging materials including the metal-insulator transition of VO2, the ground state of the doped cuprates, and the pressure dependence of magnetic properties in FeSe. By using a relatively simple implementation of QMC, at least some properties of these materials can be described truly from first principles, without any adjustable parameters. Using the QMC platform, we have developed a way of systematically deriving effective lattice models from the simulation. This procedure is particularly attractive for correlated electron systems because the QMC methods treat the one-body and many-body components of the wave function and Hamiltonian on completely equal footing. I will show some examples of using this downfolding technique and the high accuracy of QMC to connect our intuitive ideas about interacting electron systems with high fidelity simulations. The work in this presentation was supported in part by NSF DMR 1206242, the U.S. Department of Energy, Office of Science, Office of Advanced Scientific Computing Research, Scientific Discovery through Advanced Computing (SciDAC) program under Award Number FG02-12ER46875, and the Center for Emergent Superconductivity, Department of Energy Frontier Research Center under Grant No. DEAC0298CH1088. Computing resources were provided by a Blue Waters Illinois grant and INCITE PhotSuper and SuperMatSim allocations.
A 4MM-Wave composite mode multimode conical feedhorn
NASA Astrophysics Data System (ADS)
Lin, Zhisheng; Du, Zhengmi; Chen, Shener
1996-10-01
A 4MM-Wave composite mode multimode conical feedhorn has been developed. Its mode-ratios are calculated and its formulas of the radiation patterns are derived. The measurement results of one and two dimension radiation patterns, measured by the automatic measurement system which we had researched, and the properties of band width and sidelobe are given. Theoretical analyses and measurements show that at the centre frequency 69.1GHZ, down to -23dB, the radiation pattern is rotationally symmetric, in this range there is not any sidelobe existing, the band width is 4.5 GHZ. The multimode feedhorn is thus of certain practical using value.
Experimental Study on Bioluminescence Tomography with Multimodality Fusion
Lv, Yujie; Tian, Jie; Cong, Wenxiang; Wang, Ge
2007-01-01
To verify the influence of a priori information on the nonuniqueness problem of bioluminescence tomography (BLT), the multimodality imaging fusion based BLT experiment is performed by multiview noncontact detection mode, which incorporates the anatomical information obtained by the microCT scanner and the background optical properties based on diffuse reflectance measurements. In the reconstruction procedure, the utilization of adaptive finite element methods (FEMs) and a priori permissible source region refines the reconstructed results and improves numerical robustness and efficiency. The comparison between the absence and employment of a priori information shows that multimodality imaging fusion is essential to quantitative BLT reconstruction. PMID:18256736
Xu, Xiangxing; Zhuang, Jing; Wang, Xun
2008-09-17
SnO2 quantum dots (QDs) and ultrathin nanowires (NWs) with diameters of approximately 0.5-2.5 and approximately 1.5-4.5 nm, respectively, were controllably synthesized in a simple solution system. They are supposed to be ideal models for studying the continuous evolution of the quantum-confinement effect in SnO2 1D --> 0D systems. The observed transition from strong to weak quantum confinement in SnO2 QDs and ultrathin NWs is interpreted through the use of the Brus effective-mass approximation and the Nosaka finite-depth well model. Photoluminescence properties that were coinfluenced by size effects, defects (oxygen vacancies), and surface capping are discussed in detail. With the SnO2 QDs as building blocks, various 2D porous structures with ordered hexagonal, distorted hexagonal, and square patterns were prepared on silicon-wafer surfaces and exhibited optical features of 2D photonic crystals and enhanced gas sensitivity.
Yang, Jing; Zhao, Degang Jiang, Desheng; Chen, Ping; Zhu, Jianjun; Liu, Zongshun; Le, Lingcong; He, Xiaoguang; Li, Xiaojing; Wang, Hui; Yang, Hui; Jahn, Uwe
2014-09-01
Cathodoluminescence (CL) characteristics on 30-period InGaN/GaN multiple quantum well (MQW) solar cell structures are investigated, revealing the relationship between optical and structural properties of the MQW structures with a large number of quantum wells. In the bottom MQW layers, a blueshift of CL peak along the growth direction is found and attributed to the decrease of indium content due to the compositional pulling effect. An obvious split of emission peak and a redshift of the main emission energy are found in the top MQW layers when the MQW grows above the critical layer thickness. They are attributed to the segregation of In-rich InGaN clusters rather than the increase of indium content in quantum well layer. The MQW structure is identified to consist of two regions: a strained one in the bottom, where the indium content is gradually decreased, and a partly relaxed one in the top with segregated In-rich InGaN clusters.
The Effect of the Berry Phase on the Quantum Critical Properties of the Bose-Fermi Kondo model
NASA Astrophysics Data System (ADS)
Kirchner, Stefan; Si, Qimiao
2006-03-01
The theory of the quantum critical point of a T=0 transition is traditionally formulated in terms of a quantum-to-classical mapping, leading to a theory of its classical counterpart in elevated dimensions. Recently, it has been shown that this mapping breaks down in an SU(N)xSU(N/2) Bose-Fermi Kondo model (BFKM) [1], a BFKM with Ising anisotropy [2] and the spin-boson model [3]. Here we report the Quantum Monte Carlo results for the scaling properties of the quantum critical point of the BFKM with Ising anisotropy. In addition, using the Lagrangian formulation of the BFKM, we study the critical properties in the presence and absence of the spin Berry phase term. The results of the two cases are compared with the numerical results.[1] L. Zhu, S. Kirchner, Q. Si, and A. Georges, Phys. Rev. Lett. 93,267201 (2004). [2] M. Glossop and K. Ingersent, Phys. Rev. Lett. 95, 067202 (2005). [3] M. Vojta, N-H Tong, and R. Bulla, Phys. Rev. Lett. 94, 070604 (2005).
NASA Astrophysics Data System (ADS)
Ananthanarayanan, Arundithi; Wang, Yue; Routh, Parimal; Sk, Mahasin Alam; Than, Aung; Lin, Ming; Zhang, Jie; Chen, Jie; Sun, Handong; Chen, Peng
2015-04-01
Graphene quantum dots (GQDs) are emerging zero-dimensional materials promising a wide spectrum of applications, particularly, as superior fluorescent reporters for bio-imaging and optical sensing. Heteroatom doping can endow GQDs with new or improved photoluminescence properties. Here, we demonstrate a simple strategy for the synthesis of nitrogen and phosphorus co-doped GQDs from a single biomolecule precursor (adenosine triphosphate - ATP). Such ATP-GQDs exhibit high fluorescence quantum yield, strong two-photon upconversion, small molecular weight, high photostability, and good biocompatibility. Furthermore, transferrin conjugated ATP-GQDs have been used for imaging and real-time tracking of transferrin receptors in live cells.Graphene quantum dots (GQDs) are emerging zero-dimensional materials promising a wide spectrum of applications, particularly, as superior fluorescent reporters for bio-imaging and optical sensing. Heteroatom doping can endow GQDs with new or improved photoluminescence properties. Here, we demonstrate a simple strategy for the synthesis of nitrogen and phosphorus co-doped GQDs from a single biomolecule precursor (adenosine triphosphate - ATP). Such ATP-GQDs exhibit high fluorescence quantum yield, strong two-photon upconversion, small molecular weight, high photostability, and good biocompatibility. Furthermore, transferrin conjugated ATP-GQDs have been used for imaging and real-time tracking of transferrin receptors in live cells. Electronic supplementary information (ESI) available: Supplementary figures related to characterization, computational studies and protein conjugation. See DOI: 10.1039/c5nr01519g
Some properties of correlations of quantum lattice systems in thermal equilibrium
Fröhlich, Jürg; Ueltschi, Daniel
2015-05-15
Simple proofs of uniqueness of the thermodynamic limit of KMS states and of the decay of equilibrium correlations are presented for a large class of quantum lattice systems at high temperatures. New quantum correlation inequalities for general Heisenberg models are described. Finally, a simplified derivation of a general result on power-law decay of correlations in 2D quantum lattice systems with continuous symmetries is given, extending results of McBryan and Spencer for the 2D classical XY model.
NASA Astrophysics Data System (ADS)
Gisin, Nicolas
2009-05-01
The ultimate limit of direct point to point quantum key distribution is around 300-500 km. Longer distances fiber-based quantum communication will require both high-fidelity entanglement swapping and multi-mode quantum memories. A new protocol for an efficient multimode quantum memory based on atomic ensembles has been developed and demonstrated. The rare-earth ions ensemble is ``frozen'' in a crystal inside a cryostat. The protocol, named AFC (Atomic Frequency Comb) is inspired from photon echoes, but avoids any control light pulse after the single-photon(s) is (are) stored in the medium, thus avoiding any noise due to fluorescence. First results on the new protocol for quantum memories in Nd:YVO4 doped crystals demonstrate a quantum light-matter interface at the single-photon level. The coherence of the re-emitted photons is investigated in an interference experiment showing net visibilities above 95%. Further results in Nd:YSO (Geneva), Tm:YAG (Paris) and Pr:YSO (Lund) shall also be presented. Many hundreds of km long quantum communication is a long term objective. Many of the necessary building blocks have been demonstrated, but usually in independent experiments and with insufficient fidelities and specifications to meet the goal. Still, today's the roadmap is relatively clear and a lot of interesting physics shall be found along the journey.
Coherence properties and quantum state transportation in an optical conveyor belt.
Kuhr, S; Alt, W; Schrader, D; Dotsenko, I; Miroshnychenko, Y; Rosenfeld, W; Khudaverdyan, M; Gomer, V; Rauschenbeutel, A; Meschede, D
2003-11-21
We have prepared and detected quantum coherences of trapped cesium atoms with long dephasing times. Controlled transport by an "optical conveyor belt" over macroscopic distances preserves the atomic coherence with slight reduction of coherence time. The limiting dephasing effects are experimentally identified, and we present an analytical model of the reversible and irreversible dephasing mechanisms. Our experimental methods are applicable at the single-atom level. Coherent quantum bit operations along with quantum state transport open the route towards a "quantum shift register" of individual neutral atoms.
Thomas, Robert E.; Overy, Catherine; Opalka, Daniel; Alavi, Ali; Knowles, Peter J.; Booth, George H.
2015-08-07
Unbiased stochastic sampling of the one- and two-body reduced density matrices is achieved in full configuration interaction quantum Monte Carlo with the introduction of a second, “replica” ensemble of walkers, whose population evolves in imaginary time independently from the first and which entails only modest additional computational overheads. The matrices obtained from this approach are shown to be representative of full configuration-interaction quality and hence provide a realistic opportunity to achieve high-quality results for a range of properties whose operators do not necessarily commute with the Hamiltonian. A density-matrix formulated quasi-variational energy estimator having been already proposed and investigated, the present work extends the scope of the theory to take in studies of analytic nuclear forces, molecular dipole moments, and polarisabilities, with extensive comparison to exact results where possible. These new results confirm the suitability of the sampling technique and, where sufficiently large basis sets are available, achieve close agreement with experimental values, expanding the scope of the method to new areas of investigation.
The Interplay of Electronic Properties and Magnetic Anisotropy in Quantum Dots
NASA Astrophysics Data System (ADS)
Zutic, Igor; Lee, Jeongsu; Vyborny, Karel; Han, Jong; Petukhov, Andre
2012-02-01
Tunability of magnetic anisotropy (MA) in nanostructures is a fascinating topic, for both fundamental understanding of nanomagnetism and possible spintronic applications. While there have been preceding efforts to systematically study the MA in bulk [1], we still lack a fundamental understanding of that in magnetic quantum dots (QDs). We first explore electronic properties of nonmagnetic QDs that can be significantly altered from the bulk-state depending upon the material and geometry. Focusing on II-VI materials forming both cubic and non-cubic QDs, we confirm qualitatively different energy spectra between different materials [2]. These findings can guide the control of MA in magnetic QDs. Supported by DOE-BES, NSF-DMR, AFOSR-DCT, U.S. ONR, and NSF-ECCS. [4pt] [1] X. Liu, Y. Sasaki and J. K. Furdyna, Phys. Rev. B 67, 205204 (2004). [0pt] [2] K. V'yborn'y, J.E. Han, R. Oszwadowski, I. Zuti'c, and A. G. Petukhov, preprint (2011).
Modeling of magnetic polaron properties in (Zn,Mn)Te quantum dots
NASA Astrophysics Data System (ADS)
Pientka, James; Barman, B.; Schweidenback, L.; Russ, A. H.; Tsai, Y.; Murphy, J. R.; Cartwright, A. N.; Zutic, I.; McCombe, B. D.; Petrou, A.; Chou, W.-C.; Fan, W. C.; Sellers, I. R.; Petukhov, A. G.; Oszwaldowski, R.
Magnetic polarons in (Zn,Mn)Te quantum dots (QD) show unconventional behavior. These structures exhibit a small red shift of the photoluminescence peak energy in the presence of a magnetic field B and they also have a weak dependence of the polaron energy EMP on temperature T and B. We attribute these properties to a large molecular field Bm that is proportional to the heavy holes spin density. We have calculated Bm using the QD diameter and height as adjustable parameters. Assuming hole localization, this calculation yields values of Bm >20 T. The assumption that the hole localization diameter can be smaller than the QD diameter is justified due to alloy and spin disorder scattering. Using the magnetic polaron free energy, we calculate EMP as function of T and B for a variety of Bm values. To get a weak dependence of EMP on T and Bwe must assume that the polaron temperature is higher than T. This work was supported by U.S. DOE BES, Award DE-SC0004890, NSF DMR-1305770 and U.S. ONR N000141310754.
Optical and magnetic properties of zinc oxide quantum dots doped with cobalt and lanthanum.
Yu, Shiyong; Zhao, Jing; Su, Hai-Quan
2013-06-01
Cobalt and Lanthanum-doped ZnO QDs are synthesized by a modified sol-gel method under atmospheric conditions. The as-prepared quantum dots are characterized by X-ray powder diffraction (XRD), energy dispersive X-ray (EDX) analysis and high resolution transmission electron microscopy (HRTEM). The optical properties of the products are studied by fluorescent spectroscopy. With a proper Co and La doping, these nanoparticles possess exceptionally small size and enhanced fluorescence. Hysteresis loops of un-doped ZnO QDs and Co and La-doped ZnO QDs indicate that both the samples show ferromagnetic behavior at room temperature. Finally, these nanoparticles can label the BGC 803 cells successfully in short time and present no evidence of toxicity or adverse affect on cell growth even at the concentration up to 1 mM. We expect that the as-prepared Co and La-doped ZnO QDs can provide a better reliability of the collected data and find promising applications in biological, medical and other fields.
Unique self-assembly properties of a bridge-shaped protein dimer with quantum dots
NASA Astrophysics Data System (ADS)
Wang, Jianhao; Jiang, Pengju; Gao, Liqian; Yu, Yongsheng; Lu, Yao; Qiu, Lin; Wang, Cheli; Xia, Jiang
2013-09-01
How protein-protein interaction affects protein-nanoparticle self-assembly is the key to the understanding of biomolecular coating of nanoparticle in biological fluids. However, the relationship between protein shape and its interaction with nanoparticles is still under-exploited because of lack of a well-conceived binding system and a method to detect the subtle change in the protein-nanoparticle assemblies. Noticing this unresolved need, we cloned and expressed a His-tagged SpeA protein that adopts a bridge-shaped dimer structure, and utilized a high-resolution capillary electrophoresis method to monitor assembly formation between the protein and quantum dots (QDs, 5 nm in diameter). We observed that the bridge-shaped structure rendered a low SpeA:QD stoichiometry at saturation. Also, close monitoring of imidazole (Im) displacement of surface-bound protein revealed a unique two-step process. High-concentration Im could displace surface-bound SpeA protein and form a transient QD-protein intermediate, through a kinetically controlled displacement process. An affinity-driven equilibrium step then followed, resulting in re-assembling of the QD-protein complex in about 1 h. Through a temporarily formed intermediate, Im causes a rearrangement of His-tagged proteins on the surface. Thus, our work showcases that the synergistic interplay between QD-His-tag interaction and protein-protein interaction can result in unique properties of protein-nanoparticle assembly for the first time.
NASA Astrophysics Data System (ADS)
Thomas, Robert E.; Opalka, Daniel; Overy, Catherine; Knowles, Peter J.; Alavi, Ali; Booth, George H.
2015-08-01
Unbiased stochastic sampling of the one- and two-body reduced density matrices is achieved in full configuration interaction quantum Monte Carlo with the introduction of a second, "replica" ensemble of walkers, whose population evolves in imaginary time independently from the first and which entails only modest additional computational overheads. The matrices obtained from this approach are shown to be representative of full configuration-interaction quality and hence provide a realistic opportunity to achieve high-quality results for a range of properties whose operators do not necessarily commute with the Hamiltonian. A density-matrix formulated quasi-variational energy estimator having been already proposed and investigated, the present work extends the scope of the theory to take in studies of analytic nuclear forces, molecular dipole moments, and polarisabilities, with extensive comparison to exact results where possible. These new results confirm the suitability of the sampling technique and, where sufficiently large basis sets are available, achieve close agreement with experimental values, expanding the scope of the method to new areas of investigation.
Matisz, G; Kelterer, A-M; Fabian, W M F; Kunsági-Máté, S
2015-04-07
Density functional theory (B3LYP-D3, M06-2X) has been used to calculate the structures, interaction energies and vibrational frequencies of a set of 93 methanol-water clusters of different type (cubic, ring, spiro, lasso, bicyclic), size and composition. These interaction energies have been used within the framework of the Quantum Cluster Equilibrium Theory (QCE) to calculate cluster populations as well as thermodynamic properties of binary methanol-water mixtures spanning the whole range from pure water to pure methanol. The necessary parameters amf and bxv of the QCE model were obtained by fitting to experimental isobars of MeOH-H2O mixtures with different MeOH content. The cubic and spiro motifs dominate the distribution of methanol-water clusters in the mixtures with a maximum of mixed clusters at x(MeOH) = 0.365. Reasonable agreement with experimental data as well as earlier molecular dynamics simulations was found for excess enthalpies H(E), entropies S(E) as well as Gibbs free energies of mixing G(E). In contrast, heat capacities Cp and C showed only poor agreement with experimental data.
The ground state properties of In(Ga)As/GaAs low strain quantum dots
NASA Astrophysics Data System (ADS)
Pieczarka, Maciej; Sęk, Grzegorz
2016-08-01
We present theoretical studies on the confined states in low-strain In(Ga)As quantum dots (QDs). The 8-band k·p model together with the continuum elasticity theory and piezoelectric fields were employed to calculate the potential and confined electron and hole eigenstates. We focused on low-indium-content QDs with distinct in-plane asymmetry, which are naturally formed in the low strain regime of the Stranski-Krastanow growth mode. It has been found that the naturally thick wetting layer together with piezoelectric potential affect the total confinement potential to such extent that the hole eigenstates can get the spatial in-plane orientation orthogonal to the main axis of the dot elongation. This can influence both, qualitatively and quantitatively, many of the electronic and optical properties, as e.g. the polarization selection rules for the optical transition or the transitions oscillator strength. Eventually, importance of the degree of the shape asymmetry or the dots' size, and differences between the low-strain (low-In-content) QDs and pure InAs dots formed in high strain conditions are discussed.
New Insights To Simulate the Luminescence Properties of Pt(II) Complexes Using Quantum Calculations.
