Localised excitation of a single photon source by a nanowaveguide.

PubMed

Geng, Wei; Manceau, Mathieu; Rahbany, Nancy; Sallet, Vincent; De Vittorio, Massimo; Carbone, Luigi; Glorieux, Quentin; Bramati, Alberto; Couteau, Christophe

2016-01-29

Nowadays, integrated photonics is a key technology in quantum information processing (QIP) but achieving all-optical buses for quantum networks with efficient integration of single photon emitters remains a challenge. Photonic crystals and cavities are good candidates but do not tackle how to effectively address a nanoscale emitter. Using a nanowire nanowaveguide, we realise an hybrid nanodevice which locally excites a single photon source (SPS). The nanowire acts as a passive or active sub-wavelength waveguide to excite the quantum emitter. Our results show that localised excitation of a SPS is possible and is compared with free-space excitation. Our proof of principle experiment presents an absolute addressing efficiency ηa ~ 10(-4) only ~50% lower than the one using free-space optics. This important step demonstrates that sufficient guided light in a nanowaveguide made of a semiconductor nanowire is achievable to excite a single photon source. We accomplish a hybrid system offering great potentials for electrically driven SPSs and efficient single photon collection and detection, opening the way for optimum absorption/emission of nanoscale emitters. We also discuss how to improve the addressing efficiency of a dipolar nanoscale emitter with our system.

Localised excitation of a single photon source by a nanowaveguide

PubMed Central

Geng, Wei; Manceau, Mathieu; Rahbany, Nancy; Sallet, Vincent; De Vittorio, Massimo; Carbone, Luigi; Glorieux, Quentin; Bramati, Alberto; Couteau, Christophe

2016-01-01

Nowadays, integrated photonics is a key technology in quantum information processing (QIP) but achieving all-optical buses for quantum networks with efficient integration of single photon emitters remains a challenge. Photonic crystals and cavities are good candidates but do not tackle how to effectively address a nanoscale emitter. Using a nanowire nanowaveguide, we realise an hybrid nanodevice which locally excites a single photon source (SPS). The nanowire acts as a passive or active sub-wavelength waveguide to excite the quantum emitter. Our results show that localised excitation of a SPS is possible and is compared with free-space excitation. Our proof of principle experiment presents an absolute addressing efficiency ηa ~ 10−4 only ~50% lower than the one using free-space optics. This important step demonstrates that sufficient guided light in a nanowaveguide made of a semiconductor nanowire is achievable to excite a single photon source. We accomplish a hybrid system offering great potentials for electrically driven SPSs and efficient single photon collection and detection, opening the way for optimum absorption/emission of nanoscale emitters. We also discuss how to improve the addressing efficiency of a dipolar nanoscale emitter with our system. PMID:26822999

Perovskite Quantum Dots with Near Unity Solution and Neat-Film Photoluminescent Quantum Yield by Novel Spray Synthesis.

PubMed

Dai, Shu-Wen; Hsu, Bo-Wei; Chen, Chien-Yu; Lee, Chia-An; Liu, Hsiao-Yun; Wang, Hsiao-Fang; Huang, Yu-Ching; Wu, Tien-Lin; Manikandan, Arumugam; Ho, Rong-Ming; Tsao, Cheng-Si; Cheng, Chien-Hong; Chueh, Yu-Lun; Lin, Hao-Wu

2018-02-01

In this study, a novel perovskite quantum dot (QD) spray-synthesis method is developed by combining traditional perovskite QD synthesis with the technique of spray pyrolysis. By utilizing this new technique, the synthesis of cubic-shaped perovskite QDs with a homogeneous size of 14 nm is demonstrated, which shows an unprecedented stable absolute photoluminescence quantum yield ≈100% in the solution and even in the solid-state neat film. The highly emissive thin films are integrated with light emission devices (LEDs) and organic light emission displays (OLEDs). The color conversion type QD-LED (ccQD-LED) hybrid devices exhibit an extremely saturated green emission, excellent external quantum efficiency of 28.1%, power efficiency of 121 lm W -1 , and extraordinary forward-direction luminescence of 8 500 000 cd m -2 . The conceptual ccQD-OLED hybrid display also successfully demonstrates high-definition still images and moving pictures with a 119% National Television System Committee 1931 color gamut and 123% Digital Cinema Initiatives-P3 color gamut. These very-stable, ultra-bright perovskite QDs have the properties necessary for a variety of useful applications in optoelectronics. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Diffusion lengths in irradiated N/P InP-on-Si solar cells

NASA Technical Reports Server (NTRS)

Wojtczuk, Steven; Colerico, Claudia; Summers, Geoffrey P.; Walters, Robert J.; Burke, Edward A.

1996-01-01

Indium phosphide (InP) solar cells were made on silicon (Si) wafers (InP/Si) by to take advantage of both the radiation-hardness properties of the InP solar cell and the light weight and low cost of Si wafers. The InP/Si cell application is for long duration and/or high radiation orbit space missions. Spire has made N/P InP/Si cells of sizes up to 2 cm by 4 cm with beginning-of-life (BOL) AM0 efficiencies over 13% (one-sun, 28C). These InP/Si cells have higher absolute efficiency and power density after a high radiation dose than gallium arsenide (GaAs) or silicon (Si) solar cells after a fluence of about 2e15 1 MeV electrons/sq. cm. In this work, we investigate the minority carrier (electron) base diffusion lengths in the N/P InP/Si cells. A quantum efficiency model was constructed for a 12% BOL AM0 N/P InP/Si cell which agreed well with the absolutely measured quantum efficiency and the sun-simulator measured AM0 photocurrent (30.1 mA/sq. cm). This model was then used to generate a table of AM0 photocurrents for a range of base diffusion lengths. AM0 photocurrents were then measured for irradiations up to 7.7e16 1 MeV electrons/sq. cm (the 12% BOL cell was 8% after the final irradiation). By comparing the measured photocurrents with the predicted photocurrents, base diffusion lengths were assigned at each fluence level. A damage coefficient K of 4e-8 and a starting (unirradiated) base electron diffusion length of 0.8 microns fits the data well. The quantum efficiency was measured again at the end of the experiment to verify that the photocurrent predicted by the model (25.5 mA/sq. cm) agreed with the simulator-measured photocurrent after irradiation (25.7 mA/sq. cm).

Novel Multi-Party Quantum Key Agreement Protocol with G-Like States and Bell States

NASA Astrophysics Data System (ADS)

Min, Shi-Qi; Chen, Hua-Ying; Gong, Li-Hua

2018-03-01

A significant aspect of quantum cryptography is quantum key agreement (QKA), which ensures the security of key agreement protocols by quantum information theory. The fairness of an absolute security multi-party quantum key agreement (MQKA) protocol demands that all participants can affect the protocol result equally so as to establish a shared key and that nobody can determine the shared key by himself/herself. We found that it is difficult for the existing multi-party quantum key agreement protocol to withstand the collusion attacks. Put differently, it is possible for several cooperated and untruthful participants to determine the final key without being detected. To address this issue, based on the entanglement swapping between G-like state and Bell states, a new multi-party quantum key agreement protocol is put forward. The proposed protocol makes full use of EPR pairs as quantum resources, and adopts Bell measurement and unitary operation to share a secret key. Besides, the proposed protocol is fair, secure and efficient without involving a third party quantum center. It demonstrates that the protocol is capable of protecting users' privacy and meeting the requirement of fairness. Moreover, it is feasible to carry out the protocol with existing technologies.

Novel Multi-Party Quantum Key Agreement Protocol with G-Like States and Bell States

NASA Astrophysics Data System (ADS)

Min, Shi-Qi; Chen, Hua-Ying; Gong, Li-Hua

2018-06-01

A significant aspect of quantum cryptography is quantum key agreement (QKA), which ensures the security of key agreement protocols by quantum information theory. The fairness of an absolute security multi-party quantum key agreement (MQKA) protocol demands that all participants can affect the protocol result equally so as to establish a shared key and that nobody can determine the shared key by himself/herself. We found that it is difficult for the existing multi-party quantum key agreement protocol to withstand the collusion attacks. Put differently, it is possible for several cooperated and untruthful participants to determine the final key without being detected. To address this issue, based on the entanglement swapping between G-like state and Bell states, a new multi-party quantum key agreement protocol is put forward. The proposed protocol makes full use of EPR pairs as quantum resources, and adopts Bell measurement and unitary operation to share a secret key. Besides, the proposed protocol is fair, secure and efficient without involving a third party quantum center. It demonstrates that the protocol is capable of protecting users' privacy and meeting the requirement of fairness. Moreover, it is feasible to carry out the protocol with existing technologies.

Photon-number statistics of twin beams: Self-consistent measurement, reconstruction, and properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peřina, Jan Jr.; Haderka, Ondřej; Michálek, Václav

2014-12-04

A method for the determination of photon-number statistics of twin beams using the joint signal-idler photocount statistics obtained by an iCCD camera is described. It also provides absolute quantum detection efficiency of the camera. Using the measured photocount statistics, quasi-distributions of integrated intensities are obtained. They attain negative values occurring in characteristic strips an a consequence of pairing of photons in twin beams.

Ytterbium-doped glass-ceramics for optical refrigeration.

PubMed

Filho, Elton Soares de Lima; Krishnaiah, Kummara Venkata; Ledemi, Yannick; Yu, Ye-Jin; Messaddeq, Younes; Nemova, Galina; Kashyap, Raman

2015-02-23

We report for the first time the characterization of glass-ceramics for optical refrigeration. Ytterbium-doped nanocrystallites were grown in an oxyfluoride glass matrix of composition 2YbF(3):30SiO(2)-15Al(2)O(3)-25CdF(2)-22PbF(2)-4YF(3), forming bulk glass-ceramics at three different crystalisation levels. The samples are compared with a corresponding uncrystalised (glass) sample, as well as a Yb:YAG sample which has presented optical cooling. The measured X-ray diffraction spectra, and thermal capacities of the samples are reported. We also report for the first time the use of Yb:YAG as a reference for absolute photometric quantum efficiency measurement, and use the same setup to characterize the glass and glass-ceramic samples. The cooling figure-of-merit was measured by optical calorimetry using a fiber Bragg grating and found to depend on the level of crystallization of the sample, and that samples with nanocrystallites result in higher quantum efficiency and lower background absorption than the pure-glass sample. In addition to laser-induced cooling, the glass-ceramics have the potential to serve as a reference for quantum efficiency measurements.

Laboratory instrumentation and techniques for characterizing multi-junction solar cells for space applications

NASA Technical Reports Server (NTRS)

Woodyard, James R.

1995-01-01

Multi-junction solar cells are attractive for space applications because they can be designed to convert a larger fraction of AMO into electrical power at a lower cost than single-junction cells. The performance of multi-junction cells is much more sensitive to the spectral irradiance of the illuminating source than single-junction cells. The design of high efficiency multi-junction cells for space applications requires matching the optoelectronic properties of the junctions to AMO spectral irradiance. Unlike single-junction cells, it is not possible to carry out quantum efficiency measurements using only a monochromatic probe beam and determining the cell short-circuit current assuming linearity of the quantum efficiency. Additionally, current-voltage characteristics can not be calculated from measurements under non-AMO light sources using spectral-correction methods. There are reports in the literature on characterizing the performance of multi junction cells by measuring and convoluting the quantum efficiency of each junction with the spectral irradiance; the technique is of limited value for the characterization of cell performance under AMO power-generating conditions. We report the results of research to develop instrumentation and techniques for characterizing multi junction solar cells for space . An integrated system is described which consists of a standard lamp, spectral radiometer, dual-source solar simulator, and personal computer based current-voltage and quantum efficiency equipment. The spectral radiometer is calibrated regularly using the tungsten-halogen standard lamp which has a calibration based on NIST scales. The solar simulator produces the light bias beam for current-voltage and cell quantum efficiency measurements. The calibrated spectral radiometer is used to 'fit' the spectral irradiance of the dual-source solar simulator to WRL AMO data. The quantum efficiency apparatus includes a monochromatic probe beam for measuring the absolute cell quantum efficiency at various voltage biases, including the voltage bias corresponding to the maximum-power point under AMO light bias. The details of the procedures to 'fit' the spectral irradiance to AMO will be discussed. An assessment of the role of the accuracy of the 'fit' of the spectral irradiance and probe beam intensity on measured cell characteristics will be presented. quantum efficiencies were measured with both spectral light bias and AMO light bias; the measurements show striking differences. Spectral irradiances were convoluted with cell quantum efficiencies to calculate cell currents as function of voltage. The calculated currents compare with measured currents at the 1% level. Measurements on a variety of multi-junction cells will be presented. The dependence of defects in junctions on cell quantum efficiencies measured under light and voltage bias conditions will be presented. Comments will be made on issues related to standards for calibration, and limitations of the instrumentation and techniques. Expeditious development of multi-junction solar cell technology for space presents challenges for cell characterization in the laboratory.

Detection of non-classical space-time correlations with a novel type of single-photon camera.

PubMed

Just, Felix; Filipenko, Mykhaylo; Cavanna, Andrea; Michel, Thilo; Gleixner, Thomas; Taheri, Michael; Vallerga, John; Campbell, Michael; Tick, Timo; Anton, Gisela; Chekhova, Maria V; Leuchs, Gerd

2014-07-14

During the last decades, multi-pixel detectors have been developed capable of registering single photons. The newly developed hybrid photon detector camera has a remarkable property that it has not only spatial but also temporal resolution. In this work, we apply this device to the detection of non-classical light from spontaneous parametric down-conversion and use two-photon correlations for the absolute calibration of its quantum efficiency.

Absolute sensitivity calibration of an extreme ultraviolet spectrometer for tokamak measurements

NASA Astrophysics Data System (ADS)

Guirlet, R.; Schwob, J. L.; Meyer, O.; Vartanian, S.

2017-01-01

An extreme ultraviolet spectrometer installed on the Tore Supra tokamak has been calibrated in absolute units of brightness in the range 10-340 Å. This has been performed by means of a combination of techniques. The range 10-113 Å was absolutely calibrated by using an ultrasoft-X ray source emitting six spectral lines in this range. The calibration transfer to the range 113-182 Å was performed using the spectral line intensity branching ratio method. The range 182-340 Å was calibrated thanks to radiative-collisional modelling of spectral line intensity ratios. The maximum sensitivity of the spectrometer was found to lie around 100 Å. Around this wavelength, the sensitivity is fairly flat in a 80 Å wide interval. The spatial variations of sensitivity along the detector assembly were also measured. The observed trend is related to the quantum efficiency decrease as the angle of the incoming photon trajectories becomes more grazing.

Probing photochromic properties by correlation of UV-visible and infra-red absorption spectroscopy: a case study with cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene.

PubMed

Spangenberg, Arnaud; Piedras Perez, Jose Alejandro; Patra, Abhijit; Piard, Jonathan; Brosseau, Arnaud; Métivier, Rémi; Nakatani, Keitaro

2010-02-01

Quantification of the relative composition of the isomers in a photochromic system at any irradiation time interval is a critical issue in determining absolute quantum yields. For this purpose, we have developed a simple and convenient protocol involving combination of UV-visible and infra-red absorption spectroscopy. Photochromic cyclization reaction of cis-l,2-dicyano-l,2-bis(2,4,5-trimethyl-3-thieny1)ethene (CMTE) is analyzed to demonstrate the efficiency of the proposed methodology. This approach is based on the fact that the two isomers show distinctive infra-red bands. Detailed investigations of the UV-visible and infra-red spectra of the mixture obtained at different irradiation times in CCl(4) supported by quantum chemical computations lead to the unambiguous estimation of molar absorption coefficients of the closed isomer (epsilon(CF) = 4650 L mol(-1) cm(-1) at 512 nm). It facilitates the first determination of absolute quantum yields of this reversible photochromic reaction in CCl(4) by fitting the UV-visible spectral data (Phi(OF-->CF) = 0.41 +/- 0.05 and Phi(CF-->OF) = 0.12 +/- 0.02 at 405 nm and 546 nm, respectively).

On determining absolute entropy without quantum theory or the third law of thermodynamics

NASA Astrophysics Data System (ADS)

Steane, Andrew M.

2016-04-01

We employ classical thermodynamics to gain information about absolute entropy, without recourse to statistical methods, quantum mechanics or the third law of thermodynamics. The Gibbs-Duhem equation yields various simple methods to determine the absolute entropy of a fluid. We also study the entropy of an ideal gas and the ionization of a plasma in thermal equilibrium. A single measurement of the degree of ionization can be used to determine an unknown constant in the entropy equation, and thus determine the absolute entropy of a gas. It follows from all these examples that the value of entropy at absolute zero temperature does not need to be assigned by postulate, but can be deduced empirically.

High quantum-yield phosphors via quantum splitting and upconversion

NASA Astrophysics Data System (ADS)

Jeong, Joayoung

The Gd3+ ion has been used to induce quantum splitting in luminescent materials by using cross-relaxation energy transfer (CRET). In Nd:LiGdF4, quantum splitting results from a two-step CRET between Gd3+ and Nd3+, first involving a transition 6G→6I on Gd3+ and an excitation within the 4f3 configuration of Nd3+ followed by a second CRET that brings Gd3+ to 6P7/2. The excited Nd3+ ion rapidly relaxes nonradiatively to the emitting 4F3/2. The excited Gd3+ ion then transfers its energy back to Nd3+, which gives rise to the second photon. The result is a quantum yield of 1.05 +/- 0.35 with emission in the NIR following excitation at 175 nm. GdF3:Pr3+, Eu 3+ also exhibits quantum splitting, but only at very low concentration of Pr3+ (0.3%) and Eu3+ (0.2%), resulting in a quantum yield of approximately 20% under 160-nm excitation. Host intrinsic emission via a self-trapped exciton (STE) was also examined as a means to sensitize Gd3+ emission. The material ScPO4:Gd 3+ exhibits a high absolute quantum yield of 0.9 +/- 0.2 under 170-nm excitation, demonstrating a potentially new and efficient pathway for exciting quantum splitting phosphors. Single crystals of the material GdZrF7 were grown, and its structure was established via single-crystal X-ray diffraction methods. Doped samples of GdZrF7:Yb3+, Er3+ exhibit bright up-conversion luminescence with light output that is up to twice that of a commercial material based on the host Gd2O2S. When doped with Eu3+, the fluoride also emits a nearly white color under vacuum ultraviolet excitation with an absolute quantum yield near 0.9. The new compound Gd4.67(SiO4)3S was synthesized and studied. The structure was established via single-crystal X-ray methods, and the luminescence of Tb3+ samples was investigated.

Core/Shell NaGdF4:Nd3+/NaGdF4 Nanocrystals with Efficient Near-Infrared to Near-Infrared Downconversion Photoluminescence for Bioimaging Applications

PubMed Central

Chen, Guanying; Ohulchanskyy, Tymish Y.; Liu, Sha; Law, Wing-Cheung; Wu, Fang; Swihart, Mark T.; Ågren, Hans; Prasad, Paras N.

2012-01-01

We have synthesized core/shell NaGdF4:Nd3+/NaGdF4 nanocrystals with an average size of 15 nm and exceptionally high photoluminescence (PL) quantum yield. When excited at 740 nm, the nanocrystals manifest spectrally distinguished, near infrared to near infrared (NIR-to-NIR) downconversion PL peaked at ~900, ~1050, and ~1300 nm. The absolute quantum yield of NIR-to-NIR PL reached 40% for core-shell nanoparticles dispersed in hexane. Time-resolved PL measurements revealed that this high quantum yield was achieved through suppression of nonradiative recombination originating from surface states and cross relaxations between dopants. NaGdF4:Nd3+/NaGdF4 nanocrystals, synthesized in organic media, were further converted to be water-dispersible by eliminating the capping ligand of oleic acid. NIR-to-NIR PL bioimaging was demonstrated both in vitro and in vivo through visualization of the NIR-to-NIR PL at ~900 nm under incoherent lamp light excitation. The fact that both excitation and the PL of these nanocrystals are in the biological window of optical transparency, combined with their high quantum efficiency, spectral sharpness and photostability, makes these nanocrystals extremely promising as optical biomaging probes. PMID:22401578

Microlens array induced light absorption enhancement in polymer solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Yuqing; Elshobaki, Moneim; Ye, Zhuo

2013-01-24

Over the last decade, polymer solar cells (PSCs) have attracted a lot of attention and highest power conversion efficiencies (PCE) are now close to 10%. Here we employ an optical structure – the microlens array (MLA) – to increase light absorption inside the active layer, and PCE of PSCs increased even for optimized devices. Normal incident light rays are refracted at the MLA and travel longer optical paths inside the active layers. Two PSC systems – poly(3-hexylthiophene-2,5-diyl):(6,6)-phenyl C61 butyric acid methyl ester (P3HT:PCBM) and poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl]:(6,6)-phenyl C71 butyric acid methyl ester (PCDTBT:PC70BM) – were investigated. In the P3HT:PCBM system, MLA increasedmore » the absorption, absolute external quantum efficiency, and the PCE of an optimized device by [similar]4.3%. In the PCDTBT:PC70BM system, MLA increased the absorption, absolute external quantum efficiency, and PCE by more than 10%. In addition, simulations incorporating optical parameters of all structural layers were performed and they support the enhancement of absorption in the active layer with the assistance of MLA. Our results show that utilizing MLA is an effective strategy to further increase light absorption in PSCs, in which optical losses account for [similar]40% of total losses. MLA also does not pose materials processing challenges to the active layers since it is on the other side of the transparent substrate.« less

Role of electron transfer in Ce{sup 3+} sensitized Yb{sup 3+} luminescence in borate glass

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sontakke, Atul D., E-mail: sontakke.atul.55a@st.kyoto-u.ac.jp; Katayama, Yumiko; Zhuang, Yixi

2015-01-07

In a Ce{sup 3+}-Yb{sup 3+} system, two mechanisms are proposed so far namely, the quantum cutting mechanism and the electron transfer mechanism explaining Yb{sup 3+} infrared luminescence under Ce{sup 3+} excitation. Among them, the quantum cutting mechanism, where one Ce{sup 3+} photon (ultraviolet/blue) gives rise to two Yb{sup 3+} photons (near infrared) is widely sought for because of its huge potential in enhancing the solar cell efficiency. In present study on Ce{sup 3+}-Yb{sup 3+} codoped borate glasses, Ce{sup 3+} sensitized Yb{sup 3+} luminescence at ∼1 μm have been observed on Ce{sup 3+} 5d state excitation. However, the intensity of sensitized Yb{supmore » 3+} luminescence is found to be very weak compared to the strong quenching occurred in Ce{sup 3+} luminescence in Yb{sup 3+} codoped glasses. Moreover, the absolute luminescence quantum yield also showed a decreasing trend with Yb{sup 3+} codoping in the glasses. The overall behavior of the luminescence properties and the quantum yield is strongly contradicting with the quantum cutting phenomenon. The results are attributed to the energetically favorable electron transfer interactions followed by Ce{sup 3+}-Yb{sup 3+} ⇌ Ce{sup 4+}-Yb{sup 2+} inter-valence charge transfer and successfully explained using the absolute electron binding energies of dopant ions in the studied borate glass. Finally, an attempt has been presented to generalize the electron transfer mechanism among opposite oxidation/reduction property dopant ions using the vacuum referred electron binding energy (VRBE) scheme for lanthanide series.« less

Study of ground state optical transfer for ultracold alkali dimers

NASA Astrophysics Data System (ADS)

Bouloufa-Maafa, Nadia; Londono, Beatriz; Borsalino, Dimitri; Vexiau, Romain; Mahecha, Jorge; Dulieu, Olivier; Luc-Koenig, Eliane

2013-05-01

Control of molecular states by laser pulses offer promising potential applications. The manipulation of molecules by external fields requires precise knowledge of the molecular structure. Our motivation is to perform a detailed analysis of the spectroscopic properties of alkali dimers, with the aim to determine efficient optical paths to form molecules in the absolute ground state and to determine the optimal parameters of the optical lattices where those molecules are manipulated to avoid losses by collisions. To this end, we use state of the art molecular potentials, R-dependent spin-orbit coupling and transition dipole moment to perform our calculations. R-dependent SO coupling are of crucial importance because the transitions occur at internuclear distances where they are affected by this R-dependence. Efficient schemes to transfer RbCs, KRb and KCs to the absolute ground state as well as the optimal parameters of the optical lattices will be presented. This work was supported in part by ``Triangle de la Physique'' under contract 2008-007T-QCCM (Quantum Control of Cold Molecules).

Quantum glassiness in clean strongly correlated systems: an example of topological overprotection

NASA Astrophysics Data System (ADS)

Chamon, Claudio

2005-03-01

Describing matter at near absolute zero temperature requires understanding a system's quantum ground state and the low energy excitations around it, the quasiparticles, which are thermally populated by the system's contact to a heat bath. However, this paradigm breaks down if thermal equilibration is obstructed. I present solvable examples of quantum many-body Hamiltonians of systems that are unable to reach their ground states as the environment temperature is lowered to absolute zero. These examples, three dimensional generalizations of quantum Hamiltonians proposed for topological quantum computing, 1) have no quenched disorder, 2) have solely local interactions, 3) have an exactly solvable spectrum, 4) have topologically ordered ground states, and 5) have slow dynamical relaxation rates akin to those of strong structural glasses.

Heterodyne efficiency for a coherent laser radar with diffuse or aerosol targets

NASA Technical Reports Server (NTRS)

Frehlich, R. G.

1993-01-01

The performance of a Coherent Laser Radar is determined by the statistics of the coherent Doppler signal. The heterodyne efficiency is an excellent indication of performance because it is an absolute measure of beam alignment and is independent of the transmitter power, the target backscatter coefficient, the atmospheric attenuation, and the detector quantum efficiency and gain. The theoretical calculation of heterodyne efficiency for an optimal monostatic lidar with a circular aperture and Gaussian transmit laser is presented including beam misalignment in the far-field and near-field regimes. The statistical behavior of estimates of the heterodyne efficiency using a calibration hard target are considered. For space based applications, a biased estimate of heterodyne efficiency is proposed that removes the variability due to the random surface return but retains the sensitivity to misalignment. Physical insight is provided by simulation of the fields on the detector surface. The required detector calibration is also discussed.

High-efficiency frequency doubling of continuous-wave laser light.

PubMed

Ast, Stefan; Nia, Ramon Moghadas; Schönbeck, Axel; Lastzka, Nico; Steinlechner, Jessica; Eberle, Tobias; Mehmet, Moritz; Steinlechner, Sebastian; Schnabel, Roman

2011-09-01

We report on the observation of high-efficiency frequency doubling of 1550 nm continuous-wave laser light in a nonlinear cavity containing a periodically poled potassium titanyl phosphate crystal (PPKTP). The fundamental field had a power of 1.10 W and was converted into 1.05 W at 775 nm, yielding a total external conversion efficiency of 95±1%. The latter value is based on the measured depletion of the fundamental field being consistent with the absolute values derived from numerical simulations. According to our model, the conversion efficiency achieved was limited by the nonperfect mode matching into the nonlinear cavity and by the nonperfect impedance matching for the maximum input power available. Our result shows that cavity-assisted frequency conversion based on PPKTP is well suited for low-decoherence frequency conversion of quantum states of light.

The future scientific CCD

NASA Technical Reports Server (NTRS)

Janesick, J. R.; Elliott, T.; Collins, S.; Marsh, H.; Blouke, M. M.

1984-01-01

Since the first introduction of charge-coupled devices (CCDs) in 1970, CCDs have been considered for applications related to memories, logic circuits, and the detection of visible radiation. It is pointed out, however, that the mass market orientation of CCD development has left largely untapped the enormous potential of these devices for advanced scientific instrumentation. The present paper has, therefore, the objective to introduce the CCD characteristics to the scientific community, taking into account prospects for further improvement. Attention is given to evaluation criteria, a summary of current CCDs, CCD performance characteristics, absolute calibration tools, quantum efficiency, aspects of charge collection, charge transfer efficiency, read noise, and predictions regarding the characteristics of the next generation of silicon scientific CCD imagers.

Novel single photon sources for new generation of quantum communications

DTIC Science & Technology

2017-06-13

be used as building blocks for quantum cryptography and quantum key distribution There were numerous important achievements for the projects in the...single photon sources that will be used as build- ing blocks for quantum cryptography and quantum key distribution There were numerous im- portant...and enable absolutely secured information transfer between distant nodes – key prerequisite for quantum cryptography . Experiment: the experimental

Rare-Earth Ion-Host Lattice Interactions: 15. Analysis of the Spectra of Nd3+ in Gd3Sc2Ga3O12.

DTIC Science & Technology

1984-05-01

Luminescence of Cr3+ Ions in Gadolinium Gallium and Gadolinium Scandium Gallium Garnet CT’stals, Soy. J. Quant. Electron. 12 (1982), 1124. 6M. Dutoit, J. C...Shcherbakov, Absolute Quantum Efficiency of the Luminescence of Cr3+ Ions in Gadolinium Gallium and Gadolinium Scandium Gallium Garnet Crystals, Soy. J...HDL Project: 324332 19. KEY WORDS (Continue on reverse side it necessary end Identify by block number) Rare earth Mixed garnet Spectra Laser Judd-Ofelt

Assignment of absolute stereostructures through quantum mechanics electronic and vibrational circular dichroism calculations.

PubMed

Dai, Peng; Jiang, Nan; Tan, Ren-Xiang

2016-01-01

Elucidation of absolute configuration of chiral molecules including structurally complex natural products remains a challenging problem in organic chemistry. A reliable method for assigning the absolute stereostructure is to combine the experimental circular dichroism (CD) techniques such as electronic and vibrational CD (ECD and VCD), with quantum mechanics (QM) ECD and VCD calculations. The traditional QM methods as well as their continuing developments make them more applicable with accuracy. Taking some chiral natural products with diverse conformations as examples, this review describes the basic concepts and new developments of QM approaches for ECD and VCD calculations in solution and solid states.

Side-channel-free quantum key distribution.

PubMed

Braunstein, Samuel L; Pirandola, Stefano

2012-03-30

Quantum key distribution (QKD) offers the promise of absolutely secure communications. However, proofs of absolute security often assume perfect implementation from theory to experiment. Thus, existing systems may be prone to insidious side-channel attacks that rely on flaws in experimental implementation. Here we replace all real channels with virtual channels in a QKD protocol, making the relevant detectors and settings inside private spaces inaccessible while simultaneously acting as a Hilbert space filter to eliminate side-channel attacks. By using a quantum memory we find that we are able to bound the secret-key rate below by the entanglement-distillation rate computed over the distributed states.

Applications of quantum cloning

NASA Astrophysics Data System (ADS)

Pomarico, E.; Sanguinetti, B.; Sekatski, P.; Zbinden, H.; Gisin, N.

2011-10-01

Quantum Cloning Machines (QCMs) allow for the copying of information, within the limits imposed by quantum mechanics. These devices are particularly interesting in the high-gain regime, i.e., when one input qubit generates a state of many output qubits. In this regime, they allow for the study of certain aspects of the quantum to classical transition. The understanding of these aspects is the root of the two recent applications that we will review in this paper: the first one is the Quantum Cloning Radiometer, a device which is able to produce an absolute measure of spectral radiance. This device exploits the fact that in the quantum regime information can be copied with only finite fidelity, whereas when a state becomes macroscopic, this fidelity gradually increases to 1. Measuring the fidelity of the cloning operation then allows to precisely determine the absolute spectral radiance of the input optical source. We will then discuss whether a Quantum Cloning Machine could be used to produce a state visible by the naked human eye, and the possibility of a Bell Experiment with humans playing the role of detectors.

Study on negative incident photon-to-electron conversion efficiency of quantum dot-sensitized solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Chunhui; Wu, Huijue; Zhu, Lifeng

2014-02-15

Recently, negative signals are frequently observed during the measuring process of monochromatic incident photon-to-electron conversion efficiency (IPCE) for sensitized solar cells by DC method. This phenomenon is confusing and hindering the reasonable evaluation of solar cells. Here, cause of negative IPCE values is studied by taking quantum dot-sensitized solar cell (QDSC) as an example, and the accurate measurement method to avoid the negative value is suggested. The negative background signals of QDSC without illumination are found the direct cause of the negative IPCE values by DC method. Ambient noise, significant capacitance characteristics, and uncontrolled electrochemical reaction all can lead tomore » the negative background signals. When the photocurrent response of device under monochromatic light illumination is relatively weak, the actual photocurrent signals will be covered by the negative background signals and the resulting IPCE values will appear negative. To improve the signal-to-noise ratio, quasi-AC method is proposed for IPCE measurement of solar cells with weak photocurrent response based on the idea of replacing the absolute values by the relative values.« less

Using DNA origami nanostructures to determine absolute cross sections for UV photon-induced DNA strand breakage.

PubMed

Vogel, Stefanie; Rackwitz, Jenny; Schürman, Robin; Prinz, Julia; Milosavljević, Aleksandar R; Réfrégiers, Matthieu; Giuliani, Alexandre; Bald, Ilko

2015-11-19

We have characterized ultraviolet (UV) photon-induced DNA strand break processes by determination of absolute cross sections for photoabsorption and for sequence-specific DNA single strand breakage induced by photons in an energy range from 6.50 to 8.94 eV. These represent the lowest-energy photons able to induce DNA strand breaks. Oligonucleotide targets are immobilized on a UV transparent substrate in controlled quantities through attachment to DNA origami templates. Photon-induced dissociation of single DNA strands is visualized and quantified using atomic force microscopy. The obtained quantum yields for strand breakage vary between 0.06 and 0.5, indicating highly efficient DNA strand breakage by UV photons, which is clearly dependent on the photon energy. Above the ionization threshold strand breakage becomes clearly the dominant form of DNA radiation damage, which is then also dependent on the nucleotide sequence.

Site-Resolved Imaging with the Fermi Gas Microscope

NASA Astrophysics Data System (ADS)

Huber, Florian Gerhard

The recent development of quantum gas microscopy for bosonic rubidium atoms trapped in optical lattices has made it possible to study local structure and correlations in quantum many-body systems. Quantum gas microscopes are a perfect platform to perform quantum simulation of condensed matter systems, offering unprecedented control over both internal and external degrees of freedom at a single-site level. In this thesis, this technique is extended to fermionic particles, paving the way to fermionic quantum simulation, which emulate electrons in real solids. Our implementation uses lithium, the lightest atom amenable to laser cooling. The absolute timescales of dynamics in optical lattices are inversely proportional to the mass. Therefore, experiments are more than six times faster than for the only other fermionic alkali atom, potassium, and more then fourteen times faster than an equivalent rubidium experiment. Scattering and collecting a sufficient number of photons with our high-resolution imaging system requires continuous cooling of the atoms during the fluorescence imaging. The lack of a resolved excited hyperfine structure on the D2 line of lithium prevents efficient conventional sub-Doppler cooling. To address this challenge we have applied a Raman sideband cooling scheme and achieved the first site-resolved imaging of ultracold fermions in an optical lattice.

Control of the external photoluminescent quantum yield of emitters coupled to nanoantenna phased arrays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guo, Ke; Verschuuren, Marc A.; Lozano, Gabriel

2015-08-21

Optical losses in metals represent the largest limitation to the external quantum yield of emitters coupled to plasmonic antennas. These losses can be at the emission wavelength, but they can be more important at shorter wavelengths, i.e., at the excitation wavelength of the emitters, where the conductivity of metals is usually lower. We present accurate measurements of the absolute external photoluminescent quantum yield of a thin layer of emitting material deposited over a periodic nanoantenna phased array. Emission and absorptance measurements of the sample are performed using a custom-made setup including an integrating sphere and variable angle excitation. The measurementsmore » reveal a strong dependence of the external quantum yield on the angle at which the optical field excites the sample. Such behavior is attributed to the coupling between far-field illumination and near-field excitation mediated by the collective resonances supported by the array. Numerical simulations confirm that the inherent losses associated with the metal can be greatly reduced by selecting an optimum angle of illumination, which boosts the light conversion efficiency in the emitting layer. This combined experimental and numerical characterization of the emission from plasmonic arrays reveals the need to carefully design the illumination to achieve the maximum external quantum yield.« less

Absolute calibration of a charge-coupled device camera with twin beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meda, A.; Ruo-Berchera, I., E-mail: i.ruoberchera@inrim.it; Degiovanni, I. P.

2014-09-08

We report on the absolute calibration of a Charge-Coupled Device (CCD) camera by exploiting quantum correlation. This method exploits a certain number of spatial pairwise quantum correlated modes produced by spontaneous parametric-down-conversion. We develop a measurement model accounting for all the uncertainty contributions, and we reach the relative uncertainty of 0.3% in low photon flux regime. This represents a significant step forward for the characterization of (scientific) CCDs used in mesoscopic light regime.

Absolute continuity for operator valued completely positive maps on C∗-algebras

NASA Astrophysics Data System (ADS)

Gheondea, Aurelian; Kavruk, Ali Şamil

2009-02-01

Motivated by applicability to quantum operations, quantum information, and quantum probability, we investigate the notion of absolute continuity for operator valued completely positive maps on C∗-algebras, previously introduced by Parthasarathy [in Athens Conference on Applied Probability and Time Series Analysis I (Springer-Verlag, Berlin, 1996), pp. 34-54]. We obtain an intrinsic definition of absolute continuity, we show that the Lebesgue decomposition defined by Parthasarathy is the maximal one among all other Lebesgue-type decompositions and that this maximal Lebesgue decomposition does not depend on the jointly dominating completely positive map, we obtain more flexible formulas for calculating the maximal Lebesgue decomposition, and we point out the nonuniqueness of the Lebesgue decomposition as well as a sufficient condition for uniqueness. In addition, we consider Radon-Nikodym derivatives for absolutely continuous completely positive maps that, in general, are unbounded positive self-adjoint operators affiliated to a certain von Neumann algebra, and we obtain a spectral approximation by bounded Radon-Nikodym derivatives. An application to the existence of the infimum of two completely positive maps is indicated, and formulas in terms of Choi's matrices for the Lebesgue decomposition of completely positive maps in matrix algebras are obtained.

Quantum cryptography and applications in the optical fiber network

NASA Astrophysics Data System (ADS)

Luo, Yuhui

2005-09-01

Quantum cryptography, as part of quantum information and communications, can provide absolute security for information transmission because it is established on the fundamental laws of quantum theory, such as the principle of uncertainty, No-cloning theorem and quantum entanglement. In this thesis research, a novel scheme to implement quantum key distribution based on multiphoton entanglement with a new protocol is proposed. Its advantages are: a larger information capacity can be obtained with a longer transmission distance and the detection of multiple photons is easier than that of a single photon. The security and attacks pertaining to such a system are also studied. Next, a quantum key distribution over wavelength division multiplexed (WDM) optical fiber networks is realized. Quantum key distribution in networks is a long-standing problem for practical applications. Here we combine quantum cryptography and WDM to solve this problem because WDM technology is universally deployed in the current and next generation fiber networks. The ultimate target is to deploy quantum key distribution over commercial networks. The problems arising from the networks are also studied in this part. Then quantum key distribution in multi-access networks using wavelength routing technology is investigated in this research. For the first time, quantum cryptography for multiple individually targeted users has been successfully implemented in sharp contrast to that using the indiscriminating broadcasting structure. It overcomes the shortcoming that every user in the network can acquire the quantum key signals intended to be exchanged between only two users. Furthermore, a more efficient scheme of quantum key distribution is adopted, hence resulting in a higher key rate. Lastly, a quantum random number generator based on quantum optics has been experimentally demonstrated. This device is a key component for quantum key distribution as it can create truly random numbers, which is an essential requirement to perform quantum key distribution. This new generator is composed of a single optical fiber coupler with fiber pigtails, which can be easily used in optical fiber communications.

Relative and absolute level populations in beam-foil-excited neutral helium

NASA Technical Reports Server (NTRS)

Davidson, J.