Massuyeau, Florian; Faulques, Eric; Latouche, Camille
2017-03-24
The present manuscript reports a thorough quantum investigation on the luminescence properties of three monoplatinum(II) complexes. First, the simulated bond lengths at the ground state are compared to the observed ones, and the simulated electronic transitions are compared to the reported ones in the literature in order to assess our methodology. In a second time we show that geometries from the first triplet excited state are similar to the ground state ones. Simulations of the phosphorescence spectra from the first triplet excited states have been performed taking into account the vibronic coupling effects together with mode-mixing (Dushinsky) and solvent effects. Our simulations are compared with the observed ones already reported in the literature and are in good agreement. The calculations demonstrate that the normal modes of low energy are of great importance on the phosphorescence signature. When temperature effects are taken into account, the simulated phosphorescence spectra are drastically improved. An analysis of the computational time shows that the vibronic coupling simulation is cost-effective and thus can be extended to treat large transition metal complexes. In addition to the intrinsic importance of the investigated targets, this work provides a robust method to simulate phosphorescence spectra and to increase the duality experiment-theory.
The Influence of Doping on the Optoelectronic Properties of PbS Colloidal Quantum Dot Solids
Papagiorgis, P.; Stavrinadis, A.; Othonos, A.; Konstantatos, G.; Itskos, G.
2016-01-01
We report on an extensive spectroscopic investigation of the impact of substitutional doping on the optoelectronic properties of PbS colloidal quantum dot (CQD) solids. N-doping is provided by Bi incorporation during CQD synthesis as well as post-synthetically via cation exchange reactions. The spectroscopic data indicate a systematic quenching of the excitonic absorption and luminescence and the appearance of two dopant-induced contributions at lower energies to the CQD free exciton. Temperature-dependent photoluminescence indicates the presence of temperature-activated detrapping and trapping processes of photoexcitations for the films doped during and after synthesis, respectively. The data are consistent with a preferential incorporation of the dopants at the QDs surface in the case of the cation-exchange treated films versus a more uniform doping profile in the case of in-situ Bi incorporation during synthesis. Time-resolved experiments indicate the presence of fast dopant- and excitation-dependent recombination channels attributed to Auger recombination of negatively charged excitons, formed due to excess of dopant electrons. The data indicate that apart from dopant compensation and filling of dopant induced trap states, a fraction of the Bi ionized electrons feeds the QD core states resulting in n-doping of the semiconductor, confirming reported work on devices based on such doped CQD material. PMID:26743934
NASA Astrophysics Data System (ADS)
Chen, Shaopei; Tan, Jianjun; Ray, C.; Claramunt, C.; Sun, Qinqin
2008-10-01
Diversity is one of the main characteristics of transportation data collected from multiple sources or formats, which can be extremely complex and disparate. Moreover, these multimodal transportation data are usually characterised by spatial and temporal properties. Multimodal transportation network data modelling involves both an engineering and research domain that has attracted the design of a number of spatio-temporal data models in the geographic information system (GIS). However, the application of these specific models to multimodal transportation network is still a challenging task. This research addresses this challenge from both integrated multimodal data organization and object-oriented modelling perspectives, that is, how a complex urban transportation network should be organized, represented and modeled appropriately when considering a multimodal point of view, and using object-oriented modelling method. We proposed an integrated GIS-based data model for multimodal urban transportation network that lays a foundation to enhance the multimodal transportation network analysis and management. This modelling method organizes and integrates multimodal transit network data, and supports multiple representations for spatio-temporal objects and relationship as both visual and graphic views. The data model is expressed by using a spatio-temporal object-oriented modelling method, i.e., the unified modelling language (UML) extended to spatial and temporal plug-in for visual languages (PVLs), which provides an essential support to the spatio-temporal data modelling for transportation GIS.
Yang, Zhi; Liu, Shaoding; Liu, Xuguang; Yang, Yongzhen; Li, Xiuyan; Xiong, Shijie; Xu, Bingshe
2012-11-07
Using density functional theory and the non-equilibrium Green's function technique, we performed theoretical investigations on the magnetic and quantum transport properties of benzene-vanadium-borazine mixed organic/inorganic ligand sandwich clusters. The calculated results show that these finite sandwich clusters coupled to Ni electrodes exhibit novel quantum transport properties such as half-metallicity, negative differential resistance and spin-reversal effect, and can be viewed as a new kind of spin filter. However, for the infinite molecular wire, the ground state was identified as a ferromagnetic semiconductor with high stability. These findings suggest that the mixed organic/inorganic ligand sandwich clusters and molecular wires are promising materials for application in molecular electronics and spintronics.
NASA Astrophysics Data System (ADS)
Kuznetsova, Vera; Orlova, Anna; Martynenko, Irina; Kundelev, Evgeny; Maslov, Vladimir; Fedorov, Anatoly; Baranov, Alexander; Gun'ko, Yurii
2016-04-01
Here we report our investigations of the formation conditions and photophysical properties of complexes between luminescent semiconducting nanoparticles (quantum dots, QDs) and the photosensitizer chlorin e6, which is widely used for the photodynamic therapy. In our complexes, bovine serum albumin (BSA), the most abundant protein in blood serum, was used as a linker between QDs and chlorin e6 molecules. The influence of BSA on the optical properties of Ce6 and QDs in complexes was properly examined using spectral-luminescent methods. It was found that BSA passivated QD surface and substantially QD quantum yield of luminescence was increased. In addition, BSA prevented the aggregation of chlorin e6 molecules in complexes with QDs. We demonstrated that the use of BSA as a linker allows to create functional QD-chlorin e6 complexes with effective photoexcitation energy transfer from QDs to the molecules.
NASA Astrophysics Data System (ADS)
Dey, Sunita; Govindaraj, A.; Biswas, Kanishka; Rao, C. N. R.
2014-03-01
Substitution of heteroatoms in graphene is known to tailor its band gap. Another approach to alter the band gap of graphene is to create zero-dimensional graphene quantum dots (GQDs). Here we present the synthesis and photoluminescence properties of B-doped graphene quantum dots (B-GQDs) for the first time, having prepared the B-GQDs by chemical scissoring of B-doped graphene generated by arc-discharge in gas phase. We compare the photoluminescence properties of B-GQDs with nitrogen-doped GQDs and pristine GQDs. Besides, excitation wavelength independent PL emission, excellent upconversion of PL emission is observed in GQDs as well as B- and N-doped GQDs.
Multimode analysis of the light emitted from a pulsed optical parametric oscillator
Nielsen, Anne E. B.; Moelmer, Klaus
2007-09-15
We present a multimode treatment of the optical parametric oscillator, which is valid for both pulsed and continuous-wave pump fields. The two-time correlation functions of the output field are derived, and we apply the theory to analyze a scheme for heralded production of nonclassical field states that may be subsequently stored in an atomic quantum memory.
Quantum theory of the electronic and optical properties of low-dimensional semiconductor systems
NASA Astrophysics Data System (ADS)
Lau, Wayne Heung
This thesis examines the electronic and optical properties of low-dimensional semiconductor systems. A theory is developed to study the electron-hole generation-recombination process of type-II semimetallic semiconductor heterojunctions based on a 3 x 3 k·p matrix Hamiltonian (three-band model) and an 8 x 8 k·p matrix Hamiltonian (eight-band model). A novel electron-hole generation and recombination process, which is called activationless generation-recombination process, is predicted. It is demonstrated that the current through the type-II semimetallic semiconductor heterojunctions is governed by the activationless electron-hole generation-recombination process at the heterointerfaces, and that the current-voltage characteristics are essentially linear. A qualitative agreement between theory and experiments is observed. The numerical results of the eight-band model are compared with those of the threeband model. Based on a lattice gas model, a theory is developed to study the influence of a random potential on the ionization equilibrium conditions for bound electron-hole pairs (excitons) in III--V semiconductor heterostructures. It is demonstrated that ionization equilibrium conditions for bound electron-hole pairs change drastically in the presence of strong disorder. It is predicted that strong disorder promotes dissociation of excitons in III--V semiconductor heterostructures. A theory of polariton (photon dressed by phonon) spontaneous emission in a III--V semiconductor doped with semiconductor quantum dots (QDs) or quantum wells (QWs) is developed. For the first time, superradiant and subradiant polariton spontaneous emission phenomena in a polariton-QD (QW) coupled system are predicted when the resonance energies of the two identical QDs (QWs) lie outside the polaritonic energy gap. It is also predicted that when the resonance energies of the two identical QDs (QWs) lie inside the polaritonic energy gap, spontaneous emission of polariton in the polariton
Vector-Resonance-Multimode Instability
NASA Astrophysics Data System (ADS)
Sergeyev, S. V.; Kbashi, H.; Tarasov, N.; Loiko, Yu.; Kolpakov, S. A.
2017-01-01
The modulation and multimode instabilities are the main mechanisms which drive spontaneous spatial and temporal pattern formation in a vast number of nonlinear systems ranging from biology to laser physics. Using an Er-doped fiber laser as a test bed, here for the first time we demonstrate both experimentally and theoretically a new type of a low-threshold vector-resonance-multimode instability which inherits features of multimode and modulation instabilities. The same as for the multimode instability, a large number of longitudinal modes can be excited without mode synchronization. To enable modulation instability, we modulate the state of polarization of the lasing signal with the period of the beat length by an adjustment of the in-cavity birefringence and the state of polarization of the pump wave. As a result, we show the regime's tunability from complex oscillatory to periodic with longitudinal mode synchronization in the case of resonance matching between the beat and cavity lengths. Apart from the interest in laser physics for unlocking the tunability and stability of dynamic regimes, the proposed mechanism of the vector-resonance-multimode instability can be of fundamental interest for the nonlinear dynamics of various distributed systems.
Nagashima, H.; Tsuda, S.; Tsuboi, N.; Koshi, M.; Hayashi, K. A.; Tokumasu, T.
2014-04-07
In this paper, we describe the analysis of the thermodynamic properties of cryogenic hydrogen using classical molecular dynamics (MD) and path integral MD (PIMD) method to understand the effects of the quantum nature of hydrogen molecules. We performed constant NVE MD simulations across a wide density–temperature region to establish an equation of state (EOS). Moreover, the quantum effect on the difference of molecular mechanism of pressure–volume–temperature relationship was addressed. The EOS was derived based on the classical mechanism idea only using the MD simulation results. Simulation results were compared with each MD method and experimental data. As a result, it was confirmed that although the EOS on the basis of classical MD cannot reproduce the experimental data of saturation property of hydrogen in the high-density region, the EOS on the basis of PIMD well reproduces those thermodynamic properties of hydrogen. Moreover, it was clarified that taking quantum effects into account makes the repulsion force larger and the potential well shallower. Because of this mechanism, the intermolecular interaction of hydrogen molecules diminishes and the virial pressure increases.
Cellular uptake and photosensitizing properties of quantum dot-chlorin e6 complex: in vitro study.
Steponkiene, Simona; Valanciunaite, Jurga; Skripka, Artiom; Rotomskis, Ricardas
2014-04-01
Recently it has been suggested that quantum dots could be used in the photodynamic therapy of cancer as resonant energy donors for conventional porphyrin type photosensitizers. Here we summarize our results obtained by studying a non-covalent complex formed between quantum dots and a second generation photosensitizer, chlorin e6, in aqueous medium and in live pancreatic MiaPaCa2 cancer cells. Spectral changes in the absorption and photoluminescence of quantum dots and chlorin e6, as well as changes in the photoluminescence lifetime of quantum dots, revealed the formation of quantum dot-chlorin e6 complex. Fluorescence confocal microscopy with spectral imaging unit showed uptake of quantum dot-chlorin e6 complex in live cancer cells: the complex localized in plasma membrane and endocytic vesicles. Fluorescence lifetime imaging revealed Forster resonance energy transfer from quantum dots to chlorin e6 within live cells. Finally, a light-induced damage to cancer cells by the quantum dot-chlorin e6 complex was achieved.
Makarov, Nikolay S; Guo, Shaojun; Isaienko, Oleksandr; Liu, Wenyong; Robel, István; Klimov, Victor I
2016-04-13
Organic-inorganic lead-halide perovskites have been the subject of recent intense interest due to their unusually strong photovoltaic performance. A new addition to the perovskite family is all-inorganic Cs-Pb-halide perovskite nanocrystals, or quantum dots, fabricated via a moderate-temperature colloidal synthesis. While being only recently introduced to the research community, these nanomaterials have already shown promise for a range of applications from color-converting phosphors and light-emitting diodes to lasers, and even room-temperature single-photon sources. Knowledge of the optical properties of perovskite quantum dots still remains vastly incomplete. Here we apply various time-resolved spectroscopic techniques to conduct a comprehensive study of spectral and dynamical characteristics of single- and multiexciton states in CsPbX3 nanocrystals with X being either Br, I, or their mixture. Specifically, we measure exciton radiative lifetimes, absorption cross-sections, and derive the degeneracies of the band-edge electron and hole states. We also characterize the rates of intraband cooling and nonradiative Auger recombination and evaluate the strength of exciton-exciton coupling. The overall conclusion of this work is that spectroscopic properties of Cs-Pb-halide quantum dots are largely similar to those of quantum dots of more traditional semiconductors such as CdSe and PbSe. At the same time, we observe some distinctions including, for example, an appreciable effect of the halide identity on radiative lifetimes, considerably shorter biexciton Auger lifetimes, and apparent deviation of their size dependence from the "universal volume scaling" previously observed for many traditional nanocrystal systems. The high efficiency of Auger decay in perovskite quantum dots is detrimental to their prospective applications in light-emitting devices and lasers. This points toward the need for the development of approaches for effective suppression of Auger
Makarov, Nikolay Sergeevich; Guo, Shaojun; Isaienko, Oleksandr; Liu, Wenyong; Robel, Istvan; Klimov, Victor Ivanovich
2016-02-16
Organic–inorganic lead-halide perovskites have been the subject of recent intense interest due to their unusually strong photovoltaic performance. A new addition to the perovskite family is all-inorganic Cs–Pb-halide perovskite nanocrystals, or quantum dots, fabricated via a moderate-temperature colloidal synthesis. While being only recently introduced to the research community, these nanomaterials have already shown promise for a range of applications from color-converting phosphors and light-emitting diodes to lasers, and even room-temperature single-photon sources. Knowledge of the optical properties of perovskite quantum dots still remains vastly incomplete. Here we apply various time-resolved spectroscopic techniques to conduct a comprehensive study of spectral and dynamical characteristics of single- and multiexciton states in CsPbX3 nanocrystals with X being either Br, I, or their mixture. Specifically, we measure exciton radiative lifetimes, absorption cross-sections, and derive the degeneracies of the band-edge electron and hole states. We also characterize the rates of intraband cooling and nonradiative Auger recombination and evaluate the strength of exciton–exciton coupling. The overall conclusion of this work is that spectroscopic properties of Cs–Pb-halide quantum dots are largely similar to those of quantum dots of more traditional semiconductors such as CdSe and PbSe. At the same time, we observe some distinctions including, for example, an appreciable effect of the halide identity on radiative lifetimes, considerably shorter biexciton Auger lifetimes, and apparent deviation of their size dependence from the “universal volume scaling” previously observed for many traditional nanocrystal systems. The high efficiency of Auger decay in perovskite quantum dots is detrimental to their prospective applications in light-emitting devices and lasers. Furthermore, this points toward the need for the development of approaches for effective
Li, Dafang; Zhang, Ping; Yan, Jun
2013-10-07
We investigate via quantum molecular-dynamics simulations the thermophysical properties of shocked liquid ammonia up to the pressure 1.3 TPa and temperature 120,000 K. The principal Hugoniot is predicted from the wide-range equation of state, which agrees well with the available experimental measurements up to 64 GPa. Our systematic study of the structural properties demonstrates that the liquid ammonia undergoes a gradual phase transition along the Hugoniot. At about 4800 K, the system transforms into a metallic, complex mixture state consisting of NH3, N2, H2, N, and H. Furthermore, we discuss the implications for the interiors of Uranus and Neptune.
NASA Astrophysics Data System (ADS)
Xie, H.; Prioli, R.; Fischer, A. M.; Ponce, F. A.; Kawabata, R. M. S.; Pinto, L. D.; Jakomin, R.; Pires, M. P.; Souza, P. L.
2016-07-01
The properties of InAs quantum dots (QDs) have been studied for application in intermediate band solar cells. It is found that suppression of plastic relaxation in the QDs has a significant effect on the optoelectronic properties. Partial capping plus annealing is shown to be effective in controlling the height of the QDs and in suppressing plastic relaxation. A force balancing model is used to explain the relationship between plastic relaxation and QD height. A strong luminescence has been observed from strained QDs, indicating the presence of localized states in the desired energy range. No luminescence has been observed from plastically relaxed QDs.
Multimodal Hip Hop Productions as Media Literacies
ERIC Educational Resources Information Center
Turner, K. C. Nat
2012-01-01
This study draws on ethnographic data from a year-long multimodal media production (MMP) course and the experience of an African American female adolescent who used the production of multimodal Hip Hop texts to express her creativity and growing socially conscious view of the world. The study demonstrates how students made meaning multimodally and…
Locating the Semiotic Power of Multimodality
ERIC Educational Resources Information Center
Hull, Glynda A.; Nelson, Mark Evan
2005-01-01
This article reports research that attempts to characterize what is powerful about digital multimodal texts. Building from recent theoretical work on understanding the workings and implications of multimodal communication, the authors call for a continuing empirical investigation into the roles that digital multimodal texts play in real-world…
Multimodal Friction Ignition Tester
NASA Technical Reports Server (NTRS)
Davis, Eddie; Howard, Bill; Herald, Stephen
2009-01-01
The multimodal friction ignition tester (MFIT) is a testbed for experiments on the thermal and mechanical effects of friction on material specimens in pressurized, oxygen-rich atmospheres. In simplest terms, a test involves recording sensory data while rubbing two specimens against each other at a controlled normal force, with either a random stroke or a sinusoidal stroke having controlled amplitude and frequency. The term multimodal in the full name of the apparatus refers to a capability for imposing any combination of widely ranging values of the atmospheric pressure, atmospheric oxygen content, stroke length, stroke frequency, and normal force. The MFIT was designed especially for studying the tendency toward heating and combustion of nonmetallic composite materials and the fretting of metals subjected to dynamic (vibrational) friction forces in the presence of liquid oxygen or pressurized gaseous oxygen test conditions approximating conditions expected to be encountered in proposed composite material oxygen tanks aboard aircraft and spacecraft in flight. The MFIT includes a stainless-steel pressure vessel capable of retaining the required test atmosphere. Mounted atop the vessel is a pneumatic cylinder containing a piston for exerting the specified normal force between the two specimens. Through a shaft seal, the piston shaft extends downward into the vessel. One of the specimens is mounted on a block, denoted the pressure block, at the lower end of the piston shaft. This specimen is pressed down against the other specimen, which is mounted in a recess in another block, denoted the slip block, that can be moved horizontally but not vertically. The slip block is driven in reciprocating horizontal motion by an electrodynamic vibration exciter outside the pressure vessel. The armature of the electrodynamic exciter is connected to the slip block via a horizontal shaft that extends into the pressure vessel via a second shaft seal. The reciprocating horizontal
Multimodal Neuroelectric Interface Development
NASA Technical Reports Server (NTRS)
Trejo, Leonard J.; Wheeler, Kevin R.; Jorgensen, Charles C.; Totah, Joseph (Technical Monitor)
2001-01-01
This project aims to improve performance of NASA missions by developing multimodal neuroelectric technologies for augmented human-system interaction. Neuroelectric technologies will add completely new modes of interaction that operate in parallel with keyboards, speech, or other manual controls, thereby increasing the bandwidth of human-system interaction. We recently demonstrated the feasibility of real-time electromyographic (EMG) pattern recognition for a direct neuroelectric human-computer interface. We recorded EMG signals from an elastic sleeve with dry electrodes, while a human subject performed a range of discrete gestures. A machine-teaming algorithm was trained to recognize the EMG patterns associated with the gestures and map them to control signals. Successful applications now include piloting two Class 4 aircraft simulations (F-15 and 757) and entering data with a "virtual" numeric keyboard. Current research focuses on on-line adaptation of EMG sensing and processing and recognition of continuous gestures. We are also extending this on-line pattern recognition methodology to electroencephalographic (EEG) signals. This will allow us to bypass muscle activity and draw control signals directly from the human brain. Our system can reliably detect P-rhythm (a periodic EEG signal from motor cortex in the 10 Hz range) with a lightweight headset containing saline-soaked sponge electrodes. The data show that EEG p-rhythm can be modulated by real and imaginary motions. Current research focuses on using biofeedback to train of human subjects to modulate EEG rhythms on demand, and to examine interactions of EEG-based control with EMG-based and manual control. Viewgraphs on these neuroelectric technologies are also included.