1975-01-01

Relative and absolute populations of 19 levels in beam-foil-excited neutral helium at 0.275 MeV have been measured. The singlet angular-momentum sequences show dependences on principal quantum number consistent with n to the -3rd power, but the triplet sequences do not. Singlet and triplet angular-momentum sequences show similar dependences on level excitation energy. Excitation functions for six representative levels were measured in the range from 0.160 to 0.500 MeV. The absolute level populations increase with energy, whereas the neutral fraction of the beam decreases with energy. Further, the P angular-momentum levels are found to be overpopulated with respect to the S and D levels. The overpopulation decreases with increasing principal quantum number.

Limiting loss mechanisms in 23% efficient silicon solar cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aberle, A.G.; Altermatt, P.P.; Heiser, G.

1995-04-01

The ``passivated emitter and rear locally diffused`` (PERL) silicon solar cell structure presently demonstrates the highest terrestrial performance of any silicon-based solar cell. This paper presents a detailed investigation of the limiting loss mechanisms in PERL cells exhibiting independently confirmed 1-sun efficiencies of up to 23.0%. Optical, resistive, and recombinative losses are all analyzed under the full range of solar cell operating conditions with the aid of two-dimensional (2D) device simulations. The analysis is based on measurements of the reflectance, quantum efficiency, dark and illuminated current--voltage ({ital I}--{ital V}) characteristics, and properties of the Si--SiO{sub 2} interfaces employed on thesemore » cells for surface passivation. Through the use of the 2D simulations, particular attention has been paid to the magnitudes of the spatially resolved recombination losses in these cells. It is shown that approximately 50% of the recombination losses at the 1-sun maximum power point occur in the base of the cells, followed by recombination losses at the rear and front oxidized surfaces (25% and {lt}25%, respectively). The relatively low fill factors of PERL cells are principally a result of resistive losses; however, the recombination behavior in the base and at the rear surface also contributes. This work predicts that the efficiency of 23% PERL cells could be increased by about 0.7% absolute if ohmic losses were eliminated, a further 1.1% absolute if there were no reflection losses at the nonmetallized front surface regions, about 2.0% by introducing ideal light trapping and eliminating shading losses due to the front metallization, and by about 3.7% absolute if the device had no defect-related recombination losses. New design rules for future efficiency improvements, evident from this analysis, are also presented. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.« less

Absolute I(asterisk) quantum yields for the ICN A state by diode laser gain-vs-absorption spectroscopy

NASA Technical Reports Server (NTRS)

Hess, Wayne P.; Leone, Stephen R.

1987-01-01

Absolute I(asterisk) quantum yields have been measured as a function of wavelength for room temperature photodissociation of the ICN A state continuum. The yields are obtained by the technique of time-resolved diode laser gain-vs-absorption spectroscopy. Quantum yields are evaluated at seven wavelengths from 248 to 284 nm. The yield at 266 nm is 66.0 + or - 2 percent and it falls off to 53.4 + or - 2 percent and 44.0 + or - 4 percent at 284 and 248 nm, respectively. The latter values are significantly higher than those obtained by previous workers using infrared fluorescence. Estimates of I(asterisk) quantum yields obtained from analysis of CN photofragment rotational distributions, as discussed by other workers, are in good agreement with the I(asterisk) yields reported here. The results are considered in conjunction with recent theoretical and experimental work on the CN rotational distributions and with previous I(asterisk) quantum yield results.

Absolute 1* quantum yields for the ICN A state by diode laser gain versus absorption spectroscopy

NASA Technical Reports Server (NTRS)

Hess, Wayne P.; Leone, Stephen R.

1987-01-01

Absolute I* quantum yields were measured as a function of wavelength for room temperature photodissociation of the ICN A state continuum. The temperature yields are obtained by the technique of time-resolved diode laser gain-versus-absorption spectroscopy. Quantum yields are evaluated at seven wavelengths from 248 to 284 nm. The yield at 266 nm is 66.0 +/- 2% and it falls off to 53.4 +/- 2% and 44.0 +/- 4% at 284 and 248 respectively. The latter values are significantly higher than those obtained by previous workers using infrared fluorescence. Estimates of I* quantum yields obtained from analysis of CN photofragment rotational distributions, as discussed by other workers, are in good agreement with the I* yields. The results are considered in conjunction with recent theoretical and experimental work on the CN rotational distributions and with previous I* yield results.

Quantifying losses and thermodynamic limits in nanophotonic solar cells

NASA Astrophysics Data System (ADS)

Mann, Sander A.; Oener, Sebastian Z.; Cavalli, Alessandro; Haverkort, Jos E. M.; Bakkers, Erik P. A. M.; Garnett, Erik C.

2016-12-01

Nanophotonic engineering shows great potential for photovoltaics: the record conversion efficiencies of nanowire solar cells are increasing rapidly and the record open-circuit voltages are becoming comparable to the records for planar equivalents. Furthermore, it has been suggested that certain nanophotonic effects can reduce costs and increase efficiencies with respect to planar solar cells. These effects are particularly pronounced in single-nanowire devices, where two out of the three dimensions are subwavelength. Single-nanowire devices thus provide an ideal platform to study how nanophotonics affects photovoltaics. However, for these devices the standard definition of power conversion efficiency no longer applies, because the nanowire can absorb light from an area much larger than its own size. Additionally, the thermodynamic limit on the photovoltage is unknown a priori and may be very different from that of a planar solar cell. This complicates the characterization and optimization of these devices. Here, we analyse an InP single-nanowire solar cell using intrinsic metrics to place its performance on an absolute thermodynamic scale and pinpoint performance loss mechanisms. To determine these metrics we have developed an integrating sphere microscopy set-up that enables simultaneous and spatially resolved quantitative absorption, internal quantum efficiency (IQE) and photoluminescence quantum yield (PLQY) measurements. For our record single-nanowire solar cell, we measure a photocurrent collection efficiency of >90% and an open-circuit voltage of 850 mV, which is 73% of the thermodynamic limit (1.16 V).

Sub µGal Absolute Gravity Measurements with a Transportable Quantum Gravimeter

NASA Astrophysics Data System (ADS)

Desruelle, B.; Vermeulen, P.; Menoret, V.; Landragin, A.; Bouyer, P.; Le Moigne, N.; Gabalda, G.; Bonvalot, S.

2017-12-01

This paper presents a review of the last two years of operation of the first unit of the Absolute Quantum Gravimeter (AQG). The AQG is an industry-grade commercial gravimeter, which validates the feasibility to develop a matter-wave gravimeter as a transportable turn-key device. We will discuss the stability of the absolute measurement of g and demonstrate the capability of our instrument to achieve a sensitivity better than 1 µGal in various types of environment. We will in particular comment on the last measurement campaigns and comparisons performed by the AQG which have validated the ease of use and the robustness of the sensor. This paper will also present the status of the development of the field version of the AQG designed to be compatible with outdoor operation.

Control of Emission Color of High Quantum Yield CH3NH3PbBr3 Perovskite Quantum Dots by Precipitation Temperature.

PubMed

Huang, He; Susha, Andrei S; Kershaw, Stephen V; Hung, Tak Fu; Rogach, Andrey L

2015-09-01

Emission color controlled, high quantum yield CH 3 NH 3 PbBr 3 perovskite quantum dots are obtained by changing the temperature of a bad solvent during synthesis. The products for temperatures between 0 and 60 °C have good spectral purity with narrow emission line widths of 28-36 nm, high absolute emission quantum yields of 74% to 93%, and short radiative lifetimes of 13-27 ns.

Highly Luminescent Phase-Stable CsPbI3 Perovskite Quantum Dots Achieving Near 100% Absolute Photoluminescence Quantum Yield.

PubMed

Liu, Feng; Zhang, Yaohong; Ding, Chao; Kobayashi, Syuusuke; Izuishi, Takuya; Nakazawa, Naoki; Toyoda, Taro; Ohta, Tsuyoshi; Hayase, Shuzi; Minemoto, Takashi; Yoshino, Kenji; Dai, Songyuan; Shen, Qing

2017-10-24

Perovskite quantum dots (QDs) as a new type of colloidal nanocrystals have gained significant attention for both fundamental research and commercial applications owing to their appealing optoelectronic properties and excellent chemical processability. For their wide range of potential applications, synthesizing colloidal QDs with high crystal quality is of crucial importance. However, like most common QD systems such as CdSe and PbS, those reported perovskite QDs still suffer from a certain density of trapping defects, giving rise to detrimental nonradiative recombination centers and thus quenching luminescence. In this paper, we show that a high room-temperature photoluminescence quantum yield of up to 100% can be obtained in CsPbI 3 perovskite QDs, signifying the achievement of almost complete elimination of the trapping defects. This is realized with our improved synthetic protocol that involves introducing organolead compound trioctylphosphine-PbI 2 (TOP-PbI 2 ) as the reactive precursor, which also leads to a significantly improved stability for the resulting CsPbI 3 QD solutions. Ultrafast kinetic analysis with time-resolved transient absorption spectroscopy evidence the negligible electron or hole-trapping pathways in our QDs, which explains such a high quantum efficiency. We expect the successful synthesis of the "ideal" perovskite QDs will exert profound influence on their applications to both QD-based light-harvesting and -emitting devices.

Enabling High Efficiency Nanoplasmonics with Novel Nanoantenna Architectures

PubMed Central

Cohen, Moshik; Shavit, Reuven; Zalevsky, Zeev

2015-01-01

Surface plasmon polaritons (SPPs) are propagating excitations that arise from coupling of light with collective electron oscillations. Characterized by high field intensity and nanometric dimensions, SPPs fashion rapid expansion of interest from fundamental and applicative perspectives. However, high metallic losses at optical frequencies still make nanoplasmonics impractical when high absolute efficiency is paramount, with major challenge is efficient plasmon generation in deep nanoscale. Here we introduce the Plantenna, the first reported nanodevice with the potential of addressing these limitations utilizing novel plasmonic architecture. The Plantenna has simple 2D structure, ultracompact dimensions and is fabricated on Silicon chip for future CMOS integration. We design the Plantenna to feed channel (20 nm × 20 nm) nanoplasmonic waveguides, achieving 52% coupling efficiency with Plantenna dimensions of λ3/17,000. We theoretically and experimentally show that the Plantenna enormously outperforms dipole couplers, achieving 28 dB higher efficiency with broad polarization diversity and huge local field enhancement. Our findings confirm the Plantenna as enabling device for high efficiency plasmonic technologies such as quantum nanoplasmonics, molecular strong coupling and plasmon nanolasers. PMID:26620270

Accurate quantum yields by laser gain vs absorption spectroscopy - Investigation of Br/Br(asterisk) channels in photofragmentation of Br2 and IBr

NASA Technical Reports Server (NTRS)

Haugen, H. K.; Weitz, E.; Leone, S. R.

1985-01-01

Various techniques have been used to study photodissociation dynamics of the halogens and interhalogens. The quantum yields obtained by these techniques differ widely. The present investigation is concerned with a qualitatively new approach for obtaining highly accurate quantum yields for electronically excited states. This approach makes it possible to obtain an accuracy of 1 percent to 3 percent. It is shown that measurement of the initial transient gain/absorption vs the final absorption in a single time-resolved signal is a very accurate technique in the study of absolute branching fractions in photodissociation. The new technique is found to be insensitive to pulse and probe laser characteristics, molecular absorption cross sections, and absolute precursor density.

Quantum Bath Refrigeration towards Absolute Zero: Challenging the Unattainability Principle

NASA Astrophysics Data System (ADS)

Kolář, M.; Gelbwaser-Klimovsky, D.; Alicki, R.; Kurizki, G.

2012-08-01

A minimal model of a quantum refrigerator, i.e., a periodically phase-flipped two-level system permanently coupled to a finite-capacity bath (cold bath) and an infinite heat dump (hot bath), is introduced and used to investigate the cooling of the cold bath towards absolute zero (T=0). Remarkably, the temperature scaling of the cold-bath cooling rate reveals that it does not vanish as T→0 for certain realistic quantized baths, e.g., phonons in strongly disordered media (fractons) or quantized spin waves in ferromagnets (magnons). This result challenges Nernst’s third-law formulation known as the unattainability principle.

Quantum bath refrigeration towards absolute zero: challenging the unattainability principle.

PubMed

Kolář, M; Gelbwaser-Klimovsky, D; Alicki, R; Kurizki, G

2012-08-31

A minimal model of a quantum refrigerator, i.e., a periodically phase-flipped two-level system permanently coupled to a finite-capacity bath (cold bath) and an infinite heat dump (hot bath), is introduced and used to investigate the cooling of the cold bath towards absolute zero (T=0). Remarkably, the temperature scaling of the cold-bath cooling rate reveals that it does not vanish as T→0 for certain realistic quantized baths, e.g., phonons in strongly disordered media (fractons) or quantized spin waves in ferromagnets (magnons). This result challenges Nernst's third-law formulation known as the unattainability principle.

Determination of absolute chemiluminescence quantum yields for reactions of bis-(pentachlorophenyl) oxalate, hydrogen peroxide and fluorescent compounds.

PubMed

Catherall, C L; Palmer, T F; Cundall, R B

1989-01-01

Absolute chemiluminescence quantum yields (phi CL) for reactions of bis-(pentachlorophenyl) oxalate (PCPO), hydrogen peroxide (H2O2) and 9:10 diphenyl anthracene (DPA) have been determined. A fully corrected chemiluminescence monitoring spectrometer was calibrated for spectral sensitivity using the chemiluminescence of the bis-(pentachlorophenyl) oxalate system as a liquid light source, the total photon output of which had previously been determined by chemical actinometry. At high (PCPO)/(H2O2) ratios phi CL was found to be independent of PCPO and H2O2 concentrations.

Origins of low energy-transfer efficiency between patterned GaN quantum well and CdSe quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Xingsheng, E-mail: xsxu@semi.ac.cn

For hybrid light emitting devices (LEDs) consisting of GaN quantum wells and colloidal quantum dots, it is necessary to explore the physical mechanisms causing decreases in the quantum efficiencies and the energy transfer efficiency between a GaN quantum well and CdSe quantum dots. This study investigated the electro-luminescence for a hybrid LED consisting of colloidal quantum dots and a GaN quantum well patterned with photonic crystals. It was found that both the quantum efficiency of colloidal quantum dots on a GaN quantum well and the energy transfer efficiency between the patterned GaN quantum well and the colloidal quantum dots decreasedmore » with increases in the driving voltage or the driving time. Under high driving voltages, the decreases in the quantum efficiency of the colloidal quantum dots and the energy transfer efficiency can be attributed to Auger recombination, while those decreases under long driving time are due to photo-bleaching and Auger recombination.« less

Determination of absolute configuration of natural products: theoretical calculation of electronic circular dichroism as a tool

USDA-ARS?s Scientific Manuscript database

Determination of absolute configuration (AC) is one of the most challenging features in the structure elucidation of chiral natural products, especially those with complex structures. With revolutionary advancements in the area of quantum chemical calculations of chiroptical spectroscopy over the pa...

Performance of the EBIT calorimeter spectrometer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Porter, Frederick Scott; Gygax, John; Kelley, Richard L.

The EBIT calorimeter spectrometer (ECS) is a new high-resolution, broadband x-ray spectrometer that has recently been installed at the Electron Beam Ion Trap Facility (EBIT) at the Lawrence Livermore National Laboratory. The ECS is an entirely new production class spectrometer that replaces the XRS/EBIT spectrometer that has been operating at EBIT since 2000. The ECS utilizes a 32-pixel x-ray calorimeter array from the XRS instrument on the Suzaku x-ray observatory. Eighteen of the pixels are optimized for the 0.1-10 keV band and yield 4.5 eV full width at half maximum energy resolution and 95% quantum efficiency at 6 keV. Inmore » addition, the ECS includes 14 detector pixels that are optimized for the high-energy band with a bandpass from 0.5 to over 100 keV with 34 eV resolution and 32% quantum efficiency at 60 keV. The ECS detector array is operated at 50 mK using a five stage cryogenic system that is entirely automated. The instrument takes data continuously for over 65 h with a 2.5 h recycle time. The ECS is a nondispersive, broadband, highly efficient spectrometer that is one of the prime instruments at the EBIT facility. The instrument is used for studies of absolute cross sections, charge exchange recombination, and x-ray emission from nonequilibrium plasmas, among other measurements in our laboratory astrophysics program.« less

Quantum glassiness in strongly correlated clean systems: an example of topological overprotection.

PubMed

Chamon, Claudio

2005-02-04

This Letter presents solvable examples of quantum many-body Hamiltonians of systems that are unable to reach their ground states as the environment temperature is lowered to absolute zero. These examples, three-dimensional generalizations of quantum Hamiltonians proposed for topological quantum computing, (1) have no quenched disorder, (2) have solely local interactions, (3) have an exactly solvable spectrum, (4) have topologically ordered ground states, and (5) have slow dynamical relaxation rates akin to those of strong structural glasses.

Quantum Glassiness in Strongly Correlated Clean Systems: An Example of Topological Overprotection

NASA Astrophysics Data System (ADS)

Chamon, Claudio

2005-01-01

This Letter presents solvable examples of quantum many-body Hamiltonians of systems that are unable to reach their ground states as the environment temperature is lowered to absolute zero. These examples, three-dimensional generalizations of quantum Hamiltonians proposed for topological quantum computing, (1)have no quenched disorder, (2)have solely local interactions, (3)have an exactly solvable spectrum, (4)have topologically ordered ground states, and (5)have slow dynamical relaxation rates akin to those of strong structural glasses.

Solar upconversion with plasmon-enhanced bimolecular complexes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dionne, Jennifer

2017-04-14

Upconversion of sub-bandgap photons is a promising approach to exceed the Shockley-Queisser limit in solar technologies. However, due to the low quantum efficiencies and narrow absorption bandwidths of upconverters, existing systems have only led to fractional percent improvements in photovoltaic devices (~0.01%). In this project, we aimed to develop an efficient upconverting material that could improve cell efficiencies by at least one absolute percent. To achieve this goal, we first used thermodynamic calculations to determine cell efficiencies with realistic upconverting materials. Then, we designed, synthesized, and characterized nanoantennas that promise >100x enhancement in both the upconverter absorption cross-section and emissivemore » radiative rate. Concurrently, we optimized the upconverer by designing new ionic and molecular complexes that promise efficient solid-state upconversion. Lastly, with Bosch, we simulated record-efficiency semi-transparent cells that will allow for ready incorporation of our upconverting materials. While we were not successful in designing record efficiency upconverters during our three years of funding, we gained significant insight into the existing limitations of upconverters and how to best address these challenges. Ongoing work is aimed at addressing these limitations, to make upconversion a cost-competitive solar technology in future years.« less

Reducing inhomogeneity in the dynamic properties of quantum dots via self-aligned plasmonic cavities

NASA Astrophysics Data System (ADS)

Demory, Brandon; Hill, Tyler A.; Teng, Chu-Hsiang; Deng, Hui; Ku, P. C.

2018-01-01

A plasmonic cavity is shown to greatly reduce the inhomogeneity of dynamic optical properties such as quantum efficiency and radiative lifetime of InGaN quantum dots. By using an open-top plasmonic cavity structure, which exhibits a large Purcell factor and antenna quantum efficiency, the resulting quantum efficiency distribution for the quantum dots narrows and is no longer limited by the quantum dot inhomogeneity. The standard deviation of the quantum efficiency can be reduced to 2% while maintaining the overall quantum efficiency at 70%, making InGaN quantum dots a viable candidate for high-speed quantum cryptography and random number generation applications.

Reducing inhomogeneity in the dynamic properties of quantum dots via self-aligned plasmonic cavities.

PubMed

Demory, Brandon; Hill, Tyler A; Teng, Chu-Hsiang; Deng, Hui; Ku, P C

2018-01-05

A plasmonic cavity is shown to greatly reduce the inhomogeneity of dynamic optical properties such as quantum efficiency and radiative lifetime of InGaN quantum dots. By using an open-top plasmonic cavity structure, which exhibits a large Purcell factor and antenna quantum efficiency, the resulting quantum efficiency distribution for the quantum dots narrows and is no longer limited by the quantum dot inhomogeneity. The standard deviation of the quantum efficiency can be reduced to 2% while maintaining the overall quantum efficiency at 70%, making InGaN quantum dots a viable candidate for high-speed quantum cryptography and random number generation applications.

Cooperative and non-cooperative sensitization upconversion in lanthanide-doped LiYbF4 nanoparticles.

PubMed

Zou, Qilin; Huang, Ping; Zheng, Wei; You, Wenwu; Li, Renfu; Tu, Datao; Xu, Jin; Chen, Xueyuan

2017-05-18

Lanthanide (Ln 3+ )-doped upconversion nanoparticles (UCNPs) have attracted tremendous interest owing to their potential bioapplications. However, the intrinsic photophysics responsible for upconversion (UC) especially the cooperative sensitization UC (CSU) in colloidal Ln 3+ -doped UCNPs has remained untouched so far. Herein, we report a unique strategy for the synthesis of high-quality LiYbF 4 :Ln 3+ core-only and core/shell UCNPs with tunable particle sizes and shell thicknesses. Energy transfer UC from Er 3+ , Ho 3+ and Tm 3+ and CSU from Tb 3+ were comprehensively surveyed under 980 nm excitation. Through surface passivation, we achieved efficient non-cooperative sensitization UC with absolute UC quantum yields (QYs) of 3.36%, 0.69% and 0.81% for Er 3+ , Ho 3+ and Tm 3+ , respectively. Particularly, we for the first time quantitatively determined the CSU efficiency for Tb 3+ with an absolute QY of 0.0085% under excitation at a power density of 70 W cm -2 . By means of temperature-dependent steady-state and transient UC spectroscopy, we unraveled the dominant mechanisms of phonon-assisted cooperative energy transfer (T > 100 K) and sequential dimer ground-state absorption/excited-state absorption (T < 100 K) for the CSU process in LiYbF 4 :Tb 3+ UCNPs.

Optimal quantum error correcting codes from absolutely maximally entangled states

NASA Astrophysics Data System (ADS)

Raissi, Zahra; Gogolin, Christian; Riera, Arnau; Acín, Antonio

2018-02-01

Absolutely maximally entangled (AME) states are pure multi-partite generalizations of the bipartite maximally entangled states with the property that all reduced states of at most half the system size are in the maximally mixed state. AME states are of interest for multipartite teleportation and quantum secret sharing and have recently found new applications in the context of high-energy physics in toy models realizing the AdS/CFT-correspondence. We work out in detail the connection between AME states of minimal support and classical maximum distance separable (MDS) error correcting codes and, in particular, provide explicit closed form expressions for AME states of n parties with local dimension \

Quantum entanglement and informational activities of biomolecules

NASA Astrophysics Data System (ADS)

Al-Shargi, Hanan; Berkovich, Simon

2009-03-01

Our model of holographic Universe [1] explains the surprising property of quantum entanglement and reveals its biological implications. The suggested holographic mechanism handles 2D slices of the physical world as a whole. Fitting this simple holistic process in the Procrustean bed of individual particles interactions leads to intricacies of quantum theory with an unintelligible protrusion of distant correlations. Holographic medium imposes dependence of quantum effects on absolute positioning. Testing this prediction for a non-exponential radioactive decay could resolutely point to outside ``memory.'' The essence of Life is in the sophistication of macromolecules. Distinctions in biological information processing of nucleotides in DNA and amino acids in proteins are related to entropies of their structures. Randomness of genetic configurations as exposed by their maximal entropy is characteristic of passive identification rather than active storage functionality. Structural redundancy of proteins shows their operability, of which different foldings of prions is most indicative. Folding of one prion can reshape another prion without a direct contact appearing like ``quantum entanglement,'' or ``teleportation.'' Testing the surmised influence of absolute orientation on the prion reshaping can uncover the latency effects in the ``mad cow'' disease. 1. Simon Berkovich, TR-GWU-CS-07-006, http://www.cs.gwu.edu/research/reports.php

Compositionally Graded Absorber for Efficient and Stable Near‐Infrared‐Transparent Perovskite Solar Cells

PubMed Central

Pisoni, Stefano; Weiss, Thomas P.; Feurer, Thomas; Wäckerlin, Aneliia; Fuchs, Peter; Nishiwaki, Shiro; Zortea, Lukas; Tiwari, Ayodhya N.

2018-01-01

Abstract Compositional grading has been widely exploited in highly efficient Cu(In,Ga)Se2, CdTe, GaAs, quantum dot solar cells, and this strategy has the potential to improve the performance of emerging perovskite solar cells. However, realizing and maintaining compositionally graded perovskite absorber from solution processing is challenging. Moreover, the operational stability of graded perovskite solar cells under long‐term heat/light soaking has not been demonstrated. In this study, a facile partial ion‐exchange approach is reported to achieve compositionally graded perovskite absorber layers. Incorporating compositional grading improves charge collection and suppresses interface recombination, enabling to fabricate near‐infrared‐transparent perovskite solar cells with power conversion efficiency of 16.8% in substrate configuration, and demonstrate 22.7% tandem efficiency with 3.3% absolute gain when mechanically stacked on a Cu(In,Ga)Se2 bottom cell. Non‐encapsulated graded perovskite device retains over 93% of its initial efficiency after 1000 h operation at maximum power point at 60 °C under equivalent 1 sun illumination. The results open an avenue in exploring partial ion‐exchange to design graded perovskite solar cells with improved efficiency and stability. PMID:29593970

Compositionally Graded Absorber for Efficient and Stable Near-Infrared-Transparent Perovskite Solar Cells.

PubMed

Fu, Fan; Pisoni, Stefano; Weiss, Thomas P; Feurer, Thomas; Wäckerlin, Aneliia; Fuchs, Peter; Nishiwaki, Shiro; Zortea, Lukas; Tiwari, Ayodhya N; Buecheler, Stephan

2018-03-01

Compositional grading has been widely exploited in highly efficient Cu(In,Ga)Se 2 , CdTe, GaAs, quantum dot solar cells, and this strategy has the potential to improve the performance of emerging perovskite solar cells. However, realizing and maintaining compositionally graded perovskite absorber from solution processing is challenging. Moreover, the operational stability of graded perovskite solar cells under long-term heat/light soaking has not been demonstrated. In this study, a facile partial ion-exchange approach is reported to achieve compositionally graded perovskite absorber layers. Incorporating compositional grading improves charge collection and suppresses interface recombination, enabling to fabricate near-infrared-transparent perovskite solar cells with power conversion efficiency of 16.8% in substrate configuration, and demonstrate 22.7% tandem efficiency with 3.3% absolute gain when mechanically stacked on a Cu(In,Ga)Se 2 bottom cell. Non-encapsulated graded perovskite device retains over 93% of its initial efficiency after 1000 h operation at maximum power point at 60 °C under equivalent 1 sun illumination. The results open an avenue in exploring partial ion-exchange to design graded perovskite solar cells with improved efficiency and stability.

Perspective on the prospects of a carrier multiplication nanocrystal solar cell.

PubMed

Nair, Gautham; Chang, Liang-Yi; Geyer, Scott M; Bawendi, Moungi G

2011-05-11

This article presents a perspective on the experimental and theoretical work to date on the efficiency of carrier multiplication (CM) in colloidal semiconductor nanocrystals (NCs). Early reports on CM in NCs suggested large CM efficiency enhancements. However, recent experiments have shown that CM in nanocrystalline samples is not significantly stronger, and often is weaker, than in the parent bulk when compared on an absolute photon energy basis. This finding is supported by theoretical consideration of the CM process and the competing intraband relaxation. We discuss the experimental artifacts that may have led to the apparently strong CM estimated in early reports. The finding of bulklike CM in NCs suggests that the main promise of quantum confinement is to boost the photovoltage at which carriers can be extracted. With this in mind, we discuss research directions that may result in effective use of CM in a solar cell.

Ultralow-power near-infrared excited neodymium-doped nanoparticles for long-term in vivo bioimaging.

PubMed

Qin, Qing-Song; Zhang, Pei-Zhi; Sun, Ling-Dong; Shi, Shuo; Chen, Nai-Xiu; Dong, Hao; Zheng, Xiao-Yu; Li, Le-Min; Yan, Chun-Hua

2017-04-06

Lanthanide-doped luminescent nanoparticles with both emission and excitation in the near-infrared (NIR-to-NIR) region hold great promise for bioimaging. Herein, core@shell structured LiLuF 4 :Nd@LiLuF 4 (named as Nd@Lu) nanoparticles (NPs) with highly efficient NIR emission were developed for high-performance in vivo bioimaging. Strikingly, the absolute quantum yield of Nd@Lu NPs reached as high as 32%. After coating with polyethylene glycol (PEG), the water-dispersible Nd@Lu NPs showed good bio-compatibility and low toxicity. With efficient NIR emission, the Nd@Lu NPs were clearly detectable in tissues at depths of up to 20 mm. In addition, long-term in vivo biodistribution with a high signal-to-noise ratio of 25.1 was distinctly tracked upon an ultralow-power-density excitation (10 mW cm -2 ) of 732 nm for the first time.

Optically induced excitonic electroabsorption in a periodically delta-doped InGaAs/GaAs multiple quantum well structure

NASA Technical Reports Server (NTRS)

Larsson, A.; Maserjian, J.

1991-01-01

Large optically induced Stark shifts have been observed in a periodically delta-doped InGaAs/GaAs multiple quantum well structure. With an excitation intensity of 10 mW/sq cm, an absolute quantum well absorption change of 7000/cm was measured with a corresponding differential absorption change as high as 80 percent. The associated maximum change in the quantum well refractive index is 0.04. This material is promising for device development for all-optical computing and signal processing.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Davidson, J.

Relative and absolute populations of 19 levels in beam-foil--excited neutral helium at 0.275 MeV have been measured. The singlet angular-momentum sequences show dependences on principal quantum number consistent with n$sup -3$, but the triplet sequences do not. Singlet and triplet angular-momentum sequences show similar dependences on level excitation energy. Excitation functions for six representative levels were measured in the range 0.160 to 0.500 MeV. The absolute level populations increase with energy, whereas the neutral fraction of the beam decreases with energy. Further, the P angular-momentum levels are found to be overpopulated with respect to the S and D levels. Themore » overpopulation decreases with increasing principal quantum number.« less

Quantum friction on monoatomic layers and its classical analog

NASA Astrophysics Data System (ADS)

Maslovski, Stanislav I.; Silveirinha, Mário G.

2013-07-01

We consider the effect of quantum friction at zero absolute temperature resulting from polaritonic interactions in closely positioned two-dimensional arrays of polarizable atoms (e.g., graphene sheets) or thin dielectric sheets modeled as such arrays. The arrays move one with respect to another with a nonrelativistic velocity v≪c. We confirm that quantum friction is inevitably related to material dispersion, and that such friction vanishes in nondispersive media. In addition, we consider a classical analog of the quantum friction which allows us to establish a link between the phenomena of quantum friction and classical parametric generation. In particular, we demonstrate how the quasiparticle generation rate typically obtained from the quantum Fermi golden rule can be calculated classically.

Quantum Secure Direct Communication with Quantum Memory

NASA Astrophysics Data System (ADS)

Zhang, Wei; Ding, Dong-Sheng; Sheng, Yu-Bo; Zhou, Lan; Shi, Bao-Sen; Guo, Guang-Can

2017-06-01

Quantum communication provides an absolute security advantage, and it has been widely developed over the past 30 years. As an important branch of quantum communication, quantum secure direct communication (QSDC) promotes high security and instantaneousness in communication through directly transmitting messages over a quantum channel. The full implementation of a quantum protocol always requires the ability to control the transfer of a message effectively in the time domain; thus, it is essential to combine QSDC with quantum memory to accomplish the communication task. In this Letter, we report the experimental demonstration of QSDC with state-of-the-art atomic quantum memory for the first time in principle. We use the polarization degrees of freedom of photons as the information carrier, and the fidelity of entanglement decoding is verified as approximately 90%. Our work completes a fundamental step toward practical QSDC and demonstrates a potential application for long-distance quantum communication in a quantum network.

Quantum Secure Direct Communication with Quantum Memory.

PubMed

Zhang, Wei; Ding, Dong-Sheng; Sheng, Yu-Bo; Zhou, Lan; Shi, Bao-Sen; Guo, Guang-Can

2017-06-02

Quantum communication provides an absolute security advantage, and it has been widely developed over the past 30 years. As an important branch of quantum communication, quantum secure direct communication (QSDC) promotes high security and instantaneousness in communication through directly transmitting messages over a quantum channel. The full implementation of a quantum protocol always requires the ability to control the transfer of a message effectively in the time domain; thus, it is essential to combine QSDC with quantum memory to accomplish the communication task. In this Letter, we report the experimental demonstration of QSDC with state-of-the-art atomic quantum memory for the first time in principle. We use the polarization degrees of freedom of photons as the information carrier, and the fidelity of entanglement decoding is verified as approximately 90%. Our work completes a fundamental step toward practical QSDC and demonstrates a potential application for long-distance quantum communication in a quantum network.

Evaluation of saw damage using diamond-coated wire in crystalline silicon solar cells by photoluminescence imaging

NASA Astrophysics Data System (ADS)

Kinoshita, Kosuke; Kojima, Takuto; Suzuki, Ryota; Kawatsu, Tomoyuki; Nakamura, Kyotaro; Ohshita, Yoshio; Ogura, Atsushi

2018-05-01

Si ingots were sliced using a diamond-coated wire, and saw damage was observed even after damage removal etching and texturization. Since invisible microscopic damage was observed only under uncontrolled slice conditions, such damage was identified as saw damage. The wafers with saw damage exhibited the degradation of solar cell conversion efficiency (approximately 1–2% absolute). The results of external quantum efficiency (EQE) measurements showed a slight deterioration of EQE in the short wavelength region. Current–voltage characteristic measurements showed similar results that agreed with the EQE measurement results. In addition, EQE mapping measurements were carried out at various irradiation wavelengths between 350 and 1150 nm. Areas with dark contrasts in EQE mapping correspond to saw damage. In the cells with a low conversion efficiency, both EQE mapping and PL images exhibited dark areas and lines. On the other hand, in the cells with a high conversion efficiency, a uniform distribution of saw damage was observed even with the saw damage in the PL images. We believe that sophisticated control to suppress saw damage during sawing is required to realize higher conversion efficiency solar cells in the future.

Light trapping in thin-film solar cells measured by Raman spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ledinský, M., E-mail: ledinsky@fzu.cz; Photovoltaics and Thin Film Electronics Laboratory, Institute of Microengineering; Moulin, E.

2014-09-15

In this study, Raman spectroscopy is used as a tool to determine the light-trapping capability of textured ZnO front electrodes implemented in microcrystalline silicon (μc-Si:H) solar cells. Microcrystalline silicon films deposited on superstrates of various roughnesses are characterized by Raman micro-spectroscopy at excitation wavelengths of 442 nm, 514 nm, 633 nm, and 785 nm, respectively. The way to measure quantitatively and with a high level of reproducibility the Raman intensity is described in details. By varying the superstrate texture and with it the light trapping in the μc-Si:H absorber layer, we find significant differences in the absolute Raman intensity measured in the near infraredmore » wavelength region (where light trapping is relevant). A good agreement between the absolute Raman intensity and the external quantum efficiency of the μc-Si:H solar cells is obtained, demonstrating the validity of the introduced method. Applications to thin-film solar cells, in general, and other optoelectronic devices are discussed.« less

Antimicrobial Amino-Functionalized Nitrogen-Doped Graphene Quantum Dots for Eliminating Multidrug-Resistant Species in Dual-Modality Photodynamic Therapy and Bioimaging under Two-Photon Excitation.

PubMed

Kuo, Wen-Shuo; Shao, Yu-Ting; Huang, Keng-Shiang; Chou, Ting-Mao; Yang, Chih-Hui

2018-05-02

Developing a nanomaterial, for use in highly efficient dual-modality two-photon photodynamic therapy (PDT) involving reactive oxygen species (ROS) generation and for use as a two-photon imaging contrast probe, is currently desirable. Here, graphene quantum dots (GQDs) doped with nitrogen and functionalized with an amino group (amino-N-GQDs) serving as a photosensitizer in PDT had the superior ability to generate ROS as compared to unmodified GQDs. Multidrug-resistant (MDR) species were completely eliminated at an ultralow energy (239.36 nJ pixel -1 ) through only 12 s two-photon excitation (TPE) in the near-infrared region (800 nm). Furthermore, the amino-N-GQDs had an absorption wavelength of approximately 800 nm, quantum yield of 0.33, strong luminescence, an absolute cross section of approximately 54 356 Göeppert-Mayer units, a lifetime of 1.09 ns, a ratio of the radiative to nonradiative decay rates of approximately 0.49, and high two-photon stability under TPE. These favorable properties enabled the amino-N-GQDs to act as a two-photon contrast probe for tracking and localizing analytes through in-depth two-photon imaging in a three-dimensional biological environment and concurrently easily eliminating MDR species through PDT.

Kinetic isotope effects and how to describe them

PubMed Central

Karandashev, Konstantin; Xu, Zhen-Hao; Meuwly, Markus; Vaníček, Jiří; Richardson, Jeremy O.

2017-01-01

We review several methods for computing kinetic isotope effects in chemical reactions including semiclassical and quantum instanton theory. These methods describe both the quantization of vibrational modes as well as tunneling and are applied to the ⋅H + H2 and ⋅H + CH4 reactions. The absolute rate constants computed with the semiclassical instanton method both using on-the-fly electronic structure calculations and fitted potential-energy surfaces are also compared directly with exact quantum dynamics results. The error inherent in the instanton approximation is found to be relatively small and similar in magnitude to that introduced by using fitted surfaces. The kinetic isotope effect computed by the quantum instanton is even more accurate, and although it is computationally more expensive, the efficiency can be improved by path-integral acceleration techniques. We also test a simple approach for designing potential-energy surfaces for the example of proton transfer in malonaldehyde. The tunneling splittings are computed, and although they are found to deviate from experimental results, the ratio of the splitting to that of an isotopically substituted form is in much better agreement. We discuss the strengths and limitations of the potential-energy surface and based on our findings suggest ways in which it can be improved. PMID:29282447

Temperature Effect of Hydrogen-Like Impurity on the Ground State Energy of Strong Coupling Polaron in a RbCl Quantum Pseudodot

NASA Astrophysics Data System (ADS)

Xiao, Jing-Lin

2016-11-01

We study the ground state energy and the mean number of LO phonons of the strong-coupling polaron in a RbCl quantum pseudodot (QPD) with hydrogen-like impurity at the center. The variations of the ground state energy and the mean number of LO phonons with the temperature and the strength of the Coulombic impurity potential are obtained by employing the variational method of Pekar type and the quantum statistical theory (VMPTQST). Our numerical results have displayed that [InlineMediaObject not available: see fulltext.] the absolute value of the ground state energy increases (decreases) when the temperature increases at lower (higher) temperature regime, [InlineMediaObject not available: see fulltext.] the mean number of the LO phonons increases with increasing temperature, [InlineMediaObject not available: see fulltext.] the absolute value of ground state energy and the mean number of LO phonons are increasing functions of the strength of the Coulombic impurity potential.

Effects of temperature on the ground state of a strongly-coupling magnetic polaron and mean phonon number in RbCl quantum pseudodot

NASA Astrophysics Data System (ADS)

Sun, Yong; Ding, Zhao-Hua; Xiao, Jing-Lin

2016-07-01

On the condition of strong electron-LO phonon coupling in a RbCl quantum pseudodot (QPD), the ground state energy and the mean number of phonons are calculated by using the Pekar variational method and quantum statistical theory. The variations of the ground state energy and the mean number with respect to the temperature and the cyclotron frequency of the magnetic field are studied in detail. We find that the absolute value of the ground state energy increases (decreases) with increasing temperature when the temperature is in the lower (higher) temperature region, and that the mean number increases with increasing temperature. The absolute value of the ground state energy is a decreasing function of the cyclotron frequency of the magnetic field whereas the mean number is an increasing function of it. We find two ways to tune the ground state energy and the mean number: controlling the temperature and controlling the cyclotron frequency of the magnetic field.

Performance of quantum Monte Carlo for calculating molecular bond lengths

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cleland, Deidre M., E-mail: deidre.cleland@csiro.au; Per, Manolo C., E-mail: manolo.per@csiro.au

2016-03-28

This work investigates the accuracy of real-space quantum Monte Carlo (QMC) methods for calculating molecular geometries. We present the equilibrium bond lengths of a test set of 30 diatomic molecules calculated using variational Monte Carlo (VMC) and diffusion Monte Carlo (DMC) methods. The effect of different trial wavefunctions is investigated using single determinants constructed from Hartree-Fock (HF) and Density Functional Theory (DFT) orbitals with LDA, PBE, and B3LYP functionals, as well as small multi-configurational self-consistent field (MCSCF) multi-determinant expansions. When compared to experimental geometries, all DMC methods exhibit smaller mean-absolute deviations (MADs) than those given by HF, DFT, and MCSCF.more » The most accurate MAD of 3 ± 2 × 10{sup −3} Å is achieved using DMC with a small multi-determinant expansion. However, the more computationally efficient multi-determinant VMC method has a similar MAD of only 4.0 ± 0.9 × 10{sup −3} Å, suggesting that QMC forces calculated from the relatively simple VMC algorithm may often be sufficient for accurate molecular geometries.« less

Internal quantum efficiency enhancement of GaInN/GaN quantum-well structures using Ag nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Iida, Daisuke; Department of Photonics Engineering, Technical University of Denmark, 2800 Lyngby; Faculty of Science and Technology, Meijo University, 1-501 Shiogamaguchi Tempaku, 468-8502 Nagoya

2015-09-15

We report internal quantum efficiency enhancement of thin p-GaN green quantum-well structure using self-assembled Ag nanoparticles. Temperature dependent photoluminescence measurements are conducted to determine the internal quantum efficiency. The impact of excitation power density on the enhancement factor is investigated. We obtain an internal quantum efficiency enhancement by a factor of 2.3 at 756 W/cm{sup 2}, and a factor of 8.1 at 1 W/cm{sup 2}. A Purcell enhancement up to a factor of 26 is estimated by fitting the experimental results to a theoretical model for the efficiency enhancement factor.

Predictable quantum efficient detector based on n-type silicon photodiodes

NASA Astrophysics Data System (ADS)

Dönsberg, Timo; Manoocheri, Farshid; Sildoja, Meelis; Juntunen, Mikko; Savin, Hele; Tuovinen, Esa; Ronkainen, Hannu; Prunnila, Mika; Merimaa, Mikko; Tang, Chi Kwong; Gran, Jarle; Müller, Ingmar; Werner, Lutz; Rougié, Bernard; Pons, Alicia; Smîd, Marek; Gál, Péter; Lolli, Lapo; Brida, Giorgio; Rastello, Maria Luisa; Ikonen, Erkki

2017-12-01

The predictable quantum efficient detector (PQED) consists of two custom-made induced junction photodiodes that are mounted in a wedged trap configuration for the reduction of reflectance losses. Until now, all manufactured PQED photodiodes have been based on a structure where a SiO2 layer is thermally grown on top of p-type silicon substrate. In this paper, we present the design, manufacturing, modelling and characterization of a new type of PQED, where the photodiodes have an Al2O3 layer on top of n-type silicon substrate. Atomic layer deposition is used to deposit the layer to the desired thickness. Two sets of photodiodes with varying oxide thicknesses and substrate doping concentrations were fabricated. In order to predict recombination losses of charge carriers, a 3D model of the photodiode was built into Cogenda Genius semiconductor simulation software. It is important to note that a novel experimental method was developed to obtain values for the 3D model parameters. This makes the prediction of the PQED responsivity a completely autonomous process. Detectors were characterized for temperature dependence of dark current, spatial uniformity of responsivity, reflectance, linearity and absolute responsivity at the wavelengths of 488 nm and 532 nm. For both sets of photodiodes, the modelled and measured responsivities were generally in agreement within the measurement and modelling uncertainties of around 100 parts per million (ppm). There is, however, an indication that the modelled internal quantum deficiency may be underestimated by a similar amount. Moreover, the responsivities of the detectors were spatially uniform within 30 ppm peak-to-peak variation. The results obtained in this research indicate that the n-type induced junction photodiode is a very promising alternative to the existing p-type detectors, and thus give additional credibility to the concept of modelled quantum detector serving as a primary standard. Furthermore, the manufacturing of PQEDs is no longer dependent on the availability of a certain type of very lightly doped p-type silicon wafers.

The thermoelectric efficiency of quantum dots in indium arsenide/indium phosphide nanowires

NASA Astrophysics Data System (ADS)

Hoffmann, Eric A.

State of the art semiconductor materials engineering provides the possibility to fabricate devices on the lower end of the mesoscopic scale and confine only a handful of electrons to a region of space. When the thermal energy is reduced below the energetic quantum level spacing, the confined electrons assume energy levels akin to the core-shell structure of natural atoms. Such "artificial atoms", also known as quantum dots, can be loaded with electrons, one-by-one, and subsequently unloaded using source and drain electrical contacts. As such, quantum dots are uniquely tunable platforms for performing quantum transport and quantum control experiments. Voltage-biased electron transport through quantum dots has been studied extensively. Far less attention has been given to thermoelectric effects in quantum dots, that is, electron transport induced by a temperature gradient. This dissertation focuses on the efficiency of direct thermal-to-electric energy conversion in InAs/InP quantum dots embedded in nanowires. The efficiency of thermoelectric heat engines is bounded by the same maximum efficiency as cyclic heat engines; namely, by Carnot efficiency. The efficiency of bulk thermoelectric materials suffers from their inability to transport charge carriers selectively based on energy. Owing to their three-dimensional momentum quantization, quantum dots operate as electron energy filters---a property which can be harnessed to minimize entropy production and therefore maximize efficiency. This research was motivated by the possibility to realize experimentally a thermodynamic heat engine operating with near-Carnot efficiency using the unique behavior of quantum dots. To this end, a microscopic heating scheme for the application of a temperature difference across a quantum dot was developed in conjunction with a novel quantum-dot thermometry technique used for quantifying the magnitude of the applied temperature difference. While pursuing high-efficiency thermoelectric performance, many mesoscopic thermoelectric effects were observed and studied, including Coulomb-blockade thermovoltage oscillations, thermoelectric power generation, and strong nonlinear behavior. In the end, a quantum-dot-based thermoelectric heat engine was achieved and demonstrated an electronic efficiency of up to 95% Carnot efficiency.

(Indium, Aluminum) co-doped Zinc Oxide as a Novel Material System for Quantum-Well Multilayer Thermoelectrics

NASA Astrophysics Data System (ADS)

Teehan, Sean

Waste heat recovery from low efficiency industrial processes requires high performance thermoelectric materials to meet challenging requirements. The efficiency such a device is quantified by the dimensionless figure of merit ZT=S2sigmaT/kappa, where S is the Seebeck coefficient, sigma is the electrical conductivity, T is the absolute temperature and kappa is the thermal conductivity. For practical applications these devices are only cost-effective if the ZT is higher than 2. Theoretically it has been proven that by engineering nanostructures with lower dimensionality one can significantly increase ZT. A superlattice, or a system of 2-dimensional multilayer quantum wells has previously shown the potential to be used for thermoelectric structures. However, the use of conventional materials within these structures has only allowed this at low temperatures and has utilized cross-plane transport. This study focuses on both high temperature range operation and the in-plane transport properties of such structures, which benefit from both quantum confinement and an enhancement in density of states near EF. The n-type structures are fabricated by alternately sputtering barrier and well materials of Al-doped ZnO (AZO) and indium co-doped AZO, respectively. Samples investigated consist of 50 periods with targeted layer thicknesses of 10nm, which results in sufficient sampling material as well as quantum well effects. The indium doping level within the quantum well was controlled by varying the target power, and ultimately results in a 3x improvement in power factor (S 2sigma) over the parent bulk materials. The film characterization was determined by X-ray reflectometry, transmission electron microscopy, X-ray diffraction, auger electron spectroscopy, as well as other relevant techniques. In addition, process optimization was performed on material parameters such as layer thickness, interface roughness, and band-gap offset which all play a major role in determining the thermoelectric performance. Within this study we theoretically and experimentally have developed correlations between each of these material parameters and its overall effect on thermoelectric performance.

LASERS IN MEDICINE: Quantum efficiency of the laser-excited singlet-oxygen-sensitised delayed fluorescence of the zinc complex of tetra(4-tert-butyl)phthalocyanine

NASA Astrophysics Data System (ADS)

Bashtanov, M. E.; Drozdova, N. N.; Krasnovskii, A. A.

1999-12-01

An investigation was made of the ratios of the intensity Idf of the singlet-oxygen(1O2)-sensitised delayed fluorescence of the zinc complex of tetra(4-tert-butyl)phthalocyanine (ZnTBPc), with the maximum at λ = 685 nm, to the intensity I1270 of the photosensitised phosphorescence of 1O2 with the maximum at λ = 1270 nm in deuterated benzene when excited with λ = 337 nm nitrogen-laser pulses. Depending on the energy density of the laser radiation (0.25 — 0.7 mJ cm-2) and on the concentration of ZnTBPc (0.06 — 3.4 μM), the ratio of the zero-time intensities of the delayed fluorescence of ZnTBPc and of the singlet-oxygen phosphorescence Idf0/I12700 varied from 0.01 to 0.2 in air-saturated solutions of ZnTBPc. The intensity Idf0 decreased fivefold as a result of saturation with oxygen of air-saturated solutions. The quantum efficiency of the delayed fluorescence was represented by the coefficient α =(Idf0/I12700)kr/(γf[1O2]0[ZnTBPc]), where [1O2]0 is the zero-time concentration of 1O2 after a laser shot; kr is the rate constant of radiative deactivation of 1O2 in the investigated solvent; γf is the quantum yield of the ZnTBPc fluorescence. It was established that in the case of air-saturated solutions of ZnTBPc this coefficient was approximately 200 times less than for metal-free tetra(4-tert-butyl)phthalocyanine and its absolute value was ~2 × 1011 M-2 s-1.

q-bosons and the q-analogue quantized field

NASA Technical Reports Server (NTRS)

Nelson, Charles A.

1995-01-01

The q-analogue coherent states are used to identify physical signatures for the presence of a 1-analogue quantized radiation field in the q-CS classical limits where the absolute value of z is large. In this quantum-optics-like limit, the fractional uncertainties of most physical quantities (momentum, position, amplitude, phase) which characterize the quantum field are O(1). They only vanish as O(1/absolute value of z) when q = 1. However, for the number operator, N, and the N-Hamiltonian for a free q-boson gas, H(sub N) = h(omega)(N + 1/2), the fractional uncertainties do still approach zero. A signature for q-boson counting statistics is that (Delta N)(exp 2)/ (N) approaches 0 as the absolute value of z approaches infinity. Except for its O(1) fractional uncertainty, the q-generalization of the Hermitian phase operator of Pegg and Barnett, phi(sub q), still exhibits normal classical behavior. The standard number-phase uncertainty-relation, Delta(N) Delta phi(sub q) = 1/2, and the approximate commutation relation, (N, phi(sub q)) = i, still hold for the single-mode q-analogue quantized field. So, N and phi(sub q) are almost canonically conjugate operators in the q-CS classical limit. The q-analogue CS's minimize this uncertainty relation for moderate (absolute value of z)(exp 2).

Chemical Potential for the Interacting Classical Gas and the Ideal Quantum Gas Obeying a Generalized Exclusion Principle

ERIC Educational Resources Information Center

Sevilla, F. J.; Olivares-Quiroz, L.

2012-01-01

In this work, we address the concept of the chemical potential [mu] in classical and quantum gases towards the calculation of the equation of state [mu] = [mu](n, T) where n is the particle density and "T" the absolute temperature using the methods of equilibrium statistical mechanics. Two cases seldom discussed in elementary textbooks are…

The Influences of Quantum Coherence on the Positive Work and the Efficiency of Quantum Heat Engine with Working Substance of Two-Qubit Heisenberg XXX Model

NASA Astrophysics Data System (ADS)

Peng, Hu-Ping; Fang, Mao-Fa; Yu, Min; Zou, Hong-Mei

2018-03-01

We study the influences of quantum coherence on the positive work and the efficiency of quantum heat engine (QHE) based on working substance of two-qubit Heisenberg model under a constant external magnetic field. By using analytical and numerical solution, we give the relation expressions for both the positive work and the efficiency with quantum coherence, and in detail discuss the effects of the quantum coherence on the positive work and the efficiency of QHE in the absence or presence of external magnetic field, respectively.

The Influences of Quantum Coherence on the Positive Work and the Efficiency of Quantum Heat Engine with Working Substance of Two-Qubit Heisenberg XXX Model

NASA Astrophysics Data System (ADS)

Peng, Hu-Ping; Fang, Mao-Fa; Yu, Min; Zou, Hong-Mei

2018-06-01

We study the influences of quantum coherence on the positive work and the efficiency of quantum heat engine (QHE) based on working substance of two-qubit Heisenberg model under a constant external magnetic field. By using analytical and numerical solution, we give the relation expressions for both the positive work and the efficiency with quantum coherence, and in detail discuss the effects of the quantum coherence on the positive work and the efficiency of QHE in the absence or presence of external magnetic field, respectively.

The Contradiction Between the Measurement Theory of Quantum Mechanics and the Theory that the Velocity of Any Particle Can Not be Larger than the Velocity of Light

NASA Technical Reports Server (NTRS)

Shen, Y.; Shen, Z. J.; Shen, G. T.; Yang, B. C.

1996-01-01

By the measurement theory of quantum mechanics and the method of Fourier transform,we proved that the wave function psi(x,y,z,t)= (8/((2(pi)(2L(exp (1/2)))(exp 3))(Phi(L,t,x)Phi(L,t,y)Phi(L,t,z)). According to the theory that the velocity of any particle can not be larger than the velocity of light and the Born interpretation, when absolute value of delta greater than (ct+ L),Phi(L,t,delta) = 0. But according to the calculation, we proved that for some delta, even if absolute value of delta is greater than (ct+L), Phi(L,t,delta) is not equal to 0.

High resolution study of magnetic ordering at absolute zero.

PubMed

Lee, M; Husmann, A; Rosenbaum, T F; Aeppli, G

2004-05-07

High resolution pressure measurements in the zero-temperature limit provide a unique opportunity to study the behavior of strongly interacting, itinerant electrons with coupled spin and charge degrees of freedom. Approaching the precision that has become the hallmark of experiments on classical critical phenomena, we characterize the quantum critical behavior of the model, elemental antiferromagnet chromium, lightly doped with vanadium. We resolve the sharp doubling of the Hall coefficient at the quantum critical point and trace the dominating effects of quantum fluctuations up to surprisingly high temperatures.

Quantum correlations from a room-temperature optomechanical cavity

NASA Astrophysics Data System (ADS)

Purdy, T. P.; Grutter, K. E.; Srinivasan, K.; Taylor, J. M.

2017-06-01

The act of position measurement alters the motion of an object being measured. This quantum measurement backaction is typically much smaller than the thermal motion of a room-temperature object and thus difficult to observe. By shining laser light through a nanomechanical beam, we measure the beam’s thermally driven vibrations and perturb its motion with optical force fluctuations at a level dictated by the Heisenberg measurement-disturbance uncertainty relation. We demonstrate a cross-correlation technique to distinguish optically driven motion from thermally driven motion, observing this quantum backaction signature up to room temperature. We use the scale of the quantum correlations, which is determined by fundamental constants, to gauge the size of thermal motion, demonstrating a path toward absolute thermometry with quantum mechanically calibrated ticks.

Efficient classical simulation of the Deutsch-Jozsa and Simon's algorithms

NASA Astrophysics Data System (ADS)

Johansson, Niklas; Larsson, Jan-Åke

2017-09-01

A long-standing aim of quantum information research is to understand what gives quantum computers their advantage. This requires separating problems that need genuinely quantum resources from those for which classical resources are enough. Two examples of quantum speed-up are the Deutsch-Jozsa and Simon's problem, both efficiently solvable on a quantum Turing machine, and both believed to lack efficient classical solutions. Here we present a framework that can simulate both quantum algorithms efficiently, solving the Deutsch-Jozsa problem with probability 1 using only one oracle query, and Simon's problem using linearly many oracle queries, just as expected of an ideal quantum computer. The presented simulation framework is in turn efficiently simulatable in a classical probabilistic Turing machine. This shows that the Deutsch-Jozsa and Simon's problem do not require any genuinely quantum resources, and that the quantum algorithms show no speed-up when compared with their corresponding classical simulation. Finally, this gives insight into what properties are needed in the two algorithms and calls for further study of oracle separation between quantum and classical computation.

Efficiency and formalism of quantum games

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, C.F.; Johnson, Neil F.

We show that quantum games are more efficient than classical games and provide a saturated upper bound for this efficiency. We also demonstrate that the set of finite classical games is a strict subset of the set of finite quantum games. Our analysis is based on a rigorous formulation of quantum games, from which quantum versions of the minimax theorem and the Nash equilibrium theorem can be deduced.

High-Efficiency and High-Power Mid-Wave Infrared Cascade Lasers

DTIC Science & Technology

2012-10-01

internal quantum efficiency () and factor (2) is usually called the optical extraction efficiency (). The optical extraction efficiency ... quantum efficiency involves more fundamental parameters corresponding to the microscopic processes of the device operation, nevertheless, it can be...deriving parameters such as the internal quantum efficiency of a QC laser, the entire injector miniband can be treated as a single virtual state

Exciton-polaritons: In full flow

NASA Astrophysics Data System (ADS)

Stöferle, Thilo

2017-09-01

Flow without friction is a strange phenomenon usually seen in quantum fluids that are cooled to temperatures near absolute zero, but features of superfluidity have now been seen with polaritons at ambient conditions.

Fragment-based Quantum Mechanical/Molecular Mechanical Simulations of Thermodynamic and Kinetic Process of the Ru2+-Ru3+ Self-Exchange Electron Transfer.

PubMed

Zeng, Xiancheng; Hu, Xiangqian; Yang, Weitao

2012-12-11

A fragment-based fractional number of electron (FNE) approach, is developed to study entire electron transfer (ET) processes from the electron donor region to the acceptor region in condensed phase. Both regions are described by the density-fragment interaction (DFI) method while FNE as an efficient ET order parameter is applied to simulate the electron transfer process. In association with the QM/MM energy expression, the DFI-FNE method is demonstrated to describe ET processes robustly with the Ru 2+ -Ru 3+ self-exchange ET as a proof-of-concept example. This method allows for systematic calculations of redox free energies, reorganization energies, and electronic couplings, and the absolute ET rate constants within the Marcus regime.

Optical and structural properties of CsI thin film photocathode

NASA Astrophysics Data System (ADS)

Triloki; Rai, R.; Singh, B. K.

2015-06-01

In the present work, the performance of a cesium iodide thin film photocathode is studied in detail. The optical absorbance of cesium iodide films has been analyzed in the spectral range from 190 nm to 900 nm. The optical band gap energy of 500 nm thick cesium iodide film is calculated from the absorbance data using a Tauc plot. The refractive index is estimated from the envelope plot of transmittance data using Swanepoel's method. The absolute quantum efficiency measurement has been carried out in the wavelength range from 150 nm to 200 nm. The crystallographic nature and surface morphology are investigated by X-ray diffraction and transmission electron microscopy techniques. In addition, the elemental composition result obtained by energy dispersive X-ray analysis is also reported in the present work.

Metrology for industrial quantum communications: the MIQC project

NASA Astrophysics Data System (ADS)

Rastello, M. L.; Degiovanni, I. P.; Sinclair, A. G.; Kück, S.; Chunnilall, C. J.; Porrovecchio, G.; Smid, M.; Manoocheri, F.; Ikonen, E.; Kubarsepp, T.; Stucki, D.; Hong, K. S.; Kim, S. K.; Tosi, A.; Brida, G.; Meda, A.; Piacentini, F.; Traina, P.; Natsheh, A. Al; Cheung, J. Y.; Müller, I.; Klein, R.; Vaigu, A.

2014-12-01

The ‘Metrology for Industrial Quantum Communication Technologies’ project (MIQC) is a metrology framework that fosters development and market take-up of quantum communication technologies and is aimed at achieving maximum impact for the European industry in this area. MIQC is focused on quantum key distribution (QKD) technologies, the most advanced quantum-based technology towards practical application. QKD is a way of sending cryptographic keys with absolute security. It does this by exploiting the ability to encode in a photon's degree of freedom specific quantum states that are noticeably disturbed if an eavesdropper trying to decode it is present in the communication channel. The MIQC project has started the development of independent measurement standards and definitions for the optical components of QKD system, since one of the perceived barriers to QKD market success is the lack of standardization and quality assurance.

Steady bipartite coherence induced by non-equilibrium environment

NASA Astrophysics Data System (ADS)

Huangfu, Yong; Jing, Jun

2018-01-01

We study the steady state of two coupled two-level atoms interacting with a non-equilibrium environment that consists of two heat baths at different temperatures. Specifically, we analyze four cases with respect to the configuration about the interactions between atoms and heat baths. Using secular approximation, the conventional master equation usually neglects steady-state coherence, even when the system is coupled with a non-equilibrium environment. When employing the master equation with no secular approximation, we find that the system coherence in our model, denoted by the off-diagonal terms in the reduced density matrix spanned by the eigenvectors of the system Hamiltonian, would survive after a long-time decoherence evolution. The absolute value of residual coherence in the system relies on different configurations of interaction channels between the system and the heat baths. We find that a large steady quantum coherence term can be achieved when the two atoms are resonant. The absolute value of quantum coherence decreases in the presence of additional atom-bath interaction channels. Our work sheds new light on the mechanism of steady-state coherence in microscopic quantum systems in non-equilibrium environments.

On the minimum quantum requirement of photosynthesis.

PubMed

Zeinalov, Yuzeir

2009-01-01

An analysis of the shape of photosynthetic light curves is presented and the existence of the initial non-linear part is shown as a consequence of the operation of the non-cooperative (Kok's) mechanism of oxygen evolution or the effect of dark respiration. The effect of nonlinearity on the quantum efficiency (yield) and quantum requirement is reconsidered. The essential conclusions are: 1) The non-linearity of the light curves cannot be compensated using suspensions of algae or chloroplasts with high (>1.0) optical density or absorbance. 2) The values of the maxima of the quantum efficiency curves or the values of the minima of the quantum requirement curves cannot be used for estimation of the exact value of the maximum quantum efficiency and the minimum quantum requirement. The estimation of the maximum quantum efficiency or the minimum quantum requirement should be performed only after extrapolation of the linear part at higher light intensities of the quantum requirement curves to "0" light intensity.

Common mechanisms regulating dark noise and quantum bump amplification in Drosophila photoreceptors

PubMed Central

Chu, Brian; Liu, Che-Hsiung; Sengupta, Sukanya; Gupta, Amit; Raghu, Padinjat

2013-01-01

Absolute visual thresholds are limited by “dark noise,” which in Drosophila photoreceptors is dominated by brief (∼10 ms), small (∼2 pA) inward current events, occurring at ∼2/s, believed to reflect spontaneous G protein activations. These dark events were increased in rate and amplitude by a point mutation in myosin III (NINAC), which disrupts its interaction with the scaffolding protein, INAD. This phenotype mimics that previously described in null mutants of ninaC (no inactivation no afterpotential; encoding myosin III) and an associated protein, retinophilin (rtp). Dark noise was similarly increased in heterozygote mutants of diacylglycerol kinase (rdgA/+). Dark noise in ninaC, rtp, and rdgA/+ mutants was greatly suppressed by mutations of the Gq α-subunit (Gαq) and the major light-sensitive channel (trp) but not rhodopsin. ninaC, rtp, and rdgA/+ mutations also all facilitated residual light responses in Gαq and PLC hypomorphs. Raising cytosolic Ca2+ in the submicromolar range increased dark noise, facilitated activation of transient receptor potential (TRP) channels by exogenous agonist, and again facilitated light responses in Gαq hypomorphs. Our results indicate that RTP, NINAC, INAD, and diacylglycerol kinase, together with a Ca2+-dependent threshold, share common roles in suppressing dark noise and regulating quantum bump generation; consequently, most spontaneous G protein activations fail to generate dark events under normal conditions. By contrast, quantum bump generation is reliable but delayed until sufficient G proteins and PLC are activated to overcome threshold, thereby ensuring generation of full-size bumps with high quantum efficiency. PMID:23365183

Entanglement routers via a wireless quantum network based on arbitrary two qubit systems

NASA Astrophysics Data System (ADS)

Metwally, N.

2014-12-01

A wireless quantum network is generated between multi-hops, where each hop consists of two entangled nodes. These nodes share a finite number of entangled two-qubit systems randomly. Different types of wireless quantum bridges (WQBS) are generated between the non-connected nodes. The efficiency of these WQBS to be used as quantum channels between its terminals to perform quantum teleportation is investigated. We suggest a theoretical wireless quantum communication protocol to teleport unknown quantum signals from one node to another, where the more powerful WQBS are used as quantum channels. It is shown that, by increasing the efficiency of the sources that emit the initial partial entangled states, one can increase the efficiency of the wireless quantum communication protocol.

An efficient quantum circuit analyser on qubits and qudits

NASA Astrophysics Data System (ADS)

Loke, T.; Wang, J. B.

2011-10-01

This paper presents a highly efficient decomposition scheme and its associated Mathematica notebook for the analysis of complicated quantum circuits comprised of single/multiple qubit and qudit quantum gates. In particular, this scheme reduces the evaluation of multiple unitary gate operations with many conditionals to just two matrix additions, regardless of the number of conditionals or gate dimensions. This improves significantly the capability of a quantum circuit analyser implemented in a classical computer. This is also the first efficient quantum circuit analyser to include qudit quantum logic gates.

Efficient quantum walk on a quantum processor

PubMed Central

Qiang, Xiaogang; Loke, Thomas; Montanaro, Ashley; Aungskunsiri, Kanin; Zhou, Xiaoqi; O'Brien, Jeremy L.; Wang, Jingbo B.; Matthews, Jonathan C. F.

2016-01-01

The random walk formalism is used across a wide range of applications, from modelling share prices to predicting population genetics. Likewise, quantum walks have shown much potential as a framework for developing new quantum algorithms. Here we present explicit efficient quantum circuits for implementing continuous-time quantum walks on the circulant class of graphs. These circuits allow us to sample from the output probability distributions of quantum walks on circulant graphs efficiently. We also show that solving the same sampling problem for arbitrary circulant quantum circuits is intractable for a classical computer, assuming conjectures from computational complexity theory. This is a new link between continuous-time quantum walks and computational complexity theory and it indicates a family of tasks that could ultimately demonstrate quantum supremacy over classical computers. As a proof of principle, we experimentally implement the proposed quantum circuit on an example circulant graph using a two-qubit photonics quantum processor. PMID:27146471

Integer, fractional, and anomalous quantum Hall effects explained with Eyring's rate process theory and free volume concept.

PubMed

Hao, Tian

2017-02-22

The Hall effects, especially the integer, fractional and anomalous quantum Hall effects, have been addressed using Eyring's rate process theory and free volume concept. The basic assumptions are that the conduction process is a common rate controlled "reaction" process that can be described with Eyring's absolute rate process theory; the mobility of electrons should be dependent on the free volume available for conduction electrons. The obtained Hall conductivity is clearly quantized as with prefactors related to both the magnetic flux quantum number and the magnetic quantum number via the azimuthal quantum number, with and without an externally applied magnetic field. This article focuses on two dimensional (2D) systems, but the approaches developed in this article can be extended to 3D systems.

A universal quantum information processor for scalable quantum communication and networks

PubMed Central

Yang, Xihua; Xue, Bolin; Zhang, Junxiang; Zhu, Shiyao

2014-01-01

Entanglement provides an essential resource for quantum computation, quantum communication, and quantum networks. How to conveniently and efficiently realize the generation, distribution, storage, retrieval, and control of multipartite entanglement is the basic requirement for realistic quantum information processing. Here, we present a theoretical proposal to efficiently and conveniently achieve a universal quantum information processor (QIP) via atomic coherence in an atomic ensemble. The atomic coherence, produced through electromagnetically induced transparency (EIT) in the Λ-type configuration, acts as the QIP and has full functions of quantum beam splitter, quantum frequency converter, quantum entangler, and quantum repeater. By employing EIT-based nondegenerate four-wave mixing processes, the generation, exchange, distribution, and manipulation of light-light, atom-light, and atom-atom multipartite entanglement can be efficiently and flexibly achieved in a deterministic way with only coherent light fields. This method greatly facilitates the operations in quantum information processing, and holds promising applications in realistic scalable quantum communication and quantum networks. PMID:25316514

High efficiency coherent optical memory with warm rubidium vapour

PubMed Central

Hosseini, M.; Sparkes, B.M.; Campbell, G.; Lam, P.K.; Buchler, B.C.

2011-01-01

By harnessing aspects of quantum mechanics, communication and information processing could be radically transformed. Promising forms of quantum information technology include optical quantum cryptographic systems and computing using photons for quantum logic operations. As with current information processing systems, some form of memory will be required. Quantum repeaters, which are required for long distance quantum key distribution, require quantum optical memory as do deterministic logic gates for optical quantum computing. Here, we present results from a coherent optical memory based on warm rubidium vapour and show 87% efficient recall of light pulses, the highest efficiency measured to date for any coherent optical memory suitable for quantum information applications. We also show storage and recall of up to 20 pulses from our system. These results show that simple warm atomic vapour systems have clear potential as a platform for quantum memory. PMID:21285952

High efficiency coherent optical memory with warm rubidium vapour.

PubMed

Hosseini, M; Sparkes, B M; Campbell, G; Lam, P K; Buchler, B C

2011-02-01

By harnessing aspects of quantum mechanics, communication and information processing could be radically transformed. Promising forms of quantum information technology include optical quantum cryptographic systems and computing using photons for quantum logic operations. As with current information processing systems, some form of memory will be required. Quantum repeaters, which are required for long distance quantum key distribution, require quantum optical memory as do deterministic logic gates for optical quantum computing. Here, we present results from a coherent optical memory based on warm rubidium vapour and show 87% efficient recall of light pulses, the highest efficiency measured to date for any coherent optical memory suitable for quantum information applications. We also show storage and recall of up to 20 pulses from our system. These results show that simple warm atomic vapour systems have clear potential as a platform for quantum memory.

Uncertainty in quantum mechanics: faith or fantasy?

PubMed

Penrose, Roger

2011-12-13

The word 'uncertainty', in the context of quantum mechanics, usually evokes an impression of an essential unknowability of what might actually be going on at the quantum level of activity, as is made explicit in Heisenberg's uncertainty principle, and in the fact that the theory normally provides only probabilities for the results of quantum measurement. These issues limit our ultimate understanding of the behaviour of things, if we take quantum mechanics to represent an absolute truth. But they do not cause us to put that very 'truth' into question. This article addresses the issue of quantum 'uncertainty' from a different perspective, raising the question of whether this term might be applied to the theory itself, despite its unrefuted huge success over an enormously diverse range of observed phenomena. There are, indeed, seeming internal contradictions in the theory that lead us to infer that a total faith in it at all levels of scale leads us to almost fantastical implications.

[Definition of quantum efficiency of X-ray detectors].

PubMed

Zelikman, M I

2001-01-01

Different definitions available in the literature on the quantum efficiency of X-ray detectors are presented and compared. The relationship of this parameter to spatial frequencies for quantum accounting receivers and energy accumulating ones is analyzed. A procedure is proposed for evaluating the quantum efficiency of the detectors in the area of zero spatial frequencies, which is rather simple and requires no special testing equipment.

Loss of photosynthetic efficiency in the shade. An Achilles heel for the dense modern stands of our most productive C4 crops?

PubMed Central

Pignon, Charles P.; Jaiswal, Deepak; McGrath, Justin M.

2017-01-01

Abstract The wild progenitors of major C4 crops grew as individuals subjected to little shading. Today they are grown in dense stands where most leaves are shaded. Do they maintain photosynthetic efficiency in these low light conditions produced by modern cultivation? The apparent maximum quantum yield of CO2 assimilation (ΦCO2max,app), a key determinant of light-limited photosynthesis, has not been systematically studied in field stands of C4 crops. ΦCO2max,app was derived from the initial slope of the response of leaf CO2 uptake (A) to photon flux (Q). Leaf fractional light absorptance (α) was measured to determine the absolute maximum quantum yield of CO2 assimilation on an absorbed light basis (ΦCO2max,abs). Light response curves were determined on sun and shade leaves of 49 field plants of Miscanthus × giganteus and Zea mays following canopy closure. ΦCO2max,app and ΦCO2max,abs declined significantly by 15–27% (P<0.05) with canopy depth. Experimentally, leaf age was shown unlikely to cause this loss. Modeling canopy CO2 assimilation over diurnal courses suggested that the observed decline in ΦCO2max,app with canopy depth costs 10% of potential carbon gain. Overcoming this limitation could substantially increase the productivity of major C4 crops. PMID:28110277

Photoluminescence and applications of Ni:ZnS in photovoltaic cells

NASA Astrophysics Data System (ADS)

Kalya Tulasidas, Vadiraj; Belagali, Shiddappa L.; Palakkandy, Arun; Kumar, Kuldeep

2018-05-01

An enormous amount of development has been made in the field of photovoltaics in the last 50 odd years. In recent years, the uses of semiconductor nanoparticles have given a new impetus and direction to research in the field of solar cells. This is due to the excellent photoemission properties shown by semiconductors in the quantum dot (QD) state. ZnS QDs show a further interesting feature where their photoemission properties show perceivable changes on adding dopants such as nickel. In the present work, we describe the characterization studies made on Ni:ZnS thin films using photoluminescence (PL), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), and further reports their performance as an absorbing layer in a hybrid solar cell along with poly(3-hexylthiophene) (P3HT). Fabricated Ni:ZnS cell showed a conversion efficiency of 0.25 ± 0.05% with V OC and J SC of 560 mV and 0.11 mA/cm2, respectively. Although the absolute conversion efficiency appears low (only 0.25%), the addition of nickel was found to have improved the efficiency by a hundredfold compared with undoped ZnS.

An efficient quantum algorithm for spectral estimation

NASA Astrophysics Data System (ADS)

Steffens, Adrian; Rebentrost, Patrick; Marvian, Iman; Eisert, Jens; Lloyd, Seth

2017-03-01

We develop an efficient quantum implementation of an important signal processing algorithm for line spectral estimation: the matrix pencil method, which determines the frequencies and damping factors of signals consisting of finite sums of exponentially damped sinusoids. Our algorithm provides a quantum speedup in a natural regime where the sampling rate is much higher than the number of sinusoid components. Along the way, we develop techniques that are expected to be useful for other quantum algorithms as well—consecutive phase estimations to efficiently make products of asymmetric low rank matrices classically accessible and an alternative method to efficiently exponentiate non-Hermitian matrices. Our algorithm features an efficient quantum-classical division of labor: the time-critical steps are implemented in quantum superposition, while an interjacent step, requiring much fewer parameters, can operate classically. We show that frequencies and damping factors can be obtained in time logarithmic in the number of sampling points, exponentially faster than known classical algorithms.

Numerical simulation of quantum efficiency and surface recombination in HgCdTe IR photon-trapping structures

NASA Astrophysics Data System (ADS)

Schuster, Jonathan; Bellotti, Enrico

2013-06-01

We have investigated the quantum effiency in HgCdTe photovoltaic pixel arrays employing a photon-trapping structure realized with a periodic array of pillars intended to provide broadband operation. We have found that the quantum efficiency depends heavily on the passivation of the pillar surface. Pillars passivated with anodicoxide have a large fixed positive charge on the pillar surface. We use our three-dimensional numerical simulation model to study the effect of surface charge and surface recombination velocity on the exterior of the pillars. We then evaluate the quantum efficiency of this structure subject to different surface conditions. We have found that by themselves, the surface charge and surface recombination are detrimental to the quantum efficiency but the quantum efficiency is recovered when both phenomena are present. We will discuss the effects of these phenomena and the trade offs that exist between the two.

Type II GaSb quantum ring solar cells under concentrated sunlight.

PubMed

Tsai, Che-Pin; Hsu, Shun-Chieh; Lin, Shih-Yen; Chang, Ching-Wen; Tu, Li-Wei; Chen, Kun-Cheng; Lay, Tsong-Sheng; Lin, Chien-chung

2014-03-10

A type II GaSb quantum ring solar cell is fabricated and measured under the concentrated sunlight. The external quantum efficiency confirms the extended absorption from the quantum rings at long wavelength coinciding with the photoluminescence results. The short-circuit current of the quantum ring devices is 5.1% to 9.9% more than the GaAs reference's under various concentrations. While the quantum ring solar cell does not exceed its GaAs counterpart in efficiency under one-sun, the recovery of the open-circuit voltages at higher concentration helps to reverse the situation. A slightly higher efficiency (10.31% vs. 10.29%) is reported for the quantum ring device against the GaAs one.

Absolute calibration of a multichannel plate detector for low energy O, O-, and O+

NASA Astrophysics Data System (ADS)

Stephen, T. M.; Peko, B. L.

2000-03-01

Absolute detection efficiencies of a commercial multichannel plate detector have been measured for O, O+, and O-, impacting at normal incidence for energies ranging from 30-1000 eV. In addition, the detection efficiencies for O relative to its ions are presented, as they may have a more universal application. The absolute detection efficiencies are strongly energy dependent and significant differences are observed for the various charge states at lower energies. The detection efficiencies for the different charge states appear to converge at higher energies. The strongest energy dependence is for O+; the detection efficiency varies by three orders of magnitude across the energy range studied. The weakest dependence is for O-, which varies less than one order of magnitude.

Experimental demonstration of selective quantum process tomography on an NMR quantum information processor

NASA Astrophysics Data System (ADS)

Gaikwad, Akshay; Rehal, Diksha; Singh, Amandeep; Arvind, Dorai, Kavita

2018-02-01

We present the NMR implementation of a scheme for selective and efficient quantum process tomography without ancilla. We generalize this scheme such that it can be implemented efficiently using only a set of measurements involving product operators. The method allows us to estimate any element of the quantum process matrix to a desired precision, provided a set of quantum states can be prepared efficiently. Our modified technique requires fewer experimental resources as compared to the standard implementation of selective and efficient quantum process tomography, as it exploits the special nature of NMR measurements to allow us to compute specific elements of the process matrix by a restrictive set of subsystem measurements. To demonstrate the efficacy of our scheme, we experimentally tomograph the processes corresponding to "no operation," a controlled-NOT (CNOT), and a controlled-Hadamard gate on a two-qubit NMR quantum information processor, with high fidelities.

The ambiguity of simplicity in quantum and classical simulation

NASA Astrophysics Data System (ADS)

Aghamohammadi, Cina; Mahoney, John R.; Crutchfield, James P.

2017-04-01

A system's perceived simplicity depends on whether it is represented classically or quantally. This is not so surprising, as classical and quantum physics are descriptive frameworks built on different assumptions that capture, emphasize, and express different properties and mechanisms. What is surprising is that, as we demonstrate, simplicity is ambiguous: the relative simplicity between two systems can change sign when moving between classical and quantum descriptions. Here, we associate simplicity with small model-memory. We see that the notions of absolute physical simplicity at best form a partial, not a total, order. This suggests that appeals to principles of physical simplicity, via Ockham's Razor or to the ;elegance; of competing theories, may be fundamentally subjective. Recent rapid progress in quantum computation and quantum simulation suggest that the ambiguity of simplicity will strongly impact statistical inference and, in particular, model selection.

Mobile quantum gravity sensor with unprecedented stability

NASA Astrophysics Data System (ADS)

Freier, C.; Hauth, M.; Schkolnik, V.; Leykauf, B.; Schilling, M.; Wziontek, H.; Scherneck, H.-G.; Müller, J.; Peters, A.