Toward quantum plasmonic networks
Holtfrerich, M. W.; Dowran, M.; Davidson, R.; ...
2016-08-30
Here, we demonstrate the transduction of macroscopic quantum entanglement by independent, distant plasmonic structures embedded in separate thin silver films. In particular, we show that the plasmon-mediated transmission through each film conserves spatially dependent, entangled quantum images, opening the door for the implementation of parallel quantum protocols, super-resolution imaging, and quantum plasmonic sensing geometries at the nanoscale level. The conservation of quantum information by the transduction process shows that continuous variable multi-mode entanglement is momentarily transferred from entangled beams of light to the space-like separated, completely independent plasmonic structures, thus providing a first important step toward establishing a multichannel quantummore » network across separate solid-state substrates.« less
Supermode-density-wave-polariton condensation with a Bose-Einstein condensate in a multimode cavity.
Kollár, Alicia J; Papageorge, Alexander T; Vaidya, Varun D; Guo, Yudan; Keeling, Jonathan; Lev, Benjamin L
2017-02-17
Phase transitions, where observable properties of a many-body system change discontinuously, can occur in both open and closed systems. By placing cold atoms in optical cavities and inducing strong coupling between light and excitations of the atoms, one can experimentally study phase transitions of open quantum systems. Here we observe and study a non-equilibrium phase transition, the condensation of supermode-density-wave polaritons. These polaritons are formed from a superposition of cavity photon eigenmodes (a supermode), coupled to atomic density waves of a quantum gas. As the cavity supports multiple photon spatial modes and because the light-matter coupling can be comparable to the energy splitting of these modes, the composition of the supermode polariton is changed by the light-matter coupling on condensation. By demonstrating the ability to observe and understand density-wave-polariton condensation in the few-mode-degenerate cavity regime, our results show the potential to study similar questions in fully multimode cavities.
Supermode-density-wave-polariton condensation with a Bose-Einstein condensate in a multimode cavity
NASA Astrophysics Data System (ADS)
Kollár, Alicia J.; Papageorge, Alexander T.; Vaidya, Varun D.; Guo, Yudan; Keeling, Jonathan; Lev, Benjamin L.
2017-02-01
Phase transitions, where observable properties of a many-body system change discontinuously, can occur in both open and closed systems. By placing cold atoms in optical cavities and inducing strong coupling between light and excitations of the atoms, one can experimentally study phase transitions of open quantum systems. Here we observe and study a non-equilibrium phase transition, the condensation of supermode-density-wave polaritons. These polaritons are formed from a superposition of cavity photon eigenmodes (a supermode), coupled to atomic density waves of a quantum gas. As the cavity supports multiple photon spatial modes and because the light-matter coupling can be comparable to the energy splitting of these modes, the composition of the supermode polariton is changed by the light-matter coupling on condensation. By demonstrating the ability to observe and understand density-wave-polariton condensation in the few-mode-degenerate cavity regime, our results show the potential to study similar questions in fully multimode cavities.
Supermode-density-wave-polariton condensation with a Bose–Einstein condensate in a multimode cavity
Kollár, Alicia J.; Papageorge, Alexander T.; Vaidya, Varun D.; Guo, Yudan; Keeling, Jonathan; Lev, Benjamin L.
2017-01-01
Phase transitions, where observable properties of a many-body system change discontinuously, can occur in both open and closed systems. By placing cold atoms in optical cavities and inducing strong coupling between light and excitations of the atoms, one can experimentally study phase transitions of open quantum systems. Here we observe and study a non-equilibrium phase transition, the condensation of supermode-density-wave polaritons. These polaritons are formed from a superposition of cavity photon eigenmodes (a supermode), coupled to atomic density waves of a quantum gas. As the cavity supports multiple photon spatial modes and because the light–matter coupling can be comparable to the energy splitting of these modes, the composition of the supermode polariton is changed by the light–matter coupling on condensation. By demonstrating the ability to observe and understand density-wave-polariton condensation in the few-mode-degenerate cavity regime, our results show the potential to study similar questions in fully multimode cavities. PMID:28211455
Investigation of size dependent structural and optical properties of thin films of CdSe quantum dots
Sharma, Madhulika; Sharma, A.B.; Mishra, N.; Pandey, R.K.
2011-03-15
Research highlights: {yields} CdSe q-dots have been synthesized using simple chemical synthesis route. {yields} Thin film of CdSe quantum dots exhibited self-organized growth. {yields} Size dependent blue shift observed in the absorption edge of CdSe nanocrystallites. {yields} PL emission band corresponds to band edge luminescence and defect luminescence. {yields} Organized growth led to enhancement in luminescence yield of smaller size Q-dots. -- Abstract: Cadmium selenide (CdSe) quantum dots were grown on indium tin oxide substrate using wet chemical technique for possible application as light emitting devices. The structural, morphological and luminescence properties of the as deposited thin films of CdSe Q-dot have been investigated, using X-ray diffraction, transmission electron microscopy, atomic force microscopy and optical and luminescence spectroscopy. The quantum dots have been shown to deposit in an organized array on ITO/glass substrate. The as grown Q-dots exhibited size dependent blue shift in the absorption edge. The effect of quantum confinement also manifested as a blue shift of photoluminescence emission. It is shown that the nanocrystalline CdSe exhibits intense photoluminescence as compared to the large grained polycrystalline CdSe films.
NASA Astrophysics Data System (ADS)
Potasz, P.; Güçlü, A. D.; Wójs, A.; Hawrylak, P.
2012-02-01
We present a theory of electronic properties of gated triangular graphene quantum dots with zigzag edges as a function of size and carrier density. We focus on electronic correlations, spin, and geometrical effects using a combination of atomistic tight-binding, Hartree-Fock, and configuration interaction methods (TB + HF + CI), including long-range Coulomb interactions. The single-particle energy spectrum of triangular dots with zigzag edges exhibits a degenerate shell at the Fermi level with a degeneracy Nedge proportional to the edge size. We determine the effect of the electron-electron interactions on the ground state, the total spin, and the excitation spectrum as a function of a shell filling and the degeneracy of the shell using TB + HF + CI for Nedge<12 and approximate CI method for Nedge⩾12. For a half-filled neutral shell we find spin-polarized ground state for structures up to N=500 atoms in agreement with previous ab initio and mean-field calculations and in agreement with Lieb's theorem for a Hubbard model on a bipartite lattice. Adding a single electron leads to the complete spin depolarization for Nedge⩽9. For larger structures, the spin depolarization is shown to occur at different filling factors. Away from half-fillings excess electrons(holes) are shown to form Wigner-like spin-polarized triangular molecules corresponding to large gaps in the excitation spectrum. The validity of conclusions is assessed by a comparison of results obtained from different levels of approximations. While for the charge-neutral system all methods give qualitatively similar results, away from the charge neutrality an inclusion of all Coulomb scattering terms is necessary to produce results presented here.
Quantum Calculations on Salt Bridges with Water: Potentials, Structure, and Properties
Liao, Sing; Green, Michael E.
2011-01-01
Salt bridges are electrostatic links between acidic and basic amino acids in a protein; quantum calculations are used here to determine the energetics and other properties of one form of these species, in the presence of water molecules. The acidic groups are carboxylic acids (aspartic and glutamic acids); proteins have two bases with pK above physiological pH: one, arginine, with a guanidinium basic group, the other lysine, which is a primary amine. Only arginine is modeled here, by ethyl guanidinium, while propionic acid is used as a model for either carboxylic acid. The salt bridges are accompanied by 0-12 water molecules; for each of the 13 systems, the energy-bond distance relation, natural bond orbitals (NBO), frequency calculations allowing thermodynamic corrections to room temperature, and dielectric constant dependence, were all calculated. The water molecules were found to arrange themselves in hydrogen bonded rings anchored to the oxygens of the salt bridge components. This was not surprising in itself, but it was found that the rings lead to a periodicity in the energy, and to a 'water addition' rule. The latter shows that the initial rings, with four oxygen atoms, become five member rings when an additional water molecule becomes available, with the additional water filling in at the bond with the lowest Wiberg index, as calculated using NBO. The dielectric constant dependence is the expected hyperbola, and the fit of the energy to the inverse dielectric constant is determined. There is an energy periodicity related to ring formation upon addition of water molecules. When 10 water molecules have been added, all spaces near the salt bridge are filled, completing the first hydration shell, and a second shell starts to form. The potentials associated with salt bridges depend on their hydration, and potentials assigned without regard to local hydration are likely to cause errors as large as or larger than kBT, thus suggesting a serious problem if these
NASA Astrophysics Data System (ADS)
Yakar, Yusuf; Çakir, Bekir; Özmen, Ayhan
2010-06-01
We calculate the energy eigenvalues and the sate functions of one-electron Quantum Dot (QD) by using a combination of Quantum Genetic Algorithm (QGA) and Hartree-Fock-Roothaan (HFR) method. The linear and the third-order nonlinear optical absorption coefficients for the 1s-1p, 1p-1d, and 1d-1f transitions are examined as a function of the incident photon energy for three different values of the stoichiometric ratio. The results show that the stoichiometric ratio, impurity, relaxation time, and dot size have great influence on the optical absorption coefficients of QDs.
Electron quantum optics as quantum signal processing
NASA Astrophysics Data System (ADS)
Roussel, B.; Cabart, C.; Fève, G.; Thibierge, E.; Degiovanni, P.
2017-03-01
The recent developments of electron quantum optics in quantum Hall edge channels have given us new ways to probe the behavior of electrons in quantum conductors. It has brought new quantities called electronic coherences under the spotlight. In this paper, we explore the relations between electron quantum optics and signal processing through a global review of the various methods for accessing single- and two-electron coherences in electron quantum optics. We interpret electron quantum optics interference experiments as analog signal processing converting quantum signals into experimentally observable quantities such as current averages and correlations. This point of view also gives us a procedure to obtain quantum information quantities from electron quantum optics coherences. We illustrate these ideas by discussing two mode entanglement in electron quantum optics. We also sketch how signal processing ideas may open new perspectives for representing electronic coherences in quantum conductors and understand the properties of the underlying many-body electronic state.
Creating Tangible Interfaces by Augmenting Physical Objects with Multimodal Language
McGee, David R. ); Cohen, Philip R.
2001-01-01
Rasa is a tangible augmented reality environment that digitally enhances the existing paper-based command and control capability in a military command post. By observing and understanding the users' speech, pen, and touch-based multimodal language, Rasa computationally augments the physical objects on a command post map, linking these items to digital representations of the same; for example, linking a paper map to the world and Post-it notes to military units. Herein, we give a thorough account of Rasa's underlying multiagent framework, and its recognition, understanding, and multimodal integration components. Moreover, we examine five properties of language: generativity, comprehensibility, compositionality, referentiality, and, at times, persistence--that render it suitable as an augmentation approach, contrasting these properties to those of other augmentation methods. It is these properties of language that allow users of Rasa to augment physical objects, transforming them into tangible interfaces.
Quantum-Dot-Based (Aero)gels: Control of the Optical Properties.
Wolf, André; Lesnyak, Vladimir; Gaponik, Nikolai; Eychmüller, Alexander
2012-08-16
In this work, we have developed novel hybrid quantum dot gels based on the controllable and reversible assembly of nanoparticles via metal-tetrazole complexation. Combining in one hybrid network nanocrystals of different semiconductors (ZnSe and CdTe) as well as quantum dots of different sizes (green and red emitting CdTe) with different band gaps, we have examined energy relations within these systems and act out a facile route to the color design of the resulting gels. Efficient energy pumping from donor quantum dots to acceptors leads to a remarkable enhancement of the emission intensity of the gel. Furthermore, by integrating three different quantum dot types into one network, we obtained a white-light-emitting aerogel.
Reprint of : Thermodynamic properties of a quantum Hall anti-dot interferometer
NASA Astrophysics Data System (ADS)
Levy Schreier, Sarah; Stern, Ady; Rosenow, Bernd; Halperin, Bertrand I.
2016-08-01
We study quantum Hall interferometers in which the interference loop encircles a quantum anti-dot. We base our study on thermodynamic considerations, which we believe reflect the essential aspects of interference transport phenomena. We find that similar to the more conventional Fabry-Perot quantum Hall interferometers, in which the interference loop forms a quantum dot, the anti-dot interferometer is affected by the electro-static Coulomb interaction between the edge modes defining the loop. We show that in the Aharonov-Bohm regime, in which effects of fractional statistics should be visible, is easier to access in interferometers based on anti-dots than in those based on dots. We discuss the relevance of our results to recent measurements on anti-dots interferometers.
Multimodal EEG Recordings, Psychometrics and Behavioural Analysis.
Boeijinga, Peter H
2015-01-01
High spatial and temporal resolution measurements of neuronal activity are preferably combined. In an overview on how this approach can take shape, multimodal electroencephalography (EEG) is treated in 2 main parts: by experiments without a task and in the experimentally cued working brain. It concentrates first on the alpha rhythm properties and next on data-driven search for patterns such as the default mode network. The high-resolution volumic distributions of neuronal metabolic indices result in distributed cortical regions and possibly relate to numerous nuclei, observable in a non-invasive manner in the central nervous system of humans. The second part deals with paradigms in which nowadays assessment of target-related networks can align level-dependent blood oxygenation, electrical responses and behaviour, taking the temporal resolution advantages of event-related potentials. Evidence-based electrical propagation in serial tasks during performance is now to a large extent attributed to interconnected pathways, particularly chronometry-dependent ones, throughout a chain including a dorsal stream, next ventral cortical areas taking the flow of information towards inferior temporal domains. The influence of aging is documented, and results of the first multimodal studies in neuropharmacology are consistent. Finally a scope on implementation of advanced clinical applications and personalized marker strategies in neuropsychiatry is indicated.
Quantum interference between transverse spatial waveguide modes
Mohanty, Aseema; Zhang, Mian; Dutt, Avik; Ramelow, Sven; Nussenzveig, Paulo; Lipson, Michal
2017-01-01
Integrated quantum optics has the potential to markedly reduce the footprint and resource requirements of quantum information processing systems, but its practical implementation demands broader utilization of the available degrees of freedom within the optical field. To date, integrated photonic quantum systems have primarily relied on path encoding. However, in the classical regime, the transverse spatial modes of a multi-mode waveguide have been easily manipulated using the waveguide geometry to densely encode information. Here, we demonstrate quantum interference between the transverse spatial modes within a single multi-mode waveguide using quantum circuit-building blocks. This work shows that spatial modes can be controlled to an unprecedented level and have the potential to enable practical and robust quantum information processing. PMID:28106036
Quantum interference between transverse spatial waveguide modes
NASA Astrophysics Data System (ADS)
Mohanty, Aseema; Zhang, Mian; Dutt, Avik; Ramelow, Sven; Nussenzveig, Paulo; Lipson, Michal
2017-01-01
Integrated quantum optics has the potential to markedly reduce the footprint and resource requirements of quantum information processing systems, but its practical implementation demands broader utilization of the available degrees of freedom within the optical field. To date, integrated photonic quantum systems have primarily relied on path encoding. However, in the classical regime, the transverse spatial modes of a multi-mode waveguide have been easily manipulated using the waveguide geometry to densely encode information. Here, we demonstrate quantum interference between the transverse spatial modes within a single multi-mode waveguide using quantum circuit-building blocks. This work shows that spatial modes can be controlled to an unprecedented level and have the potential to enable practical and robust quantum information processing.
Quantum state engineering of pulsed light in non-linear waveguides
NASA Astrophysics Data System (ADS)
Silberhorn, Christine; Eckstein, Andreas; Christ, Andreas
2011-10-01
The standard approach for introducing the quantization of optical light is based on monochromatic light fields, however this description is not sufficient for the definition of quantum light pulses. Their finite time duration necessarily requires that polychromatic wave packets with a broad spectral distribution are considered. Pulsed multi-photon states of light typically carry an implicit spectral broadband mode structure, which is imprinted by the spectral correlations originating from the generation process. Recent developments have enabled us to control the spectral properties of such multi-mode pulsed states, which opens a new route for quantum information applications.We have implenented a pulsed parametric downconversion source in a waveguide, which can be tuned from genuine single mode to multi-mode characteristics by modifiying the bandwidth of the ultrafast pump pulses. Our generated signal and idler beams of the PDC output twin beams lie in the telecommunication regime, and the source features an exceptional brightness with 2.5 photons per pulse utilizing a single pass configuration. We verify the broadband single mode versus multi-mode structure by analysing the marginal g(2) -Glauber correlation function of the signal and idler beams while modifing the their spectral inter correlations.
Fujikura, Kyota; Shimizu, Akira
2016-07-01
For macroscopic quantum systems, we study what is measured when equilibrium fluctuations of macrovariables are measured in an ideal way that mimics classical ideal measurements as closely as possible. We find that the symmetrized time correlation is always obtained for such measurements. As an important consequence, we show that the fluctuation-dissipation theorem is partially violated as a relation between observed quantities in macroscopic quantum systems even if measurements are made in such an ideal way.
NASA Technical Reports Server (NTRS)
Lee, Hsing-Chung; Kost, A.; Kawase, M.; Hariz, A.; Dapkus, P. Daniel
1988-01-01
The nonlinear absorption properties of the excitonic resonances associated with multiple quantum wells (MQWs) in AlGaAs/GaAs grown by metalorganic chemical vapor deposition are reported. The dependence of the saturation properties on growth parameters, especially growth temperature, and the well width are described. The minimum measured saturation intensity for these materials is 250 W/sq cm, the lowest reported value to date. The low saturation intensities are the result of excellent minority carrier properties. A systematic study of minority carrier lifetimes in quantum wells are reported. Lifetimes range from 50-350 ns depending on growth temperature and well width. When corrected for lateral diffusion effects and the measured minority carrier lifetime, the saturation data suggest that saturation intensities as low as 2.3 W/sq cm can be achieved in this system. The first measurements of the dependence of the exciton area and the magnitude of the excitonic absorption on well width are prsented. The growth of MQW structures on transparent GaP substrates is demonstrated and the electroabsorption properties of these structures are reviewed.
Thermoelectric transport properties through a T-shaped single quantum dot
NASA Astrophysics Data System (ADS)
Castellanos, R.; Franco, R.; Silva-Valencia, J.; Figueira, M. S.
2010-12-01
We study the thermopower, thermal conductance, electric conductance and the thermoelectric figure of merit for a gate-defined T-shaped single quantum dot (QD). The QD is solved in the limit of strong Coulombian repulsion U→∞, inside the dot, and the quantum wire is modeled on a tight-binding linear chain. We employ the X-boson approach for the Anderson impurity model to describe the localized level within the quantum dot. Our results are in qualitative agreement with recent experimental reports and other theoretical researches for the case of a quantum dot embedded into a conduction channel, employing analogies between the two systems. The results for the thermopower sign as a function of the gate voltage (associated with the quantum dot energy) are in agreement with a recent experimental result obtained for a suspended quantum dot. The thermoelectric figure of merit times temperature results indicates that, at low temperatures and in the crossover between the intermediate valence and Kondo regimes, the system might have practical applicability in the development of thermoelectric devices.