2016-06-01

Changes of surface gravity on Earth are of great interest in geodesy, earth sciences and natural resource exploration. They are indicative of Earth system's mass redistributions and vertical surface motion, and are usually measured with falling corner-cube- and superconducting gravimeters (FCCG and SCG). Here we report on absolute gravity measurements with a mobile quantum gravimeter based on atom interferometry. The measurements were conducted in Germany and Sweden over periods of several days with simultaneous SCG and FCCG comparisons. They show the best-reported performance of mobile atomic gravimeters to date with an accuracy of 39nm/s2, long-term stability of 0.5nm/s2 and short-term noise of 96nm/s2/√Hz. These measurements highlight the unique properties of atomic sensors. The achieved level of performance in a transportable instrument enables new applications in geodesy and related fields, such as continuous absolute gravity monitoring with a single instrument under rough environmental conditions.

A self-sustaining atomic magnetometer with τ(-1) averaging property.

PubMed

Xu, C; Wang, S G; Feng, Y Y; Zhao, L; Wang, L J

2016-06-30

Quantum measurement using coherent superposition of intrinsic atomic states has the advantage of being absolute measurement and can form metrological standards. One example is the absolute measurement of magnetic field by monitoring the Larmor precession of atomic spins whilst another being the Ramsey type atomic clock. Yet, in almost all coherent quantum measurement, the precision is limited by the coherence time beyond which, the uncertainty decreases only as τ(-1/2). Here we show that by non-destructively measuring the phase of the Larmor precession and regenerating the coherence via optical pumping, the self-sustaining Larmor precession signal can persist indefinitely. Consequently, the precision of the magnetometer increases with time following a much faster τ(-1) rule. A mean sensitivity of 240  from 1 Hz to 10 Hz is realized, being close to the shot noise level. This method of coherence regeneration may also find important applications in improving the performance of atomic clocks.

Highly Efficient Coherent Optical Memory Based on Electromagnetically Induced Transparency

NASA Astrophysics Data System (ADS)

Hsiao, Ya-Fen; Tsai, Pin-Ju; Chen, Hung-Shiue; Lin, Sheng-Xiang; Hung, Chih-Chiao; Lee, Chih-Hsi; Chen, Yi-Hsin; Chen, Yong-Fan; Yu, Ite A.; Chen, Ying-Cheng

2018-05-01

Quantum memory is an important component in the long-distance quantum communication based on the quantum repeater protocol. To outperform the direct transmission of photons with quantum repeaters, it is crucial to develop quantum memories with high fidelity, high efficiency and a long storage time. Here, we achieve a storage efficiency of 92.0 (1.5)% for a coherent optical memory based on the electromagnetically induced transparency scheme in optically dense cold atomic media. We also obtain a useful time-bandwidth product of 1200, considering only storage where the retrieval efficiency remains above 50%. Both are the best record to date in all kinds of schemes for the realization of optical memory. Our work significantly advances the pursuit of a high-performance optical memory and should have important applications in quantum information science.

Highly Efficient Coherent Optical Memory Based on Electromagnetically Induced Transparency.

PubMed

Hsiao, Ya-Fen; Tsai, Pin-Ju; Chen, Hung-Shiue; Lin, Sheng-Xiang; Hung, Chih-Chiao; Lee, Chih-Hsi; Chen, Yi-Hsin; Chen, Yong-Fan; Yu, Ite A; Chen, Ying-Cheng

2018-05-04

Quantum memory is an important component in the long-distance quantum communication based on the quantum repeater protocol. To outperform the direct transmission of photons with quantum repeaters, it is crucial to develop quantum memories with high fidelity, high efficiency and a long storage time. Here, we achieve a storage efficiency of 92.0 (1.5)% for a coherent optical memory based on the electromagnetically induced transparency scheme in optically dense cold atomic media. We also obtain a useful time-bandwidth product of 1200, considering only storage where the retrieval efficiency remains above 50%. Both are the best record to date in all kinds of schemes for the realization of optical memory. Our work significantly advances the pursuit of a high-performance optical memory and should have important applications in quantum information science.

Least significant qubit algorithm for quantum images

NASA Astrophysics Data System (ADS)

Sang, Jianzhi; Wang, Shen; Li, Qiong

2016-11-01

To study the feasibility of the classical image least significant bit (LSB) information hiding algorithm on quantum computer, a least significant qubit (LSQb) information hiding algorithm of quantum image is proposed. In this paper, we focus on a novel quantum representation for color digital images (NCQI). Firstly, by designing the three qubits comparator and unitary operators, the reasonability and feasibility of LSQb based on NCQI are presented. Then, the concrete LSQb information hiding algorithm is proposed, which can realize the aim of embedding the secret qubits into the least significant qubits of RGB channels of quantum cover image. Quantum circuit of the LSQb information hiding algorithm is also illustrated. Furthermore, the secrets extracting algorithm and circuit are illustrated through utilizing control-swap gates. The two merits of our algorithm are: (1) it is absolutely blind and (2) when extracting secret binary qubits, it does not need any quantum measurement operation or any other help from classical computer. Finally, simulation and comparative analysis show the performance of our algorithm.

Quantum Tunneling of Magnetization in Ultrasmall Half-Metallic V3O4 Quantum Dots: Displaying Quantum Superparamagnetic State

PubMed Central

Xiao, Chong; Zhang, Jiajia; Xu, Jie; Tong, Wei; Cao, Boxiao; Li, Kun; Pan, Bicai; Su, Haibin; Xie, Yi

2012-01-01

Quantum tunneling of magnetization (QTMs), stemming from their importance for understanding materials with unconventional properties, has continued to attract widespread theoretical and experimental attention. However, the observation of QTMs in the most promising candidates of molecular magnets and few iron-based compounds is limited to very low temperature. Herein, we first highlight a simple system, ultrasmall half-metallic V3O4 quantum dots, as a promising candidate for the investigation of QTMs at high temperature. The quantum superparamagnetic state (QSP) as a high temperature signature of QTMs is observed at 16 K, which is beyond absolute zero temperature and much higher than that of conventional iron-based compounds due to the stronger spin-orbital coupling of V3+ ions bringing high anisotropy energy. It is undoubtedly that this ultrasmall quantum dots, V3O4, offers not only a promising candidate for theoretical understanding of QTMs but also a very exciting possibility for computers using mesoscopic magnets. PMID:23091695

Enhanced explosive sensing based on bis(methyltetraphenyl)silole nanoaggregate

NASA Astrophysics Data System (ADS)

Shin, Bomina; Sohn, Honglae

2018-01-01

New photoluminescent bis(methyltetraphenyl)silole nanoaggregates for the detection of trinitrotoluene (TNT) were developed by using aggregation-induced emission property. Bis(methyltetraphenyl)silole nanoaggregates exhibited that photoluminescence (PL) intensity was increased when the water fraction was increased to 90% by volume. Relative PL efficiency of bis(methyltetraphenyl)silole nanoaggregates was exponentially increased to the percent of water fraction and particle diameter was dependent on solvent composition. Particle size of bis(methyltetraphenyl)silole nanoaggregates was tuned by controlling the water fraction by volume. Absolute quantum yield of bis(methyltetraphenyl)silole nanoaggregates in 90% water volume fraction were 32.4%, which increases by about 40 times. Detection of TNT was achieved from the quenching PL measurement of bis(methyltetraphenyl)silole nanoaggregates by adding the TNT. A linear Stern-Volmer relationship was observed for the detection of TNT.

6.5% efficient perovskite quantum-dot-sensitized solar cell.

PubMed

Im, Jeong-Hyeok; Lee, Chang-Ryul; Lee, Jin-Wook; Park, Sang-Won; Park, Nam-Gyu

2011-10-05

Highly efficient quantum-dot-sensitized solar cell is fabricated using ca. 2-3 nm sized perovskite (CH(3)NH(3))PbI(3) nanocrystal. Spin-coating of the equimolar mixture of CH(3)NH(3)I and PbI(2) in γ-butyrolactone solution (perovskite precursor solution) leads to (CH(3)NH(3))PbI(3) quantum dots (QDs) on nanocrystalline TiO(2) surface. By electrochemical junction with iodide/iodine based redox electrolyte, perovskite QD-sensitized 3.6 μm-thick TiO(2) film shows maximum external quantum efficiency (EQE) of 78.6% at 530 nm and solar-to-electrical conversion efficiency of 6.54% at AM 1.5G 1 sun intensity (100 mW cm(-2)), which is by far the highest efficiency among the reported inorganic quantum dot sensitizers.

GaN Light-Emitting Triodes (LETs) for High-Efficiency Hole Injection and for Assessment of the Physical Origin of the Efficiency Droop

DTIC Science & Technology

2007-07-06

quantum efficiency . In AlGaN-based UV LEDs, an electron-blocking layer (EBL) is frequently inserted between the p-type cladding layer and the active...me). This limits the hole injection efficiency into the active region, and hence internal quantum efficiency . Figure 1: (a) Schematic band...less efficient than along the lateral direction because most of the holes ionized from the acceptors are localized inside the quantum wells which are

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ortiz-Ramírez, Pablo, E-mail: rapeitor@ug.uchile.cl; Ruiz, Andrés

The Monte Carlo simulation of the gamma spectroscopy systems is a common practice in these days. The most popular softwares to do this are MCNP and Geant4 codes. The intrinsic spatial efficiency method is a general and absolute method to determine the absolute efficiency of a spectroscopy system for any extended sources, but this was only demonstrated experimentally for cylindrical sources. Due to the difficulty that the preparation of sources with any shape represents, the simplest way to do this is by the simulation of the spectroscopy system and the source. In this work we present the validation of themore » intrinsic spatial efficiency method for sources with different geometries and for photons with an energy of 661.65 keV. In the simulation the matrix effects (the auto-attenuation effect) are not considered, therefore these results are only preliminaries. The MC simulation is carried out using the FLUKA code and the absolute efficiency of the detector is determined using two methods: the statistical count of Full Energy Peak (FEP) area (traditional method) and the intrinsic spatial efficiency method. The obtained results show total agreement between the absolute efficiencies determined by the traditional method and the intrinsic spatial efficiency method. The relative bias is lesser than 1% in all cases.« less

Electron spin control of optically levitated nanodiamonds in vacuum

NASA Astrophysics Data System (ADS)

Hoang, Thai; Ahn, Jonghoon; Bang, Jaehoon; Li, Tongcang

2016-05-01

Electron spins of diamond nitrogen-vacancy (NV) centers are important quantum resources for nanoscale sensing and quantum information. Combining such NV spin systems with levitated optomechanical resonators will provide a hybrid quantum system for many novel applications. Here we optically levitate a nanodiamond and demonstrate electron spin control of its built-in NV centers in low vacuum. We observe that the strength of electron spin resonance (ESR) is enhanced when the air pressure is reduced. To better understand this novel system, we also investigate the effects of trap power and measure the absolute internal temperature of levitated nanodiamonds with ESR after calibration of the strain effect.

Non-Markovianity and reservoir memory of quantum channels: a quantum information theory perspective

PubMed Central

Bylicka, B.; Chruściński, D.; Maniscalco, S.

2014-01-01

Quantum technologies rely on the ability to coherently transfer information encoded in quantum states along quantum channels. Decoherence induced by the environment sets limits on the efficiency of any quantum-enhanced protocol. Generally, the longer a quantum channel is the worse its capacity is. We show that for non-Markovian quantum channels this is not always true: surprisingly the capacity of a longer channel can be greater than of a shorter one. We introduce a general theoretical framework linking non-Markovianity to the capacities of quantum channels and demonstrate how harnessing non-Markovianity may improve the efficiency of quantum information processing and communication. PMID:25043763

Photo-acoustic spectroscopy and quantum efficiency of Yb{sup 3+} doped alumino silicate glasses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuhn, Stefan, E-mail: stefan.kuhn84@googlemail.com; Tiegel, Mirko; Herrmann, Andreas

2015-09-14

In this contribution, we analyze the effect of several preparation methods of Yb{sup 3+} doped alumino silicate glasses on their quantum efficiency by using photo-acoustic measurements in comparison to standard measurement methods including the determination via the fluorescence lifetime and an integrating sphere setup. The preparation methods focused on decreasing the OH concentration by means of fluorine-substitution and/or applying dry melting atmospheres, which led to an increase in the measured fluorescence lifetime. However, it was found that the influence of these methods on radiative properties such as the measured fluorescence lifetime alone does not per se give exact information aboutmore » the actual quantum efficiency of the sample. The determination of the quantum efficiency by means of fluorescence lifetime shows inaccuracies when refractive index changing elements such as fluorine are incorporated into the glass. Since fluorine not only eliminates OH from the glass but also increases the “intrinsic” radiative fluorescence lifetime, which is needed to calculate the quantum efficiency, it is difficult to separate lifetime quenching from purely radiative effects. The approach used in this contribution offers a possibility to disentangle radiative from non-radiative properties which is not possible by using fluorescence lifetime measurements alone and allows an accurate determination of the quantum efficiency of a given sample. The comparative determination by an integrating sphere setup leads to the well-known problem of reabsorption which embodies itself in the measurement of too low quantum efficiencies, especially for samples with small quantum efficiencies.« less

Highly-efficient quantum memory for polarization qubits in a spatially-multiplexed cold atomic ensemble.

PubMed

Vernaz-Gris, Pierre; Huang, Kun; Cao, Mingtao; Sheremet, Alexandra S; Laurat, Julien

2018-01-25

Quantum memory for flying optical qubits is a key enabler for a wide range of applications in quantum information. A critical figure of merit is the overall storage and retrieval efficiency. So far, despite the recent achievements of efficient memories for light pulses, the storage of qubits has suffered from limited efficiency. Here we report on a quantum memory for polarization qubits that combines an average conditional fidelity above 99% and efficiency around 68%, thereby demonstrating a reversible qubit mapping where more information is retrieved than lost. The qubits are encoded with weak coherent states at the single-photon level and the memory is based on electromagnetically-induced transparency in an elongated laser-cooled ensemble of cesium atoms, spatially multiplexed for dual-rail storage. This implementation preserves high optical depth on both rails, without compromise between multiplexing and storage efficiency. Our work provides an efficient node for future tests of quantum network functionalities and advanced photonic circuits.

Experimental feasibility of the airborne measurement of absolute oil fluorescence spectral conversion efficiency

NASA Technical Reports Server (NTRS)

Hoge, F. E.; Swift, R. N.

1983-01-01

Airborne lidar oil spill experiments carried out to determine the practicability of the AOFSCE (absolute oil fluorescence spectral conversion efficiency) computational model are described. The results reveal that the model is suitable over a considerable range of oil film thicknesses provided the fluorescence efficiency of the oil does not approach the minimum detection sensitivity limitations of the lidar system. Separate airborne lidar experiments to demonstrate measurement of the water column Raman conversion efficiency are also conducted to ascertain the ultimate feasibility of converting such relative oil fluorescence to absolute values. Whereas the AOFSCE model is seen as highly promising, further airborne water column Raman conversion efficiency experiments with improved temporal or depth-resolved waveform calibration and software deconvolution techniques are thought necessary for a final determination of suitability.

Improving the efficiency of quantum hash function by dense coding of coin operators in discrete-time quantum walk

NASA Astrophysics Data System (ADS)

Yang, YuGuang; Zhang, YuChen; Xu, Gang; Chen, XiuBo; Zhou, Yi-Hua; Shi, WeiMin

2018-03-01

Li et al. first proposed a quantum hash function (QHF) in a quantum-walk architecture. In their scheme, two two-particle interactions, i.e., I interaction and π-phase interaction are introduced and the choice of I or π-phase interactions at each iteration depends on a message bit. In this paper, we propose an efficient QHF by dense coding of coin operators in discrete-time quantum walk. Compared with existing QHFs, our protocol has the following advantages: the efficiency of the QHF can be doubled and even more; only one particle is enough and two-particle interactions are unnecessary so that quantum resources are saved. It is a clue to apply the dense coding technique to quantum cryptographic protocols, especially to the applications with restricted quantum resources.

Efficient quantum transmission in multiple-source networks.

PubMed

Luo, Ming-Xing; Xu, Gang; Chen, Xiu-Bo; Yang, Yi-Xian; Wang, Xiaojun

2014-04-02

A difficult problem in quantum network communications is how to efficiently transmit quantum information over large-scale networks with common channels. We propose a solution by developing a quantum encoding approach. Different quantum states are encoded into a coherent superposition state using quantum linear optics. The transmission congestion in the common channel may be avoided by transmitting the superposition state. For further decoding and continued transmission, special phase transformations are applied to incoming quantum states using phase shifters such that decoders can distinguish outgoing quantum states. These phase shifters may be precisely controlled using classical chaos synchronization via additional classical channels. Based on this design and the reduction of multiple-source network under the assumption of restricted maximum-flow, the optimal scheme is proposed for specially quantized multiple-source network. In comparison with previous schemes, our scheme can greatly increase the transmission efficiency.

Two-phase thermodynamic model for efficient and accurate absolute entropy of water from molecular dynamics simulations.

PubMed

Lin, Shiang-Tai; Maiti, Prabal K; Goddard, William A

2010-06-24

Presented here is the two-phase thermodynamic (2PT) model for the calculation of energy and entropy of molecular fluids from the trajectory of molecular dynamics (MD) simulations. In this method, the density of state (DoS) functions (including the normal modes of translation, rotation, and intramolecular vibration motions) are determined from the Fourier transform of the corresponding velocity autocorrelation functions. A fluidicity parameter (f), extracted from the thermodynamic state of the system derived from the same MD, is used to partition the translation and rotation modes into a diffusive, gas-like component (with 3Nf degrees of freedom) and a nondiffusive, solid-like component. The thermodynamic properties, including the absolute value of entropy, are then obtained by applying quantum statistics to the solid component and applying hard sphere/rigid rotor thermodynamics to the gas component. The 2PT method produces exact thermodynamic properties of the system in two limiting states: the nondiffusive solid state (where the fluidicity is zero) and the ideal gas state (where the fluidicity becomes unity). We examine the 2PT entropy for various water models (F3C, SPC, SPC/E, TIP3P, and TIP4P-Ew) at ambient conditions and find good agreement with literature results obtained based on other simulation techniques. We also validate the entropy of water in the liquid and vapor phases along the vapor-liquid equilibrium curve from the triple point to the critical point. We show that this method produces converged liquid phase entropy in tens of picoseconds, making it an efficient means for extracting thermodynamic properties from MD simulations.

Intrinsic retrieval efficiency for quantum memories: A three-dimensional theory of light interaction with an atomic ensemble

NASA Astrophysics Data System (ADS)

Gujarati, Tanvi P.; Wu, Yukai; Duan, Luming

2018-03-01

Duan-Lukin-Cirac-Zoller quantum repeater protocol, which was proposed to realize long distance quantum communication, requires usage of quantum memories. Atomic ensembles interacting with optical beams based on off-resonant Raman scattering serve as convenient on-demand quantum memories. Here, a complete free space, three-dimensional theory of the associated read and write process for this quantum memory is worked out with the aim of understanding intrinsic retrieval efficiency. We develop a formalism to calculate the transverse mode structure for the signal and the idler photons and use the formalism to study the intrinsic retrieval efficiency under various configurations. The effects of atomic density fluctuations and atomic motion are incorporated by numerically simulating this system for a range of realistic experimental parameters. We obtain results that describe the variation in the intrinsic retrieval efficiency as a function of the memory storage time for skewed beam configuration at a finite temperature, which provides valuable information for optimization of the retrieval efficiency in experiments.

Terahertz Quantum Cascade Structures Using Step Wells And Longitudinal Optical-Phonon Scattering

DTIC Science & Technology

2009-06-01

emit many photons, which allows for differential quantum efficiencies greater than unity and hence higher power output. QCLs have been successfully...maintained. The step in the well allows for high injection efficiency due to the spatial separation of the wavefunctions. A step quantum well, in which at...III.D.34), the photon density is determined to be ( )thiphotonphoton IILeAn − Γ = ητ (III.D.35) where the internal quantum efficiency

Spin manipulating vector & tensor polarized deuterons stored in COSY

NASA Astrophysics Data System (ADS)

Morozov, V. S.; Krisch, A. D.; Leonova, M. A.; Raymond, R. S.; Sivers, D. W.; Wong, V. K.; Yonehara, K.; Gebel, R.; Lehrach, A.; Lorentz, B.; Maier, R.; Prasuhn, D.; Schnase, A.; Stockhorst, H.; Eversheim, D.; Hinterberger, F.; Rohdjess, H.; Ulbrich, K.

2006-04-01

We recently studied the spin manipulation of a simultaneously vector and tensor polarized deuteron beam stored at 1.85 GeV/c in the COSY Cooler Synchrotron. Using the EDDA detector, we first calibrated the vector and tensor analyzing powers, which were earlier unmeasured at 1.85 GeV/c; this allowed us to measure the absolute values of both the vector and tensor polarizations. Then we manipulated the deuteron's polarization by sweeping the frequency of a ferrite rf dipole through an rf-induced spin resonance. We first experimentally determined the resonance's frequency and then varied the rf dipole's frequency sweep range δf and frequency ramp time δt to maximize the spin-flip efficiency. We then obtained a measured vector spin-flip efficiency of 98.5 ± 0.3% [1]. We also studied, in detail, the behavior of the tensor polarization during spin manipulation; these new data may allow a better understanding of the interesting quantum behavior of spin-1 bosons. This research was supported by the German BMBF Science Ministry. [1] V.S. Morozov et al., Phys. Rev. ST Accel. Beams 8, 061001 (2005).

Implementation of the TDCR liquid scintillation method at CNEA-LMR, Argentina.

PubMed

Arenillas, Pablo; Cassette, Philippe

2006-01-01

During the last two years, a triple-to-double coincidence ratio (TDCR) system was assembled and adjusted at the CNEA-LMR, Argentina. The new counting system will add complementary capabilities to the absolute measurements section of the CNEA-LMR. This work describes its implementation and validation. Several checks and a set of beta-emitting standard solutions were used in order to perform the validation experiments. In preliminary measurements, a 3H LNHB solution with reference activity concentration of (119.7+/-0.9) kBq/g on 11 November 2003 was used. The CNEA-LMR TDCR counter gave, at the same reference date, an activity concentration of (120+/-1) kBq/g. Results and improvements are presented in detail. Concerning the asymmetry of the system, the quantum efficiency of the three photomultiplier tubes was studied for different operating conditions of the focusing voltage. The counter also includes an automatic system to change the efficiency by defocusing the photomultipliers and on the other hand, it was coupled to a HPGe detector to also measure beta-gamma coincidences.

Efficient parallel algorithms for string editing and related problems

NASA Technical Reports Server (NTRS)

Apostolico, Alberto; Atallah, Mikhail J.; Larmore, Lawrence; Mcfaddin, H. S.

1988-01-01

The string editing problem for input strings x and y consists of transforming x into y by performing a series of weighted edit operations on x of overall minimum cost. An edit operation on x can be the deletion of a symbol from x, the insertion of a symbol in x or the substitution of a symbol x with another symbol. This problem has a well known O((absolute value of x)(absolute value of y)) time sequential solution (25). The efficient Program Requirements Analysis Methods (PRAM) parallel algorithms for the string editing problem are given. If m = ((absolute value of x),(absolute value of y)) and n = max((absolute value of x),(absolute value of y)), then the CREW bound is O (log m log n) time with O (mn/log m) processors. In all algorithms, space is O (mn).

Counterfactual quantum key distribution with high efficiency

NASA Astrophysics Data System (ADS)

Sun, Ying; Wen, Qiao-Yan

2010-11-01

In a counterfactual quantum key distribution scheme, a secret key can be generated merely by transmitting the split vacuum pulses of single particles. We improve the efficiency of the first quantum key distribution scheme based on the counterfactual phenomenon. This scheme not only achieves the same security level as the original one but also has higher efficiency. We also analyze how to achieve the optimal efficiency under various conditions.

Counterfactual quantum key distribution with high efficiency

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun Ying; Beijing Electronic Science and Technology Institute, Beijing 100070; Wen Qiaoyan

2010-11-15

In a counterfactual quantum key distribution scheme, a secret key can be generated merely by transmitting the split vacuum pulses of single particles. We improve the efficiency of the first quantum key distribution scheme based on the counterfactual phenomenon. This scheme not only achieves the same security level as the original one but also has higher efficiency. We also analyze how to achieve the optimal efficiency under various conditions.

Apparent bandgap shift in the internal quantum efficiency for solar cells with back reflectors

NASA Astrophysics Data System (ADS)

Steiner, M. A.; Perl, E. E.; Geisz, J. F.; Friedman, D. J.; Jain, N.; Levi, D.; Horner, G.

2017-04-01

We demonstrate that in solar cells with highly reflective back mirrors, the measured internal quantum efficiency exhibits a shift in bandgap relative to the measured external quantum efficiency. The shift arises from the fact that the measured reflectance at the front surface includes a superposition of waves reflecting from the front and back surfaces. We quantify the magnitude of the apparent shift and discuss the errors that can result in determination of quantities such as the photocurrent. Because of this apparent shift, it is important the bandgap be determined from the external quantum efficiency.

Apparent bandgap shift in the internal quantum efficiency for solar cells with back reflectors

DOE PAGES

Steiner, Myles A.; Perl, E. E.; Geisz, J. F.; ...

2017-04-28

Here, we demonstrate that in solar cells with highly reflective back mirrors, the measured internal quantum efficiency exhibits a shift in bandgap relative to the measured external quantum efficiency. The shift arises from the fact that the measured reflectance at the front surface includes a superposition of waves reflecting from the front and back surfaces. We quantify the magnitude of the apparent shift and discuss the errors that can result in determination of quantities such as the photocurrent. Because of this apparent shift, it is important that the bandgap be determined from the external quantum efficiency.

Ultrafast single photon emitting quantum photonic structures based on a nano-obelisk.

PubMed

Kim, Je-Hyung; Ko, Young-Ho; Gong, Su-Hyun; Ko, Suk-Min; Cho, Yong-Hoon

2013-01-01

A key issue in a single photon source is fast and efficient generation of a single photon flux with high light extraction efficiency. Significant progress toward high-efficiency single photon sources has been demonstrated by semiconductor quantum dots, especially using narrow bandgap materials. Meanwhile, there are many obstacles, which restrict the use of wide bandgap semiconductor quantum dots as practical single photon sources in ultraviolet-visible region, despite offering free space communication and miniaturized quantum information circuits. Here we demonstrate a single InGaN quantum dot embedded in an obelisk-shaped GaN nanostructure. The nano-obelisk plays an important role in eliminating dislocations, increasing light extraction, and minimizing a built-in electric field. Based on the nano-obelisks, we observed nonconventional narrow quantum dot emission and positive biexciton binding energy, which are signatures of negligible built-in field in single InGaN quantum dots. This results in efficient and ultrafast single photon generation in the violet color region.

Quantum correlations from a room-temperature optomechanical cavity.

PubMed

Purdy, T P; Grutter, K E; Srinivasan, K; Taylor, J M

2017-06-23

The act of position measurement alters the motion of an object being measured. This quantum measurement backaction is typically much smaller than the thermal motion of a room-temperature object and thus difficult to observe. By shining laser light through a nanomechanical beam, we measure the beam's thermally driven vibrations and perturb its motion with optical force fluctuations at a level dictated by the Heisenberg measurement-disturbance uncertainty relation. We demonstrate a cross-correlation technique to distinguish optically driven motion from thermally driven motion, observing this quantum backaction signature up to room temperature. We use the scale of the quantum correlations, which is determined by fundamental constants, to gauge the size of thermal motion, demonstrating a path toward absolute thermometry with quantum mechanically calibrated ticks. Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

Embedding Quantum Mechanics Into a Broader Noncontextual Theory: A Conciliatory Result

NASA Astrophysics Data System (ADS)

Garola, Claudio; Sozzo, Sandro

2010-12-01

The extended semantic realism ( ESR) model embodies the mathematical formalism of standard (Hilbert space) quantum mechanics in a noncontextual framework, reinterpreting quantum probabilities as conditional instead of absolute. We provide here an improved version of this model and show that it predicts that, whenever idealized measurements are performed, a modified Bell-Clauser-Horne-Shimony-Holt ( BCHSH) inequality holds if one takes into account all individual systems that are prepared, standard quantum predictions hold if one considers only the individual systems that are detected, and a standard BCHSH inequality holds at a microscopic (purely theoretical) level. These results admit an intuitive explanation in terms of an unconventional kind of unfair sampling and constitute a first example of the unified perspective that can be attained by adopting the ESR model.

Generation of heralded entanglement between distant quantum dot hole spins

NASA Astrophysics Data System (ADS)

Delteil, Aymeric

Entanglement plays a central role in fundamental tests of quantum mechanics as well as in the burgeoning field of quantum information processing. Particularly in the context of quantum networks and communication, some of the major challenges are the efficient generation of entanglement between stationary (spin) and propagating (photon) qubits, the transfer of information from flying to stationary qubits, and the efficient generation of entanglement between distant stationary (spin) qubits. In this talk, I will present such experimental implementations achieved in our team with semiconductor self-assembled quantum dots.Not only are self-assembled quantum dots good single-photon emitters, but they can host an electron or a hole whose spin serves as a quantum memory, and then present spin-dependent optical selection rules leading to an efficient spin-photon quantum interface. Moreover InGaAs quantum dots grown on GaAs substrate can profit from the maturity of III-V semiconductor technology and can be embedded in semiconductor structures like photonic cavities and Schottky diodes.I will report on the realization of heralded quantum entanglement between two semiconductor quantum dot hole spins separated by more than five meters. The entanglement generation scheme relies on single photon interference of Raman scattered light from both dots. A single photon detection projects the system into a maximally entangled state. We developed a delayed two-photon interference scheme that allows for efficient verification of quantum correlations. Moreover the efficient spin-photon interface provided by self-assembled quantum dots allows us to reach an unprecedented rate of 2300 entangled spin pairs per second, which represents an improvement of four orders of magnitude as compared to prior experiments carried out in other systems.Our results extend previous demonstrations in single trapped ions or neutral atoms, in atom ensembles and nitrogen vacancy centers to the domain of artificial atoms in semiconductor nanostructures that allow for on-chip integration of electronic and photonic elements. This work lays the groundwork for the realization of quantum repeaters and quantum networks on a chip.

Wide-Band, High-Quantum-Efficiency Photodetector

NASA Technical Reports Server (NTRS)

Jackson, Deborah; Wilson, Daniel; Stern, Jeffrey

2007-01-01

A design has been proposed for a photodetector that would exhibit a high quantum efficiency (as much as 90 percent) over a wide wavelength band, which would typically be centered at a wavelength of 1.55 m. This and similar photodetectors would afford a capability for detecting single photons - a capability that is needed for research in quantum optics as well as for the practical development of secure optical communication systems for distribution of quantum cryptographic keys. The proposed photodetector would be of the hot-electron, phonon-cooled, thin-film superconductor type. The superconducting film in this device would be a meandering strip of niobium nitride. In the proposed photodetector, the quantum efficiency would be increased through incorporation of optiA design has been proposed for a photodetector that would exhibit a high quantum efficiency (as much as 90 percent) over a wide wavelength band, which would typically be centered at a wavelength of 1.55 m. This and similar photodetectors would afford a capability for detecting single photons - a capability that is needed for research in quantum optics as well as for the practical development of secure optical communication systems for distribution of quantum cryptographic keys. The proposed photodetector would be of the hot-electron, phonon-cooled, thin-film superconductor type. The superconducting film in this device would be a meandering strip of niobium nitride. In the proposed photodetector, the quantum efficiency would be increased through incorporation of opti-

Efficient Merge and Insert Operations for Binary Heaps and Trees

NASA Technical Reports Server (NTRS)

Kuszmaul, Christopher Lee; Woo, Alex C. (Technical Monitor)

2000-01-01

Binary heaps and binary search trees merge efficiently. We introduce a new amortized analysis that allows us to prove the cost of merging either binary heaps or balanced binary trees is O(l), in the amortized sense. The standard set of other operations (create, insert, delete, extract minimum, in the case of binary heaps, and balanced binary trees, as well as a search operation for balanced binary trees) remain with a cost of O(log n). For binary heaps implemented as arrays, we show a new merge algorithm that has a single operation cost for merging two heaps, a and b, of O(absolute value of a + min(log absolute value of b log log absolute value of b. log absolute value of a log absolute value of b). This is an improvement over O(absolute value of a + log absolute value of a log absolute value of b). The cost of the new merge is so low that it can be used in a new structure which we call shadow heaps. to implement the insert operation to a tunable efficiency. Shadow heaps support the insert operation for simple priority queues in an amortized time of O(f(n)) and other operations in time O((log n log log n)/f (n)), where 1 less than or equal to f (n) less than or equal to log log n. More generally, the results here show that any data structure with operations that change its size by at most one, with the exception of a merge (aka meld) operation, can efficiently amortize the cost of the merge under conditions that are true for most implementations of binary heaps and search trees.

Technique for long and absolute distance measurement based on laser pulse repetition frequency sweeping

NASA Astrophysics Data System (ADS)

Castro Alves, D.; Abreu, Manuel; Cabral, A.; Jost, Michael; Rebordão, J. M.

2017-11-01

In this work we present a technique to perform long and absolute distance measurements based on mode-locked diode lasers. Using a Michelson interferometer, it is possible to produce an optical cross-correlation between laser pulses of the reference arm with the pulses from the measurement arm, adjusting externally their degree of overlap either changing the pulse repetition frequency (PRF) or the position of the reference arm mirror for two (or more) fixed frequencies. The correlation of the travelling pulses for precision distance measurements relies on ultra-short pulse durations, as the uncertainty associated to the method is dependent on the laser pulse width as well as on a highly stable PRF. Mode-locked Diode lasers are a very appealing technology for its inherent characteristics, associated to compactness, size and efficiency, constituting a positive trade-off with regard to other mode-locked laser sources. Nevertheless, main current drawback is the non-availability of frequency-stable laser diodes. The laser used is a monolithic mode-locked semiconductor quantum-dot (QD) laser. The laser PRF is locked to an external stabilized RF reference. In this work we will present some of the preliminary results and discuss the importance of the requirements related to laser PRF stability in the final metrology system accuracy.

Quantum transport in the FMO photosynthetic light-harvesting complex.

PubMed

Karafyllidis, Ioannis G

2017-06-01

The very high light-harvesting efficiency of natural photosynthetic systems in conjunction with recent experiments, which showed quantum-coherent energy transfer in photosynthetic complexes, raised questions regarding the presence of non-trivial quantum effects in photosynthesis. Grover quantum search, quantum walks, and entanglement have been investigated as possible effects that lead to this efficiency. Here we explain the near-unit photosynthetic efficiency without invoking non-trivial quantum effects. Instead, we use non-equilibrium Green's functions, a mesoscopic method used to study transport in nano-conductors to compute the transmission function of the Fenna-Matthews-Olson (FMO) complex using an experimentally derived exciton Hamiltonian. The chlorosome antenna and the reaction center play the role of input and output contacts, connected to the FMO complex. We show that there are two channels for which the transmission is almost unity. Our analysis also revealed a dephasing-driven regulation mechanism that maintains the efficiency in the presence of varying dephasing potentials.

A Biomimetic-Computational Approach to Optimizing the Quantum Efficiency of Photovoltaics

NASA Astrophysics Data System (ADS)

Perez, Lisa M.; Holzenburg, Andreas

The most advanced low-cost organic photovoltaic cells have a quantum efficiency of 10%. This is in stark contrast to plant/bacterial light-harvesting systems which offer quantum efficiencies close to unity. Of particular interest is the highly effective quantum coherence-enabled energy transfer (Fig. 1). Noting that quantum coherence is promoted by charged residues and local dielectrics, classical atomistic simulations and time-dependent density functional theory (DFT) are used to identify charge/dielectric patterns and electronic coupling at exactly defined energy transfer interfaces. The calculations make use of structural information obtained on photosynthetic protein-pigment complexes while still in the native membrane making it possible to establish a link between supramolecular organization and quantum coherence in terms of what length scales enable fast energy transport and prevent quenching. Calculating energy transfer efficiencies between components based on different proximities will permit the search for patterns that enable defining material properties suitable for advanced photovoltaics.

Highly efficient frequency conversion with bandwidth compression of quantum light

PubMed Central

Allgaier, Markus; Ansari, Vahid; Sansoni, Linda; Eigner, Christof; Quiring, Viktor; Ricken, Raimund; Harder, Georg; Brecht, Benjamin; Silberhorn, Christine

2017-01-01

Hybrid quantum networks rely on efficient interfacing of dissimilar quantum nodes, as elements based on parametric downconversion sources, quantum dots, colour centres or atoms are fundamentally different in their frequencies and bandwidths. Although pulse manipulation has been demonstrated in very different systems, to date no interface exists that provides both an efficient bandwidth compression and a substantial frequency translation at the same time. Here we demonstrate an engineered sum-frequency-conversion process in lithium niobate that achieves both goals. We convert pure photons at telecom wavelengths to the visible range while compressing the bandwidth by a factor of 7.47 under preservation of non-classical photon-number statistics. We achieve internal conversion efficiencies of 61.5%, significantly outperforming spectral filtering for bandwidth compression. Our system thus makes the connection between previously incompatible quantum systems as a step towards usable quantum networks. PMID:28134242

On the effect of ballistic overflow on the temperature dependence of the quantum efficiency of InGaN/GaN multiple quantum well light-emitting diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prudaev, I. A., E-mail: funcelab@gmail.com; Kopyev, V. V.; Romanov, I. S.

The dependences of the quantum efficiency of InGaN/GaN multiple quantum well light-emitting diodes on the temperature and excitation level are studied. The experiment is performed for two luminescence excitation modes. A comparison of the results obtained during photo- and electroluminescence shows an additional (to the loss associated with Auger recombination) low-temperature loss in the high-density current region. This causes inversion of the temperature dependence of the quantum efficiency at temperatures lower than 220–300 K. Analysis shows that the loss is associated with electron leakage from the light-emitting-diode active region. The experimental data are explained using the ballistic-overflow model. The simulationmore » results are in qualitative agreement with the experimental dependences of the quantum efficiency on temperature and current density.« less

Emulsion Synthesis of Size-Tunable CH3NH3PbBr3 Quantum Dots: An Alternative Route toward Efficient Light-Emitting Diodes.

PubMed

Huang, Hailong; Zhao, Fangchao; Liu, Lige; Zhang, Feng; Wu, Xian-gang; Shi, Lijie; Zou, Bingsuo; Pei, Qibing; Zhong, Haizheng

2015-12-30

We report a facile nonaqueous emulsion synthesis of colloidal halide perovskite quantum dots by controlled addition of a demulsifier into an emulsion of precursors. The size of resulting CH3NH3PbBr3 quantum dots can be tuned from 2 to 8 nm by varying the amount of demulsifier. Moreover, this emulsion synthesis also allows the purification of these quantum dots by precipitation from the colloidal solution and obtains solid-state powder which can be redissolved for thin film coating and device fabrication. The photoluminescence quantum yields of the quantum dots is generally in the range of 80-92%, and can be well-preserved after purification (∼80%). Green light-emitting diodes fabricated comprising a spin-cast layer of the colloidal CH3NH3PbBr3 quantum dots exhibited maximum current efficiency of 4.5 cd/A, power efficiency of 3.5 lm/W, and external quantum efficiency of 1.1%. This provides an alternative route toward high efficient solution-processed perovskite-based light-emitting diodes. In addition, the emulsion synthesis is versatile and can be extended for the fabrication of inorganic halide perovskite colloidal CsPbBr3 nanocrystals.

Quantum autoencoders for efficient compression of quantum data

NASA Astrophysics Data System (ADS)

Romero, Jonathan; Olson, Jonathan P.; Aspuru-Guzik, Alan

2017-12-01

Classical autoencoders are neural networks that can learn efficient low-dimensional representations of data in higher-dimensional space. The task of an autoencoder is, given an input x, to map x to a lower dimensional point y such that x can likely be recovered from y. The structure of the underlying autoencoder network can be chosen to represent the data on a smaller dimension, effectively compressing the input. Inspired by this idea, we introduce the model of a quantum autoencoder to perform similar tasks on quantum data. The quantum autoencoder is trained to compress a particular data set of quantum states, where a classical compression algorithm cannot be employed. The parameters of the quantum autoencoder are trained using classical optimization algorithms. We show an example of a simple programmable circuit that can be trained as an efficient autoencoder. We apply our model in the context of quantum simulation to compress ground states of the Hubbard model and molecular Hamiltonians.

Efficient Quantum Transmission in Multiple-Source Networks

PubMed Central

Luo, Ming-Xing; Xu, Gang; Chen, Xiu-Bo; Yang, Yi-Xian; Wang, Xiaojun

2014-01-01

A difficult problem in quantum network communications is how to efficiently transmit quantum information over large-scale networks with common channels. We propose a solution by developing a quantum encoding approach. Different quantum states are encoded into a coherent superposition state using quantum linear optics. The transmission congestion in the common channel may be avoided by transmitting the superposition state. For further decoding and continued transmission, special phase transformations are applied to incoming quantum states using phase shifters such that decoders can distinguish outgoing quantum states. These phase shifters may be precisely controlled using classical chaos synchronization via additional classical channels. Based on this design and the reduction of multiple-source network under the assumption of restricted maximum-flow, the optimal scheme is proposed for specially quantized multiple-source network. In comparison with previous schemes, our scheme can greatly increase the transmission efficiency. PMID:24691590

Effects of quantum well growth temperature on the recombination efficiency of InGaN/GaN multiple quantum wells that emit in the green and blue spectral regions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hammersley, S.; Dawson, P.; Kappers, M. J.

2015-09-28

InGaN-based light emitting diodes and multiple quantum wells designed to emit in the green spectral region exhibit, in general, lower internal quantum efficiencies than their blue-emitting counter parts, a phenomenon referred to as the “green gap.” One of the main differences between green-emitting and blue-emitting samples is that the quantum well growth temperature is lower for structures designed to emit at longer wavelengths, in order to reduce the effects of In desorption. In this paper, we report on the impact of the quantum well growth temperature on the optical properties of InGaN/GaN multiple quantum wells designed to emit at 460 nmmore » and 530 nm. It was found that for both sets of samples increasing the temperature at which the InGaN quantum well was grown, while maintaining the same indium composition, led to an increase in the internal quantum efficiency measured at 300 K. These increases in internal quantum efficiency are shown to be due reductions in the non-radiative recombination rate which we attribute to reductions in point defect incorporation.« less

Resolving the vacuum fluctuations of an optomechanical system using an artificial atom

NASA Astrophysics Data System (ADS)

Lecocq, F.; Teufel, J. D.; Aumentado, J.; Simmonds, R. W.

2015-08-01

Heisenberg’s uncertainty principle results in one of the strangest quantum behaviours: a mechanical oscillator can never truly be at rest. Even at a temperature of absolute zero, its position and momentum are still subject to quantum fluctuations. However, direct energy detection of the oscillator in its ground state makes it seem motionless, and in linear position measurements detector noise can masquerade as mechanical fluctuations. Thus, how can we resolve quantum fluctuations? Here, we parametrically couple a micromechanical oscillator to a microwave cavity to prepare the system in its quantum ground state and then amplify the remaining vacuum fluctuations into real energy quanta. We monitor the photon/phonon-number distributions using a superconducting qubit, allowing us to resolve the quantum vacuum fluctuations of the macroscopic oscillator’s motion. Our results further demonstrate the ability to control a long-lived mechanical oscillator using a non-Gaussian resource, directly enabling applications in quantum information processing and enhanced detection of displacement and forces.

Efficient multiuser quantum cryptography network based on entanglement.

PubMed

Xue, Peng; Wang, Kunkun; Wang, Xiaoping

2017-04-04

We present an efficient quantum key distribution protocol with a certain entangled state to solve a special cryptographic task. Also, we provide a proof of security of this protocol by generalizing the proof of modified of Lo-Chau scheme. Based on this two-user scheme, a quantum cryptography network protocol is proposed without any quantum memory.

Efficient multiuser quantum cryptography network based on entanglement

PubMed Central

Xue, Peng; Wang, Kunkun; Wang, Xiaoping

2017-01-01

We present an efficient quantum key distribution protocol with a certain entangled state to solve a special cryptographic task. Also, we provide a proof of security of this protocol by generalizing the proof of modified of Lo-Chau scheme. Based on this two-user scheme, a quantum cryptography network protocol is proposed without any quantum memory. PMID:28374854

Efficient multiuser quantum cryptography network based on entanglement

NASA Astrophysics Data System (ADS)

Xue, Peng; Wang, Kunkun; Wang, Xiaoping

2017-04-01

We present an efficient quantum key distribution protocol with a certain entangled state to solve a special cryptographic task. Also, we provide a proof of security of this protocol by generalizing the proof of modified of Lo-Chau scheme. Based on this two-user scheme, a quantum cryptography network protocol is proposed without any quantum memory.

Quantum entanglement helps in improving economic efficiency

NASA Astrophysics Data System (ADS)

Du, Jiangfeng; Ju, Chenyong; Li, Hui

2005-02-01

We propose an economic regulation approach based on quantum game theory for the government to reduce the abuses of oligopolistic competition. Theoretical analysis shows that this approach can help government improve the economic efficiency of the oligopolistic market, and help prevent monopoly due to incorrect information. These advantages are completely attributed to the quantum entanglement, a unique quantum mechanical character.

Single-hidden-layer feed-forward quantum neural network based on Grover learning.

PubMed

Liu, Cheng-Yi; Chen, Chein; Chang, Ching-Ter; Shih, Lun-Min

2013-09-01

In this paper, a novel single-hidden-layer feed-forward quantum neural network model is proposed based on some concepts and principles in the quantum theory. By combining the quantum mechanism with the feed-forward neural network, we defined quantum hidden neurons and connected quantum weights, and used them as the fundamental information processing unit in a single-hidden-layer feed-forward neural network. The quantum neurons make a wide range of nonlinear functions serve as the activation functions in the hidden layer of the network, and the Grover searching algorithm outstands the optimal parameter setting iteratively and thus makes very efficient neural network learning possible. The quantum neuron and weights, along with a Grover searching algorithm based learning, result in a novel and efficient neural network characteristic of reduced network, high efficient training and prospect application in future. Some simulations are taken to investigate the performance of the proposed quantum network and the result show that it can achieve accurate learning. Copyright © 2013 Elsevier Ltd. All rights reserved.

Energy dispersive X-ray analysis on an absolute scale in scanning transmission electron microscopy.

PubMed

Chen, Z; D'Alfonso, A J; Weyland, M; Taplin, D J; Allen, L J; Findlay, S D

2015-10-01

We demonstrate absolute scale agreement between the number of X-ray counts in energy dispersive X-ray spectroscopy using an atomic-scale coherent electron probe and first-principles simulations. Scan-averaged spectra were collected across a range of thicknesses with precisely determined and controlled microscope parameters. Ionization cross-sections were calculated using the quantum excitation of phonons model, incorporating dynamical (multiple) electron scattering, which is seen to be important even for very thin specimens. Copyright © 2015 Elsevier B.V. All rights reserved.

Exponential bound in the quest for absolute zero

NASA Astrophysics Data System (ADS)

Stefanatos, Dionisis

2017-10-01

In most studies for the quantification of the third law of thermodynamics, the minimum temperature which can be achieved with a long but finite-time process scales as a negative power of the process duration. In this article, we use our recent complete solution for the optimal control problem of the quantum parametric oscillator to show that the minimum temperature which can be obtained in this system scales exponentially with the available time. The present work is expected to motivate further research in the active quest for absolute zero.

Exponential bound in the quest for absolute zero.

PubMed

Stefanatos, Dionisis

2017-10-01

In most studies for the quantification of the third law of thermodynamics, the minimum temperature which can be achieved with a long but finite-time process scales as a negative power of the process duration. In this article, we use our recent complete solution for the optimal control problem of the quantum parametric oscillator to show that the minimum temperature which can be obtained in this system scales exponentially with the available time. The present work is expected to motivate further research in the active quest for absolute zero.

Hybrid quantum computing with ancillas

NASA Astrophysics Data System (ADS)

Proctor, Timothy J.; Kendon, Viv

2016-10-01

In the quest to build a practical quantum computer, it is important to use efficient schemes for enacting the elementary quantum operations from which quantum computer programs are constructed. The opposing requirements of well-protected quantum data and fast quantum operations must be balanced to maintain the integrity of the quantum information throughout the computation. One important approach to quantum operations is to use an extra quantum system - an ancilla - to interact with the quantum data register. Ancillas can mediate interactions between separated quantum registers, and by using fresh ancillas for each quantum operation, data integrity can be preserved for longer. This review provides an overview of the basic concepts of the gate model quantum computer architecture, including the different possible forms of information encodings - from base two up to continuous variables - and a more detailed description of how the main types of ancilla-mediated quantum operations provide efficient quantum gates.

Efficiency and its bounds for a quantum Einstein engine at maximum power.

PubMed

Yan, H; Guo, Hao

2012-11-01

We study a quantum thermal engine model for which the heat transfer law is determined by Einstein's theory of radiation. The working substance of the quantum engine is assumed to be a two-level quantum system of which the constituent particles obey Maxwell-Boltzmann (MB), Fermi-Dirac (FD), or Bose-Einstein (BE) distributions, respectively, at equilibrium. The thermal efficiency and its bounds at maximum power of these models are derived and discussed in the long and short thermal contact time limits. The similarity and difference between these models are discussed. We also compare the efficiency bounds of this quantum thermal engine to those of its classical counterpart.

Light storage in a cold atomic ensemble with a high optical depth

NASA Astrophysics Data System (ADS)

Park, Kwang-Kyoon; Chough, Young-Tak; Kim, Yoon-Ho

2017-06-01

A quantum memory with a high storage efficiency and a long coherence time is an essential element in quantum information applications. Here, we report our recent development of an optical quantum memory with a rubidium-87 cold atom ensemble. By increasing the optical depth of the medium, we have achieved a storage efficiency of 65% and a coherence time of 51 μs for a weak laser pulse. The result of a numerical analysis based on the Maxwell-Bloch equations agrees well with the experimental results. Our result paves the way toward an efficient optical quantum memory and may find applications in photonic quantum information processing.

The quantum efficiency of HgCdTe photodiodes in relation to the direction of illumination and to their geometry

NASA Technical Reports Server (NTRS)

Rosenfeld, D.; Bahir, G.

1993-01-01

A theoretical study of the effect of the direction of the incident light on the quantum efficiency of homogeneous HgCdTe photodiodes suitable for sensing infrared radiation in the 8-12 microns atmospheric window is presented. The probability of an excess minority carrier to reach the junction is derived as a function of its distance from the edge of the depletion region. Accordingly, the quantum efficiency of photodiodes is presented for two geometries. In the first, the light is introduced directly to the area in which it is absorbed (opaque region), while in the second, the light passes through a transparent region before it reaches the opaque region. Finally, the performance of the two types of diodes is analyzed with the objective of finding the optimal width of the absorption area. The quantum efficiency depends strongly on the way in which the light is introduced. The structure in which the radiation is absorbed following its crossing the transparent region is associated with both higher quantum efficiency and homogeneity. In addition, for absorption region widths higher than a certain minimum, the quantum efficiency in this case is insensitive to the width of the absorption region.

Preparation of reflective CsI photocathodes with reproducible high quantum efficiency

NASA Astrophysics Data System (ADS)

Maier-Komor, P.; Bauer, B. B.; Friese, J.; Gernhäuser, R.; Kienle, P.; Körner, H. J.; Montermann, G.; Zeitelhack, K.

1995-02-01

CsI as a solid UV-photocathode material has many promising applications in fast gaseous photon detectors. They are proposed in large area Ring Imaging CHerenkov (RICH) devices in forthcoming experiments at various high-energy particle accelerators. A high photon-to-electron conversion efficiency is a basic requirement for the successful operation of these devices. High reproducible quantum efficiencies could be achieved with CsI layers prepared by electron beam evaporation from a water-cooled copper crucible. CsI films were deposited in the thickness range of 30 to 500 μg/cm 2. Absorption coefficients and quantum efficiencies were measured in the wavelength region of 150 nm to 250 nm. The influence of various evaporation parameters on the quantum efficiency were investigated.

Multiple-state quantum Otto engine, 1D box system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Latifah, E., E-mail: enylatifah@um.ac.id; Purwanto, A.

2014-03-24

Quantum heat engines produce work using quantum matter as their working substance. We studied adiabatic and isochoric processes and defined the general force according to quantum system. The processes and general force are used to evaluate a quantum Otto engine based on multiple-state of one dimensional box system and calculate the efficiency. As a result, the efficiency depends on the ratio of initial and final width of system under adiabatic processes.

Analysis of the external and internal quantum efficiency of multi-emitter, white organic light emitting diodes

NASA Astrophysics Data System (ADS)

Furno, Mauro; Rosenow, Thomas C.; Gather, Malte C.; Lüssem, Björn; Leo, Karl

2012-10-01

We report on a theoretical framework for the efficiency analysis of complex, multi-emitter organic light emitting diodes (OLEDs). The calculation approach makes use of electromagnetic modeling to quantify the overall OLED photon outcoupling efficiency and a phenomenological description for electrical and excitonic processes. From the comparison of optical modeling results and measurements of the total external quantum efficiency, we obtain reliable estimates of internal quantum yield. As application of the model, we analyze high-efficiency stacked white OLEDs and comment on the various efficiency loss channels present in the devices.

Fundamental rate-loss trade-off for the quantum internet

NASA Astrophysics Data System (ADS)

Azuma, Koji; Mizutani, Akihiro; Lo, Hoi-Kwong

2016-11-01

The quantum internet holds promise for achieving quantum communication--such as quantum teleportation and quantum key distribution (QKD)--freely between any clients all over the globe, as well as for the simulation of the evolution of quantum many-body systems. The most primitive function of the quantum internet is to provide quantum entanglement or a secret key to two points efficiently, by using intermediate nodes connected by optical channels with each other. Here we derive a fundamental rate-loss trade-off for a quantum internet protocol, by generalizing the Takeoka-Guha-Wilde bound to be applicable to any network topology. This trade-off has essentially no scaling gap with the quantum communication efficiencies of protocols known to be indispensable to long-distance quantum communication, such as intercity QKD and quantum repeaters. Our result--putting a practical but general limitation on the quantum internet--enables us to grasp the potential of the future quantum internet.

Fundamental rate-loss trade-off for the quantum internet

PubMed Central

Azuma, Koji; Mizutani, Akihiro; Lo, Hoi-Kwong

2016-01-01

The quantum internet holds promise for achieving quantum communication—such as quantum teleportation and quantum key distribution (QKD)—freely between any clients all over the globe, as well as for the simulation of the evolution of quantum many-body systems. The most primitive function of the quantum internet is to provide quantum entanglement or a secret key to two points efficiently, by using intermediate nodes connected by optical channels with each other. Here we derive a fundamental rate-loss trade-off for a quantum internet protocol, by generalizing the Takeoka–Guha–Wilde bound to be applicable to any network topology. This trade-off has essentially no scaling gap with the quantum communication efficiencies of protocols known to be indispensable to long-distance quantum communication, such as intercity QKD and quantum repeaters. Our result—putting a practical but general limitation on the quantum internet—enables us to grasp the potential of the future quantum internet. PMID:27886172

Fundamental rate-loss trade-off for the quantum internet.

PubMed

Azuma, Koji; Mizutani, Akihiro; Lo, Hoi-Kwong

2016-11-25

The quantum internet holds promise for achieving quantum communication-such as quantum teleportation and quantum key distribution (QKD)-freely between any clients all over the globe, as well as for the simulation of the evolution of quantum many-body systems. The most primitive function of the quantum internet is to provide quantum entanglement or a secret key to two points efficiently, by using intermediate nodes connected by optical channels with each other. Here we derive a fundamental rate-loss trade-off for a quantum internet protocol, by generalizing the Takeoka-Guha-Wilde bound to be applicable to any network topology. This trade-off has essentially no scaling gap with the quantum communication efficiencies of protocols known to be indispensable to long-distance quantum communication, such as intercity QKD and quantum repeaters. Our result-putting a practical but general limitation on the quantum internet-enables us to grasp the potential of the future quantum internet.

Radiometric characterization of type-II InAs/GaSb superlattice (t2sl) midwave infrared photodetectors and focal plane arrays

NASA Astrophysics Data System (ADS)

Nghiem, Jean; Giard, E.; Delmas, M.; Rodriguez, J. B.; Christol, P.; Caes, M.; Martijn, H.; Costard, E.; Ribet-Mohamed, I.

2017-09-01

In recent years, Type-II InAs/GaSb superlattice (T2SL) has emerged as a new material technology suitable for high performance infrared (IR) detectors operating from Near InfraRed (NIR, 2-3μm) to Very Long Wavelength InfraRed (LWIR, λ > 15μm) wavelength domains. To compare their performances with well-established IR technologies such as MCT, InSb or QWIP cooled detectors, specific electrical and radiometric characterizations are needed: dark current, spectral response, quantum efficiency, temporal and spatial noises, stability… In this paper, we first present quantum efficiency measurements performed on T2SL MWIR (3-5μm) photodiodes and on one focal plane array (320x256 pixels with 30μm pitch, realized in the scope of a french collaboration ). Different T2SL structures (InAs-rich versus GaSb-rich) with the same cutoff wavelength (λc= 5μm at 80K) were studied. Results are analysed in term of carrier diffusion length in order to define the optimum thickness and type of doping of the absorbing zone. We then focus on the stability over time of a commercial T2SL FPA (320x256 pixels with 30μm pitch), measuring the commonly used residual fixed pattern noise (RFPN) figure of merit. Results are excellent, with a very stable behaviour over more than 3 weeks, and less than 10 flickering pixels, possibly giving access to long-term stability of IR absolute calibration.

Universality of Generalized Bunching and Efficient Assessment of Boson Sampling.

PubMed

Shchesnovich, V S

2016-03-25

It is found that identical bosons (fermions) show a generalized bunching (antibunching) property in linear networks: the absolute maximum (minimum) of the probability that all N input particles are detected in a subset of K output modes of any nontrivial linear M-mode network is attained only by completely indistinguishable bosons (fermions). For fermions K is arbitrary; for bosons it is either (i) arbitrary for only classically correlated bosons or (ii) satisfies K≥N (or K=1) for arbitrary input states of N particles. The generalized bunching allows us to certify in a polynomial in N number of runs that a physical device realizing boson sampling with an arbitrary network operates in the regime of full quantum coherence compatible only with completely indistinguishable bosons. The protocol needs only polynomial classical computations for the standard boson sampling, whereas an analytic formula is available for the scattershot version.

Network of time-multiplexed optical parametric oscillators as a coherent Ising machine

NASA Astrophysics Data System (ADS)

Marandi, Alireza; Wang, Zhe; Takata, Kenta; Byer, Robert L.; Yamamoto, Yoshihisa

2014-12-01

Finding the ground states of the Ising Hamiltonian maps to various combinatorial optimization problems in biology, medicine, wireless communications, artificial intelligence and social network. So far, no efficient classical and quantum algorithm is known for these problems and intensive research is focused on creating physical systems—Ising machines—capable of finding the absolute or approximate ground states of the Ising Hamiltonian. Here, we report an Ising machine using a network of degenerate optical parametric oscillators (OPOs). Spins are represented with above-threshold binary phases of the OPOs and the Ising couplings are realized by mutual injections. The network is implemented in a single OPO ring cavity with multiple trains of femtosecond pulses and configurable mutual couplings, and operates at room temperature. We programmed a small non-deterministic polynomial time-hard problem on a 4-OPO Ising machine and in 1,000 runs no computational error was detected.

United time-frequency spectroscopy for dynamics and global structure.

PubMed

Marian, Adela; Stowe, Matthew C; Lawall, John R; Felinto, Daniel; Ye, Jun

2004-12-17

Ultrashort laser pulses have thus far been used in two distinct modes. In the time domain, the pulses have allowed probing and manipulation of dynamics on a subpicosecond time scale. More recently, phase stabilization has produced optical frequency combs with absolute frequency reference across a broad bandwidth. Here we combine these two applications in a spectroscopic study of rubidium atoms. A wide-bandwidth, phase-stabilized femtosecond laser is used to monitor the real-time dynamic evolution of population transfer. Coherent pulse accumulation and quantum interference effects are observed and well modeled by theory. At the same time, the narrow linewidth of individual comb lines permits a precise and efficient determination of the global energy-level structure, providing a direct connection among the optical, terahertz, and radio-frequency domains. The mechanical action of the optical frequency comb on the atomic sample is explored and controlled, leading to precision spectroscopy with an appreciable reduction in systematic errors.

Photoluminescence Spectra From The Direct Energy Gap of a-SiQDs

NASA Astrophysics Data System (ADS)

Abdul-Ameer, Nidhal M.; Abdulrida, Moafak C.; Abdul-Hakeem, Shatha M.

2018-05-01

A theoretical model for radiative recombination in amorphous silicon quantum dots (a-SiQDs) was developed. In this model, for the first time, the coexistence of both spatial and quantum confinements were considered. Also, it is found that the photoluminescence exhibits significant size dependence in the range (1-4) nm of the quantum dots. a-SiQDs show visible light emission peak energies and high radiative quantum efficiency at room temperature,in contrast to bulk a-Si structures. The quantum efficiency is sensitive to any change in defect density (the volume nonradiative centers density and/or the surface nonradiative centers density) but, with small dots sizes, the quantum efficiency is insensitive to such defects. Our analysis shows that the photoluminescence intensity increases or decreases by the effect of radiative quantum efficiency. By controlling the size of a-SiQDs, we note that the energy of emission can be tuned. The blue shift is attributed to quantum confinement effect. Meanwhile, the spatial confinement effect is clearly observed in red shift in emission spectra. we found a good agreement with the experimental published data. Therefore, we assert that a-SiQDs material is a promising candidate for visible, tunable, and high performance devices of light emitting.

Efficiency at Maximum Power Output of a Quantum-Mechanical Brayton Cycle

NASA Astrophysics Data System (ADS)

Yuan, Yuan; He, Ji-Zhou; Gao, Yong; Wang, Jian-Hui

2014-03-01

The performance in finite time of a quantum-mechanical Brayton engine cycle is discussed, without introduction of temperature. The engine model consists of two quantum isoenergetic and two quantum isobaric processes, and works with a single particle in a harmonic trap. Directly employing the finite-time thermodynamics, the efficiency at maximum power output is determined. Extending the harmonic trap to a power-law trap, we find that the efficiency at maximum power is independent of any parameter involved in the model, but depends on the confinement of the trapping potential.

Reliable quantum communication over a quantum relay channel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gyongyosi, Laszlo, E-mail: gyongyosi@hit.bme.hu; Imre, Sandor

2014-12-04

We show that reliable quantum communication over an unreliable quantum relay channels is possible. The coding scheme combines the results on the superadditivity of quantum channels and the efficient quantum coding approaches.

Direct determination of quantum efficiency of semiconducting films

DOEpatents

Faughnan, Brian W.; Hanak, Joseph J.

1986-01-01

Photovoltaic quantum efficiency of semiconductor samples is determined directly, without requiring that a built-in photovoltage be generated by the sample. Electrodes are attached to the sample so as to form at least one Schottky barrier therewith. When illuminated, the generated photocurrent carriers are collected by an external bias voltage impressed across the electrodes. The generated photocurrent is measured, and photovoltaic quantum efficiency is calculated therefrom.

Direct determination of quantum efficiency of semiconducting films

DOEpatents

Faughnan, B.W.; Hanak, J.J.

Photovoltaic quantum efficiency of semiconductor samples is determined directly, without requiring that a built-in photovoltage be generated by the sample. Electrodes are attached to the sample so as to form at least one Schottky barrier therewith. When illuminated, the generated photocurrent carriers are collected by an external bias voltage impressed across the electrodes. The generated photocurrent is measured, and photovoltaic quantum efficiency is calculated therefrom.

Communications: quantum teleportation across the Danube.

PubMed

Ursin, Rupert; Jennewein, Thomas; Aspelmeyer, Markus; Kaltenbaek, Rainer; Lindenthal, Michael; Walther, Philip; Zeilinger, Anton

2004-08-19

Efficient long-distance quantum teleportation is crucial for quantum communication and quantum networking schemes. Here we describe the high-fidelity teleportation of photons over a distance of 600 metres across the River Danube in Vienna, with the optimal efficiency that can be achieved using linear optics. Our result is a step towards the implementation of a quantum repeater, which will enable pure entanglement to be shared between distant parties in a public environment and eventually on a worldwide scale.

Efficient entanglement distillation without quantum memory.

PubMed

Abdelkhalek, Daniela; Syllwasschy, Mareike; Cerf, Nicolas J; Fiurášek, Jaromír; Schnabel, Roman

2016-05-31

Entanglement distribution between distant parties is an essential component to most quantum communication protocols. Unfortunately, decoherence effects such as phase noise in optical fibres are known to demolish entanglement. Iterative (multistep) entanglement distillation protocols have long been proposed to overcome decoherence, but their probabilistic nature makes them inefficient since the success probability decays exponentially with the number of steps. Quantum memories have been contemplated to make entanglement distillation practical, but suitable quantum memories are not realised to date. Here, we present the theory for an efficient iterative entanglement distillation protocol without quantum memories and provide a proof-of-principle experimental demonstration. The scheme is applied to phase-diffused two-mode-squeezed states and proven to distil entanglement for up to three iteration steps. The data are indistinguishable from those that an efficient scheme using quantum memories would produce. Since our protocol includes the final measurement it is particularly promising for enhancing continuous-variable quantum key distribution.

Efficient entanglement distillation without quantum memory

PubMed Central

Abdelkhalek, Daniela; Syllwasschy, Mareike; Cerf, Nicolas J.; Fiurášek, Jaromír; Schnabel, Roman

2016-01-01

Entanglement distribution between distant parties is an essential component to most quantum communication protocols. Unfortunately, decoherence effects such as phase noise in optical fibres are known to demolish entanglement. Iterative (multistep) entanglement distillation protocols have long been proposed to overcome decoherence, but their probabilistic nature makes them inefficient since the success probability decays exponentially with the number of steps. Quantum memories have been contemplated to make entanglement distillation practical, but suitable quantum memories are not realised to date. Here, we present the theory for an efficient iterative entanglement distillation protocol without quantum memories and provide a proof-of-principle experimental demonstration. The scheme is applied to phase-diffused two-mode-squeezed states and proven to distil entanglement for up to three iteration steps. The data are indistinguishable from those that an efficient scheme using quantum memories would produce. Since our protocol includes the final measurement it is particularly promising for enhancing continuous-variable quantum key distribution. PMID:27241946

High Storage Efficiency and Large Fractional Delay of EIT-Based Memory

NASA Astrophysics Data System (ADS)

Chen, Yi-Hsin; Lee, Meng-Jung; Wang, I.-Chung; Du, Shengwang; Chen, Yong-Fan; Chen, Ying-Cheng; Yu, Ite

2013-05-01

In long-distance quantum communication and optical quantum computation, an efficient and long-lived quantum memory is an important component. We first experimentally demonstrated that a time-space-reversing method plus the optimum pulse shape can improve the storage efficiency (SE) of light pulses to 78% in cold media based on the effect of electromagnetically induced transparency (EIT). We obtain a large fractional delay of 74 at 50% SE, which is the best record so far. The measured classical fidelity of the recalled pulse is higher than 90% and nearly independent of the storage time, implying that the optical memory maintains excellent phase coherence. Our results suggest the current result may be readily applied to single-photon quantum states due to quantum nature of the EIT light-matter inference. This study advances the EIT-based quantum memory in practical quantum information applications.

Efficient hydrogen isotopologues separation through a tunable potential barrier: The case of a C2N membrane.

PubMed

Qu, Yuanyuan; Li, Feng; Zhao, Mingwen

2017-05-03

Isotopes separation through quantum sieving effect of membranes is quite promising for industrial applications. For the light hydrogen isotopologues (eg. H 2 , D 2 ), the confinement of potential wells in porous membranes to isotopologues was commonly regarded to be crucial for highly efficient separation ability. Here, we demonstrate from first-principles that a potential barrier is also favorable for efficient hydrogen isotopologues separation. Taking an already-synthesized two-dimensional carbon nitride (C 2 N-h2D) as an example, we predict that the competition between quantum tunneling and zero-point-energy (ZPE) effects regulated by the tensile strain leads to high selectivity and permeance. Both kinetic quantum sieving and equilibrium quantum sieving effects are considered. The quantum effects revealed in this work offer a prospective strategy for highly efficient hydrogen isotopologues separation.

Light Emission Mechanisms in CuInS 2 Quantum Dots Evaluated by Spectral Electrochemistry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fuhr, Addis S.; Yun, Hyeong Jin; Makarov, Nikolay S.

Luminescent CuInS 2 (CIS) quantum dots (QDs) exhibit highly efficient intragap emission and long, hundreds-of-nanoseconds radiative lifetimes. These spectral properties, distinct from structurally similar II–VI QDs, can be explained by the involvement of intragap defect states containing a localized hole capable of coupling with a conduction band electron for a radiative transition. However, the absolute energies of the intragap and band-edge states, the structure of the emissive defect(s), and the role and origin of nonemissive decay channels still remain poorly understood. Here, we address these questions by applying methods of spectral electrochemistry. Cyclic voltammetry measurements reveal a well-defined intragap statemore » whose redox potential is close to that of the Cu x defect state (where x = 1+ or 2+). The energy offset of this state from the valence band accounts well for the apparent photoluminescence Stokes shift observed in optical spectra. These results provide direct evidence that Cu-related defects serve as emission centers responsible for strong intragap emission from CIS QDs. We then use in situ spectroelectrochemistry to reveal two distinct emission pathways based on the differing oxidation states of Cu defects, which can be controlled by altering QD stoichiometry (1+ for stoichiometric QDs and 2+ for Cu-deficient QDs).« less

Light Emission Mechanisms in CuInS 2 Quantum Dots Evaluated by Spectral Electrochemistry

DOE PAGES

Fuhr, Addis S.; Yun, Hyeong Jin; Makarov, Nikolay S.; ...

2017-09-07

Luminescent CuInS 2 (CIS) quantum dots (QDs) exhibit highly efficient intragap emission and long, hundreds-of-nanoseconds radiative lifetimes. These spectral properties, distinct from structurally similar II–VI QDs, can be explained by the involvement of intragap defect states containing a localized hole capable of coupling with a conduction band electron for a radiative transition. However, the absolute energies of the intragap and band-edge states, the structure of the emissive defect(s), and the role and origin of nonemissive decay channels still remain poorly understood. Here, we address these questions by applying methods of spectral electrochemistry. Cyclic voltammetry measurements reveal a well-defined intragap statemore » whose redox potential is close to that of the Cu x defect state (where x = 1+ or 2+). The energy offset of this state from the valence band accounts well for the apparent photoluminescence Stokes shift observed in optical spectra. These results provide direct evidence that Cu-related defects serve as emission centers responsible for strong intragap emission from CIS QDs. We then use in situ spectroelectrochemistry to reveal two distinct emission pathways based on the differing oxidation states of Cu defects, which can be controlled by altering QD stoichiometry (1+ for stoichiometric QDs and 2+ for Cu-deficient QDs).« less

Mechanisms of removal of three widespread pharmaceuticals by two clay materials.

PubMed

Dordio, A V; Miranda, S; Prates Ramalho, J P; Carvalho, A J Palace

2017-02-05

Pharmaceutical residues presence in the environment is among nowadays top emergent environmental issues. For removal of such pollutants, adsorption is a generally efficient process that can be complementary to conventional treatment. Research of cheap, widely available adsorbents may make this process economically attractive. The aim of the present work was to evaluate the capacity of two clay materials (exfoliated vermiculite, LECA) to adsorb gemfibrozil, mefenamic acid and naproxen in lab-scale batch assays. Results show that both adsorbents are able to remove the pharmaceuticals from aqueous medium. Although vermiculite exhibited higher adsorption capacities per unit mass of adsorbent, LECA yielded higher absolute removals of the pharmaceuticals due to the larger mass of adsorbent. Quantum chemistry calculations predicted that the forms of binding of the three molecules to the vermiculite surface are essentially identical, but the adsorption isotherm of naproxen differs substantially from the other two's. The linear forms of the latter impose limits at lower concentrations to the removal efficiencies of these pharmaceuticals by vermiculite, thereby electing LECA as more efficient. Notwithstanding, vermiculite's high specific adsorption capacity and also its much faster adsorption kinetics suggest that there may be some benefits in combining both materials as a composite adsorbent solution. Copyright © 2016 Elsevier B.V. All rights reserved.

Bright colloidal quantum dot light-emitting diodes enabled by efficient chlorination

NASA Astrophysics Data System (ADS)

Li, Xiyan; Zhao, Yong-Biao; Fan, Fengjia; Levina, Larissa; Liu, Min; Quintero-Bermudez, Rafael; Gong, Xiwen; Quan, Li Na; Fan, James; Yang, Zhenyu; Hoogland, Sjoerd; Voznyy, Oleksandr; Lu, Zheng-Hong; Sargent, Edward H.

2018-03-01

The external quantum efficiencies of state-of-the-art colloidal quantum dot light-emitting diodes (QLEDs) are now approaching the limit set by the out-coupling efficiency. However, the brightness of these devices is constrained by the use of poorly conducting emitting layers, a consequence of the present-day reliance on long-chain organic capping ligands. Here, we report how conductive and passivating halides can be implemented in Zn chalcogenide-shelled colloidal quantum dots to enable high-brightness green QLEDs. We use a surface management reagent, thionyl chloride (SOCl2), to chlorinate the carboxylic group of oleic acid and graft the surfaces of the colloidal quantum dots with passivating chloride anions. This results in devices with an improved mobility that retain high external quantum efficiencies in the high-injection-current region and also feature a reduced turn-on voltage of 2.5 V. The treated QLEDs operate with a brightness of 460,000 cd m-2, significantly exceeding that of all previously reported solution-processed LEDs.

Hybrid Integration of Solid-State Quantum Emitters on a Silicon Photonic Chip.

PubMed

Kim, Je-Hyung; Aghaeimeibodi, Shahriar; Richardson, Christopher J K; Leavitt, Richard P; Englund, Dirk; Waks, Edo

2017-12-13

Scalable quantum photonic systems require efficient single photon sources coupled to integrated photonic devices. Solid-state quantum emitters can generate single photons with high efficiency, while silicon photonic circuits can manipulate them in an integrated device structure. Combining these two material platforms could, therefore, significantly increase the complexity of integrated quantum photonic devices. Here, we demonstrate hybrid integration of solid-state quantum emitters to a silicon photonic device. We develop a pick-and-place technique that can position epitaxially grown InAs/InP quantum dots emitting at telecom wavelengths on a silicon photonic chip deterministically with nanoscale precision. We employ an adiabatic tapering approach to transfer the emission from the quantum dots to the waveguide with high efficiency. We also incorporate an on-chip silicon-photonic beamsplitter to perform a Hanbury-Brown and Twiss measurement. Our approach could enable integration of precharacterized III-V quantum photonic devices into large-scale photonic structures to enable complex devices composed of many emitters and photons.

Internal quantum efficiency in yellow-amber light emitting AlGaN-InGaN-GaN heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ngo, Thi Huong; Gil, Bernard; Valvin, Pierre

2015-09-21

We determine the internal quantum efficiency of strain-balanced AlGaN-InGaN-GaN hetero-structures designed for yellow-amber light emission, by using a recent model based on the kinetics of the photoluminescence decay initiated by Iwata et al. [J. Appl. Phys. 117, 075701 (2015)]. Our results indicate that low temperature internal quantum efficiencies sit in the 50% range and we measure that adding an AlGaN layer increases the internal quantum efficiency from 50% up to 57% with respect to the GaN-InGaN case. More dramatic, it almost doubles from 2.5% up to 4.3% at room temperature.

Fused Silica Ion Trap Chip with Efficient Optical Collection System for Timekeeping, Sensing, and Emulation

DTIC Science & Technology

2015-01-22

applications in fast single photon sources, quantum repeater circuitry, and high fidelity remote entanglement of atoms for quantum information protocols. We...fluorescence for motion/force sensors through Doppler velocimetry; and for the efficient collection of single photons from trapped ions for...Doppler velocimetry; and for the efficient collection of single photons from trapped ions for applications in fast single photon sources, quantum

All-photonic quantum repeaters

PubMed Central

Azuma, Koji; Tamaki, Kiyoshi; Lo, Hoi-Kwong

2015-01-01

Quantum communication holds promise for unconditionally secure transmission of secret messages and faithful transfer of unknown quantum states. Photons appear to be the medium of choice for quantum communication. Owing to photon losses, robust quantum communication over long lossy channels requires quantum repeaters. It is widely believed that a necessary and highly demanding requirement for quantum repeaters is the existence of matter quantum memories. Here we show that such a requirement is, in fact, unnecessary by introducing the concept of all-photonic quantum repeaters based on flying qubits. In particular, we present a protocol based on photonic cluster-state machine guns and a loss-tolerant measurement equipped with local high-speed active feedforwards. We show that, with such all-photonic quantum repeaters, the communication efficiency scales polynomially with the channel distance. Our result paves a new route towards quantum repeaters with efficient single-photon sources rather than matter quantum memories. PMID:25873153

Very high quantum efficiency in InAs/GaSb superlattice for very long wavelength detection with cutoff of 21 μm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Dongwei; Guo, Fengyun, E-mail: guowen@hit.edu.cn; Li, Xiaochao

2016-03-21

The authors report the dependence of the quantum efficiency on beryllium concentration in the active region of type-II InAs/GaSb superlattice infrared detector with a cutoff wavelength around 21 μm. It is found that the quantum efficiency and responsivity show a clear delineation in comparison to the doping concentration. The quantum efficiency is further improved by gradually doping in the absorbing region. At 77 K, the 50% cutoff wavelength of the VLWIR detector is 18 μm, and the R{sub 0}A is kept at a stable value of 6 Ω cm{sup 2}. Different beryllium concentration leads to an increase of an average quantum efficiency in the 8–15 μmmore » window from 35% to 55% with a π-region thickness of 3.0 μm, for U{sub bias} = −0.3 V, and no anti-reflection coating. As for a further result, the quantum efficiency reaches at a maximum value of 66% by gradually doping in the absorbing region with the peak detectivity of 3.33 × 10{sup 10 }cm Hz{sup 1/2}/W at 15 μm.« less

Quantum melting of a two-dimensional Wigner crystal

NASA Astrophysics Data System (ADS)

Dolgopolov, V. T.

2017-10-01

The paper reviews theoretical predictions about the behavior of two-dimensional low-density electron systems at nearly absolute zero temperatures, including the formation of an electron (Wigner) crystal, crystal melting at a critical electron density, and transitions between crystal modifications in more complex (for example, two-layer) systems. The paper presents experimental results obtained from real two-dimensional systems in which the nonconducting (solid) state of the electronic system with indications of collective localization is actually realized. Experimental methods for detecting a quantum liquid-solid phase interface are discussed.

Concentration Independent Calibration of β-γ Coincidence Detector Using 131mXe and 133Xe

DOE Office of Scientific and Technical Information (OSTI.GOV)

McIntyre, Justin I.; Cooper, Matthew W.; Carman, April J.