Luminescent properties of fluorine phosphate glasses doped with PbSe and PbS quantum dots
NASA Astrophysics Data System (ADS)
Kolobkova, Elena; Lipatova, Zhanna; Abdrshin, Albert; Nikonorov, Nikolay
2017-03-01
Optical properties of the PbS/PbSe molecular clusters (MCs) and PbS/PbSe quantum dots (QDs) in fluorine phosphate glasses were studied. Luminescence of MCs (excited by UV radiation) was obtained in visible spectral region and it's absolute quantum yield was up to 10%. It was found, that PbS QDs with sizes 3 nm, 3.5 nm and 4.9 nm demonstrate strong luminescence at 970, 1300 and 1500 nm with Stokes shift 80 -50 meV. PbSe QDs with sizes 2.5, 2.6, 3.0, 3,7 and 5.1 nm have strong luminescence at 1050, 1100, 1300, 1500 and 1650 nm with Stokes shift 355-60 meV. Glasses doped with PbS(Se) QDs provide potential as robust materials for broadband optic amplifiers.
Toyoda, Taro; Shen, Qing
2012-07-19
There is a great deal of interest in dye-sensitized solar cells (DSCs) fabricated with nanostructured TiO2 electrodes. Many different dye molecules have been designed and synthesized to achieve high photovoltaic conversion efficiency. Recently, as an alternative to organic dyes, semiconductor quantum dots (QDs) have been studied for their light-harvesting capability compared with other sensitizers. Accordingly, an attractive configuration to exploit these fascinating properties of semiconductor QDs is the quantum-dot-sensitized solar cell (QDSC) due to their high photoactivity, process realization, and low cost of production. The morphology of TiO2 electrodes included with surface orientation is important for satisfactory assembly of QDSCs in order to improve the efficiency. Breakthroughs allowing an increase in efficiency will advance on two areas of electrode morphology control, namely, (A) TiO2 nanotube electrodes and (B) inverse opal TiO2 electrodes.
NASA Astrophysics Data System (ADS)
Bardajee, Ghasem Rezanejade; Hooshyar, Zari
2013-10-01
Water soluble CdSe quantum dots (QDs) were modified using a novel biopolymer based on the graft copolymerization of poly (acrylic acid) as a monomer onto sodium alginate as a backbone at room temperature. The obtained CdSe QDs were characterized by Fourier transform infrared spectrometer, thermo-gravimetry analysis, transmission electron microscopy, and dynamic light scattering. Optical properties of the prepared CdSe QDs were investigated by absorption and fluorescence spectra. It was found that the resultant QDs incredibly exhibited high fluorescence intensity and quantum yields. Lastly, the influence of the aging time on the fluorescence intensity of the modified CdSe QDs was studied by their fluorescence spectra. Due to the optical behavior of this modified QDs; it could be of potential interest in biological systems.
Håkansson, Pär
2017-01-25
Molecular dynamics and quantum chemistry methods are implemented to quantify nuclear spin-1/2 pair singlet-state relaxation rates for three molecular systems at low magnetic field and room temperature. Computational methodology is developed for weak interactions, particularly important for singlet states at low field. These include spin-rotation and spin-internal-motion effects, which describe the coupling of the spin-carrying nuclei to fluctuating local magnetic fields induced by the overall and internal molecular fluctuations, respectively. A high-dimensional tensor property surface using Kriging interpolation is developed to circumvent costly quantum-chemical calculations. Together with the intramolecular dipolar relaxation, all the simulated relaxation mechanisms are accounted for with a common theoretical framework. Comparison with experiment indicates that quantitative accuracy is obtained, sufficient to enable guidance in the molecular design of molecules with long-lived singlet order.
A Learning Algorithm for Multimodal Grammar Inference.
D'Ulizia, A; Ferri, F; Grifoni, P
2011-12-01
The high costs of development and maintenance of multimodal grammars in integrating and understanding input in multimodal interfaces lead to the investigation of novel algorithmic solutions in automating grammar generation and in updating processes. Many algorithms for context-free grammar inference have been developed in the natural language processing literature. An extension of these algorithms toward the inference of multimodal grammars is necessary for multimodal input processing. In this paper, we propose a novel grammar inference mechanism that allows us to learn a multimodal grammar from its positive samples of multimodal sentences. The algorithm first generates the multimodal grammar that is able to parse the positive samples of sentences and, afterward, makes use of two learning operators and the minimum description length metrics in improving the grammar description and in avoiding the over-generalization problem. The experimental results highlight the acceptable performances of the algorithm proposed in this paper since it has a very high probability of parsing valid sentences.
Correlation steering in the angularly multimode Raman atomic memory
NASA Astrophysics Data System (ADS)
Mazelanik, Mateusz; Dąbrowski, Michał; Wasilewski, Wojciech
2016-09-01
We present the possibility of steering the direction of correlations between the off-resonant Raman scattered photons from the angularly multimode atomic memory based on warm rubidium vapors. Using acousto-optic deflectors (AOD) driven by different modulation frequencies we experimentally change the angle of incidence of the laser beams on the atomic ensemble. Performing correlations measurements for various deflection angles we verify that we can choose the anti-Stokes light propagation direction independently of the correlated Stokes scattered light in the continuous way. As a result we can select the spatial mode of photons retrieved from the memory, which may be important for future development of quantum information processing.
NASA Astrophysics Data System (ADS)
Braun, Daniel; Giraud, Olivier; Braun, Peter A.
2010-03-01
We introduce and study a measure of ``quantumness'' of a quantum state based on its Hilbert-Schmidt distance from the set of classical states. ``Classical states'' were defined earlier as states for which a positive P-function exists, i.e. they are mixtures of coherent states [1]. We study invariance properties of the measure, upper bounds, and its relation to entanglement measures. We evaluate the quantumness of a number of physically interesting states and show that for any physical system in thermal equilibrium there is a finite critical temperature above which quantumness vanishes. We then use the measure for identifying the ``most quantum'' states. Such states are expected to be potentially most useful for quantum information theoretical applications. We find these states explicitly for low-dimensional spin-systems, and show that they possess beautiful, highly symmetric Majorana representations. [4pt] [1] Classicality of spin states, Olivier Giraud, Petr Braun, and Daniel Braun, Phys. Rev. A 78, 042112 (2008)
Multimodal Revision Techniques in Webtexts
ERIC Educational Resources Information Center
Ball, Cheryl E.
2014-01-01
This article examines how an online scholarly journal, "Kairos: Rhetoric, Technology, Pedagogy," mentors authors to revise their webtexts (interactive, digital media scholarship) for publication. Using an editorial pedagogy in which multimodal and rhetorical genre theories are merged with revision techniques found in process-based…
Multimodality as a Sociolinguistic Resource
ERIC Educational Resources Information Center
Collister, Lauren Brittany
2013-01-01
This work explores the use of multimodal communication in a community of expert "World of Warcraft"® players and its impact on politeness, identity, and relationships. Players in the community regularly communicated using three linguistic modes quasi-simultaneously: text chat, voice chat, and face-to-face interaction. Using the…
Multimodal imaging of ischemic wounds
NASA Astrophysics Data System (ADS)
Zhang, Shiwu; Gnyawali, Surya; Huang, Jiwei; Liu, Peng; Gordillo, Gayle; Sen, Chandan K.; Xu, Ronald
2012-12-01
The wound healing process involves the reparative phases of inflammation, proliferation, and remodeling. Interrupting any of these phases may result in chronically unhealed wounds, amputation, or even patient death. Quantitative assessment of wound tissue ischemia, perfusion, and inflammation provides critical information for appropriate detection, staging, and treatment of chronic wounds. However, no method is available for noninvasive, simultaneous, and quantitative imaging of these tissue parameters. We integrated hyperspectral, laser speckle, and thermographic imaging modalities into a single setup for multimodal assessment of tissue oxygenation, perfusion, and inflammation characteristics. Advanced algorithms were developed for accurate reconstruction of wound oxygenation and appropriate co-registration between different imaging modalities. The multimodal wound imaging system was validated by an ongoing clinical trials approved by OSU IRB. In the clinical trial, a wound of 3mm in diameter was introduced on a healthy subject's lower extremity and the healing process was serially monitored by the multimodal imaging setup. Our experiments demonstrated the clinical usability of multimodal wound imaging.
Multi-Modality Phantom Development
Huber, Jennifer S.; Peng, Qiyu; Moses, William W.
2009-03-20
Multi-modality imaging has an increasing role in the diagnosis and treatment of a large number of diseases, particularly if both functional and anatomical information are acquired and accurately co-registered. Hence, there is a resulting need for multi modality phantoms in order to validate image co-registration and calibrate the imaging systems. We present our PET-ultrasound phantom development, including PET and ultrasound images of a simple prostate phantom. We use agar and gelatin mixed with a radioactive solution. We also present our development of custom multi-modality phantoms that are compatible with PET, transrectal ultrasound (TRUS), MRI and CT imaging. We describe both our selection of tissue mimicking materials and phantom construction procedures. These custom PET-TRUS-CT-MRI prostate phantoms use agargelatin radioactive mixtures with additional contrast agents and preservatives. We show multi-modality images of these custom prostate phantoms, as well as discuss phantom construction alternatives. Although we are currently focused on prostate imaging, this phantom development is applicable to many multi-modality imaging applications.
Underwater Multimode Directional Transducer Evaluation
2003-12-01
The work described in the present thesis is intended to establish a procedure for analyzing directional transducers for future underwater wireless...networks, as well as to carry out the performance evaluation of a multimode transducer prototype with respect to its main operational requirements
Quantum Storage of Three-Dimensional Orbital-Angular-Momentum Entanglement in a Crystal
NASA Astrophysics Data System (ADS)
Zhou, Zong-Quan; Hua, Yi-Lin; Liu, Xiao; Chen, Geng; Xu, Jin-Shi; Han, Yong-Jian; Li, Chuan-Feng; Guo, Guang-Can
2015-08-01
Here we present the quantum storage of three-dimensional orbital-angular-momentum photonic entanglement in a rare-earth-ion-doped crystal. The properties of the entanglement and the storage process are confirmed by the violation of the Bell-type inequality generalized to three dimensions after storage (S =2.152 ±0.033 ). The fidelity of the memory process is 0.993 ±0.002 , as determined through complete quantum process tomography in three dimensions. An assessment of the visibility of the stored weak coherent pulses in higher-dimensional spaces demonstrates that the memory is highly reliable for 51 spatial modes. These results pave the way towards the construction of high-dimensional and multiplexed quantum repeaters based on solid-state devices. The multimode capacity of rare-earth-based optical processors goes beyond the temporal and the spectral degree of freedom, which might provide a useful tool for photonic information processing.
Electronic structure and quantum transport properties of metallic and semiconducting nanowires
NASA Astrophysics Data System (ADS)
Simbeck, Adam J.
The future of the semiconductor industry hinges upon new developments to combat the scaling issues that currently afflict two main chip components: transistors and interconnects. For transistors this means investigating suitable materials to replace silicon for both the insulating gate and the semiconducting channel in order to maintain device performance with decreasing size. For interconnects this equates to overcoming the challenges associated with copper when the wire dimensions approach the confinement limit, as well as continuing to develop low-k dielectric materials that can assure minimal cross-talk between lines. In addition, such challenges make it increasingly clear that device design must move from a top-down to a bottom-up approach in which the desired electronic characteristics are tailored from first-principles. It is with such fundamental hurdles in mind that ab initio calculations on the electronic and quantum transport properties of nanoscale metallic and semiconducting wires have been performed. More specifically, this study seeks to elaborate on the role played by confinement, contacts, dielectric environment, edge decoration, and defects in altering the electronic and transport characteristics of such systems. As experiments continue to achieve better control over the synthesis and design of nanowires, these results are expected to become increasingly more important for not only the interpretation of electronic and transport trends, but also in engineering the electronic structure of nanowires for the needs of the devices of the future. For the metallic atomic wires, the quantum transport properties are first investigated by considering finite, single-atom chains of aluminum, copper, gold, and silver sandwiched between gold contacts. Non-equilibrium Green's function based transport calculations reveal that even in the presence of the contact the conductivity of atomic-scale aluminum is greater than that of the other metals considered. This is
Theory of coherent control with quantum light
NASA Astrophysics Data System (ADS)
Schlawin, Frank; Buchleitner, Andreas
2017-01-01
We develop a coherent control theory for multimode quantum light. It allows us to examine a fundamental problem in quantum optics: what is the optimal pulse form to drive a two-photon-transition? In formulating the question as a coherent control problem, we show that—and quantify how much—the strong frequency quantum correlations of entangled photons enhance the transition compared to shaped classical pulses. In ensembles of collectively driven two-level systems, such enhancement requires nonvanishing interactions.
Exact quantum scattering calculations of transport properties for the H{sub 2}O–H system
Dagdigian, Paul J.; Alexander, Millard H.
2013-11-21
Transport properties for collisions of water with hydrogen atoms are computed by means of exact quantum scattering calculations. For this purpose, a potential energy surface (PES) was computed for the interaction of rigid H{sub 2}O, frozen at its equilibrium geometry, with a hydrogen atom, using a coupled-cluster method that includes all singles and doubles excitations, as well as perturbative contributions of connected triple excitations. To investigate the importance of the anisotropy of the PES on transport properties, calculations were performed with the full potential and with the spherical average of the PES. We also explored the determination of the spherical average of the PES from radial cuts in six directions parallel and perpendicular to the C{sub 2} axis of the molecule. Finally, the computed transport properties were compared with those computed with a Lennard-Jones 12-6 potential.
NASA Astrophysics Data System (ADS)
Tavakoli, Mohammad Mahdi; Tayyebi, Ahmad; Simchi, Abdolreza; Aashuri, Hossein; Outokesh, Mohmmad; Fan, Zhiyong
2015-01-01
Recently, hybrid graphene-quantum dot systems have attracted increasing attention for the next-generation optoelectronic devices such as ultrafast photo-detectors and solar energy harvesting. In this paper, a novel, one-step, reproducible, and solution-processed method is introduced to prepare hybrid graphene-PbS colloids by employing supercritical ethanol. In the hybrid nanocomposite, PbS quantum dots ( 3 nm) are decorated on the reduced graphene oxide (rGO) nanosheets ( 1 nm thickness and less than 1 micron lengths). By employing X-ray photoelectron and Raman and infrared spectroscopy techniques, it is shown that the rGO nanosheets are bonded to PbS nanocrystals through carboxylic bonds. Passivation of {111} planes of PbS quantum dots with rGO nanosheets is demonstrated by employing density function theory. Quenching of the photoluminescence emission of PbS nanocrystals through coupling with graphene sheets is also shown. In order to illustrate that the developed preparation method does not impair the quantum efficiency of the PbS nanocrystals, the photovoltaic efficiency of solar cell device is reported and compared with oleic acid-capped PbS colloidal quantum dot solar cells. By employing the "Hall effect" measurement, it is shown that the carrier mobility is significantly increased (by two orders of magnitudes) in the presence of graphene nanosheets.
Fabrication and optical properties of multishell InAs quantum dots on GaAs nanowires
Yan, Xin; Zhang, Xia Li, Junshuai; Cui, Jiangong; Ren, Xiaomin
2015-02-07
Hybrid nanostructures combining nanowires with quantum dots promote the development of nanoelectronic and nanophotonic devices with integrated functionalities. In this work, we present a complex nanostructure with multishell quantum dots grown on nanowires. 1–4 shells of Stranski-Krastanov InAs quantum dots are grown on the sidewalls of GaAs nanowires by metal organic chemical vapor deposition. Different dot shells are separated by 8 nm GaAs spacer shells. With increasing the number of shells, the quantum dots become sparser and tend to align in one array, which is caused by the shrinkage of facets on which dots prefer to grow as well as the strain fields produced by the lower set of dots which influences the migration of In adatoms. The size of quantum dots increases with the increase of shell number due to enhanced strain fields coupling. The spectra of multishell dots exhibit multiwavelength emission, and each peak corresponds to a dot shell. This hybrid structure may serve as a promising element in nanowire intermediate band solar cells, infrared nanolasers, and photodetectors.
Properties of strong-coupling magneto-bipolaron qubit in quantum dot under magnetic field
NASA Astrophysics Data System (ADS)
Xu-Fang, Bai; Ying, Zhang; Wuyunqimuge; Eerdunchaolu
2016-07-01
Based on the variational method of Pekar type, we study the energies and the wave-functions of the ground and the first-excited states of magneto-bipolaron, which is strongly coupled to the LO phonon in a parabolic potential quantum dot under an applied magnetic field, thus built up a quantum dot magneto-bipolaron qubit. The results show that the oscillation period of the probability density of the two electrons in the qubit decreases with increasing electron-phonon coupling strength α, resonant frequency of the magnetic field ω c, confinement strength of the quantum dot ω 0, and dielectric constant ratio of the medium η the probability density of the two electrons in the qubit oscillates periodically with increasing time t, angular coordinate φ 2, and dielectric constant ratio of the medium η the probability of electron appearing near the center of the quantum dot is larger, and the probability of electron appearing away from the center of the quantum dot is much smaller. Project supported by the Natural Science Foundation of Hebei Province, China (Grant No. E2013407119) and the Items of Institution of Higher Education Scientific Research of Hebei Province and Inner Mongolia, China (Grant Nos. ZD20131008, Z2015149, Z2015219, and NJZY14189).
Quantum games as quantum types
NASA Astrophysics Data System (ADS)
Delbecque, Yannick
In this thesis, we present a new model for higher-order quantum programming languages. The proposed model is an adaptation of the probabilistic game semantics developed by Danos and Harmer [DH02]: we expand it with quantum strategies which enable one to represent quantum states and quantum operations. Some of the basic properties of these strategies are established and then used to construct denotational semantics for three quantum programming languages. The first of these languages is a formalisation of the measurement calculus proposed by Danos et al. [DKP07]. The other two are new: they are higher-order quantum programming languages. Previous attempts to define a denotational semantics for higher-order quantum programming languages have failed. We identify some of the key reasons for this and base the design of our higher-order languages on these observations. The game semantics proposed in this thesis is the first denotational semantics for a lambda-calculus equipped with quantum types and with extra operations which allow one to program quantum algorithms. The results presented validate the two different approaches used in the design of these two new higher-order languages: a first one where quantum states are used through references and a second one where they are introduced as constants in the language. The quantum strategies presented in this thesis allow one to understand the constraints that must be imposed on quantum type systems with higher-order types. The most significant constraint is the fact that abstraction over part of the tensor product of many unknown quantum states must not be allowed. Quantum strategies are a new mathematical model which describes the interaction between classical and quantum data using system-environment dialogues. The interactions between the different parts of a quantum system are described using the rich structure generated by composition of strategies. This approach has enough generality to be put in relation with other
Zhao, Jiang; Yu, Yue; Yang, Xiaolong; Yan, Xiaogang; Zhang, Huiming; Xu, Xianbin; Zhou, Guijiang; Wu, Zhaoxin; Ren, Yixia; Wong, Wai-Yeung
2015-11-11
A series of heteroleptic functional Ir(III) complexes bearing different fluorinated aromatic sulfonyl groups has been synthesized. Their photophysical features, electrochemical behaviors, and electroluminescent (EL) properties have been characterized in detail. These complexes emit intense yellow phosphorescence with exceptionally high quantum yields (ΦP > 0.9) at room temperature, and the emission maxima of these complexes can be finely tuned depending upon the number of the fluorine substituents on the pendant phenyl ring of the sulfonyl group. Furthermore, the electrochemical properties and electron injection/transporting (EI/ET) abilities of these Ir(III) phosphors can also be effectively tuned by the fluorinated aromatic sulfonyl group to furnish some desired characters for enhancing the EL performance. Hence, the maximum luminance efficiency (ηL) of 81.2 cd A(-1), corresponding to power efficiency (ηP) of 64.5 lm W(-1) and external quantum efficiency (ηext) of 19.3%, has been achieved, indicating the great potential of these novel phosphors in the field of organic light-emitting diodes (OLEDs). Furthermore, a clear picture has been drawn for the relationship between their optoelectronic properties and chemical structures. These results should provide important information for developing highly efficient phosphors.