Absolute efficiency calibration of radiometric detectors is frequently difficult and requires careful detector modeling and accurate knowledge of the radioactive source used. In the past we have calibrated the b-g coincidence detector of the Automated Radioxenon Sampler/Analyzer (ARSA) using a variety of sources and techniques which have proven to be less than desirable.[1] A superior technique has been developed that uses the conversion-electron (CE) and x-ray coincidence of 131mXe to provide a more accurate absolute gamma efficiency of the detector. The 131mXe is injected directly into the beta cell of the coincident counting system and no knowledge of absolute sourcemore » strength is required. In addition, 133Xe is used to provide a second independent means to obtain the absolute efficiency calibration. These two data points provide the necessary information for calculating the detector efficiency and can be used in conjunction with other noble gas isotopes to completely characterize and calibrate the ARSA nuclear detector. In this paper we discuss the techniques and results that we have obtained.« less

Hyperresonance Unifying Theory and the resulting Law

NASA Astrophysics Data System (ADS)

Omerbashich, Mensur

2012-07-01

Hyperresonance Unifying Theory (HUT) is herein conceived based on theoretical and experimental geophysics, as that absolute extension of both Multiverse and String Theories, in which all universes (the Hyperverse) - of non-prescribed energies and scales - mutually orbit as well as oscillate in tune. The motivation for this is to explain oddities of "attraction at a distance" and physical unit(s) attached to the Newtonian gravitational constant G. In order to make sure HUT holds absolutely, we operate over non-temporal, unitless and quantities with derived units only. A HUT's harmonic geophysical localization (here for the Earth-Moon system; the Georesonator) is indeed achieved for mechanist and quantum scales, in form of the Moon's Equation of Levitation (of Anti-gravity). HUT holds true for our Solar system the same as its localized equation holds down to the precision of terrestrial G-experiments, regardless of the scale: to 10^-11 and 10^-39 for mechanist and quantum scales, respectively. Due to its absolute accuracy (within NIST experimental limits), the derived equation is regarded a law. HUT can indeed be demonstrated for our entire Solar system in various albeit empirical ways. In summary, HUT shows: (i) how classical gravity can be expressed in terms of scale and the speed of light; (ii) the tuning-forks principle is universal; (iii) the body's fundamental oscillation note is not a random number as previously believed; (iv) earthquakes of about M6 and stronger arise mainly due to Earth's alignments longer than three days to two celestial objects in our Solar system, whereas M7+ earthquakes occur mostly during two simultaneous such alignments; etc. HUT indicates: (v) quantum physics is objectocentric, i.e. trivial in absolute terms so it cannot be generalized beyond classical mass-bodies; (vi) geophysics is largely due to the magnification of mass resonance; etc. HUT can be extended to multiverse (10^17) and string scales (10^-67) too, providing a constraint to String Theory. HUT is the unifying theory as it demotes classical forces to states of stringdom. The String Theory's paradigm on vibrational rather than particlegenic reality has thus been confirmed.

A Single Chiroptical Spectroscopic Method May Not Be Able To Establish the Absolute Configurations of Diastereomers: Dimethylesters of Hibiscus and Garcinia Acids

PubMed Central

Polavarapu, Prasad L.; Donahue, Emily A.; Shanmugam, Ganesh; Scalmani, Giovanni; Hawkins, Edward K.; Rizzo, Carmelo; Ibnusaud, Ibrahim; Thomas, Grace; Habel, Deenamma; Sebastian, Dellamol

2013-01-01

Electronic circular dichroism (ECD), optical rotatory dispersion (ORD), and vibrational circular dichroism (VCD) spectra of hibiscus acid dimethyl ester have been measured and analyzed in combination with quantum chemical calculations of corresponding spectra. These results, along with those reported previously for garcinia acid dimethyl ester, reveal that none of these three (ECD, ORD, or VCD) spectroscopic methods, in isolation, can unequivocally establish the absolute configurations of diastereomers. This deficiency is eliminated when a combined spectral analysis of either ECD and VCD or ORD and VCD methods is used. It is also found that the ambiguities in the assignment of absolute configurations of diastereomers may also be overcome when unpolarized vibrational absorption is included in the spectral analysis. PMID:21568330

Coherent Optical Memory with High Storage Efficiency and Large Fractional Delay

NASA Astrophysics Data System (ADS)

Chen, Yi-Hsin; Lee, Meng-Jung; Wang, I.-Chung; Du, Shengwang; Chen, Yong-Fan; Chen, Ying-Cheng; Yu, Ite A.

2013-02-01

A high-storage efficiency and long-lived quantum memory for photons is an essential component in long-distance quantum communication and optical quantum computation. Here, we report a 78% storage efficiency of light pulses in a cold atomic medium based on the effect of electromagnetically induced transparency. At 50% storage efficiency, we obtain a fractional delay of 74, which is the best up-to-date record. The classical fidelity of the recalled pulse is better than 90% and nearly independent of the storage time, as confirmed by the direct measurement of phase evolution of the output light pulse with a beat-note interferometer. Such excellent phase coherence between the stored and recalled light pulses suggests that the current result may be readily applied to single photon wave packets. Our work significantly advances the technology of electromagnetically induced transparency-based optical memory and may find practical applications in long-distance quantum communication and optical quantum computation.

Coherent optical memory with high storage efficiency and large fractional delay.

PubMed

Chen, Yi-Hsin; Lee, Meng-Jung; Wang, I-Chung; Du, Shengwang; Chen, Yong-Fan; Chen, Ying-Cheng; Yu, Ite A

2013-02-22

A high-storage efficiency and long-lived quantum memory for photons is an essential component in long-distance quantum communication and optical quantum computation. Here, we report a 78% storage efficiency of light pulses in a cold atomic medium based on the effect of electromagnetically induced transparency. At 50% storage efficiency, we obtain a fractional delay of 74, which is the best up-to-date record. The classical fidelity of the recalled pulse is better than 90% and nearly independent of the storage time, as confirmed by the direct measurement of phase evolution of the output light pulse with a beat-note interferometer. Such excellent phase coherence between the stored and recalled light pulses suggests that the current result may be readily applied to single photon wave packets. Our work significantly advances the technology of electromagnetically induced transparency-based optical memory and may find practical applications in long-distance quantum communication and optical quantum computation.

High efficiency quantum cascade laser frequency comb.

PubMed

Lu, Quanyong; Wu, Donghai; Slivken, Steven; Razeghi, Manijeh

2017-03-06

An efficient mid-infrared frequency comb source is of great interest to high speed, high resolution spectroscopy and metrology. Here we demonstrate a mid-IR quantum cascade laser frequency comb with a high power output and narrow beatnote linewidth at room temperature. The active region was designed with a strong-coupling between the injector and the upper lasing level for high internal quantum efficiency and a broadband gain. The group velocity dispersion was engineered for efficient, broadband mode-locking via four wave mixing. The comb device exhibits a narrow intermode beatnote linewidth of 50.5 Hz and a maximum wall-plug efficiency of 6.5% covering a spectral coverage of 110 cm -1 at λ ~ 8 μm. The efficiency is improved by a factor of 6 compared with previous demonstrations. The high power efficiency and narrow beatnote linewidth will greatly expand the applications of quantum cascade laser frequency combs including high-precision remote sensing and spectroscopy.

High efficiency quantum cascade laser frequency comb

PubMed Central

Lu, Quanyong; Wu, Donghai; Slivken, Steven; Razeghi, Manijeh

2017-01-01

An efficient mid-infrared frequency comb source is of great interest to high speed, high resolution spectroscopy and metrology. Here we demonstrate a mid-IR quantum cascade laser frequency comb with a high power output and narrow beatnote linewidth at room temperature. The active region was designed with a strong-coupling between the injector and the upper lasing level for high internal quantum efficiency and a broadband gain. The group velocity dispersion was engineered for efficient, broadband mode-locking via four wave mixing. The comb device exhibits a narrow intermode beatnote linewidth of 50.5 Hz and a maximum wall-plug efficiency of 6.5% covering a spectral coverage of 110 cm−1 at λ ~ 8 μm. The efficiency is improved by a factor of 6 compared with previous demonstrations. The high power efficiency and narrow beatnote linewidth will greatly expand the applications of quantum cascade laser frequency combs including high-precision remote sensing and spectroscopy. PMID:28262834

Molecular beam study of the a 3Σ+ state of NaK up to the dissociation limit

NASA Astrophysics Data System (ADS)

Temelkov, I.; Knöckel, H.; Pashov, A.; Tiemann, E.

2015-03-01

We provide spectroscopic data for the a 3Σ+ state of the 23Na39K molecule. The experiment is done in an ultrasonic beam apparatus, starting from the ground state X 1Σ+and driving the population to the a 3Σ+ state, using a Λ scheme with fixed pump and scanning dump laser. The signals are observed as dips of the total fluorescence. The intermediate level is chosen to be strongly perturbed by the B 1Π/c 3Σ+ states mixing to overcome the singlet-triplet transfer prohibition. We observed highly resolved hyperfine spectra of various rovibrational levels of the a 3Σ+state from va=2 up to the highest vibrational levels for rotational quantum numbers Na=4 ,6 ,8 . By the typical experimental linewidth of 17 MHz, the vibrational dependence of the hyperfine splitting is clearly revealed for NaK. The absolute frequency measurements of the vibrational levels are used for improvement of the a 3Σ+ potential curve and of the derived scattering length of all natural isotope combinations. Applying the Λ scheme in the reverse direction can provide a pathway for efficient transfer of ultracold 23Na39K molecules from the Na(3 s )+K(4 s ) asymptote to the lowest levels of the ground state. We show spectra that couple the absolute ground state vX=0 ,J =0 with an appropriate intermediate state for direct realization of the reverse path. The refined theoretical model of the coupled excited states of the Na(3 s )+K(4 p ) asymptote allows predictions of efficient paths for 23Na40K ; one example is calculated.

Understanding/Modelling of Thermal and Radiation Benefits of Quantum Dot Solar Cells

DTIC Science & Technology

2008-07-11

GaAs solar cells have been investigated. Strain compensation is a key step in realizing high- efficiency quantum dots solar cells (QDSC). InAs...factor. A strong correlation between the temperature dependent quantum dot electroluminescence peak emission wavelength and the sub-GaAs bandgap...increased efficiency and radiation resistance devices. The incorporation of quantum dots (QDs) into traditional single or multi-junction crystalline solar

Efficiency of quantum vs. classical annealing in nonconvex learning problems

PubMed Central

Zecchina, Riccardo

2018-01-01

Quantum annealers aim at solving nonconvex optimization problems by exploiting cooperative tunneling effects to escape local minima. The underlying idea consists of designing a classical energy function whose ground states are the sought optimal solutions of the original optimization problem and add a controllable quantum transverse field to generate tunneling processes. A key challenge is to identify classes of nonconvex optimization problems for which quantum annealing remains efficient while thermal annealing fails. We show that this happens for a wide class of problems which are central to machine learning. Their energy landscapes are dominated by local minima that cause exponential slowdown of classical thermal annealers while simulated quantum annealing converges efficiently to rare dense regions of optimal solutions. PMID:29382764

Strained-layer InGaAs/GaAs/AlGaAs single quantum well lasers with high internal quantum efficiency

NASA Technical Reports Server (NTRS)

Larsson, Anders; Cody, Jeffrey; Lang, Robert J.

1989-01-01

Low threshold current density strained-layer In(0.2)Ga(0.8)As/GaAs/AlGaAs single quantum well lasers, emitting at 980 nm, have been grown by molecular beam epitaxy. Contrary to what has been reported for broad-area lasers with pseudomorphic InGaAs active layers grown by metalorganic chemical vapor deposition, these layers exhibit a high internal quantum efficiency (about 90 percent). The maximum external differential quantum efficiency is 70 percent, limited by an anomalously high internal loss possibly caused by a large lateral spreading of the optical mode. In addition, experimental results supporting the theoretically predicted strain-induced reduction of the valence-band nonparabolicity and density of states are presented.

Highly retrievable spin-wave-photon entanglement source.

PubMed

Yang, Sheng-Jun; Wang, Xu-Jie; Li, Jun; Rui, Jun; Bao, Xiao-Hui; Pan, Jian-Wei

2015-05-29

Entanglement between a single photon and a quantum memory forms the building blocks for a quantum repeater and quantum network. Previous entanglement sources are typically with low retrieval efficiency, which limits future larger-scale applications. Here, we report a source of highly retrievable spin-wave-photon entanglement. Polarization entanglement is created through interaction of a single photon with an ensemble of atoms inside a low-finesse ring cavity. The cavity is engineered to be resonant for dual spin-wave modes, which thus enables efficient retrieval of the spin-wave qubit. An intrinsic retrieval efficiency up to 76(4)% has been observed. Such a highly retrievable atom-photon entanglement source will be very useful in future larger-scale quantum repeater and quantum network applications.

On-Demand Single Photons with High Extraction Efficiency and Near-Unity Indistinguishability from a Resonantly Driven Quantum Dot in a Micropillar.

PubMed

Ding, Xing; He, Yu; Duan, Z-C; Gregersen, Niels; Chen, M-C; Unsleber, S; Maier, S; Schneider, Christian; Kamp, Martin; Höfling, Sven; Lu, Chao-Yang; Pan, Jian-Wei

2016-01-15

Scalable photonic quantum technologies require on-demand single-photon sources with simultaneously high levels of purity, indistinguishability, and efficiency. These key features, however, have only been demonstrated separately in previous experiments. Here, by s-shell pulsed resonant excitation of a Purcell-enhanced quantum dot-micropillar system, we deterministically generate resonance fluorescence single photons which, at π pulse excitation, have an extraction efficiency of 66%, single-photon purity of 99.1%, and photon indistinguishability of 98.5%. Such a single-photon source for the first time combines the features of high efficiency and near-perfect levels of purity and indistinguishabilty, and thus opens the way to multiphoton experiments with semiconductor quantum dots.

High external quantum efficiency and fill-factor InGaN/GaN heterojunction solar cells grown by NH3-based molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Lang, J. R.; Neufeld, C. J.; Hurni, C. A.; Cruz, S. C.; Matioli, E.; Mishra, U. K.; Speck, J. S.

2011-03-01

High external quantum efficiency (EQE) p-i-n heterojunction solar cells grown by NH3-based molecular beam epitaxy are presented. EQE values including optical losses are greater than 50% with fill-factors over 72% when illuminated with a 1 sun AM0 spectrum. Optical absorption measurements in conjunction with EQE measurements indicate an internal quantum efficiency greater than 90% for the InGaN absorbing layer. By adjusting the thickness of the top p-type GaN window contact layer, it is shown that the short-wavelength (<365 nm) quantum efficiency is limited by the minority carrier diffusion length in highly Mg-doped p-GaN.

An Introduction to the Problem of the Existence of Classical and Quantum Information

NASA Astrophysics Data System (ADS)

Rocchi, Paolo; Gianfagna, Leonida

2006-01-01

Quantum computing raises novel meditation upon the nature of information, notably a number of theorists set out the critical elements of Shannon's work, which currently emerges as the most popular reference in the quantum territory. The present paper follows this vein and highlights how the prerequisites of the information theory, which should detail the precise hypotheses of this theory, appear rather obscure and the problem of the existence of information is still open. This work puts forward a theoretical scheme that calculates the existence of elementary items. These results clarify basic assumptions in information engineering. Later we bring evidence how information is not an absolute quantity and close with a discussion upon the information relativity.

Ballistic Transport for Limit-Periodic Jacobi Matrices with Applications to Quantum Many-Body Problems

NASA Astrophysics Data System (ADS)

Fillman, Jake

2017-03-01

We study Jacobi matrices that are uniformly approximated by periodic operators. We show that if the rate of approximation is sufficiently rapid, then the associated quantum dynamics are ballistic in a rather strong sense; namely, the (normalized) Heisenberg evolution of the position operator converges strongly to a self-adjoint operator that is injective on the space of absolutely summable sequences. In particular, this means that all transport exponents corresponding to well-localized initial states are equal to one. Our result may be applied to a class of quantum many-body problems. Specifically, we establish a lower bound on the Lieb-Robinson velocity for an isotropic XY spin chain on the integers with limit-periodic couplings.

Calculation and Comparative Analysis of the IR Spectra of Homobrassinolide and (22S,23S)-Homobrassinolide

NASA Astrophysics Data System (ADS)

Andrianov, V. M.; Korolevich, M. V.

2015-09-01

Normal vibrational frequencies and absolute IR band intensities of the biologically active steroid phytohormones homobrassinolide and (22S,23S)-homobrassinolide were calculated in the framework of an original approach that combined classical analysis of normal modes using molecular mechanics with quantum-chemical estimation of the absolute intensities. IR absorption bands were interpreted based on a comparison of the experimental and theoretical absorption spectra. The impact of structural differences in the side chains of these molecules on the formation of their IR spectra in the region 1500-950 cm -1 was estimated.

Multi-party semi-quantum key distribution-convertible multi-party semi-quantum secret sharing

NASA Astrophysics Data System (ADS)

Yu, Kun-Fei; Gu, Jun; Hwang, Tzonelih; Gope, Prosanta

2017-08-01

This paper proposes a multi-party semi-quantum secret sharing (MSQSS) protocol which allows a quantum party (manager) to share a secret among several classical parties (agents) based on GHZ-like states. By utilizing the special properties of GHZ-like states, the proposed scheme can easily detect outside eavesdropping attacks and has the highest qubit efficiency among the existing MSQSS protocols. Then, we illustrate an efficient way to convert the proposed MSQSS protocol into a multi-party semi-quantum key distribution (MSQKD) protocol. The proposed approach is even useful to convert all the existing measure-resend type of semi-quantum secret sharing protocols into semi-quantum key distribution protocols.

Quantum power source: putting in order of a Brownian motion without Maxwell's demon

NASA Astrophysics Data System (ADS)

Aristov, Vitaly V.; Nikulov, A. V.

2003-07-01

The problem of possible violation of the second law of thermodynamics is discussed. It is noted that the task of the well known challenge to the second law called Maxwell's demon is put in order a chaotic perpetual motion and if any ordered Brownian motion exists then the second law can be broken without this hypothetical intelligent entity. The postulate of absolute randomness of any Brownian motion saved the second law in the beginning of the 20th century when it was realized as perpetual motion. This postulate can be proven in the limits of classical mechanics but is not correct according to quantum mechanics. Moreover some enough known quantum phenomena, such as the persistent current at non-zero resistance, are an experimental evidence of the non-chaotic Brownian motion with non-zero average velocity. An experimental observation of a dc quantum power soruce is interperted as evidence of violation of the second law.

Electron spin control of optically levitated nanodiamonds in vacuum.

PubMed

Hoang, Thai M; Ahn, Jonghoon; Bang, Jaehoon; Li, Tongcang

2016-07-19

Electron spins of diamond nitrogen-vacancy (NV) centres are important quantum resources for nanoscale sensing and quantum information. Combining NV spins with levitated optomechanical resonators will provide a hybrid quantum system for novel applications. Here we optically levitate a nanodiamond and demonstrate electron spin control of its built-in NV centres in low vacuum. We observe that the strength of electron spin resonance (ESR) is enhanced when the air pressure is reduced. To better understand this system, we investigate the effects of trap power and measure the absolute internal temperature of levitated nanodiamonds with ESR after calibration of the strain effect. We also observe that oxygen and helium gases have different effects on both the photoluminescence and the ESR contrast of nanodiamond NV centres, indicating potential applications of NV centres in oxygen gas sensing. Our results pave the way towards a levitated spin-optomechanical system for studying macroscopic quantum mechanics.

Electron spin control of optically levitated nanodiamonds in vacuum

PubMed Central

Hoang, Thai M.; Ahn, Jonghoon; Bang, Jaehoon; Li, Tongcang

2016-01-01

Electron spins of diamond nitrogen-vacancy (NV) centres are important quantum resources for nanoscale sensing and quantum information. Combining NV spins with levitated optomechanical resonators will provide a hybrid quantum system for novel applications. Here we optically levitate a nanodiamond and demonstrate electron spin control of its built-in NV centres in low vacuum. We observe that the strength of electron spin resonance (ESR) is enhanced when the air pressure is reduced. To better understand this system, we investigate the effects of trap power and measure the absolute internal temperature of levitated nanodiamonds with ESR after calibration of the strain effect. We also observe that oxygen and helium gases have different effects on both the photoluminescence and the ESR contrast of nanodiamond NV centres, indicating potential applications of NV centres in oxygen gas sensing. Our results pave the way towards a levitated spin–optomechanical system for studying macroscopic quantum mechanics. PMID:27432560

Electron spin control of optically levitated nanodiamonds in vacuum

NASA Astrophysics Data System (ADS)

Hoang, Thai M.; Ahn, Jonghoon; Bang, Jaehoon; Li, Tongcang

2016-07-01

Electron spins of diamond nitrogen-vacancy (NV) centres are important quantum resources for nanoscale sensing and quantum information. Combining NV spins with levitated optomechanical resonators will provide a hybrid quantum system for novel applications. Here we optically levitate a nanodiamond and demonstrate electron spin control of its built-in NV centres in low vacuum. We observe that the strength of electron spin resonance (ESR) is enhanced when the air pressure is reduced. To better understand this system, we investigate the effects of trap power and measure the absolute internal temperature of levitated nanodiamonds with ESR after calibration of the strain effect. We also observe that oxygen and helium gases have different effects on both the photoluminescence and the ESR contrast of nanodiamond NV centres, indicating potential applications of NV centres in oxygen gas sensing. Our results pave the way towards a levitated spin-optomechanical system for studying macroscopic quantum mechanics.

Lead Telluride Quantum Dot Solar Cells Displaying External Quantum Efficiencies Exceeding 120%

PubMed Central

2015-01-01

Multiple exciton generation (MEG) in semiconducting quantum dots is a process that produces multiple charge-carrier pairs from a single excitation. MEG is a possible route to bypass the Shockley-Queisser limit in single-junction solar cells but it remains challenging to harvest charge-carrier pairs generated by MEG in working photovoltaic devices. Initial yields of additional carrier pairs may be reduced due to ultrafast intraband relaxation processes that compete with MEG at early times. Quantum dots of materials that display reduced carrier cooling rates (e.g., PbTe) are therefore promising candidates to increase the impact of MEG in photovoltaic devices. Here we demonstrate PbTe quantum dot-based solar cells, which produce extractable charge carrier pairs with an external quantum efficiency above 120%, and we estimate an internal quantum efficiency exceeding 150%. Resolving the charge carrier kinetics on the ultrafast time scale with pump–probe transient absorption and pump–push–photocurrent measurements, we identify a delayed cooling effect above the threshold energy for MEG. PMID:26488847

Energy efficient quantum machines

NASA Astrophysics Data System (ADS)

Abah, Obinna; Lutz, Eric

2017-05-01

We investigate the performance of a quantum thermal machine operating in finite time based on shortcut-to-adiabaticity techniques. We compute efficiency and power for a paradigmatic harmonic quantum Otto engine by taking the energetic cost of the shortcut driving explicitly into account. We demonstrate that shortcut-to-adiabaticity machines outperform conventional ones for fast cycles. We further derive generic upper bounds on both quantities, valid for any heat engine cycle, using the notion of quantum speed limit for driven systems. We establish that these quantum bounds are tighter than those stemming from the second law of thermodynamics.

Highly Efficient Perovskite-Quantum-Dot Light-Emitting Diodes by Surface Engineering.

PubMed

Pan, Jun; Quan, Li Na; Zhao, Yongbiao; Peng, Wei; Murali, Banavoth; Sarmah, Smritakshi P; Yuan, Mingjian; Sinatra, Lutfan; Alyami, Noktan M; Liu, Jiakai; Yassitepe, Emre; Yang, Zhenyu; Voznyy, Oleksandr; Comin, Riccardo; Hedhili, Mohamed N; Mohammed, Omar F; Lu, Zheng Hong; Kim, Dong Ha; Sargent, Edward H; Bakr, Osman M

2016-10-01

A two-step ligand-exchange strategy is developed, in which the long-carbon- chain ligands on all-inorganic perovskite (CsPbX 3 , X = Br, Cl) quantum dots (QDs) are replaced with halide-ion-pair ligands. Green and blue light-emitting diodes made from the halide-ion-pair-capped quantum dots exhibit high external quantum efficiencies compared with the untreated QDs. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Primary quantum yields of NO2 photodissociation

NASA Technical Reports Server (NTRS)

Gardner, Edward P.; Sperry, Paul D.; Calvert, Jack G.

1987-01-01

The quantum yields of formation of NO, O2, and NO2 loss are measured for NO2 vapor at low pressures (0.13-0.30 torr) irradiated at 334-405 nm wavelengths and temperature in the range 273-370 K in order to study the primary quantum efficiencies of NO2 photodecomposition. The temperature and wavelength dependences of the primary quantum efficiencies are examined. It is observed that the primary quantum efficiencies increase rapidly from near zero at 424 nm to near unity for excitation at wavelengths less than 394 nm. The theory of Pitts et al. (1964) that the energy deficiency for photodissociation of NO2 excited at wavelengths greater than 397.9 nm is due to the rotational and vibrational energy of the NO2 molecules is confirmed by the data. Values for the primary quantum yields of NO2 photodecomposition as a function of wavelength are presented.

High-efficiency tomographic reconstruction of quantum states by quantum nondemolition measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, J. S.; Centre for Quantum Technologies and Department of Physics, National University of Singapore, 3 Science Drive 2, Singapore 117542; Wei, L. F.

We propose a high-efficiency scheme to tomographically reconstruct an unknown quantum state by using a series of quantum nondemolition (QND) measurements. The proposed QND measurements of the qubits are implemented by probing the stationary transmissions through a driven dispersively coupled resonator. It is shown that only one kind of QND measurement is sufficient to determine all the diagonal elements of the density matrix of the detected quantum state. The remaining nondiagonal elements can be similarly determined by transferring them to the diagonal locations after a series of unitary operations. Compared with the tomographic reconstructions based on the usual destructive projectivemore » measurements (wherein one such measurement can determine only one diagonal element of the density matrix), the present reconstructive approach exhibits significantly high efficiency. Specifically, our generic proposal is demonstrated by the experimental circuit quantum electrodynamics systems with a few Josephson charge qubits.« less

Determination of the Quantum Efficiency of a Light Detector

ERIC Educational Resources Information Center

Kraftmakher, Yaakov

2008-01-01

The "quantum efficiency" (QE) is an important property of a light detector. This quantity can be determined in the undergraduate physics laboratory. The experimentally determined QE of a silicon photodiode appeared to be in reasonable agreement with expected values. The experiment confirms the quantum properties of light and seems to be a useful…

Nanocrystal Size-Dependent Efficiency of Quantum Dot Sensitized Solar Cells in the Strongly Coupled CdSe Nanocrystals/TiO2 System.

PubMed

Yun, Hyeong Jin; Paik, Taejong; Diroll, Benjamin; Edley, Michael E; Baxter, Jason B; Murray, Christopher B

2016-06-15

Light absorption and electron injection are important criteria determining solar energy conversion efficiency. In this research, monodisperse CdSe quantum dots (QDs) are synthesized with five different diameters, and the size-dependent solar energy conversion efficiency of CdSe quantum dot sensitized solar cell (QDSSCs) is investigated by employing the atomic inorganic ligand, S(2-). Absorbance measurements and transmission electron microscopy show that the diameters of the uniform CdSe QDs are 2.5, 3.2, 4.2, 6.4, and 7.8 nm. Larger CdSe QDs generate a larger amount of charge under the irradiation of long wavelength photons, as verified by the absorbance results and the measurements of the external quantum efficiencies. However, the smaller QDs exhibit faster electron injection kinetics from CdSe QDs to TiO2 because of the high energy level of CBCdSe, as verified by time-resolved photoluminescence and internal quantum efficiency results. Importantly, the S(2-) ligand significantly enhances the electronic coupling between the CdSe QDs and TiO2, yielding an enhancement of the charge transfer rate at the interfacial region. As a result, the S(2-) ligand helps improve the new size-dependent solar energy conversion efficiency, showing best performance with 4.2-nm CdSe QDs, whereas conventional ligand, mercaptopropionic acid, does not show any differences in efficiency according to the size of the CdSe QDs. The findings reported herein suggest that the atomic inorganic ligand reinforces the influence of quantum confinement on the solar energy conversion efficiency of QDSSCs.

Quantum communication for satellite-to-ground networks with partially entangled states

NASA Astrophysics Data System (ADS)

Chen, Na; Quan, Dong-Xiao; Pei, Chang-Xing; Yang-Hong

2015-02-01

To realize practical wide-area quantum communication, a satellite-to-ground network with partially entangled states is developed in this paper. For efficiency and security reasons, the existing method of quantum communication in distributed wireless quantum networks with partially entangled states cannot be applied directly to the proposed quantum network. Based on this point, an efficient and secure quantum communication scheme with partially entangled states is presented. In our scheme, the source node performs teleportation only after an end-to-end entangled state has been established by entanglement swapping with partially entangled states. Thus, the security of quantum communication is guaranteed. The destination node recovers the transmitted quantum bit with the help of an auxiliary quantum bit and specially defined unitary matrices. Detailed calculations and simulation analyses show that the probability of successfully transferring a quantum bit in the presented scheme is high. In addition, the auxiliary quantum bit provides a heralded mechanism for successful communication. Based on the critical components that are presented in this article an efficient, secure, and practical wide-area quantum communication can be achieved. Project supported by the National Natural Science Foundation of China (Grant Nos. 61072067 and 61372076), the 111 Project (Grant No. B08038), the Fund from the State Key Laboratory of Integrated Services Networks (Grant No. ISN 1001004), and the Fundamental Research Funds for the Central Universities (Grant Nos. K5051301059 and K5051201021).

Finding the quantum thermoelectric with maximal efficiency and minimal entropy production at given power output

NASA Astrophysics Data System (ADS)

Whitney, Robert S.

2015-03-01

We investigate the nonlinear scattering theory for quantum systems with strong Seebeck and Peltier effects, and consider their use as heat engines and refrigerators with finite power outputs. This paper gives detailed derivations of the results summarized in a previous paper [R. S. Whitney, Phys. Rev. Lett. 112, 130601 (2014), 10.1103/PhysRevLett.112.130601]. It shows how to use the scattering theory to find (i) the quantum thermoelectric with maximum possible power output, and (ii) the quantum thermoelectric with maximum efficiency at given power output. The latter corresponds to a minimal entropy production at that power output. These quantities are of quantum origin since they depend on system size over electronic wavelength, and so have no analog in classical thermodynamics. The maximal efficiency coincides with Carnot efficiency at zero power output, but decreases with increasing power output. This gives a fundamental lower bound on entropy production, which means that reversibility (in the thermodynamic sense) is impossible for finite power output. The suppression of efficiency by (nonlinear) phonon and photon effects is addressed in detail; when these effects are strong, maximum efficiency coincides with maximum power. Finally, we show in particular limits (typically without magnetic fields) that relaxation within the quantum system does not allow the system to exceed the bounds derived for relaxation-free systems, however, a general proof of this remains elusive.

Quantum efficiency measurements of eROSITA pnCCDs

NASA Astrophysics Data System (ADS)

Ebermayer, Stefanie; Andritschke, Robert; Elbs, Johannes; Meidinger, Norbert; Strüder, Lothar; Hartmann, Robert; Gottwald, Alexander; Krumrey, Michael; Scholze, Frank

2010-07-01

For the eROSITA X-ray telescope, which is planned to be launched in 2012, detectors were developed and fabricated at the MPI Semiconductor Laboratory. The fully depleted, back-illuminated pnCCDs have an ultrathin pn-junction to improve the low-energy X-ray response function and quantum efficiency. The device thickness of 450 μm is fully sensitive to X-ray photons yielding high quantum efficiency of more than 90% at photon energies of 10 keV. An on-chip filter is deposited on top of the entrance window to suppress visible and UV light which would interfere with the X-ray observations. The pnCCD type developed for the eROSITA telescope was characterized in terms of quantum efficiency and spectral response function. The described measurements were performed in 2009 at the synchrotron radiation sources BESSY II and MLS as cooperation between the MPI Semiconductor Laboratory and the Physikalisch-Technische Bundesanstalt (PTB). Quantum efficiency measurements over a wide range of photon energies from 3 eV to 11 keV as well as spectral response measurements are presented. For X-ray energies from 3 keV to 10 keV the quantum efficiency of the CCD including on-chip filter is shown to be above 90% with an attenuation of visible light of more than five orders of magnitude. A detector response model is described and compared to the measurements.

Recommender engine for continuous-time quantum Monte Carlo methods

NASA Astrophysics Data System (ADS)

Huang, Li; Yang, Yi-feng; Wang, Lei

2017-03-01

Recommender systems play an essential role in the modern business world. They recommend favorable items such as books, movies, and search queries to users based on their past preferences. Applying similar ideas and techniques to Monte Carlo simulations of physical systems boosts their efficiency without sacrificing accuracy. Exploiting the quantum to classical mapping inherent in the continuous-time quantum Monte Carlo methods, we construct a classical molecular gas model to reproduce the quantum distributions. We then utilize powerful molecular simulation techniques to propose efficient quantum Monte Carlo updates. The recommender engine approach provides a general way to speed up the quantum impurity solvers.

Simple and Efficient Single Photon Filter for a Rb-based Quantum Memory

NASA Astrophysics Data System (ADS)

Stack, Daniel; Li, Xiao; Quraishi, Qudsia

2015-05-01

Distribution of entangled quantum states over significant distances is important to the development of future quantum technologies such as long-distance cryptography, networks of atomic clocks, distributed quantum computing, etc. Long-lived quantum memories and single photons are building blocks for systems capable of realizing such applications. The ability to store and retrieve quantum information while filtering unwanted light signals is critical to the operation of quantum memories based on neutral-atom ensembles. We report on an efficient frequency filter which uses a glass cell filled with 85Rb vapor to attenuate noise photons by an order of magnitude with little loss to the single photons associated with the operation of our cold 87Rb quantum memory. An Ar buffer gas is required to differentiate between signal and noise photons or similar statement. Our simple, passive filter requires no optical pumping or external frequency references and provides an additional 18 dB attenuation of our pump laser for every 1 dB loss of the single photon signal. We observe improved non-classical correlations and our data shows that the addition of a frequency filter increases the non-classical correlations and readout efficiency of our quantum memory by ~ 35%.

De-quantisation

NASA Astrophysics Data System (ADS)

Gruska, Jozef

2012-06-01

One of the most basic tasks in quantum information processing, communication and security (QIPCC) research, theoretically deep and practically important, is to find bounds on how really important are inherently quantum resources for speeding up computations. This area of research is bringing a variety of results that imply, often in a very unexpected and counter-intuitive way, that: (a) surprisingly large classes of quantum circuits and algorithms can be efficiently simulated on classical computers; (b) the border line between quantum processes that can and cannot be efficiently simulated on classical computers is often surprisingly thin; (c) the addition of a seemingly very simple resource or a tool often enormously increases the power of available quantum tools. These discoveries have put also a new light on our understanding of quantum phenomena and quantum physics and on the potential of its inherently quantum and often mysteriously looking phenomena. The paper motivates and surveys research and its outcomes in the area of de-quantisation, especially presents various approaches and their outcomes concerning efficient classical simulations of various families of quantum circuits and algorithms. To motivate this area of research some outcomes in the area of de-randomization of classical randomized computations.

Photovoltaic Performance of a Nanowire/Quantum Dot Hybrid Nanostructure Array Solar Cell.

PubMed

Wu, Yao; Yan, Xin; Zhang, Xia; Ren, Xiaomin

2018-02-23

An innovative solar cell based on a nanowire/quantum dot hybrid nanostructure array is designed and analyzed. By growing multilayer InAs quantum dots on the sidewalls of GaAs nanowires, not only the absorption spectrum of GaAs nanowires is extended by quantum dots but also the light absorption of quantum dots is dramatically enhanced due to the light-trapping effect of the nanowire array. By incorporating five layers of InAs quantum dots into a 500-nm high-GaAs nanowire array, the power conversion efficiency enhancement induced by the quantum dots is six times higher than the power conversion efficiency enhancement in thin-film solar cells which contain the same amount of quantum dots, indicating that the nanowire array structure can benefit the photovoltaic performance of quantum dot solar cells.

Photovoltaic Performance of a Nanowire/Quantum Dot Hybrid Nanostructure Array Solar Cell

NASA Astrophysics Data System (ADS)

Wu, Yao; Yan, Xin; Zhang, Xia; Ren, Xiaomin

2018-02-01

An innovative solar cell based on a nanowire/quantum dot hybrid nanostructure array is designed and analyzed. By growing multilayer InAs quantum dots on the sidewalls of GaAs nanowires, not only the absorption spectrum of GaAs nanowires is extended by quantum dots but also the light absorption of quantum dots is dramatically enhanced due to the light-trapping effect of the nanowire array. By incorporating five layers of InAs quantum dots into a 500-nm high-GaAs nanowire array, the power conversion efficiency enhancement induced by the quantum dots is six times higher than the power conversion efficiency enhancement in thin-film solar cells which contain the same amount of quantum dots, indicating that the nanowire array structure can benefit the photovoltaic performance of quantum dot solar cells.

Thermodynamic universality of quantum Carnot engines

DOE PAGES

Gardas, Bartłomiej; Deffner, Sebastian

2015-10-12

The Carnot statement of the second law of thermodynamics poses an upper limit on the efficiency of all heat engines. Recently, it has been studied whether generic quantum features such as coherence and quantum entanglement could allow for quantum devices with efficiencies larger than the Carnot efficiency. The present study shows that this is not permitted by the laws of thermodynamic —independent of the model. We will show that rather the definition of heat has to be modified to account for the thermodynamic cost of maintaining non-Gibbsian equilibrium states. As a result, our theoretical findings are illustrated for two experimentallymore » relevant examples.« less

Efficient quantum circuits for dense circulant and circulant like operators

PubMed Central

Zhou, S. S.

2017-01-01

Circulant matrices are an important family of operators, which have a wide range of applications in science and engineering-related fields. They are, in general, non-sparse and non-unitary. In this paper, we present efficient quantum circuits to implement circulant operators using fewer resources and with lower complexity than existing methods. Moreover, our quantum circuits can be readily extended to the implementation of Toeplitz, Hankel and block circulant matrices. Efficient quantum algorithms to implement the inverses and products of circulant operators are also provided, and an example application in solving the equation of motion for cyclic systems is discussed. PMID:28572988

Quantum engine efficiency bound beyond the second law of thermodynamics.

PubMed

Niedenzu, Wolfgang; Mukherjee, Victor; Ghosh, Arnab; Kofman, Abraham G; Kurizki, Gershon

2018-01-11

According to the second law, the efficiency of cyclic heat engines is limited by the Carnot bound that is attained by engines that operate between two thermal baths under the reversibility condition whereby the total entropy does not increase. Quantum engines operating between a thermal and a squeezed-thermal bath have been shown to surpass this bound. Yet, their maximum efficiency cannot be determined by the reversibility condition, which may yield an unachievable efficiency bound above unity. Here we identify the fraction of the exchanged energy between a quantum system and a bath that necessarily causes an entropy change and derive an inequality for this change. This inequality reveals an efficiency bound for quantum engines energised by a non-thermal bath. This bound does not imply reversibility, unless the two baths are thermal. It cannot be solely deduced from the laws of thermodynamics.

Multiple-exciton generation in lead selenide nanorod solar cells with external quantum efficiencies exceeding 120%

PubMed Central

Davis, Nathaniel J. L. K.; Böhm, Marcus L.; Tabachnyk, Maxim; Wisnivesky-Rocca-Rivarola, Florencia; Jellicoe, Tom C.; Ducati, Caterina; Ehrler, Bruno; Greenham, Neil C.

2015-01-01

Multiple-exciton generation—a process in which multiple charge-carrier pairs are generated from a single optical excitation—is a promising way to improve the photocurrent in photovoltaic devices and offers the potential to break the Shockley–Queisser limit. One-dimensional nanostructures, for example nanorods, have been shown spectroscopically to display increased multiple exciton generation efficiencies compared with their zero-dimensional analogues. Here we present solar cells fabricated from PbSe nanorods of three different bandgaps. All three devices showed external quantum efficiencies exceeding 100% and we report a maximum external quantum efficiency of 122% for cells consisting of the smallest bandgap nanorods. We estimate internal quantum efficiencies to exceed 150% at relatively low energies compared with other multiple exciton generation systems, and this demonstrates the potential for substantial improvements in device performance due to multiple exciton generation. PMID:26411283

Solving search problems by strongly simulating quantum circuits

PubMed Central

Johnson, T. H.; Biamonte, J. D.; Clark, S. R.; Jaksch, D.