Electronic properties of Hg1-xCdxSe lens-shaped quantum dots under external fields
NASA Astrophysics Data System (ADS)
Herrera, J. R.; Gutierrez, W.; Miranda, D. A.
2016-02-01
Hg1-xCdxSe are II-VI semiconductors alloys with optoelectronic properties that depend upon the molar fraction x, which can be further controlled by nanostructuring. In this work one electron confined in a zero-dimensional lens-shaped nanostructure of Hg1-xCdxSe surrounded by a matrix of different molar fraction is analyzed and its electronic properties are studied under external magnetic and electric fields. Our system was modeled by means of the 3D Schrodinger equation in the framework of the effective mass approximation, which was solved using a finite element method. The model is described by a discontinuous space with Ben Daniel-Duke boundary conditions. We calculated the energy spectrum and the corresponding probability density of the electron for some low-lying energy levels as a function of: electric field strength on plane and magnetic field strength applied along the growth direction. Also, the effect of finite confinement potential was studied in presence of a uniform magnetic field. Our results shown that the electronic properties of Hg1-xCdxSe quantum dots are highly sensitive to a threading magnetic field because the degenerate energy levels are split. On the other hand, the effect of electric and magnetic fields applied simultaneously on a quantum dot can increase the system stability against external perturbation, e.g. thermal interactions.
Chang, Jin; Ogomi, Yuhei; Ding, Chao; Zhang, Yao Hong; Toyoda, Taro; Hayase, Shuzi; Katayama, Kenji; Shen, Qing
2017-03-01
The surface chemistry of colloidal quantum dots (QDs) plays an important role in determining the photoelectric properties of QD films and the corresponding quantum dot heterojunction solar cells (QDHSCs). To investigate the effects of the ligand structure on the photovoltaic performance and exciton dynamics of QDHSCs, PbS QDHSCs were fabricated by the solid state ligand exchange method with mercaptoalkanoic acid as the cross-linking ligand. Temperature-dependent photoluminescence and ultrafast transient absorption spectra show that the electronic coupling and charge transfer rate within QD ensembles were monotonically enhanced as the ligand length decreased. However, in practical QDHSCs, the second shortest ligand 3-mercaptopropionic acid (MPA) showed higher power conversion efficiency than the shortest ligand thioglycolic acid (TGA). This could be attributed to the difference in their surface trap states, supported by thermally stimulated current measurements. Moreover, compared with the non-conjugated ligand MPA, the conjugated ligand 4-mercaptobenzoic acid (MBA) introduces less trap states and has a similar charge transfer rate in QD ensembles, but has poor photovoltaic properties. This unexpected result could be contributed by the QD-ligand orbital mixing, leading to the charge transfer from QDs to ligands instead of charge transfer between adjacent QDs. This work highlights the significant effects of ligand structures on the photovoltaic properties and exciton dynamics of QDHSCs, which would shed light on the further development of QD-based photoelectric devices.
NASA Astrophysics Data System (ADS)
Ronde, Christian De
In classical physics, probabilistic or statistical knowledge has been always related to ignorance or inaccurate subjective knowledge about an actual state of affairs. This idea has been extended to quantum mechanics through a completely incoherent interpretation of the Fermi-Dirac and Bose-Einstein statistics in terms of "strange" quantum particles. This interpretation, naturalized through a widespread "way of speaking" in the physics community, contradicts Born's physical account of Ψ as a "probability wave" which provides statistical information about outcomes that, in fact, cannot be interpreted in terms of `ignorance about an actual state of affairs'. In the present paper we discuss how the metaphysics of actuality has played an essential role in limiting the possibilities of understating things differently. We propose instead a metaphysical scheme in terms of immanent powers with definite potentia which allows us to consider quantum probability in a new light, namely, as providing objective knowledge about a potential state of affairs.
Tunable Quantum Dot Solids: Impact of Interparticle Interactions on Bulk Properties
Sinclair, Michael B.; Fan, Hongyou; Brener, Igal; Liu, Sheng; Luk, Ting S.; Li, Binsong
2015-09-01
QD-solids comprising self-assembled semiconductor nanocrystals such as CdSe are currently under investigation for use in a wide array of applications including light emitting diodes, solar cells, field effect transistors, photodetectors, and biosensors. The goal of this LDRD project was develop a fundamental understanding of the relationship between nanoparticle interactions and the different regimes of charge and energy transport in semiconductor quantum dot (QD) solids. Interparticle spacing was tuned through the application of hydrostatic pressure in a diamond anvil cell, and the impact on interparticle interactions was probed using x-ray scattering and a variety of static and transient optical spectroscopies. During the course of this LDRD, we discovered a new, previously unknown, route to synthesize semiconductor quantum wires using high pressure sintering of self-assembled quantum dot crystals. We believe that this new, pressure driven synthesis approach holds great potential as a new tool for nanomaterials synthesis and engineering.
Photophysical properties gallium octacarboxy phthalocyanines conjugated to CdSe@ZnS quantum dots.
Tshangana, Charmaine; Nyokong, Tebello
2015-01-01
L-Glutathione (GSH) capped core CdSe (2.3 nm) and core shell CdSe@ZnS quantum dots (QDs) (3.0 nm and 3.5 nm) were coordinated to gallium octacarboxy phthalocyanine (ClGaPc(COOH)8) to form ClGaPc(COOH)8-QDs conjugates. An efficient transfer of energy from the QDs to the Pcs was demonstrated through Förster resonance energy transfer (FRET), the FRET efficiencies in all cases was above 50%. The photophysical parameters (triplet state and fluorescence quantum yields and lifetimes) were also determined for the conjugates. There was a decrease in the fluorescence lifetimes of ClGaPc(COOH)8 in the presence of all the QDs, due to the heavy atom effect. The triplet quantum yields increased in the conjugates. The lifetimes also became longer for the conjugates compared to Pc alone.
Electrical Properties of InAs/InGaAs/GaAs Quantum-Dot Infrared Photodetectors
NASA Astrophysics Data System (ADS)
Kim, Jin Soak; Kim, Eun Kyu; Choi, Won Jun; Song, Jin Dong; Lee, Jung Il
2006-06-01
The energy band structure and defect state of an InAs/InGaAs/GaAs quantum dot-infrared photodetector (QDIP) were characterized by performing capacitance-voltage and deep level transient spectroscopy measurements. We found a confined energy level of the InAs/InGaAs quantum dot in the InGaAs/GaAs quantum well. The confined energy in this QDIP structure was measured to be approximately 340 meV below the barrier edge which is located at the conduction band edge of the GaAs layer. This QDIP structure has also a point defect with an activation energy of 0.60 eV, which may be considered as an EL2 family in a GaAs material.
Role of Quantum Vibrations on the Structural, Electronic, and Optical Properties of 9-Methylguanine.
Law, Yu Kay; Hassanali, Ali A
2015-11-05
In this work, we report theoretical predictions of the UV-absorption spectra of 9-methylguanine using time dependent density functional theory (TDDFT). Molecular dynamics simulations of the hydrated DNA base are peformed using an empirical force field, Born-Oppenheimer ab initio molecular dynamics (AIMD), and finally path-integral AIMD to understand the role of the underlying electronic potential, solvation, and nuclear quantum vibrations on the absorption spectra. It is shown that the conformational distributions, including hydrogen bonding interactions, are perturbed by the inclusion of nuclear quantum effects, leading to significant changes in the total charge and dipole fluctuations of the DNA base. The calculated absorption spectra using the different sampling protocols shows that the inclusion of nuclear quantum effects causes a significant broadening and red shift of the spectra bringing it into closer agreement with experiments.
NASA Astrophysics Data System (ADS)
Baghdasaryan, D. A.; Kazaryan, E. M.; Sarkisyan, H. A.
2017-04-01
The electronic, optical and electrostatic properties of the spherical core/shell/shell quantum nanolayer with an off-centered impurity have been studied. Spherical nanolayers of both "small" and "large" radii have been considered in the framework of perturbation theory and the variational method. Photoionization cross-section that corresponds to the electron transitions from the impurity ground state to the size-quantized levels have been studied. The dependence of the photoionization cross section on the photon energy, impurity position and the geometrical parameters of the spherical nanolayer have been obtained. The electrostatic multipoles of the considered system have been investigated.
Electro-optical and dielectric properties of CdSe quantum dots and 6CHBT liquid crystals composites
Singh, U. B.; Pandey, M. B.; Dhar, R; Pandey, A. S.; Kumar, S.; Dabrowski, R.
2014-11-15
We have prepared the composites of a room temperature nematic liquid crystal namely 4-(trans-4-n-hexylcyclohexyl) isothiocyanatobenzoate (6CHBT) and Cadmium Selenide Quantum Dots (CdSe-QDs) and investigated their electro-optical and dielectric properties. Effect of dispersion of CdSe-QDs on various electro-optical and display parameters of host liquid crystalline material have been studied. Physical parameters, such as switching threshold voltage and splay elastic constant have been altered drastically for composites. Dispersion of QDs in a liquid crystals medium destabilizes nematic ordering of the host and decreases the nematic-to-isotropic transition temperature.
Electro-optical and dielectric properties of CdSe quantum dots and 6CHBT liquid crystals composites
NASA Astrophysics Data System (ADS)
Singh, U. B.; Dhar, R.; Pandey, A. S.; Kumar, S.; Dabrowski, R.; Pandey, M. B.
2014-11-01
We have prepared the composites of a room temperature nematic liquid crystal namely 4-(trans-4-n-hexylcyclohexyl) isothiocyanatobenzoate (6CHBT) and Cadmium Selenide Quantum Dots (CdSe-QDs) and investigated their electro-optical and dielectric properties. Effect of dispersion of CdSe-QDs on various electro-optical and display parameters of host liquid crystalline material have been studied. Physical parameters, such as switching threshold voltage and splay elastic constant have been altered drastically for composites. Dispersion of QDs in a liquid crystals medium destabilizes nematic ordering of the host and decreases the nematic-to-isotropic transition temperature.
NASA Astrophysics Data System (ADS)
Ramos, E.; Franco, R.; Silva-Valencia, J.; Figueira, M. S.
2014-11-01
We study thermoelectric transport properties through a gate defined T-coupled quantum dot, describing the system at base with the single impurity Anderson model (SIAM), whose corresponding Green's functions are calculated employing the finite correlation U atomic approach. We compute, with the linear approximation for the thermoelectric transport coefficients, the electrical and thermal conductance (G and K), the thermopower S, the product of the thermoelectric figure of merit and the temperature ZT, for all the regimes of the SIAM: empty quantum dot, intermediate valence, Kondo, and double occupation, at different temperatures; the treatment employed extends the results obtained for the limit of infinite U-Coulomb repulsion in the quantum dot, and has a many-body character, which is absent in Green's function descriptions that employ mean field approximations. Our main result connects the ZT behavior with the interplay between the thermopower and the violation of the Wiedemann-Franz relation; the results are in good agreement with other recent theoretical papers that employ the numerical renormalization group (NRG), different Green's function approximations, and some experimental reports.
Stránský, Pavel; Macek, Michal; Cejnar, Pavel
2014-06-15
Quantum systems with a finite number of freedom degrees f develop robust singularities in the energy spectrum of excited states as the system’s size increases to infinity. We analyze the general form of these singularities for low f, particularly f=2, clarifying the relation to classical stationary points of the corresponding potential. Signatures in the smoothed energy dependence of the quantum state density and in the flow of energy levels with an arbitrary control parameter are described along with the relevant thermodynamical consequences. The general analysis is illustrated with specific examples of excited-state singularities accompanying the first-order quantum phase transition. -- Highlights: •ESQPTs found in infinite-size limit of systems with low numbers of freedom degrees f. •ESQPTs related to non-analytical evolutions of classical phase–space properties. •ESQPT signatures analyzed for general f, particularly f=2, extending known case f=1. •ESQPT signatures identified in smoothened density and flow of energy spectrum. •ESQPTs shown to induce a new type of thermodynamic anomalies.
Multimode-singlemode-multimode fiber sensor for alcohol sensing application
NASA Astrophysics Data System (ADS)
Rofi'ah, Iftihatur; Hatta, A. M.; Sekartedjo, Sekartedjo
2016-11-01
Alcohol is volatile and flammable liquid which is soluble substances both on polar and non polar substances that has been used in some industrial sectors. Alcohol detection method now widely used one of them is the optical fiber sensor. In this paper used fiber optic sensor based on Multimode-Single-mode-Multimode (MSM) to detect alcohol solution at a concentration range of 0-3%. The working principle of sensor utilizes the modal interference between the core modes and the cladding modes, thus make the sensor sensitive to environmental changes. The result showed that characteristic of the sensor not affect the length of the single-mode fiber (SMF). We obtain that the sensor with a length of 5 mm of single-mode can sensing the alcohol with a sensitivity of 0.107 dB/v%.
Advanced Technology for Improved Quantum Device Properties Using Highly Strained Materials
1989-06-15
PREPARED BY: W.J. Schaff S.D. OffseyI DL)L.,C ;.. $T A H. Park At~pio-ved tc- ;p7ua~ic tel-e:a~o L.F. Eastman q uoig4 04 Table of Contents Page...Graded-Index Separate-Confinement Heterostructure Single Quantum Well Lasers Grown by Molecular Beam Epitaxy", S.D. Offsey, W.J. Schaff , P.J. Tasker, H...gle Confinement Single Quantum Well Lasers Grown by Molecular Beam Epitaxy", S.D. Offsey, W.J. Schaff , P.J. Tasker and L.F. Eastman, Device Research
Ab Initio Study on Atomic Structures and Physical Properties of CdSe Quantum Nanodots
2009-11-25
CdSe quantum dots , with magic number (( CdSe )13, ( CdSe )19, ( CdSe )33 and ( CdSe )34 ). Effects of organic ligand binding on the stability of CdSe as well...calculations of optical absorption spectra for CdSe quantum dots , with magic number (( CdSe )13, ( CdSe )19, ( CdSe )33 and ( CdSe )34 ), have been calculated in...1 AOARD-08-4037 Title of Proposed Project: Ab initio study on atomic structures and physical
Radu, A.; Kirakosyan, A. A.; Baghramyan, H. M.; Barseghyan, M. G.; Laroze, D.
2014-09-07
The influence of an intense laser field on one-electron states and intraband optical absorption coefficients is investigated in two-dimensional GaAs/Ga{sub 0.7}Al{sub 0.3}As quantum rings. An analytical expression of the effective lateral confining potential induced by the laser field is obtained. The one-electron energy spectrum and wave functions are found using the effective mass approximation and exact diagonalization technique. We have shown that changes in the incident light polarization lead to blue- or redshifts in the intraband optical absorption spectrum. Moreover, we found that only blueshift is obtained with increasing outer radius of the quantum ring.
Makhloufi, Hajer; Boonpeng, Poonyasiri; Mazzucato, Simone; Nicolai, Julien; Arnoult, Alexandre; Hungria, Teresa; Lacoste, Guy; Gatel, Christophe; Ponchet, Anne; Carrère, Hélène; Marie, Xavier; Fontaine, Chantal
2014-03-17
We have grown GaAsBi quantum wells by molecular beam epitaxy. We have studied the properties of a 7% Bi GaAsBi quantum well and their variation with thermal annealing. High-resolution X-ray diffraction, secondary ion mass spectrometry, and transmission electron microscopy have been employed to get some insight into its structural properties. Stationary and time-resolved photoluminescence shows that the quantum well emission, peaking at 1.23 μm at room temperature, can be improved by a rapid annealing at 650°C, while the use of a higher annealing temperature leads to emission degradation and blue-shifting due to the activation of non-radiative centers and bismuth diffusion from the quantum well.
NASA Astrophysics Data System (ADS)
Stapp, Henry P.
2012-05-01
Robert Griffiths has recently addressed, within the framework of a `consistent quantum theory' that he has developed, the issue of whether, as is often claimed, quantum mechanics entails a need for faster-than-light transfers of information over long distances. He argues that the putative proofs of this property that involve hidden variables include in their premises some essentially classical-physics-type assumptions that are not entailed by the precepts of quantum mechanics. Thus whatever is proved is not a feature of quantum mechanics, but is a property of a theory that tries to combine quantum theory with quasi-classical features that go beyond what is entailed by quantum theory itself. One cannot logically prove properties of a system by establishing, instead, properties of a system modified by adding properties alien to the original system. Hence Griffiths' rejection of hidden-variable-based proofs is logically warranted. Griffiths mentions the existence of a certain alternative proof that does not involve hidden variables, and that uses only macroscopically described observable properties. He notes that he had examined in his book proofs of this general kind, and concluded that they provide no evidence for nonlocal influences. But he did not examine the particular proof that he cites. An examination of that particular proof by the method specified by his `consistent quantum theory' shows that the cited proof is valid within that restrictive version of quantum theory. An added section responds to Griffiths' reply, which cites general possibilities of ambiguities that might make what is to be proved ill-defined, and hence render the pertinent `consistent framework' ill defined. But the vagaries that he cites do not upset the proof in question, which, both by its physical formulation and by explicit identification, specify the framework to be used. Griffiths confirms the validity of the proof insofar as that pertinent framework is used. The section also shows
Makarov, Nikolay Sergeevich; Guo, Shaojun; Isaienko, Oleksandr; ...
2016-02-16
Organic–inorganic lead-halide perovskites have been the subject of recent intense interest due to their unusually strong photovoltaic performance. A new addition to the perovskite family is all-inorganic Cs–Pb-halide perovskite nanocrystals, or quantum dots, fabricated via a moderate-temperature colloidal synthesis. While being only recently introduced to the research community, these nanomaterials have already shown promise for a range of applications from color-converting phosphors and light-emitting diodes to lasers, and even room-temperature single-photon sources. Knowledge of the optical properties of perovskite quantum dots still remains vastly incomplete. Here we apply various time-resolved spectroscopic techniques to conduct a comprehensive study of spectral andmore » dynamical characteristics of single- and multiexciton states in CsPbX3 nanocrystals with X being either Br, I, or their mixture. Specifically, we measure exciton radiative lifetimes, absorption cross-sections, and derive the degeneracies of the band-edge electron and hole states. We also characterize the rates of intraband cooling and nonradiative Auger recombination and evaluate the strength of exciton–exciton coupling. The overall conclusion of this work is that spectroscopic properties of Cs–Pb-halide quantum dots are largely similar to those of quantum dots of more traditional semiconductors such as CdSe and PbSe. At the same time, we observe some distinctions including, for example, an appreciable effect of the halide identity on radiative lifetimes, considerably shorter biexciton Auger lifetimes, and apparent deviation of their size dependence from the “universal volume scaling” previously observed for many traditional nanocrystal systems. The high efficiency of Auger decay in perovskite quantum dots is detrimental to their prospective applications in light-emitting devices and lasers. Furthermore, this points toward the need for the development of approaches for effective
Karkov, Hanne Sophie; Woo, James; Krogh, Berit Olsen; Ahmadian, Haleh; Cramer, Steven M
2015-12-24
This study describes the in silico design, surface property analyses, production and chromatographic evaluations of a diverse set of antibody Fab fragment variants. Based on previous findings, we hypothesized that the complementarity-determining regions (CDRs) constitute important binding sites for multimodal chromatographic ligands. Given that antibodies are highly diversified molecules and in particular the CDRs, we set out to examine the generality of this result. For this purpose, four different Fab fragments with different CDRs and/or framework regions of the variable domains were identified and related variants were designed in silico. The four Fab variant libraries were subsequently generated by site-directed mutagenesis and produced by recombinant expression and affinity purification to enable examination of their chromatographic retention behavior. The effects of geometric re-arrangement of the functional moieties on the multimodal resin ligands were also investigated with respect to Fab variant retention profiles by comparing two commercially available multimodal cation-exchange ligands, Capto MMC and Nuvia cPrime, and two novel multimodal ligand prototypes. Interestingly, the chromatographic data demonstrated distinct selectivity trends between the four Fab variant libraries. For three of the Fab libraries, the CDR regions appeared as major binding sites for all multimodal ligands. In contrast, the fourth Fab library displayed a distinctly different chromatographic behavior, where Nuvia cPrime and related multimodal ligand prototypes provided markedly improved selectivity over Capto MMC. Clearly, the results illustrate that the discriminating power of multimodal ligands differs between different Fab fragments. The results are promising indications that multimodal chromatography using the appropriate multimodal ligands can be employed in downstream bioprocessing for challenging selective separation of product related variants.