2013-01-01

Simulating quantum circuits using classical computers lets us analyse the inner workings of quantum algorithms. The most complete type of simulation, strong simulation, is believed to be generally inefficient. Nevertheless, several efficient strong simulation techniques are known for restricted families of quantum circuits and we develop an additional technique in this article. Further, we show that strong simulation algorithms perform another fundamental task: solving search problems. Efficient strong simulation techniques allow solutions to a class of search problems to be counted and found efficiently. This enhances the utility of strong simulation methods, known or yet to be discovered, and extends the class of search problems known to be efficiently simulable. Relating strong simulation to search problems also bounds the computational power of efficiently strongly simulable circuits; if they could solve all problems in P this would imply that all problems in NP and #P could be solved in polynomial time. PMID:23390585

Coherent spin control of a nanocavity-enhanced qubit in diamond

DOE PAGES

Li, Luozhou; Lu, Ming; Schroder, Tim; ...

2015-01-28

A central aim of quantum information processing is the efficient entanglement of multiple stationary quantum memories via photons. Among solid-state systems, the nitrogen-vacancy centre in diamond has emerged as an excellent optically addressable memory with second-scale electron spin coherence times. Recently, quantum entanglement and teleportation have been shown between two nitrogen-vacancy memories, but scaling to larger networks requires more efficient spin-photon interfaces such as optical resonators. Here we report such nitrogen-vacancy nanocavity systems in strong Purcell regime with optical quality factors approaching 10,000 and electron spin coherence times exceeding 200 µs using a silicon hard-mask fabrication process. This spin-photon interfacemore » is integrated with on-chip microwave striplines for coherent spin control, providing an efficient quantum memory for quantum networks.« less

III-nitride quantum dots for ultra-efficient solid-state lighting

DOE PAGES

Wierer, Jr., Jonathan J.; Tansu, Nelson; Fischer, Arthur J.; ...

2016-05-23

III-nitride light-emitting diodes (LEDs) and laser diodes (LDs) are ultimately limited in performance due to parasitic Auger recombination. For LEDs, the consequences are poor efficiencies at high current densities; for LDs, the consequences are high thresholds and limited efficiencies. Here, we present arguments for III-nitride quantum dots (QDs) as active regions for both LEDs and LDs, to circumvent Auger recombination and achieve efficiencies at higher current densities that are not possible with quantum wells. QD-based LDs achieve gain and thresholds at lower carrier densities before Auger recombination becomes appreciable. QD-based LEDs achieve higher efficiencies at higher currents because of highermore » spontaneous emission rates and reduced Auger recombination. The technical challenge is to control the size distribution and volume of the QDs to realize these benefits. In conclusion, if constructed properly, III-nitride light-emitting devices with QD active regions have the potential to outperform quantum well light-emitting devices, and enable an era of ultra-efficient solidstate lighting.« less

Laser diode bars based on AlGaAs/GaAs quantum-well heterostructures with an efficiency up to 70%

NASA Astrophysics Data System (ADS)

Ladugin, M. A.; Marmalyuk, A. A.; Padalitsa, A. A.; Bagaev, T. A.; Andreev, A. Yu.; Telegin, K. Yu.; Lobintsov, A. V.; Davydova, E. I.; Sapozhnikov, S. M.; Danilov, A. I.; Podkopaev, A. V.; Ivanova, E. B.; Simakov, V. A.

2017-05-01

The results of the development and fabrication of laser diode bars (λ = 800 - 810 nm) based on AlGaAs/GaAs quantum-well heterostructures with a high efficiency are presented. An increase in the internal quantum and external differential efficiencies together with a decrease in the working voltage and the series resistance allowed us to improve the output parameters of the semiconductor laser under quasi-cw pumping. The output power of the laser diode bars with a 5-mm transverse length reached 210 W, and the efficiency was ~70%.

Multipulse addressing of a Raman quantum memory: configurable beam splitting and efficient readout.

PubMed

Reim, K F; Nunn, J; Jin, X-M; Michelberger, P S; Champion, T F M; England, D G; Lee, K C; Kolthammer, W S; Langford, N K; Walmsley, I A

2012-06-29

Quantum memories are vital to the scalability of photonic quantum information processing (PQIP), since the storage of photons enables repeat-until-success strategies. On the other hand, the key element of all PQIP architectures is the beam splitter, which allows us to coherently couple optical modes. Here, we show how to combine these crucial functionalities by addressing a Raman quantum memory with multiple control pulses. The result is a coherent optical storage device with an extremely large time bandwidth product, that functions as an array of dynamically configurable beam splitters, and that can be read out with arbitrarily high efficiency. Networks of such devices would allow fully scalable PQIP, with applications in quantum computation, long distance quantum communications and quantum metrology.

A set of interesting sequoiatones stereoisomers from a wetland soil-derived fungus Talaromyces flavus.

PubMed

Sun, Tianyu; Zou, Jian; Chen, Guodong; Hu, Dan; Wu, Bin; Liu, Xingzhong; Yao, Xinsheng; Gao, Hao

2017-03-01

Four interesting sequoiatones stereoisomers ( 1 - 4 ) were isolated from a wetland soil-derived fungus Talaromyces flavus by chiral HPLC. On the basis of comprehensive NMR and mass analyses, their planar structures were elucidated as the same as that of sequoiatone B. Among them, 1 and 3 (or 2 and 4 ) were a pair of enantiomers, and 1 and 2 (or 3 and 4 ) were a pair of stereoisomers with epimerization at C-12, which indicated that sequoiatione-type metabolites exist as enantiomers rather than as optically pure compounds in some strains. With the quantum chemical ECD calculations, the absolute configurations of C-8 in 1 - 4 were determined, which is the first report to establish the absolute configuration of C-8 in sequoiatones. However, the absolute configurations of C-12 in sequoiatones are still unsolved.

Electrical Activation Studies of Silicon Implanted Aluminum Gallium Nitride with High Aluminum Mole Fraction

DTIC Science & Technology

2007-12-01

realized with silicon due to its indirect band gap that results in poor quantum efficiency . The first LEDs and laser diodes were developed with...deep UV (λ < 340 nm) still face many challenges and have low internal quantum efficiency . Jong Kyu Kim et al. have developed a light emitting triode...LET) to try to overcome some of the challenges and 16 have produced a lighting device with increased quantum efficiency (16). AlxGa1-xN has been

How to squeeze high quantum efficiency and high time resolution out of a SPAD

NASA Technical Reports Server (NTRS)

Lacaita, A.; Zappa, F.; Cova, Sergio; Ripamonti, Giancarlo; Spinelli, A.

1993-01-01

We address the issue whether Single-Photon Avalanche Diodes (SPADs) can be suitably designed to achieve a trade-off between quantum efficiency and time resolution performance. We briefly recall the physical mechanisms setting the time resolution of avalanche photodiodes operated in single-photon counting, and we give some criteria for the design of SPADs with a quantum efficiency better than l0 percent at 1064 nm together with a time resolution below 50 ps rms.

Absolute and angular efficiencies of a microchannel-plate position-sensitive detector

NASA Technical Reports Server (NTRS)

Gao, R. S.; Gibner, P. S.; Newman, J. H.; Smith, K. A.; Stebbings, R. F.

1984-01-01

This paper presents a characterization of a commercially available position-sensitive detector of energetic ions and neutrals. The detector consists of two microchannel plates followed by a resistive position-encoding anode. The work includes measurement of absolute efficiencies of H(+), He(+), and O(+) ions in the energy range between 250 and 5000 eV, measurement of relative detection efficiencies as a function of particle impact angle, and a simple method for accurate measurement of the time at which a particle strikes the detector.

Photonic transistor and router using a single quantum-dot-confined spin in a single-sided optical microcavity

NASA Astrophysics Data System (ADS)

Hu, C. Y.

2017-03-01

The future Internet is very likely the mixture of all-optical Internet with low power consumption and quantum Internet with absolute security guaranteed by the laws of quantum mechanics. Photons would be used for processing, routing and com-munication of data, and photonic transistor using a weak light to control a strong light is the core component as an optical analogue to the electronic transistor that forms the basis of modern electronics. In sharp contrast to previous all-optical tran-sistors which are all based on optical nonlinearities, here I introduce a novel design for a high-gain and high-speed (up to terahertz) photonic transistor and its counterpart in the quantum limit, i.e., single-photon transistor based on a linear optical effect: giant Faraday rotation induced by a single electronic spin in a single-sided optical microcavity. A single-photon or classical optical pulse as the gate sets the spin state via projective measurement and controls the polarization of a strong light to open/block the photonic channel. Due to the duality as quantum gate for quantum information processing and transistor for optical information processing, this versatile spin-cavity quantum transistor provides a solid-state platform ideal for all-optical networks and quantum networks.

Photonic transistor and router using a single quantum-dot-confined spin in a single-sided optical microcavity

PubMed Central

Hu, C. Y.

2017-01-01

The future Internet is very likely the mixture of all-optical Internet with low power consumption and quantum Internet with absolute security guaranteed by the laws of quantum mechanics. Photons would be used for processing, routing and com-munication of data, and photonic transistor using a weak light to control a strong light is the core component as an optical analogue to the electronic transistor that forms the basis of modern electronics. In sharp contrast to previous all-optical tran-sistors which are all based on optical nonlinearities, here I introduce a novel design for a high-gain and high-speed (up to terahertz) photonic transistor and its counterpart in the quantum limit, i.e., single-photon transistor based on a linear optical effect: giant Faraday rotation induced by a single electronic spin in a single-sided optical microcavity. A single-photon or classical optical pulse as the gate sets the spin state via projective measurement and controls the polarization of a strong light to open/block the photonic channel. Due to the duality as quantum gate for quantum information processing and transistor for optical information processing, this versatile spin-cavity quantum transistor provides a solid-state platform ideal for all-optical networks and quantum networks. PMID:28349960

Tandem luminescent solar concentrators based on engineered quantum dots

NASA Astrophysics Data System (ADS)

Wu, Kaifeng; Li, Hongbo; Klimov, Victor I.

2018-02-01

Luminescent solar concentrators (LSCs) can serve as large-area sunlight collectors for terrestrial and space-based photovoltaics. Due to their high emission efficiencies and readily tunable emission and absorption spectra, colloidal quantum dots have emerged as a new and promising type of LSC fluorophore. Spectral tunability of the quantum dots also facilitates the realization of stacked multilayered LSCs, where enhanced performance is obtained through spectral splitting of incident sunlight, as in multijunction photovoltaics. Here, we demonstrate a large-area (>230 cm2) tandem LSC based on two types of nearly reabsorption-free quantum dots spectrally tuned for optimal solar-spectrum splitting. This prototype device exhibits a high optical quantum efficiency of 6.4% for sunlight illumination and solar-to-electrical power conversion efficiency of 3.1%. The efficiency gains due to the tandem architecture over single-layer devices quickly increase with increasing LSC size and can reach more than 100% in structures with window sizes of more than 2,500 cm2.

A novel EPID design for enhanced contrast and detective quantum efficiency

NASA Astrophysics Data System (ADS)

Rottmann, Joerg; Morf, Daniel; Fueglistaller, Rony; Zentai, George; Star-Lack, Josh; Berbeco, Ross

2016-09-01

Beams-eye-view imaging applications such as real-time soft-tissue motion estimation are hindered by the inherently low image contrast of electronic portal imaging devices (EPID) currently available for clinical use. We introduce and characterize a novel EPID design that provides substantially increased detective quantum efficiency (DQE), contrast-to-noise ratio (CNR) and sensitivity without degradation in spatial resolution. The prototype design features a stack of four conventional EPID layers combined with low noise integrated readout electronics. Each layer consists of a copper plate, a scintillator (\\text{G}{{\\text{d}}2}{{\\text{O}}2}{{\\text{S}}{}}\\text{:Tb} ) and a photodiode/TFT-switch (aSi:H). We characterize the prototype’s signal response to a 6 MV photon beam in terms of modulation transfer function (MTF), DQE and CNR. The presampled MTF is estimated using a slanted slit technique, the DQE is calculated from measured normalized noise power spectra (nNPS) and the MTF and CNR is estimated using a Las Vegas contrast phantom. The prototype has been designed and built to be interchangeable with the current clinical EPID on the Varian TrueBeam platform (AS-1200) in terms of size and data output specifications. Performance evaluation is conducted in absolute values as well as in relative terms using the Varian AS-1200 EPID as a reference detector. A fivefold increase of DQE(0) to about 6.7% was observed by using the four-layered design versus the AS-1200 reference detector. No substantial differences are observed between each layer’s individual MTF and the one for all four layers operating combined indicating that defocusing due to beam divergence is negligible. Also, using four layers instead of one increases the signal to noise ratio by a factor of 1.7.

Conservation of quantum efficiency in quantum well intermixing by stress engineering with dielectric bilayers

NASA Astrophysics Data System (ADS)

Arslan, Seval; Demir, Abdullah; Şahin, Seval; Aydınlı, Atilla

2018-02-01

In semiconductor lasers, quantum well intermixing (QWI) with high selectivity using dielectrics often results in lower quantum efficiency. In this paper, we report on an investigation regarding the effect of thermally induced dielectric stress on the quantum efficiency of quantum well structures in impurity-free vacancy disordering (IFVD) process using photoluminescence and device characterization in conjunction with microscopy. SiO2 and Si x O2/SrF2 (versus SrF2) films were employed for the enhancement and suppression of QWI, respectively. Large intermixing selectivity of 75 nm (125 meV), consistent with the theoretical modeling results, with negligible effect on the suppression region characteristics, was obtained. Si x O2 layer compensates for the large thermal expansion coefficient mismatch of SrF2 with the semiconductor and mitigates the detrimental effects of SrF2 without sacrificing its QWI benefits. The bilayer dielectric approach dramatically improved the dielectric-semiconductor interface quality. Fabricated high power semiconductor lasers demonstrated high quantum efficiency in the lasing region using the bilayer dielectric film during the intermixing process. Our results reveal that stress engineering in IFVD is essential and the thermal stress can be controlled by engineering the dielectric strain opening new perspectives for QWI of photonic devices.

A non-genetic approach to labelling acute myeloid leukemia and bone marrow cells with quantum dots.

PubMed

Zheng, Yanwen; Tan, Dongming; Chen, Zheng; Hu, Chenxi; Mao, Zhengwei J; Singleton, Timothy P; Zeng, Yan; Shao, Xuejun; Yin, Bin

2014-06-01

The difficulty in manipulation of leukemia cells has long hindered the dissection of leukemia pathogenesis. We have introduced a non-genetic approach of marking blood cells, using quantum dots. We compared quantum dots complexed with different vehicles, including a peptide Tat, cationic polymer Turbofect and liposome. Quantum dots-Tat showed the highest efficiency of marking hematopoietic cells among the three vehicles. Quantum dots-Tat could also label a panel of leukemia cell lines at varied efficiencies. More uniform intracellular distributions of quantum dots in mouse bone marrow and leukemia cells were obtained with quantum dots-Tat, compared with the granule-like formation obtained with quantum dots-liposome. Our results suggest that quantum dots have provided a photostable and non-genetic approach that labels normal and malignant hematopoietic cells, in a cell type-, vehicle-, and quantum dot concentration-dependent manner. We expect for potential applications of quantum dots as an easy and fast marking tool assisting investigations of various types of blood cells in the future.

Quantum refrigerators and the third law of thermodynamics.

PubMed

Levy, Amikam; Alicki, Robert; Kosloff, Ronnie

2012-06-01

The rate of temperature decrease of a cooled quantum bath is studied as its temperature is reduced to absolute zero. The third law of thermodynamics is then quantified dynamically by evaluating the characteristic exponent ζ of the cooling process dT(t)/dt∼-T^{ζ} when approaching absolute zero, T→0. A continuous model of a quantum refrigerator is employed consisting of a working medium composed either by two coupled harmonic oscillators or two coupled two-level systems. The refrigerator is a nonlinear device merging three currents from three heat baths: a cold bath to be cooled, a hot bath as an entropy sink, and a driving bath which is the source of cooling power. A heat-driven refrigerator (absorption refrigerator) is compared to a power-driven refrigerator. When optimized, both cases lead to the same exponent ζ, showing a lack of dependence on the form of the working medium and the characteristics of the drivers. The characteristic exponent is therefore determined by the properties of the cold reservoir and its interaction with the system. Two generic heat bath models are considered: a bath composed of harmonic oscillators and a bath composed of ideal Bose/Fermi gas. The restrictions on the interaction Hamiltonian imposed by the third law are discussed. In the Appendices, the theory of periodically driven open systems and its implication for thermodynamics are outlined.

Thermodynamic equilibrium with acceleration and the Unruh effect

NASA Astrophysics Data System (ADS)

Becattini, F.

2018-04-01

We address the problem of thermodynamic equilibrium with constant acceleration along the velocity field lines in a quantum relativistic statistical mechanics framework. We show that for a free scalar quantum field, after vacuum subtraction, all mean values vanish when the local temperature T is as low as the Unruh temperature TU=A /2 π where A is the magnitude of the acceleration four-vector. We argue that the Unruh temperature is an absolute lower bound for the temperature of any accelerated fluid at global thermodynamic equilibrium. We discuss the conditions of this bound to be applicable in a local thermodynamic equilibrium situation.

Novel quantum criticality in CeRu2Si2 near absolute zero observed by thermal expansion and magnetostriction.

PubMed

Yoshida, J; Abe, S; Takahashi, D; Segawa, Y; Komai, Y; Tsujii, H; Matsumoto, K; Suzuki, H; Onuki, Y

2008-12-19

We report linear thermal expansion and magnetostriction measurements for CeRu2Si2 in magnetic fields up to 52.6 mT and at temperatures down to 1 mK. At high temperatures, this compound showed Landau-Fermi-liquid behavior: The linear thermal expansion coefficient and the magnetostriction coefficient were proportional to the temperature and magnetic field, respectively. In contrast, a pronounced non-Fermi-liquid effect was found below 50 mK. The negative contribution of thermal expansion and magnetostriction suggests the existence of an additional quantum critical point.

A Hilbert Space Representation of Generalized Observables and Measurement Processes in the ESR Model

NASA Astrophysics Data System (ADS)

Sozzo, Sandro; Garola, Claudio

2010-12-01

The extended semantic realism ( ESR) model recently worked out by one of the authors embodies the mathematical formalism of standard (Hilbert space) quantum mechanics in a noncontextual framework, reinterpreting quantum probabilities as conditional instead of absolute. We provide here a Hilbert space representation of the generalized observables introduced by the ESR model that satisfy a simple physical condition, propose a generalization of the projection postulate, and suggest a possible mathematical description of the measurement process in terms of evolution of the compound system made up of the measured system and the measuring apparatus.

Quantum Correlations in Nonlocal Boson Sampling.

PubMed

Shahandeh, Farid; Lund, Austin P; Ralph, Timothy C

2017-09-22

Determination of the quantum nature of correlations between two spatially separated systems plays a crucial role in quantum information science. Of particular interest is the questions of if and how these correlations enable quantum information protocols to be more powerful. Here, we report on a distributed quantum computation protocol in which the input and output quantum states are considered to be classically correlated in quantum informatics. Nevertheless, we show that the correlations between the outcomes of the measurements on the output state cannot be efficiently simulated using classical algorithms. Crucially, at the same time, local measurement outcomes can be efficiently simulated on classical computers. We show that the only known classicality criterion violated by the input and output states in our protocol is the one used in quantum optics, namely, phase-space nonclassicality. As a result, we argue that the global phase-space nonclassicality inherent within the output state of our protocol represents true quantum correlations.

Efficient Measurement of Multiparticle Entanglement with Embedding Quantum Simulator.

PubMed

Chen, Ming-Cheng; Wu, Dian; Su, Zu-En; Cai, Xin-Dong; Wang, Xi-Lin; Yang, Tao; Li, Li; Liu, Nai-Le; Lu, Chao-Yang; Pan, Jian-Wei

2016-02-19

The quantum measurement of entanglement is a demanding task in the field of quantum information. Here, we report the direct and scalable measurement of multiparticle entanglement with embedding photonic quantum simulators. In this embedding framework [R. Di Candia et al. Phys. Rev. Lett. 111, 240502 (2013)], the N-qubit entanglement, which does not associate with a physical observable directly, can be efficiently measured with only two (for even N) and six (for odd N) local measurement settings. Our experiment uses multiphoton quantum simulators to mimic dynamical concurrence and three-tangle entangled systems and to track their entanglement evolutions.

Optimal architectures for long distance quantum communication.

PubMed

Muralidharan, Sreraman; Li, Linshu; Kim, Jungsang; Lütkenhaus, Norbert; Lukin, Mikhail D; Jiang, Liang

2016-02-15

Despite the tremendous progress of quantum cryptography, efficient quantum communication over long distances (≥ 1000 km) remains an outstanding challenge due to fiber attenuation and operation errors accumulated over the entire communication distance. Quantum repeaters (QRs), as a promising approach, can overcome both photon loss and operation errors, and hence significantly speedup the communication rate. Depending on the methods used to correct loss and operation errors, all the proposed QR schemes can be classified into three categories (generations). Here we present the first systematic comparison of three generations of quantum repeaters by evaluating the cost of both temporal and physical resources, and identify the optimized quantum repeater architecture for a given set of experimental parameters for use in quantum key distribution. Our work provides a roadmap for the experimental realizations of highly efficient quantum networks over transcontinental distances.

Optimal architectures for long distance quantum communication

PubMed Central

Muralidharan, Sreraman; Li, Linshu; Kim, Jungsang; Lütkenhaus, Norbert; Lukin, Mikhail D.; Jiang, Liang

2016-01-01

Despite the tremendous progress of quantum cryptography, efficient quantum communication over long distances (≥1000 km) remains an outstanding challenge due to fiber attenuation and operation errors accumulated over the entire communication distance. Quantum repeaters (QRs), as a promising approach, can overcome both photon loss and operation errors, and hence significantly speedup the communication rate. Depending on the methods used to correct loss and operation errors, all the proposed QR schemes can be classified into three categories (generations). Here we present the first systematic comparison of three generations of quantum repeaters by evaluating the cost of both temporal and physical resources, and identify the optimized quantum repeater architecture for a given set of experimental parameters for use in quantum key distribution. Our work provides a roadmap for the experimental realizations of highly efficient quantum networks over transcontinental distances. PMID:26876670

Optimal architectures for long distance quantum communication

NASA Astrophysics Data System (ADS)

Muralidharan, Sreraman; Li, Linshu; Kim, Jungsang; Lütkenhaus, Norbert; Lukin, Mikhail D.; Jiang, Liang

2016-02-01

Despite the tremendous progress of quantum cryptography, efficient quantum communication over long distances (≥1000 km) remains an outstanding challenge due to fiber attenuation and operation errors accumulated over the entire communication distance. Quantum repeaters (QRs), as a promising approach, can overcome both photon loss and operation errors, and hence significantly speedup the communication rate. Depending on the methods used to correct loss and operation errors, all the proposed QR schemes can be classified into three categories (generations). Here we present the first systematic comparison of three generations of quantum repeaters by evaluating the cost of both temporal and physical resources, and identify the optimized quantum repeater architecture for a given set of experimental parameters for use in quantum key distribution. Our work provides a roadmap for the experimental realizations of highly efficient quantum networks over transcontinental distances.

Cavity-based quantum networks with single atoms and optical photons

NASA Astrophysics Data System (ADS)

Reiserer, Andreas; Rempe, Gerhard

2015-10-01

Distributed quantum networks will allow users to perform tasks and to interact in ways which are not possible with present-day technology. Their implementation is a key challenge for quantum science and requires the development of stationary quantum nodes that can send and receive as well as store and process quantum information locally. The nodes are connected by quantum channels for flying information carriers, i.e., photons. These channels serve both to directly exchange quantum information between nodes and to distribute entanglement over the whole network. In order to scale such networks to many particles and long distances, an efficient interface between the nodes and the channels is required. This article describes the cavity-based approach to this goal, with an emphasis on experimental systems in which single atoms are trapped in and coupled to optical resonators. Besides being conceptually appealing, this approach is promising for quantum networks on larger scales, as it gives access to long qubit coherence times and high light-matter coupling efficiencies. Thus, it allows one to generate entangled photons on the push of a button, to reversibly map the quantum state of a photon onto an atom, to transfer and teleport quantum states between remote atoms, to entangle distant atoms, to detect optical photons nondestructively, to perform entangling quantum gates between an atom and one or several photons, and even provides a route toward efficient heralded quantum memories for future repeaters. The presented general protocols and the identification of key parameters are applicable to other experimental systems.

Efficient quantum circuits for one-way quantum computing.

PubMed

Tanamoto, Tetsufumi; Liu, Yu-Xi; Hu, Xuedong; Nori, Franco

2009-03-13

While Ising-type interactions are ideal for implementing controlled phase flip gates in one-way quantum computing, natural interactions between solid-state qubits are most often described by either the XY or the Heisenberg models. We show an efficient way of generating cluster states directly using either the imaginary SWAP (iSWAP) gate for the XY model, or the sqrt[SWAP] gate for the Heisenberg model. Our approach thus makes one-way quantum computing more feasible for solid-state devices.

High Performance Organic Materials and Devices

DTIC Science & Technology

2006-03-31

on this material exhibited external quantum efficiency of 2.48% and electroluminescence efficiency as high as 3.33 cd/A. 15. SUBJECT TERMS 16...International de L’Eclairage coordinate at (0.164, 0.188). The external quantum efficiency of 2.48% and electroluminescence efficiency as high as 3.33 cd...more than 90% absorption in active layer, and highly balanced carrier transport. 4 5. High efficient blue- electroluminescence device shows maximum

Highly efficient multiple-layer CdS quantum dot sensitized III-V solar cells.

PubMed

Lin, Chien-Chung; Han, Hau-Vei; Chen, Hsin-Chu; Chen, Kuo-Ju; Tsai, Yu-Lin; Lin, Wein-Yi; Kuo, Hao-Chung; Yu, Peichen

2014-02-01

In this review, the concept of utilization of solar spectrum in order to increase the solar cell efficiency is discussed. Among the three mechanisms, down-shifting effect is investigated in detail. Organic dye, rare-earth minerals and quantum dots are three most popular down-shift materials. While the enhancement of solar cell efficiency was not clearly observed in the past, the advances in quantum dot fabrication have brought strong response out of the hybrid platform of a quantum dot solar cell. A multiple layer structure, including PDMS as the isolation layer, is proposed and demonstrated. With the help of pulse spray system, precise control can be achieved and the optimized concentration can be found.

Low quantum defect laser performance

NASA Astrophysics Data System (ADS)

Bowman, Steven R.

2017-01-01

Low quantum defect lasers are possible using near-resonant optical pumping. This paper examines the laser material performance as the quantum defect of the laser is reduced. A steady-state model is developed, which incorporates the relevant physical processes in these materials and predicts extraction efficiency and waste heat generation. As the laser quantum defect is reduced below a few percent, the impact of fluorescence cooling must be included in the analysis. The special case of a net zero quantum defect laser is examined in detail. This condition, referred to as the radiation balance laser (RBL), is shown to provide two orders of magnitude lower heat generation at the cost of roughly 10% loss in extraction efficiency. Numerical examples are presented with the host materials Yb:YAG and Yb:Silica. The general conditions, which yield optimal laser efficiency, are derived and explored.

Efficient multiparty quantum-secret-sharing schemes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xiao Li; Deng Fuguo; Key Laboratory for Quantum Information and Measurements, MOE, Beijing 100084

In this work, we generalize the quantum-secret-sharing scheme of Hillery, Buzek, and Berthiaume [Phys. Rev. A 59, 1829 (1999)] into arbitrary multiparties. Explicit expressions for the shared secret bit is given. It is shown that in the Hillery-Buzek-Berthiaume quantum-secret-sharing scheme the secret information is shared in the parity of binary strings formed by the measured outcomes of the participants. In addition, we have increased the efficiency of the quantum-secret-sharing scheme by generalizing two techniques from quantum key distribution. The favored-measuring-basis quantum-secret-sharing scheme is developed from the Lo-Chau-Ardehali technique [H. K. Lo, H. F. Chau, and M. Ardehali, e-print quant-ph/0011056] wheremore » all the participants choose their measuring-basis asymmetrically, and the measuring-basis-encrypted quantum-secret-sharing scheme is developed from the Hwang-Koh-Han technique [W. Y. Hwang, I. G. Koh, and Y. D. Han, Phys. Lett. A 244, 489 (1998)] where all participants choose their measuring basis according to a control key. Both schemes are asymptotically 100% in efficiency, hence nearly all the Greenberger-Horne-Zeilinger states in a quantum-secret-sharing process are used to generate shared secret information.« less

Extreme Quantum Memory Advantage for Rare-Event Sampling

NASA Astrophysics Data System (ADS)

Aghamohammadi, Cina; Loomis, Samuel P.; Mahoney, John R.; Crutchfield, James P.

2018-02-01

We introduce a quantum algorithm for memory-efficient biased sampling of rare events generated by classical memoryful stochastic processes. Two efficiency metrics are used to compare quantum and classical resources for rare-event sampling. For a fixed stochastic process, the first is the classical-to-quantum ratio of required memory. We show for two example processes that there exists an infinite number of rare-event classes for which the memory ratio for sampling is larger than r , for any large real number r . Then, for a sequence of processes each labeled by an integer size N , we compare how the classical and quantum required memories scale with N . In this setting, since both memories can diverge as N →∞ , the efficiency metric tracks how fast they diverge. An extreme quantum memory advantage exists when the classical memory diverges in the limit N →∞ , but the quantum memory has a finite bound. We then show that finite-state Markov processes and spin chains exhibit memory advantage for sampling of almost all of their rare-event classes.

Matroids and quantum-secret-sharing schemes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sarvepalli, Pradeep; Raussendorf, Robert

A secret-sharing scheme is a cryptographic protocol to distribute a secret state in an encoded form among a group of players such that only authorized subsets of the players can reconstruct the secret. Classically, efficient secret-sharing schemes have been shown to be induced by matroids. Furthermore, access structures of such schemes can be characterized by an excluded minor relation. No such relations are known for quantum secret-sharing schemes. In this paper we take the first steps toward a matroidal characterization of quantum-secret-sharing schemes. In addition to providing a new perspective on quantum-secret-sharing schemes, this characterization has important benefits. While previousmore » work has shown how to construct quantum-secret-sharing schemes for general access structures, these schemes are not claimed to be efficient. In this context the present results prove to be useful; they enable us to construct efficient quantum-secret-sharing schemes for many general access structures. More precisely, we show that an identically self-dual matroid that is representable over a finite field induces a pure-state quantum-secret-sharing scheme with information rate 1.« less

Adaptive recurrence quantum entanglement distillation for two-Kraus-operator channels

NASA Astrophysics Data System (ADS)

Ruan, Liangzhong; Dai, Wenhan; Win, Moe Z.

2018-05-01

Quantum entanglement serves as a valuable resource for many important quantum operations. A pair of entangled qubits can be shared between two agents by first preparing a maximally entangled qubit pair at one agent, and then sending one of the qubits to the other agent through a quantum channel. In this process, the deterioration of entanglement is inevitable since the noise inherent in the channel contaminates the qubit. To address this challenge, various quantum entanglement distillation (QED) algorithms have been developed. Among them, recurrence algorithms have advantages in terms of implementability and robustness. However, the efficiency of recurrence QED algorithms has not been investigated thoroughly in the literature. This paper puts forth two recurrence QED algorithms that adapt to the quantum channel to tackle the efficiency issue. The proposed algorithms have guaranteed convergence for quantum channels with two Kraus operators, which include phase-damping and amplitude-damping channels. Analytical results show that the convergence speed of these algorithms is improved from linear to quadratic and one of the algorithms achieves the optimal speed. Numerical results confirm that the proposed algorithms significantly improve the efficiency of QED.

Highly efficient non-degenerate four-wave mixing under dual-mode injection in InP/InAs quantum-dash and quantum-dot lasers at 1.55 μm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sadeev, T., E-mail: tagir@mailbox.tu-berlin.de; Arsenijević, D.; Huang, H.

2015-11-09

This work reports on non-degenerate four-wave mixing under dual-mode injection in metalorganic vapor phase epitaxy grown InP/InAs quantum-dash and quantum dot Fabry-Perot laser operating at 1550 nm. High values of normalized conversion efficiency of −18.6 dB, optical signal-to-noise ratio of 37 dB, and third order optical susceptibility normalized to material gain χ{sup (3)}/g{sub 0} of ∼4 × 10{sup −19} m{sup 3}/V{sup 3} are measured for 1490 μm long quantum-dash lasers. These values are similar to those obtained with distributed-feedback lasers and semiconductor optical amplifiers, which are much more complicated to fabricate. On the other hand, due to the faster gain saturation and enhanced modulation of carriermore » populations, quantum-dot lasers demonstrate 12 dB lower conversion efficiency and 4 times lower χ{sup (3)}/g{sub 0} compared to quantum dash lasers.« less

Error regions in quantum state tomography: computational complexity caused by geometry of quantum states

NASA Astrophysics Data System (ADS)

Suess, Daniel; Rudnicki, Łukasz; maciel, Thiago O.; Gross, David

2017-09-01

The outcomes of quantum mechanical measurements are inherently random. It is therefore necessary to develop stringent methods for quantifying the degree of statistical uncertainty about the results of quantum experiments. For the particularly relevant task of quantum state tomography, it has been shown that a significant reduction in uncertainty can be achieved by taking the positivity of quantum states into account. However—the large number of partial results and heuristics notwithstanding—no efficient general algorithm is known that produces an optimal uncertainty region from experimental data, while making use of the prior constraint of positivity. Here, we provide a precise formulation of this problem and show that the general case is NP-hard. Our result leaves room for the existence of efficient approximate solutions, and therefore does not in itself imply that the practical task of quantum uncertainty quantification is intractable. However, it does show that there exists a non-trivial trade-off between optimality and computational efficiency for error regions. We prove two versions of the result: one for frequentist and one for Bayesian statistics.

Calendar effects in quantum mechanics in view of interactive holography

NASA Astrophysics Data System (ADS)

Berkovich, Simon

2013-04-01

Quantum mechanics in terms of interactive holography appears as `normal' science [1]. With the holography quantum behavior is determined by the interplay of material formations and their conjugate images. To begin with, this effortlessly elucidates the nonlocality in quantum entanglements. Then, it has been shown that Schr"odinger's dynamics for a single particle arises from Bi-Fragmental random walks of the particle itself and its holographic image. For many particles this picture blurs with fragments merging as bosons or fermions. In biomolecules, swapping of particles and their holographic placeholders leads to self-replication of the living matter. Because of broad interpretations of quantum formalism direct experiments attributing it to holography may not be very compelling. The holographic mechanism better reveals as an absolute frame of reference. A number of physical and biological events exhibit annual variations when Earth orbital position changes with respect to the universal holographic mechanism. The well established calendar variations of heart attacks can be regarded as a positive outcome of a generalization of the Michelson experiment, where holography is interferometry and ailing hearts are detectors of pathologically replicated proteins. Also, there have been already observed calendar changes in radioactive decay rates. The same could be expected for various fine quantum experiences, like, e.g., Josephson tunneling. In other words, Quantum Mechanics (February) Quantum Mechanics (August). [1] S. Berkovich, ``A comprehensive explanation of quantum mechanics,'' www.cs.gwu.edu/research/technical-report/170 .

Spectral purity and tunability of terahertz quantum cascade laser sources based on intracavity difference-frequency generation.

PubMed

Consolino, Luigi; Jung, Seungyong; Campa, Annamaria; De Regis, Michele; Pal, Shovon; Kim, Jae Hyun; Fujita, Kazuue; Ito, Akio; Hitaka, Masahiro; Bartalini, Saverio; De Natale, Paolo; Belkin, Mikhail A; Vitiello, Miriam Serena

2017-09-01

Terahertz sources based on intracavity difference-frequency generation in mid-infrared quantum cascade lasers (THz DFG-QCLs) have recently emerged as the first monolithic electrically pumped semiconductor sources capable of operating at room temperature across the 1- to 6-THz range. Despite tremendous progress in power output, which now exceeds 1 mW in pulsed and 10 μW in continuous-wave regimes at room temperature, knowledge of the major figure of merits of these devices for high-precision spectroscopy, such as spectral purity and absolute frequency tunability, is still lacking. By exploiting a metrological grade system comprising a terahertz frequency comb synthesizer, we measure, for the first time, the free-running emission linewidth (LW), the tuning characteristics, and the absolute center frequency of individual emission lines of these sources with an uncertainty of 4 × 10 -10 . The unveiled emission LW (400 kHz at 1-ms integration time) indicates that DFG-QCLs are well suited to operate as local oscillators and to be used for a variety of metrological, spectroscopic, communication, and imaging applications that require narrow-LW THz sources.

High-performance magnetic field sensor based on superconducting quantum interference filters

NASA Astrophysics Data System (ADS)

Caputo, P.; Oppenländer, J.; Häussler, Ch.; Tomes, J.; Friesch, A.; Träuble, T.; Schopohl, N.

2004-08-01

We have developed an absolute magnetic field sensor using a superconducting quantum interference filter (SQIF) made of high-Tc grain-boundary Josephson junctions. The device shows the typical magnetic-field-dependent voltage response V(B ), which is a sharp deltalike dip in the vicinity of zero-magnetic field. When the SQIF is cooled with magnetic shield, and then the shield is removed, the presence of the ambient magnetic field induces a shift of the dip position from B0≈0 to a value B ≈B1, which is about the average value of the Earth's magnetic field, at our latitude. When the SQIF is cooled in the ambient field without shielding, the dip is first found at B ≈B1, and the further shielding of the SQIF results in a shift of the dip towards B0≈0. The low hysteresis observed in the sequence of experiments (less than 5% of B1) makes SQIFs suitable for high precision measurements of the absolute magnetic field. The experimental results are discussed in view of potential applications of high-Tc SQIFs in magnetometry.

Macroscopic superpositions and gravimetry with quantum magnetomechanics.

PubMed

Johnsson, Mattias T; Brennen, Gavin K; Twamley, Jason

2016-11-21

Precision measurements of gravity can provide tests of fundamental physics and are of broad practical interest for metrology. We propose a scheme for absolute gravimetry using a quantum magnetomechanical system consisting of a magnetically trapped superconducting resonator whose motion is controlled and measured by a nearby RF-SQUID or flux qubit. By driving the mechanical massive resonator to be in a macroscopic superposition of two different heights our we predict that our interferometry protocol could, subject to systematic errors, achieve a gravimetric sensitivity of Δg/g ~ 2.2 × 10 -10  Hz -1/2 , with a spatial resolution of a few nanometres. This sensitivity and spatial resolution exceeds the precision of current state of the art atom-interferometric and corner-cube gravimeters by more than an order of magnitude, and unlike classical superconducting interferometers produces an absolute rather than relative measurement of gravity. In addition, our scheme takes measurements at ~10 kHz, a region where the ambient vibrational noise spectrum is heavily suppressed compared the ~10 Hz region relevant for current cold atom gravimeters.

Macroscopic superpositions and gravimetry with quantum magnetomechanics

PubMed Central

Johnsson, Mattias T.; Brennen, Gavin K.; Twamley, Jason

2016-01-01

Precision measurements of gravity can provide tests of fundamental physics and are of broad practical interest for metrology. We propose a scheme for absolute gravimetry using a quantum magnetomechanical system consisting of a magnetically trapped superconducting resonator whose motion is controlled and measured by a nearby RF-SQUID or flux qubit. By driving the mechanical massive resonator to be in a macroscopic superposition of two different heights our we predict that our interferometry protocol could, subject to systematic errors, achieve a gravimetric sensitivity of Δg/g ~ 2.2 × 10−10 Hz−1/2, with a spatial resolution of a few nanometres. This sensitivity and spatial resolution exceeds the precision of current state of the art atom-interferometric and corner-cube gravimeters by more than an order of magnitude, and unlike classical superconducting interferometers produces an absolute rather than relative measurement of gravity. In addition, our scheme takes measurements at ~10 kHz, a region where the ambient vibrational noise spectrum is heavily suppressed compared the ~10 Hz region relevant for current cold atom gravimeters. PMID:27869142

Influence of quantum dot's quantum yield to chemiluminescent resonance energy transfer.