NASA Astrophysics Data System (ADS)
Sarkar, Sucharita; Ghosh, Arghya Pratim; Mandal, Arkajit; Ghosh, Manas
2016-02-01
The influence of anisotropy on various nonlinear optical (NLO) properties such as total optical absorption coefficient (TOAC), nonlinear optical rectification (NOR), second harmonic generation (SHG) and third harmonic generation (THG) of impurity doped quantum dots (QDs) have been investigated in presence and absence of noise. Noise has been applied to the system additively and multiplicatively. The impurity potential is modeled by a Gaussian function and the noise applied being Gaussian white noise. A perpendicular magnetic field emerges out as a confinement source and a static external electric field has been applied. Profiles of the optical properties have been monitored as a function of incident photon energy for different values of anisotropy. In this connection the role of mode of application of noise (additive/multiplicative) has also been analysed. The interplay between noise and anisotropy has been found to profoundly affect the NLO properties. The investigation reveals that there are only one or two anisotropy regimes (depending on the particular NLO property under consideration) where noise-induced enhancement of the NLO property can be realized. Thus, anisotropy appears to be the central parameter by which the noise-induced enhancement of NLO properties of doped QD systems can be tailored.
Barettin, Daniele Auf der Maur, Matthias; De Angelis, Roberta; Prosposito, Paolo; Casalboni, Mauro; Pecchia, Alessandro
2015-03-07
We report on numerical simulations of InP surface lateral quantum-dot molecules on In{sub 0.48}Ga{sub 0.52 }P buffer, using a model strictly derived by experimental results by extrapolation of the molecules shape from atomic force microscopy images. Our study has been inspired by the comparison of a photoluminescence spectrum of a high-density InP surface quantum dot sample with a numerical ensemble average given by a weighted sum of simulated single quantum-dot spectra. A lack of experimental optical response from the smaller dots of the sample is found to be due to strong inter-dot strain fields, which influence the optoelectronic properties of lateral quantum-dot molecules. Continuum electromechanical, k{sup →}·p{sup →} bandstructure, and optical calculations are presented for two different molecules, the first composed of two dots of nearly identical dimensions (homonuclear), the second of two dots with rather different sizes (heteronuclear). We show that in the homonuclear molecule the hydrostatic strain raises a potential barrier for the electrons in the connection zone between the dots, while conversely the holes do not experience any barrier, which considerably increases the coupling. Results for the heteronuclear molecule show instead that its dots do not appear as two separate and distinguishable structures, but as a single large dot, and no optical emission is observed in the range of higher energies where the smaller dot is supposed to emit. We believe that in samples of such a high density the smaller dots result as practically incorporated into bigger molecular structures, an effect strongly enforced by the inter-dot strain fields, and consequently it is not possible to experimentally obtain a separate optical emission from the smaller dots.
NASA Astrophysics Data System (ADS)
Majumder, Saikat; Ghosh, Amarnath; Roy, Bapita; Chakraborty, Rajib
2015-06-01
Multimode Interference (MMI) based on self imaging phenomenon is investigated using matrix approach. Experimentally MMI is verified using singlemode-multimode-singlemode and multimodesinglemode structures of optical fiber. The results obtained are also verified by BPM technique.
Comparisons of electronic transport properties computed via classical and quantum molecular dynamics
NASA Astrophysics Data System (ADS)
Whitley, Heather; Scullard, Christian; Benedict, Lorin; Desjarlais, Michael; Graziani, Frank; Cimarron Collaboration
2013-10-01
We have applied the ddcMD molecular dynamics (MD) code to the computation of the electrical conductivity and thermal conductivity of hydrogen plasmas at several points in phase space. Quantum mechanical effects on the electronic degrees of freedom are incorporated through the use of temperature-dependent statistical potentials. In order to examine the validity of this approach, we make comparisons with results from quantum MD simulations. We find that, while the electrical conductivities computed via classical MD are in reasonably good agreement with the quantum MD calculations, the thermal conductivity computed via classical MD is lower than the quantum MD result by a factor of 2-3. The Lorenz number determined from the classical MD is a factor of 2-3 lower than the Spitzer prediction. Similar discrepancies with Spitzer were also observed by Bernu and Hansen. LLNL-ABS-640881 This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC.
ERIC Educational Resources Information Center
Niketic, Nemanja; Milanovic, Vitomir; Radovanovic, Jelena
2012-01-01
In this paper we provide a detailed analysis of the energy position and type of transmission maxima in rectangular quantum wells (QWs), taking into consideration the difference of electron effective masses in the barrier and well layers. Particular attention is given to transmission maxima that are less than unity and the implications of effective…
Quantum Monte Carlo with density matrix: potential energy curve derived properties.
Bonfim, Víctor S; Borges, Nádia M; Martins, João B L; Gargano, Ricardo; Politi, José Roberto Dos S
2017-04-01
In this work, we used diffusion quantum Monte Carlo with density matrix (d-DMC) and variational quantum Monte Carlo (d-VMC) to determine the potential energy curve (PEC) and obtain the spectroscopic constants of H2 molecule in the ground state, in order to evaluate the capability of these methods to provide an accurate PEC description. These quantum Monte Carlo methods build with density matrix are new approaches to conventional quantum Monte Carlo methods based on wave function formed by product of α and β determinants. To investigate the robustness of d-DMC, we performed calculations with two different basis sets and analyzed the influence of the size of these sets on results. To the best of our knowledge, this is the first study that shows the dissociation energy and rotational constant obtained from d-QMC. We found that the quality of PEC described by the d-DMC is essentially coincident with the most accurate results available in the literature, regardless of the complexity of basis set employed.
Cho, Myungje; Lim, Kipil; Woo, Kyoungja
2010-08-14
We present colloidal silica microspheres encapsulating a homogeneous quantum dot layer at radial equidistance from the centre by utilizing electrostatic interaction between surface-engineered silica microspheres and QDs. The microspheres show dramatically enhanced optical absorption and emission with an appropriate silica shell thickness.
Quantum correlation of an optically controlled open quantum system
NASA Astrophysics Data System (ADS)
Chan, Ching-Kit; Sham, L. J.
2012-02-01
A precise time-dependent optical control of an open quantum system relies on an accurate account of the quantum interference among the system, the photon control and the dissipative environment. In the spirit of the Keldysh non-equilibrium Green's function approach, we develop a diagrammatic technique to precisely calculate this quantum correlation for a fast multimode coherent photon control against slow relaxation, valid for both Markovian and non-Markovian systems. We demonstrate how this novel formalism can lead to a better accuracy than existing approximations of the master equation. We also describe extensions to cases with controls by photon state other than the coherent Glauber state.
Quantum Fidelity for Arbitrary Gaussian States.
Banchi, Leonardo; Braunstein, Samuel L; Pirandola, Stefano
2015-12-31
We derive a computable analytical formula for the quantum fidelity between two arbitrary multimode Gaussian states which is simply expressed in terms of their first- and second-order statistical moments. We also show how such a formula can be written in terms of symplectic invariants and used to derive closed forms for a variety of basic quantities and tools, such as the Bures metric, the quantum Fisher information, and various fidelity-based bounds. Our result can be used to extend the study of continuous-variable protocols, such as quantum teleportation and cloning, beyond the current one-mode or two-mode analyses, and paves the way to solve general problems in quantum metrology and quantum hypothesis testing with arbitrary multimode Gaussian resources.
Quantum Fidelity for Arbitrary Gaussian States
NASA Astrophysics Data System (ADS)
Banchi, Leonardo; Braunstein, Samuel L.; Pirandola, Stefano
2015-12-01
We derive a computable analytical formula for the quantum fidelity between two arbitrary multimode Gaussian states which is simply expressed in terms of their first- and second-order statistical moments. We also show how such a formula can be written in terms of symplectic invariants and used to derive closed forms for a variety of basic quantities and tools, such as the Bures metric, the quantum Fisher information, and various fidelity-based bounds. Our result can be used to extend the study of continuous-variable protocols, such as quantum teleportation and cloning, beyond the current one-mode or two-mode analyses, and paves the way to solve general problems in quantum metrology and quantum hypothesis testing with arbitrary multimode Gaussian resources.
One-way quantum computing in the optical frequency comb.
Menicucci, Nicolas C; Flammia, Steven T; Pfister, Olivier
2008-09-26
One-way quantum computing allows any quantum algorithm to be implemented easily using just measurements. The difficult part is creating the universal resource, a cluster state, on which the measurements are made. We propose a scalable method that uses a single, multimode optical parametric oscillator (OPO). The method is very efficient and generates a continuous-variable cluster state, universal for quantum computation, with quantum information encoded in the quadratures of the optical frequency comb of the OPO.
NASA Astrophysics Data System (ADS)
Tartakovskii, Alexander
2012-07-01
Part I. Nanostructure Design and Structural Properties of Epitaxially Grown Quantum Dots and Nanowires: 1. Growth of III/V semiconductor quantum dots C. Schneider, S. Hofling and A. Forchel; 2. Single semiconductor quantum dots in nanowires: growth, optics, and devices M. E. Reimer, N. Akopian, M. Barkelid, G. Bulgarini, R. Heeres, M. Hocevar, B. J. Witek, E. Bakkers and V. Zwiller; 3. Atomic scale analysis of self-assembled quantum dots by cross-sectional scanning tunneling microscopy and atom probe tomography J. G. Keizer and P. M. Koenraad; Part II. Manipulation of Individual Quantum States in Quantum Dots Using Optical Techniques: 4. Studies of the hole spin in self-assembled quantum dots using optical techniques B. D. Gerardot and R. J. Warburton; 5. Resonance fluorescence from a single quantum dot A. N. Vamivakas, C. Matthiesen, Y. Zhao, C.-Y. Lu and M. Atature; 6. Coherent control of quantum dot excitons using ultra-fast optical techniques A. J. Ramsay and A. M. Fox; 7. Optical probing of holes in quantum dot molecules: structure, symmetry, and spin M. F. Doty and J. I. Climente; Part III. Optical Properties of Quantum Dots in Photonic Cavities and Plasmon-Coupled Dots: 8. Deterministic light-matter coupling using single quantum dots P. Senellart; 9. Quantum dots in photonic crystal cavities A. Faraon, D. Englund, I. Fushman, A. Majumdar and J. Vukovic; 10. Photon statistics in quantum dot micropillar emission M. Asmann and M. Bayer; 11. Nanoplasmonics with colloidal quantum dots V. Temnov and U. Woggon; Part IV. Quantum Dot Nano-Laboratory: Magnetic Ions and Nuclear Spins in a Dot: 12. Dynamics and optical control of an individual Mn spin in a quantum dot L. Besombes, C. Le Gall, H. Boukari and H. Mariette; 13. Optical spectroscopy of InAs/GaAs quantum dots doped with a single Mn atom O. Krebs and A. Lemaitre; 14. Nuclear spin effects in quantum dot optics B. Urbaszek, B. Eble, T. Amand and X. Marie; Part V. Electron Transport in Quantum Dots Fabricated by
NASA Astrophysics Data System (ADS)
Caspani, Lucia; Reimer, Christian; Kues, Michael; Roztocki, Piotr; Clerici, Matteo; Wetzel, Benjamin; Jestin, Yoann; Ferrera, Marcello; Peccianti, Marco; Pasquazi, Alessia; Razzari, Luca; Little, Brent E.; Chu, Sai T.; Moss, David J.; Morandotti, Roberto
2016-06-01
Recent developments in quantum photonics have initiated the process of bringing photonic-quantumbased systems out-of-the-lab and into real-world applications. As an example, devices to enable the exchange of a cryptographic key secured by the laws of quantum mechanics are already commercially available. In order to further boost this process, the next step is to transfer the results achieved by means of bulky and expensive setups into miniaturized and affordable devices. Integrated quantum photonics is exactly addressing this issue. In this paper, we briefly review the most recent advancements in the generation of quantum states of light on-chip. In particular, we focus on optical microcavities, as they can offer a solution to the problem of low efficiency that is characteristic of the materials typically used in integrated platforms. In addition, we show that specifically designed microcavities can also offer further advantages, such as compatibility with telecom standards (for exploiting existing fibre networks) and quantum memories (necessary to extend the communication distance), as well as giving a longitudinal multimode character for larger information transfer and processing. This last property (i.e., the increased dimensionality of the photon quantum state) is achieved through the ability to generate multiple photon pairs on a frequency comb, corresponding to the microcavity resonances. Further achievements include the possibility of fully exploiting the polarization degree of freedom, even for integrated devices. These results pave the way for the generation of integrated quantum frequency combs that, in turn, may find important applications toward the realization of a compact quantum-computing platform.
Nonlinear optics of multi-mode planar photonic crystal microcavities
NASA Astrophysics Data System (ADS)
McCutcheon, Murray William
The nonlinear properties of multi-mode InP and Si planar photonic crystal microcavities are investigated in experiments relevant to integrated schemes for classical and quantum optical information processing. Normally incident, short laser pulses are used to coherently initialize the relative phase and amplitudes of two modes of a single-missing-hole InP microcavity. The two modes are orthogonally polarized, and separated by less than the bandwidth of the ˜ 130 fs excitation pulses. The relative amplitudes of the two modes can be controlled by adjusting the polarization and the centre frequency of the excitation beam. Cross-polarized detection of the resonantly scattered light reveals a well-defined relative phase between the modes that is characteristic of their coherence. When the short-pulse excitation is used to coherently excite two modes in a three-hole line-defect (L3) InP microcavity, second-order harmonic radiation is observed due to the interactions of the resonant fields with the second-order nonlinear susceptibility (chi(2)) of the host InP slab. Second-harmonic and sum-frequency generated signals are observed due to the intra- and inter-mode nonlinear mixing of the microcavity fields. When a separate non-resonant pulse is focussed onto an InP microcavity, sum-frequency light is generated conditional to the resonant mode population of the microcavity. The conditionally generated signals can be tuned by tuning the frequency of the non-resonant pulse. All of the results can be explained with reference to the bulk chi(2) properties of the InP slab. While the transient, multi-mode response of the microcavities is harnessed with the short-pulse technique, a continuous wave excitation laser exploits the local-field enhancement intrinsic to these wavelength-scale microcavities. A single-mode InP L3-microcavity with Q = 3,800 is pumped on resonance with a CW laser, and the 2D pattern of far-field second-harmonic radiation is directly imaged. The second
Multi-Mode Broadband Patch Antenna
NASA Technical Reports Server (NTRS)
Romanofsky, Robert R. (Inventor)
2001-01-01
A multi-mode broad band patch antenna is provided that allows for the same aperture to be used at independent frequencies such as reception at 19 GHz and transmission at 29 GHz. Furthermore, the multi-mode broadband patch antenna provides a ferroelectric film that allows for tuning capability of the multi-mode broadband patch antenna over a relatively large tuning range. The alternative use of a semiconductor substrate permits reduced control voltages since the semiconductor functions as a counter electrode.
Multimodal CT in stroke imaging: new concepts.
Ledezma, Carlos J; Wintermark, Max
2009-01-01
A multimodal CT protocol provides a comprehensive noninvasive survey of acute stroke patients with accurate demonstration of the site of arterial occlusion and its hemodynamic tissue status. It combines widespread availability with the ability to provide functional characterization of cerebral ischemia, and could potentially allow more accurate selection of candidates for acute stroke reperfusion therapy. This article discusses the individual components of multimodal CT and addresses the potential role of a combined multimodal CT stroke protocol in acute stroke therapy.
Feng, Miao; Sun, Ruiqing; Zhan, Hongbing; Chen, Yu
2010-02-19
The implantation and growth of metal nanoparticles on graphene nanosheets (GNS) leads directly to severe damage to the regular structure of the graphene sheets, which disrupts the extended pi conjugation, resulting in an impaired device performance. In this paper, we describe a facile approach for achieving the lossless formation of graphene composite decorated with tiny cadmium sulfide quantum dots (QDs) with excellent nonlinear optical properties by using benzyl mercaptan (BM) as the interlinker. The mercapto substituent of BM binds to the CdS QDs during their nucleation and growth process, and then the phenyl comes into contact with the GNS via the pi-pi stacking interaction. Using this strategy, CdS QDs with an average diameter of 3 nm are uniformly dispersed over the surface of graphene, and the resulting QD-graphene composite exhibits excellent optical limiting properties, mainly contributed by nonlinear scattering and nonlinear absorption, upon both 532 and 1064 nm excitations, in the nanosecond laser pulse regime.
Ning, Feng; Tang, Li-Ming Zhang, Yong; Chen, Ke-Qiu
2013-12-14
We have used first principles methods to systematically investigate the quantum confinement effect on the electronic properties of zinc-blende (ZB) and wurtzite (WZ) InAs nanowires (NWs) with different orientations and diameters, and compared their electronic properties before and after pseudo-hydrogen passivation. The results show that the calculated carrier effective masses are dependent on the NW diameter, except for [110] ZB NWs, and the hole effective masses of [111] ZB NWs are larger than the electron effective masses when the NW diameter is ≥26 Å. The band alignments of [111] ZB and [0001] WZ NWs reveal that the effect of quantum confinement on the conduction bands is greater than on the valence bands, and the position of the valence band maximum level changes little with increasing NW diameter. The pseudo-hydrogen passivated NWs have larger band gaps than the corresponding unpassivated NWs. The carrier effective masses and mobilities can be adjusted by passivating the surface dangling bonds.
Li, Xin; Carravetta, Vincenzo; Li, Cui; Monti, Susanna; Rinkevicius, Zilvinas; Ågren, Hans
2016-07-12
Motivated by the growing importance of organometallic nanostructured materials and nanoparticles as microscopic devices for diagnostic and sensing applications, and by the recent considerable development in the simulation of such materials, we here choose a prototype system - para-nitroaniline (pNA) on gold nanoparticles - to demonstrate effective strategies for designing metal nanoparticles with organic conjugates from fundamental principles. We investigated the motion, adsorption mode, and physical chemistry properties of gold-pNA particles, increasing in size, through classical molecular dynamics (MD) simulations in connection with quantum chemistry (QC) calculations. We apply the quantum mechanics-capacitance molecular mechanics method [Z. Rinkevicius et al. J. Chem. Theory Comput. 2014, 10, 989] for calculations of the properties of the conjugate nanoparticles, where time dependent density functional theory is used for the QM part and a capacitance-polarizability parametrization of the MM part, where induced dipoles and charges by metallic charge transfer are considered. Dispersion and short-range repulsion forces are included as well. The scheme is applied to one- and two-photon absorption of gold-pNA clusters increasing in size toward the nanometer scale. Charge imaging of the surface introduces red-shifts both because of altered excitation energy dependence and variation of the relative intensity of the inherent states making up for the total band profile. For the smaller nanoparticles the difference in the crystal facets are important for the spectral outcome which is also influenced by the surrounding MM environment.
Jovanović, Svetlana P; Syrgiannis, Zois; Marković, Zoran M; Bonasera, Aurelio; Kepić, Dejan P; Budimir, Milica D; Milivojević, Dušan D; Spasojević, Vuk D; Dramićanin, Miroslav D; Pavlović, Vladimir B; Todorović Marković, Biljana M
2015-11-25
Herein, the ability of gamma irradiation to enhance the photoluminescence properties of graphene quantum dots (GQDs) was investigated. Different doses of γ-irradiation were used on GQDs to examine the way in which their structure and optical properties can be affected. The photoluminescence quantum yield was increased six times for the GQDs irradiated with high doses compared to the nonirradiated material. Both photoluminescence lifetime and values of optical band gap were increased with the dose of applied gamma irradiation. In addition, the exploitation of the gamma-irradiated GQDs as photosensitizers was examined by monitoring the production of singlet oxygen under UV illumination. The main outcome was that the GQDs irradiated at lower doses act as better photoproducers than the ones irradiated at higher doses. These results corroborate that the structural changes caused by gamma irradiation have a direct impact on GQD ability to produce singlet oxygen and their photostability under prolonged UV illumination. This makes low-dose irradiated GQDs promising candidates for photodynamic therapy.
NASA Astrophysics Data System (ADS)
Ratnesh, R. K.; Mehata, Mohan Singh
2017-02-01
We report two port synthesis of CdSe/CdS/ZnS core-multi-shell quantum dots (Q-dots) and their structural properties. The multi-shell structures of Q-dots were developed by using successive ionic layer adsorption and reaction (SILAR) technique. The obtained Q-dots show high crystallinity with the step-wise adjustment of lattice parameters in the radial direction. The size of the core and core-shell Q-dots estimated by transmission electron microscopy images and absorption spectra is about 3.4 and 5.3 nm, respectively. The water soluble Q-dots (scheme-1) were prepared by using ligand exchange method, and the effect of pH was discussed regarding the variation of quantum yield (QY). The decrease of a lifetime of core-multi-shell Q-dots with respect to core CdSe indicates that the shell growth may be tuned by the lifetimes. Thus, the study clearly demonstrates that the core-shell approach can be used to substantially improve the optical properties of Q-dots desired for various applications.
Quantum-size effect on the electronic and optical properties of hybrid TiO{sub 2}/Au clusters
Liu, Chun-Sheng E-mail: yexiaojuan1980@gmail.com; Wang, Xiangfu; Yan, Xiaohong; Ye, Xiaojuan E-mail: yexiaojuan1980@gmail.com; Zeng, Zhi
2014-08-07
Although TiO{sub 2}/Au nanosystems exhibit high photocatalytic activities under solar radiation in the experiment, the quantum-size effect of TiO{sub 2} on the growth, electronic properties, and reactivity of Au clusters remains elusive. Using (time dependent) density functional theory, it is found that Au atoms attach to low-coordinated Ti and O atoms and serve as seeds for the growth of Au clusters, and the electronic (optical) properties of hybrid Au-TiO{sub 2} nano-clusters depend strongly upon the type of supported Au clusters. Interestingly, decorating TiO{sub 2} nano-particles with even-numbered Au clusters (Au{sub 8} or Au{sub 10}) can enhance the photocatalytic activity by: (i) spatially separating electron and hole states and (ii) balancing redox strength and visible light absorption. Furthermore, the interactions between the Au-TiO{sub 2} clusters and a single water molecule have been studied. It will open up new avenues for exploring controlled photocatalysts in semiconductor-based quantum-confined systems.
NASA Astrophysics Data System (ADS)
Morton, Seth Michael; Jensen, Lasse
2010-08-01
A new polarizable quantum mechanics/molecular mechanics method for the calculation of response properties of molecules adsorbed on metal nanoparticles is presented. This method, which we denote the discrete interaction model/quantum mechanics (DIM/QM) method, represents the nanoparticle atomistically which enables the modeling of the influence of the local environment of a nanoparticle surface on the optical properties of a molecule. Using DIM/QM, we investigate the excitation energies of rhodamine-6G (R6G) and crystal violet (CV) adsorbed on silver and gold nanoparticles of different quasispherical shapes and sizes. The metal nanoparticle is characterized by its static total polarizability, a reasonable approximation for frequencies far from the plasmon resonance. We observe that for both R6G and CV, the presence of the nanoparticle shifts the strongest excitation to the red ˜40 nm and also increases the oscillator strength of that excitation. The shifts in excitation energies due to the nanoparticle surface are found to be comparable to those due to solvation. We find that these shifts decay quickly as the molecule is moved away from the surface. We also find that the wavelength shift is largest when the transition dipole moment is aligned with the edges of the nanoparticle surface where the electric field is expected to be the largest. These results show that the molecular excitations are sensitive to the local environment on the nanoparticle as well as the specific orientation of the molecule relative to the surface.
NASA Astrophysics Data System (ADS)
Shahid, Robina; Muhammad, Nawshad; Gonfa, Girma; Toprak, Muhammet S.; Muhammed, Mamoun
2015-10-01
Zinc sulfide (ZnS) quantum dots (QDs) were synthesized using the microwave assisted ionic liquid (MAIL) route. Three ionic liquids (ILs), namely, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4]), trihexyl(tetradecyl) phosphonium bis(trifluoromethanesulfonyl) amide ([P6,6,6,14][TSFA]) and trihexyl(tetradecyl) phosphonium chloride ([P6,6,6,14][Cl]) were used in this study. The size and structure of the QDs were characterized by high-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) pattern, respectively. The synthesized QDs were of wurtzite crystalline structure with size less than 5 nm. The QDs were more uniformly distributed while using the phosponium based ILs as a reaction medium during synthesis. The optical properties were investigated by UV-vis absorption and photoluminescence (PL) emission spectroscopy. The optical properties of QDs showed the quantum confinement effect in their absorption and the effect of cation and anion structural moiety was observed on their bandedge emission. The QDs emission intensity was measured higher for [P6,6,6,14][Cl] due to their better dispersion as well as high charge density of Cl anion. The capability of the ILs in stabilizing the QDs was interpreted by density functional theory (DFT) computations. The obtained results are in good agreement with the theoretical prediction.
Quantum-size effect on the electronic and optical properties of hybrid TiO2/Au clusters
NASA Astrophysics Data System (ADS)
Liu, Chun-Sheng; Ye, Xiaojuan; Wang, Xiangfu; Yan, Xiaohong; Zeng, Zhi
2014-08-01
Although TiO2/Au nanosystems exhibit high photocatalytic activities under solar radiation in the experiment, the quantum-size effect of TiO2 on the growth, electronic properties, and reactivity of Au clusters remains elusive. Using (time dependent) density functional theory, it is found that Au atoms attach to low-coordinated Ti and O atoms and serve as seeds for the growth of Au clusters, and the electronic (optical) properties of hybrid Au-TiO2 nano-clusters depend strongly upon the type of supported Au clusters. Interestingly, decorating TiO2 nano-particles with even-numbered Au clusters (Au8 or Au10) can enhance the photocatalytic activity by: (i) spatially separating electron and hole states and (ii) balancing redox strength and visible light absorption. Furthermore, the interactions between the Au-TiO2 clusters and a single water molecule have been studied. It will open up new avenues for exploring controlled photocatalysts in semiconductor-based quantum-confined systems.
Quantum-size effect on the electronic and optical properties of hybrid TiO₂/Au clusters.
Liu, Chun-Sheng; Ye, Xiaojuan; Wang, Xiangfu; Yan, Xiaohong; Zeng, Zhi
2014-08-07
Although TiO2/Au nanosystems exhibit high photocatalytic activities under solar radiation in the experiment, the quantum-size effect of TiO2 on the growth, electronic properties, and reactivity of Au clusters remains elusive. Using (time dependent) density functional theory, it is found that Au atoms attach to low-coordinated Ti and O atoms and serve as seeds for the growth of Au clusters, and the electronic (optical) properties of hybrid Au-TiO2 nano-clusters depend strongly upon the type of supported Au clusters. Interestingly, decorating TiO2 nano-particles with even-numbered Au clusters (Au8 or Au10) can enhance the photocatalytic activity by: (i) spatially separating electron and hole states and (ii) balancing redox strength and visible light absorption. Furthermore, the interactions between the Au-TiO2 clusters and a single water molecule have been studied. It will open up new avenues for exploring controlled photocatalysts in semiconductor-based quantum-confined systems.
Multimodal Estimation of Distribution Algorithms.
Yang, Qiang; Chen, Wei-Neng; Li, Yun; Chen, C L Philip; Xu, Xiang-Min; Zhang, Jun
2016-02-15
Taking the advantage of estimation of distribution algorithms (EDAs) in preserving high diversity, this paper proposes a multimodal EDA. Integrated with clustering strategies for crowding and speciation, two versions of this algorithm are developed, which operate at the niche level. Then these two algorithms are equipped with three distinctive techniques: 1) a dynamic cluster sizing strategy; 2) an alternative utilization of Gaussian and Cauchy distributions to generate offspring; and 3) an adaptive local search. The dynamic cluster sizing affords a potential balance between exploration and exploitation and reduces the sensitivity to the cluster size in the niching methods. Taking advantages of Gaussian and Cauchy distributions, we generate the offspring at the niche level through alternatively using these two distributions. Such utilization can also potentially offer a balance between exploration and exploitation. Further, solution accuracy is enhanced through a new local search scheme probabilistically conducted around seeds of niches with probabilities determined self-adaptively according to fitness values of these seeds. Extensive experiments conducted on 20 benchmark multimodal problems confirm that both algorithms can achieve competitive performance compared with several state-of-the-art multimodal algorithms, which is supported by nonparametric tests. Especially, the proposed algorithms are very promising for complex problems with many local optima.
Advances in multimodality molecular imaging
Zaidi, Habib; Prasad, Rameshwar
2009-01-01
Multimodality molecular imaging using high resolution positron emission tomography (PET) combined with other modalities is now playing a pivotal role in basic and clinical research. The introduction of combined PET/CT systems in clinical setting has revolutionized the practice of diagnostic imaging. The complementarity between the intrinsically aligned anatomic (CT) and functional or metabolic (PET) information provided in a “one-stop shop” and the possibility to use CT images for attenuation correction of the PET data has been the driving force behind the success of this technology. On the other hand, combining PET with Magnetic Resonance Imaging (MRI) in a single gantry is technically more challenging owing to the strong magnetic fields. Nevertheless, significant progress has been made resulting in the design of few preclinical PET systems and one human prototype dedicated for simultaneous PET/MR brain imaging. This paper discusses recent advances in PET instrumentation and the advantages and challenges of multimodality imaging systems. Future opportunities and the challenges facing the adoption of multimodality imaging instrumentation will also be addressed. PMID:20098557
Radioactive Nanomaterials for Multimodality Imaging
Chen, Daiqin; Dougherty, Casey A.; Yang, Dongzhi; Wu, Hongwei; Hong, Hao
2016-01-01
Nuclear imaging techniques, including primarily positron emission tomography (PET) and single-photon emission computed tomography (SPECT), can provide quantitative information for a biological event in vivo with ultra-high sensitivity, however, the comparatively low spatial resolution is their major limitation in clinical application. By convergence of nuclear imaging with other imaging modalities like computed tomography (CT), magnetic resonance imaging (MRI) and optical imaging, the hybrid imaging platforms can overcome the limitations from each individual imaging technique. Possessing versatile chemical linking ability and good cargo-loading capacity, radioactive nanomaterials can serve as ideal imaging contrast agents. In this review, we provide a brief overview about current state-of-the-art applications of radioactive nanomaterials in the circumstances of multimodality imaging. We present strategies for incorporation of radioisotope(s) into nanomaterials along with applications of radioactive nanomaterials in multimodal imaging. Advantages and limitations of radioactive nanomaterials for multimodal imaging applications are discussed. Finally, a future perspective of possible radioactive nanomaterial utilization is presented for improving diagnosis and patient management in a variety of diseases. PMID:27227167
NASA Astrophysics Data System (ADS)
Pancholi, Anup
The last few years have seen rapid advances in nanoscience and nanotechnology, allowing unprecedented manipulation of nanostructures controlling solar energy capture, conversion, and storage. Quantum confined nanostructures, such as quantum wells (QWs) and quantum dots (QDs) have been projected as potential candidates for the implementation of some high efficiency photovoltaic device concepts, including the intermediate band solar cell (IBSC). In this dissertation research, we investigated multiple inter-related themes, with the main objective of providing a deeper understanding of the physical and optical properties of QD structures relevant to the IBSC concept. These themes are: (i) Quantum engineering and control of energy levels in QDs, via a detailed study of the electronic coupling in multilayer QD structures; (ii) Controlled synthesis of well-organized, good quality, high volume density, and uniform-size QD arrays, in order to maximize the absorption efficiency and to ensure the coupling between the dots and the formation of the minibands; and (iii) Characterization of carrier dynamics and development of techniques to enhance the charge transport and efficient light harvesting. A major issue in a QD-based IBSC is the occurrence of charge trapping, followed by recombination in the dots, which results in fewer carriers being collected and hence low quantum efficiency. In order to collect most of the light-generated carriers, long radiative lifetimes, higher mobilities, and a lower probability of non-radiative recombination events in the solar cell would be desirable. QD size-dependent radiative lifetime and electronic coupling in multilayer QD structures were studied using photoluminescence (PL) and time-resolved photoluminescence (TRPL). For the uncoupled QD structures with thick barriers between the adjacent QD layers, the radiative lifetime was found to increase with the QD size, which was attributed to increased oscillator strength in smaller size dots. On
Wegele, Tatjana; Beyer, Andreas; Gies, Sebastian; Zimprich, Martin; Heimbrodt, Wolfram; Stolz, Wolfgang; Volz, Kerstin
2016-01-14
Ga(NAsP) quantum wells grown pseudomorphically on Si substrate are promising candidates for optically active light sources in future optoelectronically integrated circuits on Si substrates. As the material is typically grown at low temperatures, it has to be thermally annealed after growth to remove defects and optimize optoelectronic properties. Here we show by quantitative transmission electron microscopy that two different kinds of structural development are associated with the annealing. First of all, the quantum well homogeneity improves with increasing annealing temperature. For annealing temperatures above 925 °C the composition becomes less homogeneous again. Second, voids form in the quantum well for annealing temperatures above 850 °C. Their density and size increase continuously with increasing annealing temperature. These results are correlated to the optical properties of the samples, where we find from temperature-dependent photoluminescence measurements two scales of disorder, which show the same temperature dependence as the structural properties.
Transport properties of continuous-time quantum walks on Sierpinski fractals.
Darázs, Zoltán; Anishchenko, Anastasiia; Kiss, Tamás; Blumen, Alexander; Mülken, Oliver
2014-09-01
We model quantum transport, described by continuous-time quantum walks (CTQWs), on deterministic Sierpinski fractals, differentiating between Sierpinski gaskets and Sierpinski carpets, along with their dual structures. The transport efficiencies are defined in terms of the exact and the average return probabilities, as well as by the mean survival probability when absorbing traps are present. In the case of gaskets, localization can be identified already for small networks (generations). For carpets, our numerical results indicate a trend towards localization, but only for relatively large structures. The comparison of gaskets and carpets further implies that, distinct from the corresponding classical continuous-time random walk, the spectral dimension does not fully determine the evolution of the CTQW.
Can, T; Chiu, Y H; Laskin, M; Wiegmann, P
2016-12-23
We study quantum Hall states on surfaces with conical singularities. We show that the electronic fluid at the cone tip possesses an intrinsic angular momentum, which is due solely to the gravitational anomaly. We also show that quantum Hall states behave as conformal primaries near singular points, with a conformal dimension equal to the angular momentum. Finally, we argue that the gravitational anomaly and conformal dimension determine the fine structure of the electronic density at the conical point. The singularities emerge as quasiparticles with spin and exchange statistics arising from adiabatically braiding conical singularities. Thus, the gravitational anomaly, which appears as a finite size correction on smooth surfaces, dominates geometric transport on singular surfaces.
Laser and Optical Properties of Green-Emitting ZnCdSe Quantum Dot Based Heterostructures
NASA Astrophysics Data System (ADS)
Vainilovich, Aliaksei G.; Lutsenko, E. V.; Yablonskii, G. P.; Sedova, I. V.; Sorokin, S. V.; Gronin, S. V.; Ivanov, S. V.; Kop'ev, P. S.
Green-emitting laser diodes are in great demand for mobile projection media (pico-projector), navigation, underwater communication but they are still absent on the market. InGaN/GaN-based quantum well structures are approaching green spectral region by use of polar, semipolar as well as free-standing GaN substrates. However such heterostructures suffer from high laser thresholds with increase of indium content. A promising alternative way is the use of highly efficient green-emitting undoped ZnCdSe based quantum dot (QD) laser heterostructures optically pumped by blue InGaN laser diodes. Operation of blue-green laser converter based on MBE grown heterostructure with two ZnCdSe QD layers was shown for the first time in [1].
A potential from quantum chemistry for thermodynamic property predictions for methanethiol.
Garrison, Stephen L; Sandler, Stanley I
2005-08-01
An ab initio potential for methanethiol is determined by computing quantum-chemical interaction energies for a range of orientations and center-of-mass separation distances. These energies are initially fitted to a pairwise-additive, site-site Morse-C6 intermolecular potential. Additional interaction energies were then calculated at separation distances determined to be important from the angle-averaged Mayer f function calculated with the initial potential. This expanded set of interaction energies is then fitted using Boltzmann-type weighting to obtain the final intermolecular potential. Although there are some discrepancies in the fit for a particular type of orientation, the phase behavior calculated from Gibbs ensemble Monte Carlo simulations using this final potential is in very good agreement with experimental data. The prescription used here for obtaining the optimum potential from quantum-chemical methods should be applicable to other systems.
A potential from quantum chemistry for thermodynamic property predictions for methanethiol
NASA Astrophysics Data System (ADS)
Garrison, Stephen L.; Sandler, Stanley I.
2005-08-01
An ab initio potential for methanethiol is determined by computing quantum-chemical interaction energies for a range of orientations and center-of-mass separation distances. These energies are initially fitted to a pairwise-additive, site-site Morse-C6 intermolecular potential. Additional interaction energies were then calculated at separation distances determined to be important from the angle-averaged Mayer f function calculated with the initial potential. This expanded set of interaction energies is then fitted using Boltzmann-type weighting to obtain the final intermolecular potential. Although there are some discrepancies in the fit for a particular type of orientation, the phase behavior calculated from Gibbs ensemble Monte Carlo simulations using this final potential is in very good agreement with experimental data. The prescription used here for obtaining the optimum potential from quantum-chemical methods should be applicable to other systems.
NASA Astrophysics Data System (ADS)
Bishop, S. A.; Ayoola, E. O.
2016-03-01
In this paper, we establish results on continuous mappings of the space of the matrix elements of an arbitrary nonempty set of pseudo solutions of non Lipschitz quantum Stochastic differential inclusion (QSDI) into the space of the matrix elements of its solutions. we show that under the non Lipschitz condition, the space of the matrix elements of solutions is still an absolute retract, contractible, locally and integrally connected in an arbitrary dimension. The results here generalize existing results in the literature.
Quantum properties of the radiation emitted by a conductor in the Coulomb blockade regime
NASA Astrophysics Data System (ADS)
Mora, C.; Altimiras, C.; Joyez, P.; Portier, F.
2017-03-01
We present an input-output formalism describing a tunnel junction strongly coupled to its electromagnetic environment. We exploit it in order to investigate the dynamics of the radiation being emitted and scattered by the junction. We find that the nonlinearity imprinted in the electronic transport by a properly designed environment generates strongly squeezed radiation. Our results show that the interaction between a quantum conductor and electromagnetic fields can be exploited as a resource to design simple sources of nonclassical radiation.
Zhu, X; Schülzgen, A; Li, H; Li, L; Han, L; Moloney, J V; Peyghambarian, N
2008-10-13
Properties of the self-imaging effect based on multimode interference (MMI) in large-core passive optical fibers are investigated and analyzed in detail, with the purpose of using multimode active fibers for high power single-transverse-mode emission. Although perfect self-imaging of the input field from a standard single-mode fiber (SMF-28) in a multimode fiber becomes practically impossible as its core diameter is larger than 50 microm, a quasi-reproduction of the input field occurs when the phase difference between the excited modes and the peak mode inside the multimode fiber is very small. Our simulation and experimental results indicate that, if the length of the multimode fiber segment can be controlled accurately, reproduction of the input field with a self-imaging quality factor larger than 0.9 can be obtained. In this case, a low-loss hybrid fiber cavity composed of a SMF-28 segment and a very-large-core active multimode fiber segment can be built. It is also found that for the hybrid fiber cavity, increasing the mode-field diameter of the single-mode fiber improves both the self-imaging quality and the tolerance on the required length accuracy of the multimode fiber segment. Moreover, in this paper key parameters for the design of MMI-based fiber devices are defined and their corresponding values are provided for multimode fibers with core diameters of 50 microm and 105 microm.
Zhao, Jing-Ya; Chen, Gang; Gu, Yi-Ping; Cui, Ran; Zhang, Zhi-Ling; Yu, Zi-Li; Tang, Bo; Zhao, Yi-Fang; Pang, Dai-Wen
2016-02-17
Cell-derived microvesicles (MVs) are natural carriers that can transport biological molecules between cells, which are expected to be promising delivery vehicles for therapeutic purposes. Strategies to label MVs are very important for investigation and application of MVs. Herein, ultrasmall Mn-magnetofunctionalized Ag2Se quantum dots (Ag2Se@Mn QDs) integrated with excellent near-infrared (NIR) fluorescence and magnetic resonance (MR) imaging capabilities have been developed for instant efficient labeling of MVs for their in vivo high-resolution dual-mode tracking. The Ag2Se@Mn QDs were fabricated by controlling the reaction of Mn(2+) with the Ag2Se nanocrystals having been pretreated in 80 °C NaOH solution, with an ultrasmall size of ca. 1.8 nm, water dispersibility, high NIR fluorescence quantum yield of 13.2%, and high longitudinal relaxivity of 12.87 mM(-1) s(-1) (almost four times that of the commercial contrast agent Gd-DTPA). The ultrasmall size of the Ag2Se@Mn QDs enables them to be directly and efficiently loaded into MVs by electroporation, instantly and reliably conferring both NIR fluorescence and MR traceability on MVs. Our method for labeling MVs of different origins is universal and free of unfavorable influence on intrinsic behaviors of MVs. The complementary imaging capabilities of the Ag2Se@Mn QDs have made the long-term noninvasive whole-body high-resolution dual-mode tracking of MVs in vivo realized, by which the dynamic biodistribution of MVs has been revealed in a real-time and in situ quantitative manner. This work not only opens a new window for labeling with QDs, but also facilitates greatly the investigation and application of MVs.
Wu, Yinghua; Herman, Michael F
2007-07-28
A previously developed nonadiabatic semiclassical surface hopping propagator [M. F. Herman J. Chem. Phys. 103, 8081 (1995)] is further studied. The propagator has been shown to satisfy the time-dependent Schrodinger equation (TDSE) through order h, and the O(h2) terms are treated as small errors, consistent with standard semiclassical analysis. Energy is conserved at each hopping point and the change in momentum accompanying each hop is parallel to the direction of the nonadiabatic coupling vector resulting in both transmission and reflection types of hops. Quantum mechanical analysis and numerical calculations presented in this paper show that the h2 terms involving the interstate coupling functions have significant effects on the quantum transition probabilities. Motivated by these data, the h2 terms are analyzed for the nonadiabatic semiclassical propagator. It is shown that the propagator can satisfy the TDSE for multidimensional systems by including another type of nonclassical trajectories that reflect on the same surfaces. This h2 analysis gives three conditions for these three types of trajectories so that their coefficients are uniquely determined. Besides the nonadiabatic semiclassical propagator, a numerically useful quantum propagator in the adiabatic representation is developed to describe nonadiabatic transitions.
NASA Astrophysics Data System (ADS)
Ly, Sonny
Generation of quantum optical states from ultrashort laser-molecule interactions have led to fascinating discoveries in physics and chemistry. In recent years, these interactions have been extended to probe phenomena in single molecule biophysics. Photons emitted from a single fluorescent molecule contains important properties about how the molecule behave and function in that particular environment. Analysis of the second order coherence function through fluorescence correlation spectroscopy plays a pivotal role in quantum optics. At very short nanosecond timescales, the coherence function predicts photon antibunching, a purely quantum optical phenomena which states that a single molecule can only emit one photon at a time. Photon antibunching is the only direct proof of single molecule emission. From the nanosecond to microsecond timescale, the coherence function gives information about rotational diffusion coefficients, and at longer millisecond timescales, gives information regarding the translational diffusion coefficients. In addition, energy transfer between molecules from dipole-dipole interaction results in FRET, a highly sensitive method to probe conformational dynamics at nanometer distances. Here I apply the quantum optical techniques of photon antibunching, fluorescence correlation spectroscopy and FRET to probe how lipid nanodiscs form and function at the single molecule level. Lipid nanodiscs are particles that contain two apolipoprotein (apo) A-I circumventing a lipid bilayer in a belt conformation. From a technological point of view, nanodiscs mimics a patch of cell membrane that have recently been used to reconstitute a variety of membrane proteins including cytochrome P450 and bacteriorhodopsin. They are also potential drug transport vehicles due to its small and stable 10nm diameter size. Biologically, nanodiscs resemble to high degree, high density lipoproteins (HDL) in our body and provides a model platform to study lipid-protein interactions
Gasparyan, V K
2014-09-01
Effects of various factors on synthesis and fluorescent properties of CdSe quantum dots were studied. It was shown that variation of pH, stabilizer and concentration of precursors brings to obtaining of quantum dots with various fluorescent properties. The nanoparticles prepared were conjugated with rabbit antibodies to C-Reactive protein and C-Reactive protein for competitive immunoassay for determination of CRP. It was shown that interaction of these dots as a result of antigen-antibody reaction brings to resonance energy transfer and these changes in fluorescence spectra correlate with concentration of CRP. This approach permits to determine CRP in range between 4-100 ng.
NASA Astrophysics Data System (ADS)
Gong, Longyan; Zheng, Yongcui; Wang, Haihong; Cheng, Weiwen; Zhao, Shengmei
2014-09-01
Shannon information entropy (SE), concurrence (CC), quantum discord (QD) and localization properties for various one-dimensional one-electron wave functions are intensively studied, respectively. They include Gaussian functions, power-law functions, and functions in the Anderson model and the Harper ones. For all these wave functions, we find that SE, CC and QD increase as the localization length of a wave function increases, respectively. There are linear or quadratic relationships between two of them. Therefore, we can confirm for the analyzed models that SE, CC and QD are statistically equivalent quantities to reflect the localization properties of wave functions though they are different measures of quantum information.
NASA Astrophysics Data System (ADS)
Naquin, Clint Alan
Introducing explicit quantum transport into silicon (Si) transistors in a manner compatible with industrial fabrication has proven challenging, yet has the potential to transform the performance horizons of large scale integrated Si devices and circuits. Explicit quantum transport as evidenced by negative differential transconductances (NDTCs) has been observed in a set of quantum well (QW) n-channel metal-oxide-semiconductor (NMOS) transistors fabricated using industrial silicon complementary MOS processing. The QW potential was formed via lateral ion implantation doping on a commercial 45 nm technology node process line, and measurements of the transfer characteristics show NDTCs up to room temperature. Detailed gate length and temperature dependence characteristics of the NDTCs in these devices have been measured. Gate length dependence of NDTCs shows a correlation of the interface channel length with the number of NDTCs formed as well as with the gate voltage (VG) spacing between NDTCs. The VG spacing between multiple NDTCs suggests a quasi-parabolic QW potential profile. The temperature dependence is consistent with partial freeze-out of carrier concentration against a degenerately doped background. A folding amplifier frequency multiplier circuit using a single QW NMOS transistor to generate a folded current-voltage transfer function via a NDTC was demonstrated. Time domain data shows frequency doubling in the kHz range at room temperature, and Fourier analysis confirms that the output is dominated by the second harmonic of the input. De-embedding the circuit response characteristics from parasitic cable and contact impedances suggests that in the absence of parasitics the doubling bandwidth could be as high as 10 GHz in a monolithic integrated circuit, limited by the transresistance magnitude of the QW NMOS. This is the first example of a QW device fabricated by mainstream Si CMOS technology being used in a circuit application and establishes the feasibility
NASA Astrophysics Data System (ADS)
Benchamekh, R.; Schulz, S.; O'Reilly, E. P.
2016-09-01
We use an s p3d5s* tight-binding model to investigate the electronic and optical properties of realistic site-controlled (111)-oriented InGaAs/GaAs quantum dots. Special attention is paid to the impact of random alloy fluctuations on several factors that determine the fine-structure splitting in these systems. Using a pure InAs/GaAs quantum dot as a reference system, we show that the combination of spin-orbit coupling and biaxial strain effects can lead to sizable spin-splitting effects in these systems. Then, a realistic alloyed InGaAs/GaAs quantum dot with 25% InAs content is studied. Our analysis reveals that the impact of random alloy fluctuations on the electronic and optical properties of (111)-oriented InGaAs/GaAs quantum dots reduces strongly as the lateral size of the dot increases and approaches realistic sizes. For instance the optical matrix element shows an almost vanishing anisotropy in the (111)-growth plane. Furthermore, conduction and valence band mixing effects in the system under consideration are strongly reduced compared to standard (100)-oriented InGaAs/GaAs systems. All these factors indicate a reduced fine-structure splitting in site-controlled (111)-oriented InGaAs/GaAs quantum dots. Thus, we conclude that quantum dots with realistic (50-80 nm) base length represent promising candidates for polarization-entangled-photon generation, consistent with recent experimental data.
NASA Astrophysics Data System (ADS)
Wang, Yongbo; Si, Boni; Lu, Siwu; Ma, Xuan; Liu, Enzhou; Fan, Jun; Li, Xinghua; Hu, Xiaoyun
2016-09-01
Efficient synthesis of high-quality quantum dots (QDs) with excellent optical properties by aqueous synthesis is still of great significance for extended optical applications. Herein we highlight the advantages in optical properties of colloidal CdTe@ZnS QDs prepared by a facile and highly effective aqueous synthesis method. These achievements were realized by delicate manipulation of the conditions involved in nucleation and the growth process. Transmission electron microscopy (TEM) images indicated the QDs were uniform size and well dispersible. The emission peaks of the as-prepared QDs could shift from 496 to 698 nm with narrow full width at half maximum (FWHM), and the corresponding fluorescent color changed from green to red. Moreover, the emission could even reach to the near-infrared (NIR) region (706-796 nm) by extending the reaction time. The highest photoluminescence (PL) quantum yield (QY) of the QDs could reach to 60%, and the average of FWHM was about 55 nm. To address the problem of wide size-distribution in PL QY decrease and FWHM broadening, the colloids of QDs prepared at long reaction time (above 3 h) were centrifuged (12 000 r min-1). In addition, the assessment of QD cytotoxicity indicated the CdTe@ZnS QDs were much less cytotoxic and showed good biocompatibility. Compared with organic synthesis, our aqueous synthesis of QDs could be carried out efficiently on a large scale and showed good batch-to-batch reproducibility. The as-prepared CdTe@ZnS QDs exhibited excellent optical properties and hold a good potential to be applied in optoelectronic and biological applications.
Angular momentum effects in multimodal fission of 226Th
NASA Astrophysics Data System (ADS)
Chubarian, G. G.; Hurst, B. J.; O'Kelly, D.; Schmitt, R. P.; Itkis, M. G.; Kondratiev, N. A.; Kozulin, E. M.; Oganessian, Yu. Ts.; Pashkevich, V. V.; Pokrovsky, I. V.; Salamatin, V. S.; Rusanov, A. Ya.; Calabretta, L.; Maiolino, C.; Lukashin, K.; Agodi, C.; Bellia, G.; Hanappe, F.; Liatard, E.; Huck, A.; Stuttgé, L.
1998-12-01
The γ-rays from the multimodal fission of the 226Th formed in 18O+208Pb was investigated at the near- and sub-barrier energies. The corresponding excitation energies at the saddle point, Esp*, ranged from 23 to 26 MeV. The average γ-ray multiplicities and relative γ-ray energies as a function of the mass of the fission fragments exhibits a complex structure and strong variations. Such strong variations have never been previously observed in heavy ion-induced fusion-fission reactions. Obtained results may be explained with the influence of shell effects on the properties of the fission fragments. Present work is the one in series of investigation of the multimodal fission phenomena in At-Th region.
Angular momentum effects in multimodal fission of {sup 226}Th
Chubarian, G.G.; Hurst, B.J.; OKelly, D.; Schmitt, R.P.; Itkis, M.G.; Kondratiev, N.A.; Kozulin, E.M.; Oganessian, Y.T.; Pashkevich, V.V.; Pokrovsky, I.V.; Salamatin, V.S.; Rusanov, A.Y.; Calabretta, L.; Maiolino, C.; Lukashin, K.; Agodi, C.; Bellia, G.; Hanappe, F.; Liatard, E.; Huck, A.; Stuttge, L.
1998-12-01
The {gamma}-rays from the multimodal fission of the {sup 226}Th formed in {sup 18}O+{sup 208}Pb was investigated at the near- and sub-barrier energies. The corresponding excitation energies at the saddle point, E{sub sp}{sup {asterisk}}, ranged from 23 to 26 MeV. The average {gamma}-ray multiplicities and relative {gamma}-ray energies as a function of the mass of the fission fragments exhibits a complex structure and strong variations. Such strong variations have never been previously observed in heavy ion-induced fusion-fission reactions. Obtained results may be explained with the influence of shell effects on the properties of the fission fragments. Present work is the one in series of investigation of the multimodal fission phenomena in At-Th region. {copyright} {ital 1998 American Institute of Physics.}
NASA Astrophysics Data System (ADS)
Shen, M. Y.; Goto, T.; Kurtz, E.; Zhu, Z.; Yao, T.
1998-03-01
The photoluminescence of single CdSe quantum dots in ZnSe grown by molecular beam epitaxy and that of the same system grown by atomic layer epitaxy were investigated. The spectral diffusion and on/off behaviour of single CdSe quantum dots were observed, and the spectral diffusion range was only about 1 meV. The spectral peak shifting became quicker as the temperature rose. The spectral change from blue-shift to red-shift (or vice versa) was much quicker than that found in CdSe quantum dots synthesized as colloids. The phenomena are qualitatively explained by a Stark effect which originated from an Auger ionization process. The spectral diffusion may be a common property among single quantum dots.
Loh, Guan Chee
2016-04-18
With the rise of 2D materials, such as graphene and transition metal dichalcogenides, as viable materials for numerous experimental applications, it becomes more necessary to maintain fine control of their properties. One expedient and efficacious technique to regulate their properties is surface functionalization. In this study, DFT calculations are performed on triangular MoS2 quantum dots (QDs) either partially or completely doped with nanoparticles (NPs) of the noble metals Au, Ag, and Pt. The effects of these dopants on the geometry, electronic properties, magnetic properties, and chemical bonding of the QDs are investigated. The calculations show that the structural stability of the QDs is reduced by Au or Ag dopants, whereas Pt dopants have a contrasting effect. The NPs diminish the metallicity of the QD, the extent of which is contingent on the number of NPs adsorbed on the QD. However, these NPs exert distinctly disparate charge transfer effects-Ag NPs n-dope the QDs, whereas Au and Pt NPs either n- or p-dope. The molecular electrostatic potential maps of the occupied states show that metallic states are removed from the doping sites. Notwithstanding the decrease of magnetization in all three types of hybrid QD, the distribution of spin density in the Pt-doped QD is inherently different from that in the other QDs. Bond analyses using the quantum theory of atoms in molecules and the crystal orbital Hamilton population suggest that bonds between the Pt NPs and the QDs are the most covalent and the strongest, followed by the Au-QD bonds, and then Ag-QD bonds. The versatility of these hybrid QDs is further examined by applying an external electric field in the three orthogonal orientations, and comparing their properties with those in the absence of the electric field. There are two primary observations: 1) dopants at the tail, head and tail, and in the fully encased configuration are most effective in modifying the distribution of metallic states if the
Quantum interference of independently generated telecom-band single photons
Patel, Monika; Altepeter, Joseph B.; Huang, Yu-Ping; Oza, Neal N.; Kumar, Prem
2014-12-04
We report on high-visibility quantum interference of independently generated telecom O-band (1310 nm) single photons using standard single-mode fibers. The experimental data are shown to agree well with the results of simulations using a comprehensive quantum multimode theory without the need for any fitting parameter.
Multimodal Literacies in the Secondary English Classroom
ERIC Educational Resources Information Center
Sewell, William C.; Denton, Shawn
2011-01-01
To provide insight into the issue of multimodal literacy instruction, the authors explore presentation techniques and instructional activities employed in their secondary language arts classes. They collaborate on assignments that focus students on "anchored media instruction" and engage them in producing multimodal, technology-infused projects,…
Multimodal Narrative Inquiry: Six Teacher Candidates Respond
ERIC Educational Resources Information Center
Morawski, Cynthia M.; Rottmann, Jennifer
2016-01-01
In this paper we present findings of a study on the implementation of a multimodal teacher narrative inquiry component, theoretically grounded by Rosenblatt's theory of transaction analysis, methodologically supported by action research and practically enacted by narrative inquiry and multimodal learning. In particular, the component offered…
A Cuckoo Search Algorithm for Multimodal Optimization
2014-01-01
Interest in multimodal optimization is expanding rapidly, since many practical engineering problems demand the localization of multiple optima within a search space. On the other hand, the cuckoo search (CS) algorithm is a simple and effective global optimization algorithm which can not be directly applied to solve multimodal optimization problems. This paper proposes a new multimodal optimization algorithm called the multimodal cuckoo search (MCS). Under MCS, the original CS is enhanced with multimodal capacities by means of (1) the incorporation of a memory mechanism to efficiently register potential local optima according to their fitness value and the distance to other potential solutions, (2) the modification of the original CS individual selection strategy to accelerate the detection process of new local minima, and (3) the inclusion of a depuration procedure to cyclically eliminate duplicated memory elements. The performance of the proposed approach is compared to several state-of-the-art multimodal optimization algorithms considering a benchmark suite of fourteen multimodal problems. Experimental results indicate that the proposed strategy is capable of providing better and even a more consistent performance over existing well-known multimodal algorithms for the majority of test problems yet avoiding any serious computational deterioration. PMID:25147850
A cuckoo search algorithm for multimodal optimization.
Cuevas, Erik; Reyna-Orta, Adolfo
2014-01-01
Interest in multimodal optimization is expanding rapidly, since many practical engineering problems demand the localization of multiple optima within a search space. On the other hand, the cuckoo search (CS) algorithm is a simple and effective global optimization algorithm which can not be directly applied to solve multimodal optimization problems. This paper proposes a new multimodal optimization algorithm called the multimodal cuckoo search (MCS). Under MCS, the original CS is enhanced with multimodal capacities by means of (1) the incorporation of a memory mechanism to efficiently register potential local optima according to their fitness value and the distance to other potential solutions, (2) the modification of the original CS individual selection strategy to accelerate the detection process of new local minima, and (3) the inclusion of a depuration procedure to cyclically eliminate duplicated memory elements. The performance of the proposed approach is compared to several state-of-the-art multimodal optimization algorithms considering a benchmark suite of fourteen multimodal problems. Experimental results indicate that the proposed strategy is capable of providing better and even a more consistent performance over existing well-known multimodal algorithms for the majority of test problems yet avoiding any serious computational deterioration.
Filter. Remix. Make.: Cultivating Adaptability through Multimodality
ERIC Educational Resources Information Center
Dusenberry, Lisa; Hutter, Liz; Robinson, Joy
2015-01-01
This article establishes traits of adaptable communicators in the 21st century, explains why adaptability should be a goal of technical communication educators, and shows how multimodal pedagogy supports adaptability. Three examples of scalable, multimodal assignments (infographics, research interviews, and software demonstrations) that evidence…