PubMed

Wang, Hai-Qiao; Li, Yong-Qiang; Wang, Jian-Hao; Xu, Qiao; Li, Xiu-Qing; Zhao, Yuan-Di

2008-03-03

The resonance energy transfer between chemiluminescence donor (luminol-H2O2 system) and quantum dots (QDs, emission at 593 nm) acceptors (CRET) was investigated. The resonance energy transfer efficiencies were compared while the oil soluble QDs, water soluble QDs (modified with thioglycolate) and QD-HRP conjugates were used as acceptor. The fluorescence of QD can be observed in the three cases, indicating that the CRET occurs while QD acceptor in different status was used. The highest CRET efficiency (10.7%) was obtained in the case of oil soluble QDs, and the lowest CRET efficiency (2.7%) was observed in the QD-HRP conjugates case. This result is coincident with the quantum yields of the acceptors (18.3% and 0.4%). The same result was observed in another similar set of experiment, in which the amphiphilic polymer modified QDs (emission at 675 nm) were used. It suggests that the quantum yield of the QD in different status is the crucial factor to the CRET efficiency. Furthermore, the multiplexed CRET between luminol donor and three different sizes QD acceptors was observed simultaneously. This work will offer useful support for improving the CRET studies based on quantum dots.

Deterministic generation of remote entanglement with active quantum feedback

DOE PAGES

Martin, Leigh; Motzoi, Felix; Li, Hanhan; ...

2015-12-10

We develop and study protocols for deterministic remote entanglement generation using quantum feedback, without relying on an entangling Hamiltonian. In order to formulate the most effective experimentally feasible protocol, we introduce the notion of average-sense locally optimal feedback protocols, which do not require real-time quantum state estimation, a difficult component of real-time quantum feedback control. We use this notion of optimality to construct two protocols that can deterministically create maximal entanglement: a semiclassical feedback protocol for low-efficiency measurements and a quantum feedback protocol for high-efficiency measurements. The latter reduces to direct feedback in the continuous-time limit, whose dynamics can bemore » modeled by a Wiseman-Milburn feedback master equation, which yields an analytic solution in the limit of unit measurement efficiency. Our formalism can smoothly interpolate between continuous-time and discrete-time descriptions of feedback dynamics and we exploit this feature to derive a superior hybrid protocol for arbitrary nonunit measurement efficiency that switches between quantum and semiclassical protocols. Lastly, we show using simulations incorporating experimental imperfections that deterministic entanglement of remote superconducting qubits may be achieved with current technology using the continuous-time feedback protocol alone.« less

Frequency locking of compact laser-diode modules at 633 nm

NASA Astrophysics Data System (ADS)

Nölleke, Christian; Leisching, Patrick; Blume, Gunnar; Jedrzejczyk, Daniel; Pohl, Johannes; Feise, David; Sahm, Alexander; Paschke, Katrin

2018-02-01

This work reports on a compact diode-laser module emitting at 633 nm. The emission frequency can be tuned with temperature and current, while optical feedback of an internal DBR grating ensures single-mode operation. The laser diode is integrated into a micro-fabricated package, which includes optics for beam shaping, a miniaturized optical isolator, and a vapor cell as frequency reference. The achieved absolute frequency stability is below 10-8 , while the output power can be more than 10 mW. This compact absolute frequency-stabilized laser system can replace gas lasers and may be integrated in future quantum technology devices.

Loading a single photon into an optical cavity

NASA Astrophysics Data System (ADS)

Du, Shengwang; Liu, Chang; Sun, Yuan; Zhao, Luwei; Zhang, Shanchao; Loy, M. M. T.

2015-05-01

Confining and manipulating single photons inside a reflective optical cavity is an essential task of cavity quantum electrodynamics (CQED) for probing the quantum nature of light quanta. Such systems are also elementary building blocks for many protocols of quantum network, where remote cavity quantum nodes are coupled through flying photons. The connectivity and scalability of such a quantum network strongly depends on the efficiency of loading a single photon into cavity. In this work we demonstrate that a single photon with an optimal temporal waveform can be efficiently loaded into a cavity. Using heralded narrow-band single photons with exponential growth wave packet whose time constant matches the photon lifetime in the cavity, we demonstrate a loading efficiency of more than 87 percent from free space to a single-sided Fabry-Perot cavity. Our result and approach may enable promising applications in realizing large-scale CQED-based quantum networks. The work was supported by the Hong Kong RGC (Project No. 601411).

An Efficient and Secure Arbitrary N-Party Quantum Key Agreement Protocol Using Bell States

NASA Astrophysics Data System (ADS)

Liu, Wen-Jie; Xu, Yong; Yang, Ching-Nung; Gao, Pei-Pei; Yu, Wen-Bin

2018-01-01

Two quantum key agreement protocols using Bell states and Bell measurement were recently proposed by Shukla et al. (Quantum Inf. Process. 13(11), 2391-2405, 2014). However, Zhu et al. pointed out that there are some security flaws and proposed an improved version (Quantum Inf. Process. 14(11), 4245-4254, 2015). In this study, we will show Zhu et al.'s improvement still exists some security problems, and its efficiency is not high enough. For solving these problems, we utilize four Pauli operations { I, Z, X, Y} to encode two bits instead of the original two operations { I, X} to encode one bit, and then propose an efficient and secure arbitrary N-party quantum key agreement protocol. In the protocol, the channel checking with decoy single photons is introduced to avoid the eavesdropper's flip attack, and a post-measurement mechanism is used to prevent against the collusion attack. The security analysis shows the present protocol can guarantee the correctness, security, privacy and fairness of quantum key agreement.

Modeling and simulation of InGaN/GaN quantum dots solar cell

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aissat, A., E-mail: sakre23@yahoo.fr; LASICOMLaboratory, Faculty of Sciences, University of Blida 1; Benyettou, F.

2016-07-25

Currently, quantum dots have attracted attention in the field of optoelectronics, and are used to overcome the limits of a conventional solar cell. Here, an In{sub 0.25}Ga{sub 0.75}N/GaN Quantum Dots Solar Cell has been modeled and simulated using Silvaco Atlas. Our results show that the short circuit current increases with the insertion of the InGaN quantum dots inside the intrinsic region of a GaN pin solar cell. In contrary, the open circuit voltage decreases. A relative optimization of the conversion efficiency of 54.77% was achieved comparing a 5-layers In{sub 0.25}Ga{sub 0.75}N/GaN quantum dots with pin solar cell. The conversion efficiencymore » begins to decline beyond 5-layers quantum dots introduced. Indium composition of 10 % improves relatively the efficiency about 42.58% and a temperature of 285 K gives better conversion efficiency of 13.14%.« less

High heralding-efficiency of near-IR fiber coupled photon pairs for quantum technologies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dixon, P. Ben; Murphy, Ryan; Rosenberg, Danna

We report on the development and use of a high heralding-efficiency, single-mode-fiber coupled telecom-band source of entangled photons for quantum technology applications. The source development efforts consisted of theoretical and experimental efforts and we demonstrated a correlated-mode coupling efficiency of 97% 2%, the highest efficiency yet achieved for this type of system. We then incorporated these beneficial source development techniques in a Sagnac configured telecom-band entangled photon source that generates photon pairs entangled in both time/energy and polarization degrees of freedom. We made use of these highly desirable entangled states to investigate several promising quantum technologies.

Quantum discord and Maxwell's demons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zurek, Wojciech Hubert

2003-01-01

Quantum discord was proposed as an information-theoretic measure of the 'quantumness' of correlations. I show that discord determines the difference between the efficiency of quantum and classical Maxwell's demons - that is, entities that can or cannot measure nonlocal observables or carry out conditional quantum operations - in extracting work from collections of correlated quantum systems.

Quantum order, entanglement and localization in many-body systems

NASA Astrophysics Data System (ADS)

Khemani, Vedika

The interplay of disorder and interactions can have remarkable effects on the physics of quantum systems. A striking example is provided by the long conjectured--and recently confirmed--phenomenon of many-body localization. Many-body localized (MBL) phases violate foundational assumptions about ergodicity and thermalization in interacting systems, and represent a new frontier for non-equilibrium quantum statistical mechanics. We start with a study of the dynamical response of MBL phases to time-dependent perturbations. We find that that an asymptotically slow, local perturbation induces a highly non-local response, a surprising result for a localized insulator. A complementary calculation in the linear-response regime elucidates the structure of many-body resonances contributing to the dynamics of this phase. We then turn to a study of quantum order in MBL systems. It was shown that localization can allow novel high-temperature phases and phase transitions that are disallowed in equilibrium. We extend this idea of "localization protected order'' to the case of symmetry-protected topological phases and to the elucidation of phase structure in periodically driven Floquet systems. We show that Floquet systems can display nontrivial phases, some of which show a novel form of correlated spatiotemporal order and are absolutely stable to all generic perturbations. The next part of the thesis addresses the role of quantum entanglement, broadly speaking. Remarkably, it was shown that even highly-excited MBL eigenstates have low area-law entanglement. We exploit this feature to develop tensor-network based algorithms for efficiently computing and representing highly-excited MBL eigenstates. We then switch gears from disordered, localized systems and examine the entanglement Hamiltonian and its low energy spectrum from a statistical mechanical lens, particularly focusing on issues of universality and thermalization. We close with two miscellaneous results on topologically ordered phases. The first studies the nonequilibrium "Kibble-Zurek'' dynamics resulting from driving a system through a phase transition from a topologically ordered phase to a trivial one at a finite rate. The second shows that the four-state Potts model on the pyrochlore lattice exhibits a "Coulomb Phase'' characterized by three emergent gauge fields.

Spectral gain measurements of quantum confined emitters, and design and fabrication of intersubband quantum box laser structures

NASA Astrophysics Data System (ADS)

Tsvid, Gene

Semiconductor laser active regions are commonly characterized by photo- and electro-luminescence (PL, EL) and cavity length analysis. However quantitative spectral information is not readily extracted from PL and EL data and comparison of different active region materials can be difficult. More quantifiable spectral information is contained in the optical gain spectra. This work reports on spectral gain studies, using multi-segmented interband devices, of InGaAs quantum well and quantum dot active regions grown by metalorganic chemical vapor deposition (MOCVD). Using the fundamental connection between gain and spontaneous emission spectra, the spontaneous radiative current and spontaneous radiative efficiency is evaluated for these active regions. The spectral gain and spontaneous radiative efficiency measurements of 980 nm emitting InGaAs quantum well (QW) material provides a benchmark comparison to previous results obtained on highly-strained, 1200 nm emitting InGaAs QW material. These studies provide insight into carrier recombination and the role of the current injection efficiency in InGaAs QW lasers. The spectral gain of self-assembled MOCVD grown InGaAs quantum dots (QD) active regions are also investigated, allowing for comparison to InGaAs QW material. The second part of my talk will cover intersubband-transition QW and quantum-box (QB) lasers. Quantum cascade (QC) lasers have emerged as compact and technologically important light sources in the mid-infrared (IR) and far-IR wavelength ranges infringing on the near-IR and terahertz spectral regions respectively. However, the overall power conversion efficiency, so-called wallplug efficiency, of the best QC lasers, emitting around 5 microns, is ˜9% in CW operation and very unlikely to exceed 15%. In order to dramatically improve the wallplug efficiency of mid-IR lasers (i.e., to about 50%), intersubband QB (IQB) lasers have been proposed. The basic idea, the optimal design and the progress towards the fabrication of IQB lasers will be presented.

High Quantum Efficiency Nanopillar Photodiodes Overcoming the Diffraction Limit of Light.

PubMed

Lee, Wook-Jae; Senanayake, Pradeep; Farrell, Alan C; Lin, Andrew; Hung, Chung-Hong; Huffaker, Diana L

2016-01-13

InAs1-xSbx nanowires have recently attracted interest for infrared sensing applications due to the small bandgap and high thermal conductivity. However, previous reports on nanowire-based infrared sensors required low operating temperatures in order to mitigate the high dark current and have shown poor sensitivities resulting from reduced light coupling efficiency beyond the diffraction limit. Here, InAsSb nanopillar photodiodes with high quantum efficiency are achieved by partially coating the nanopillar with metal that excites localized surface plasmon resonances, leading to quantum efficiencies of ∼29% at 2390 nm. These high quantum efficiency nanopillar photodiodes, with 180 nm diameters and 1000 nm heights, allow operation at temperatures as high as 220 K and exhibit a detection wavelength up to 3000 nm, well beyond the diffraction limit. The InAsSb nanopillars are grown on low cost GaAs (111)B substrates using an InAs buffer layer, making our device architecture a promising path toward low-cost infrared focal plane arrays with high operating temperature.

Efficiency versus speed in quantum heat engines: Rigorous constraint from Lieb-Robinson bound

NASA Astrophysics Data System (ADS)

Shiraishi, Naoto; Tajima, Hiroyasu

2017-08-01

A long-standing open problem whether a heat engine with finite power achieves the Carnot efficiency is investgated. We rigorously prove a general trade-off inequality on thermodynamic efficiency and time interval of a cyclic process with quantum heat engines. In a first step, employing the Lieb-Robinson bound we establish an inequality on the change in a local observable caused by an operation far from support of the local observable. This inequality provides a rigorous characterization of the following intuitive picture that most of the energy emitted from the engine to the cold bath remains near the engine when the cyclic process is finished. Using this description, we prove an upper bound on efficiency with the aid of quantum information geometry. Our result generally excludes the possibility of a process with finite speed at the Carnot efficiency in quantum heat engines. In particular, the obtained constraint covers engines evolving with non-Markovian dynamics, which almost all previous studies on this topic fail to address.

Efficiency versus speed in quantum heat engines: Rigorous constraint from Lieb-Robinson bound.

PubMed

Shiraishi, Naoto; Tajima, Hiroyasu

2017-08-01

A long-standing open problem whether a heat engine with finite power achieves the Carnot efficiency is investgated. We rigorously prove a general trade-off inequality on thermodynamic efficiency and time interval of a cyclic process with quantum heat engines. In a first step, employing the Lieb-Robinson bound we establish an inequality on the change in a local observable caused by an operation far from support of the local observable. This inequality provides a rigorous characterization of the following intuitive picture that most of the energy emitted from the engine to the cold bath remains near the engine when the cyclic process is finished. Using this description, we prove an upper bound on efficiency with the aid of quantum information geometry. Our result generally excludes the possibility of a process with finite speed at the Carnot efficiency in quantum heat engines. In particular, the obtained constraint covers engines evolving with non-Markovian dynamics, which almost all previous studies on this topic fail to address.

Maximizing the quantum efficiency of microchannel plate detectors - The collection of photoelectrons from the interchannel web using an electric field

NASA Technical Reports Server (NTRS)

Taylor, R. C.; Hettrick, M. C.; Malina, R. F.

1983-01-01

High quantum efficiency and two-dimensional imaging capabilities make the microchannel plate (MCP) a suitable detector for a sky survey instrument. The Extreme Ultraviolet Explorer satellite, to be launched in 1987, will use MCP detectors. A feature which limits MCP efficiency is related to the walls of individual channels. The walls are of finite thickness and thus form an interchannel web. Under normal circumstances, this web does not contribute to the detector's quantum efficiency. Panitz and Foesch (1976) have found that in the case of a bombardment with ions, electrons were ejected from the electrode material coating the web. By applying a small electric field, the electrons were returned to the MCP surface where they were detected. The present investigation is concerned with the enhancement of quantum efficiencies in the case of extreme UV wavelengths. Attention is given to a model and a computer simulation which quantitatively reproduce the experimental results.

Study on Locally Confined Deposition of Si Nanocrystals in High-Aspect-Ratio Si Nano-Pillar Array for Nano-Electronic and Nano-Photonic Applications

DTIC Science & Technology

2010-02-23

reflection, thus increasing the quantum efficiency by one order of magnitude and improving the light extraction from the nano-roughened device surface by...respectively. At a biased current of 400 A, the highest external quantum efficiency is over 0.2% to obtain the maximum EL power of >1 W. In...processing techniques for improving the internal and external quantum efficiencies of Si MOSLEDs via detuning the size and density of high-aspect-ratio Si

How noise affects quantum detector tomography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Q., E-mail: wang@physics.leidenuniv.nl; Renema, J. J.; Exter, M. P.van

2015-10-07

We determine the full photon number response of a NbN superconducting nanowire single photon detector via quantum detector tomography, and the results show the separation of linear, effective absorption efficiency from the internal detection efficiencies. In addition, we demonstrate an error budget for the complete quantum characterization of the detector. We find that for short times, the dominant noise source is shot noise, while laser power fluctuations limit the accuracy for longer timescales. The combined standard uncertainty of the internal detection efficiency derived from our measurements is about 2%.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Steiner, Myles A.; Perl, E. E.; Geisz, J. F.

Here, we demonstrate that in solar cells with highly reflective back mirrors, the measured internal quantum efficiency exhibits a shift in bandgap relative to the measured external quantum efficiency. The shift arises from the fact that the measured reflectance at the front surface includes a superposition of waves reflecting from the front and back surfaces. We quantify the magnitude of the apparent shift and discuss the errors that can result in determination of quantities such as the photocurrent. Because of this apparent shift, it is important that the bandgap be determined from the external quantum efficiency.

Factors concerned in the efficient steam sterilization of surgical dressings

PubMed Central

Fallon, R. J.

1961-01-01

Some of the factors affecting the efficient steam sterilization of dressings have been examined. A jacketed sterilizer will process a load more quickly than a sterilizer without a jacket. The level of fore-vacuum is critical and must reach an absolute pressure of 20 mm. Hg (29·2 in.Hg vacuum) or less. This will overcome all conditions of overpacking studied. The level of after-vacuum should be 100 mm. Hg absolute or less, preferably near 50 mm. Hg absolute. Overpacking cannot be defined in terms of weight of a fabric per unit volume of container but occurs when a load is compressed in its container. PMID:13891475

Quantum Chemistry on Quantum Computers: A Polynomial-Time Quantum Algorithm for Constructing the Wave Functions of Open-Shell Molecules.

PubMed

Sugisaki, Kenji; Yamamoto, Satoru; Nakazawa, Shigeaki; Toyota, Kazuo; Sato, Kazunobu; Shiomi, Daisuke; Takui, Takeji

2016-08-18

Quantum computers are capable to efficiently perform full configuration interaction (FCI) calculations of atoms and molecules by using the quantum phase estimation (QPE) algorithm. Because the success probability of the QPE depends on the overlap between approximate and exact wave functions, efficient methods to prepare accurate initial guess wave functions enough to have sufficiently large overlap with the exact ones are highly desired. Here, we propose a quantum algorithm to construct the wave function consisting of one configuration state function, which is suitable for the initial guess wave function in QPE-based FCI calculations of open-shell molecules, based on the addition theorem of angular momentum. The proposed quantum algorithm enables us to prepare the wave function consisting of an exponential number of Slater determinants only by a polynomial number of quantum operations.

Quantum Brownian motion model for the stock market

NASA Astrophysics Data System (ADS)

Meng, Xiangyi; Zhang, Jian-Wei; Guo, Hong

2016-06-01

It is believed by the majority today that the efficient market hypothesis is imperfect because of market irrationality. Using the physical concepts and mathematical structures of quantum mechanics, we construct an econophysical framework for the stock market, based on which we analogously map massive numbers of single stocks into a reservoir consisting of many quantum harmonic oscillators and their stock index into a typical quantum open system-a quantum Brownian particle. In particular, the irrationality of stock transactions is quantitatively considered as the Planck constant within Heisenberg's uncertainty relationship of quantum mechanics in an analogous manner. We analyze real stock data of Shanghai Stock Exchange of China and investigate fat-tail phenomena and non-Markovian behaviors of the stock index with the assistance of the quantum Brownian motion model, thereby interpreting and studying the limitations of the classical Brownian motion model for the efficient market hypothesis from a new perspective of quantum open system dynamics.

Quantum Chemistry in Great Britain: Developing a Mathematical Framework for Quantum Chemistry

NASA Astrophysics Data System (ADS)

Simões, Ana; Gavroglu, Kostas

By 1935 quantum chemistry was already delineated as a distinct sub-discipline due to the contributions of Fritz London, Walter Heitler, Friedrich Hund, Erich Hückel, Robert Mulliken, Linus Pauling, John van Vleck and John Slater. These people are credited with showing that the application of quantum mechanics to the solution of chemical problems was, indeed, possible, especially so after the introduction of a number of new concepts and the adoption of certain approximation methods. And though a number of chemists had started talking of the formation of theoretical or, even, mathematical chemistry, a fully developed mathematical framework of quantum chemistry was still wanting. The work of three persons in particular-of John E. Lennard-Jones, Douglas R. Hartree, and Charles Alfred Coulson-has been absolutely crucial in the development of such a framework. In this paper we shall discuss the work of these three researchers who started their careers in the Cambridge tradition of mathematical physics and who at some point of their careers all became professors of applied mathematics. We shall argue that their work consisted of decisive contributions to the development of such a mathematical framework for quantum chemistry.

Quantum criticality and black holes.

PubMed

Sachdev, Subir; Müller, Markus

2009-04-22

Many condensed matter experiments explore the finite temperature dynamics of systems near quantum critical points. Often, there are no well-defined quasiparticle excitations, and so quantum kinetic equations do not describe the transport properties completely. The theory shows that the transport coefficients are not proportional to a mean free scattering time (as is the case in the Boltzmann theory of quasiparticles), but are completely determined by the absolute temperature and by equilibrium thermodynamic observables. Recently, explicit solutions of this quantum critical dynamics have become possible via the anti-de Sitter/conformal field theory duality discovered in string theory. This shows that the quantum critical theory provides a holographic description of the quantum theory of black holes in a negatively curved anti-de Sitter space, and relates its transport coefficients to properties of the Hawking radiation from the black hole. We review how insights from this connection have led to new results for experimental systems: (i) the vicinity of the superfluid-insulator transition in the presence of an applied magnetic field, and its possible application to measurements of the Nernst effect in the cuprates, (ii) the magnetohydrodynamics of the plasma of Dirac electrons in graphene and the prediction of a hydrodynamic cyclotron resonance.

Quantum algorithms for Gibbs sampling and hitting-time estimation

DOE PAGES

Chowdhury, Anirban Narayan; Somma, Rolando D.

2017-02-01

In this paper, we present quantum algorithms for solving two problems regarding stochastic processes. The first algorithm prepares the thermal Gibbs state of a quantum system and runs in time almost linear in √Nβ/Ζ and polynomial in log(1/ϵ), where N is the Hilbert space dimension, β is the inverse temperature, Ζ is the partition function, and ϵ is the desired precision of the output state. Our quantum algorithm exponentially improves the dependence on 1/ϵ and quadratically improves the dependence on β of known quantum algorithms for this problem. The second algorithm estimates the hitting time of a Markov chain. Formore » a sparse stochastic matrix Ρ, it runs in time almost linear in 1/(ϵΔ 3/2), where ϵ is the absolute precision in the estimation and Δ is a parameter determined by Ρ, and whose inverse is an upper bound of the hitting time. Our quantum algorithm quadratically improves the dependence on 1/ϵ and 1/Δ of the analog classical algorithm for hitting-time estimation. Finally, both algorithms use tools recently developed in the context of Hamiltonian simulation, spectral gap amplification, and solving linear systems of equations.« less

Mechanical equivalent of quantum heat engines.

PubMed

Arnaud, Jacques; Chusseau, Laurent; Philippe, Fabrice

2008-06-01

Quantum heat engines employ as working agents multilevel systems instead of classical gases. We show that under some conditions quantum heat engines are equivalent to a series of reservoirs at different altitudes containing balls of various weights. A cycle consists of picking up at random a ball from one reservoir and carrying it to the next, thereby performing or absorbing some work. In particular, quantum heat engines, employing two-level atoms as working agents, are modeled by reservoirs containing balls of weight 0 or 1. The mechanical model helps us prove that the maximum efficiency of quantum heat engines is the Carnot efficiency. Heat pumps and negative temperatures are considered.

Holographic assembly of semiconductor CdSe quantum dots in polymer for volume Bragg grating structures with diffraction efficiency near 100%

NASA Astrophysics Data System (ADS)

Liu, Xiangming; Tomita, Yasuo; Oshima, Juro; Chikama, Katsumi; Matsubara, Koutatsu; Nakashima, Takuya; Kawai, Tsuyoshi

2009-12-01

We report on the fabrication of centimeter-size transmission Bragg gratings in semiconductor CdSe quantum dots dispersed 50 μm thick photopolymer films. This was done by holographic assembly of CdSe quantum dots in a photopolymerizable monomer blend. Periodic patterning of CdSe quantum dots in polymer was confirmed by a fluorescence microscope and confocal Raman imaging. The diffraction efficiency from the grating of 1 μm spacing was near 100% in the green with 0.34 vol % CdSe quantum dots, giving the refractive index modulation as large as 5.1×10-3.

Realizing Rec. 2020 color gamut with quantum dot displays.

PubMed

Zhu, Ruidong; Luo, Zhenyue; Chen, Haiwei; Dong, Yajie; Wu, Shin-Tson

2015-09-07

We analyze how to realize Rec. 2020 wide color gamut with quantum dots. For photoluminescence, our simulation indicates that we are able to achieve over 97% of the Rec. 2020 standard with quantum dots by optimizing the emission spectra and redesigning the color filters. For electroluminescence, by optimizing the emission spectra of quantum dots is adequate to render over 97% of the Rec. 2020 standard. We also analyze the efficiency and angular performance of these devices, and then compare results with LCDs using green and red phosphors-based LED backlight. Our results indicate that quantum dot display is an outstanding candidate for achieving wide color gamut and high optical efficiency.

Two-party quantum key agreement protocols under collective noise channel

NASA Astrophysics Data System (ADS)

Gao, Hao; Chen, Xiao-Guang; Qian, Song-Rong

2018-06-01

Recently, quantum communication has become a very popular research field. The quantum key agreement (QKA) plays an important role in the field of quantum communication, based on its unconditional security in terms of theory. Among all kinds of QKA protocols, QKA protocols resisting collective noise are widely being studied. In this paper, we propose improved two-party QKA protocols resisting collective noise and present a feasible plan for information reconciliation. Our protocols' qubit efficiency has achieved 26.67%, which is the best among all the two-party QKA protocols against collective noise, thus showing that our protocol can improve the transmission efficiency of quantum key agreement.

Demonstration of quantum synchronization based on second-order quantum coherence of entangled photons

PubMed Central

Quan, Runai; Zhai, Yiwei; Wang, Mengmeng; Hou, Feiyan; Wang, Shaofeng; Xiang, Xiao; Liu, Tao; Zhang, Shougang; Dong, Ruifang

2016-01-01

Based on the second-order quantum interference between frequency entangled photons that are generated by parametric down conversion, a quantum strategic algorithm for synchronizing two spatially separated clocks has been recently presented. In the reference frame of a Hong-Ou-Mandel (HOM) interferometer, photon correlations are used to define simultaneous events. Once the HOM interferometer is balanced by use of an adjustable optical delay in one arm, arrival times of simulta- neously generated photons are recorded by each clock. The clock offset is determined by correlation measurement of the recorded arrival times. Utilizing this algorithm, we demonstrate a proof-of-principle experiment for synchronizing two clocks separated by 4 km fiber link. A minimum timing stability of 0.44 ps at averaging time of 16000 s is achieved with an absolute time accuracy of 73.2 ps. The timing stability is verified to be limited by the correlation measurement device and ideally can be better than 10 fs. Such results shine a light to the application of quantum clock synchronization in the real high-accuracy timing system. PMID:27452276

Bit-level quantum color image encryption scheme with quantum cross-exchange operation and hyper-chaotic system

NASA Astrophysics Data System (ADS)

Zhou, Nanrun; Chen, Weiwei; Yan, Xinyu; Wang, Yunqian

2018-06-01

In order to obtain higher encryption efficiency, a bit-level quantum color image encryption scheme by exploiting quantum cross-exchange operation and a 5D hyper-chaotic system is designed. Additionally, to enhance the scrambling effect, the quantum channel swapping operation is employed to swap the gray values of corresponding pixels. The proposed color image encryption algorithm has larger key space and higher security since the 5D hyper-chaotic system has more complex dynamic behavior, better randomness and unpredictability than those based on low-dimensional hyper-chaotic systems. Simulations and theoretical analyses demonstrate that the presented bit-level quantum color image encryption scheme outperforms its classical counterparts in efficiency and security.

Optimal approach to quantum communication using dynamic programming.

PubMed

Jiang, Liang; Taylor, Jacob M; Khaneja, Navin; Lukin, Mikhail D

2007-10-30

Reliable preparation of entanglement between distant systems is an outstanding problem in quantum information science and quantum communication. In practice, this has to be accomplished by noisy channels (such as optical fibers) that generally result in exponential attenuation of quantum signals at large distances. A special class of quantum error correction protocols, quantum repeater protocols, can be used to overcome such losses. In this work, we introduce a method for systematically optimizing existing protocols and developing more efficient protocols. Our approach makes use of a dynamic programming-based searching algorithm, the complexity of which scales only polynomially with the communication distance, letting us efficiently determine near-optimal solutions. We find significant improvements in both the speed and the final-state fidelity for preparing long-distance entangled states.

Quasideterministic generation of maximally entangled states of two mesoscopic atomic ensembles by adiabatic quantum feedback

DOE Office of Scientific and Technical Information (OSTI.GOV)

Di Lisi, Antonio; De Siena, Silvio; Illuminati, Fabrizio

2005-09-15

We introduce an efficient, quasideterministic scheme to generate maximally entangled states of two atomic ensembles. The scheme is based on quantum nondemolition measurements of total atomic populations and on adiabatic quantum feedback conditioned by the measurements outputs. The high efficiency of the scheme is tested and confirmed numerically for ideal photodetection as well as in the presence of losses.

Enhancement of Radiative Efficiency with Staggered InGaN Quantum Well Light Emitting Diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tansu, Nelson; Dierolf, Volkmar; Huang, Gensheng

2011-07-14

The technology on the large overlap InGaN QWs developed in this program is currently implemented in commercial technology in enhancing the internal quantum efficiency in major LED industry in US and Asia. The scientific finding from this work supported by the DOE enabled the implementation of this step-like staggered quantum well in the commercial LEDs.

Quantum key distribution using basis encoding of Gaussian-modulated coherent states

NASA Astrophysics Data System (ADS)

Huang, Peng; Huang, Jingzheng; Zhang, Zheshen; Zeng, Guihua

2018-04-01

The continuous-variable quantum key distribution (CVQKD) has been demonstrated to be available in practical secure quantum cryptography. However, its performance is restricted strongly by the channel excess noise and the reconciliation efficiency. In this paper, we present a quantum key distribution (QKD) protocol by encoding the secret keys on the random choices of two measurement bases: the conjugate quadratures X and P . The employed encoding method can dramatically weaken the effects of channel excess noise and reconciliation efficiency on the performance of the QKD protocol. Subsequently, the proposed scheme exhibits the capability to tolerate much higher excess noise and enables us to reach a much longer secure transmission distance even at lower reconciliation efficiency. The proposal can work alternatively to strengthen significantly the performance of the known Gaussian-modulated CVQKD protocol and serve as a multiplier for practical secure quantum cryptography with continuous variables.

Mid-infrared coincidence measurements on twin photons at room temperature

PubMed Central

Mancinelli, M.; Trenti, A.; Piccione, S.; Fontana, G.; Dam, J. S.; Tidemand-Lichtenberg, P.; Pedersen, C.; Pavesi, L.

2017-01-01

Quantum measurements using single-photon detectors are opening interesting new perspectives in diverse fields such as remote sensing, quantum cryptography and quantum computing. A particularly demanding class of applications relies on the simultaneous detection of correlated single photons. In the visible and near infrared wavelength ranges suitable single-photon detectors do exist. However, low detector quantum efficiency or excessive noise has hampered their mid-infrared (MIR) counterpart. Fast and highly efficient single-photon detectors are thus highly sought after for MIR applications. Here we pave the way to quantum measurements in the MIR by the demonstration of a room temperature coincidence measurement with non-degenerate twin photons at about 3.1 μm. The experiment is based on the spectral translation of MIR radiation into the visible region, by means of efficient up-converter modules. The up-converted pairs are then detected with low-noise silicon avalanche photodiodes without the need for cryogenic cooling. PMID:28504244

Dual-band quantum well infrared photodetector with metallic structure

NASA Astrophysics Data System (ADS)

Wu, Yang; Liu, Hongmei; Li, Pingzhou

2018-02-01

The quantum efficiency of the dual bands quantum well infrared photodetectors(QWIP) has been widely concerned in recent years. A novel structure for the dual-band quantum well infrared detectors which is based on GaAs/AlGaAs designed in this paper is aimed to improve the absorption efficiency. The structure replaces the conventional grating with a metallic grating based on surface plasmon polaritons(SPPS), and we further insert a metal structure in the periodic quantum well layer. The simulation result shows that the use of the different shapes of the metal holes can remarkably improve the optical coupling efficiency due to the surface plasmon effect. By optimizing parameters of the structure, it can work in the dual infrared bands of 3-5um and 8-12um. Moreover, the absorption rate increased by 20% compared with traditional structure of Dual-band QWIP.

Conversion efficiency of an energy harvester based on resonant tunneling through quantum dots with heat leakage.

PubMed

Kano, Shinya; Fujii, Minoru

2017-03-03

We study the conversion efficiency of an energy harvester based on resonant tunneling through quantum dots with heat leakage. Heat leakage current from a hot electrode to a cold electrode is taken into account in the analysis of the harvester operation. Modeling of electrical output indicates that a maximum heat leakage current is not negligible because it is larger than that of the heat current harvested into electrical power. A reduction of heat leakage is required in this energy harvester in order to obtain efficient heat-to-electrical conversion. Multiple energy levels of a quantum dot can increase the output power of the harvester. Heavily doped colloidal semiconductor quantum dots are a possible candidate for a quantum-dot monolayer in the energy harvester to reduce heat leakage, scaling down device size, and increasing electrical output via multiple discrete energy levels.

Comparative studies of efficiency droop in polar and non-polar InGaN quantum wells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Davies, M. J.; Dawson, P.; Hammersley, S.

We report on a comparative study of efficiency droop in polar and non-polar InGaN quantum well structures at T = 10 K. To ensure that the experiments were carried out with identical carrier densities for any particular excitation power density, we used laser pulses of duration ∼100 fs at a repetition rate of 400 kHz. For both types of structures, efficiency droop was observed to occur for carrier densities of above 7 × 10{sup 11 }cm{sup −2 }pulse{sup −1} per quantum well; also both structures exhibited similar spectral broadening in the droop regime. These results show that efficiency droop is intrinsic in InGaN quantum wells, whether polar or non-polar,more » and is a function, specifically, of carrier density.« less

Multiple exciton generation for photoelectrochemical hydrogen evolution reactions with quantum yields exceeding 100%

DOE PAGES

Yan, Yong; Crisp, Ryan W.; Gu, Jing; ...

2017-04-03

Multiple exciton generation (MEG) in quantum dots (QDs) has the potential to greatly increase the power conversion efficiency in solar cells and in solar-fuel production. During the MEG process, two electron-hole pairs (excitons) are created from the absorption of one high-energy photon, bypassing hot-carrier cooling via phonon emission. Here we demonstrate that extra carriers produced via MEG can be used to drive a chemical reaction with quantum efficiency above 100%. We developed a lead sulfide (PbS) QD photoelectrochemical cell that is able to drive hydrogen evolution from aqueous Na 2S solution with a peak external quantum efficiency exceeding 100%. QDmore » photoelectrodes that were measured all demonstrated MEG when the incident photon energy was larger than 2.7 times the bandgap energy. Finally, our results demonstrate a new direction in exploring high-efficiency approaches to solar fuels.« less

Quantum-Carnot engine for particle confined to cubic potential

NASA Astrophysics Data System (ADS)

Sutantyo, Trengginas Eka P.; Belfaqih, Idrus H.; Prayitno, T. B.

2015-09-01

Carnot cycle consists of isothermal and adiabatic processes which are reversible. Using analogy in quantum mechanics, these processes can be well explained by replacing variables in classical process with a quantum system. Quantum system which is shown in this paper is a particle that moves under the influence of a cubic potential which is restricted only to the state of the two energy levels. At the end, the efficiency of the system is shown as a function of the width ratio between the initial conditions and the farthest wall while expanding. Furthermore, the system efficiency will be considered 1D and 2D cases. The providing efficiencies are different due to the influence of the degeneration of energy and the degrees of freedom of the system.

Efficiency at maximum power of a laser quantum heat engine enhanced by noise-induced coherence

NASA Astrophysics Data System (ADS)

Dorfman, Konstantin E.; Xu, Dazhi; Cao, Jianshu

2018-04-01

Quantum coherence has been demonstrated in various systems including organic solar cells and solid state devices. In this article, we report the lower and upper bounds for the performance of quantum heat engines determined by the efficiency at maximum power. Our prediction based on the canonical three-level Scovil and Schulz-Dubois maser model strongly depends on the ratio of system-bath couplings for the hot and cold baths and recovers the theoretical bounds established previously for the Carnot engine. Further, introducing a fourth level to the maser model can enhance the maximal power and its efficiency, thus demonstrating the importance of quantum coherence in the thermodynamics and operation of the heat engines beyond the classical limit.

Functionalization of Cadmium Selenide Quantum Dots with Poly(ethylene glycol): Ligand Exchange, Surface Coverage, and Dispersion Stability.

PubMed

Wenger, Whitney Nowak; Bates, Frank S; Aydil, Eray S

2017-08-22

Semiconductor quantum dots synthesized using rapid mixing of precursors by injection into a hot solution of solvents and surfactants have surface ligands that sterically stabilize the dispersions in nonpolar solvents. Often, these ligands are exchanged to disperse the quantum dots in polar solvents, but quantitative studies of quantum dot surfaces before and after ligand exchange are scarce. We studied exchanging trioctylphosphine (TOP) and trioctylphosphine oxide (TOPO) ligands on as-synthesized CdSe quantum dots dispersed in hexane with a 2000 g/mol thiolated poly(ethylene glycol) (PEG) polymer. Using infrared spectroscopy we quantify the absolute surface concentration of TOP/TOPO and PEG ligands per unit area before and after ligand exchange. While 50-85% of the TOP/TOPO ligands are removed upon ligand exchange, only a few are replaced with PEG. Surprisingly, the remaining TOP/TOPO ligands outnumber the PEG ligands, but these few PEG ligands are sufficient to disperse the quantum dots in polar solvents such as chloroform, tetrahydrofuran, and water. Moreover, as-synthesized quantum dots once easily dispersed in hexane are no longer dispersible in nonpolar solvents after ligand exchange. A subtle coverage-dependent balance between attractive PEG-solvent interactions and repulsive TOP/TOPO-solvent interactions determines the dispersion stability.

Absolute quantum yield measurement of powder samples.

PubMed

Moreno, Luis A

2012-05-12

Measurement of fluorescence quantum yield has become an important tool in the search for new solutions in the development, evaluation, quality control and research of illumination, AV equipment, organic EL material, films, filters and fluorescent probes for bio-industry. Quantum yield is calculated as the ratio of the number of photons absorbed, to the number of photons emitted by a material. The higher the quantum yield, the better the efficiency of the fluorescent material. For the measurements featured in this video, we will use the Hitachi F-7000 fluorescence spectrophotometer equipped with the Quantum Yield measuring accessory and Report Generator program. All the information provided applies to this system. Measurement of quantum yield in powder samples is performed following these steps: 1. Generation of instrument correction factors for the excitation and emission monochromators. This is an important requirement for the correct measurement of quantum yield. It has been performed in advance for the full measurement range of the instrument and will not be shown in this video due to time limitations. 2. Measurement of integrating sphere correction factors. The purpose of this step is to take into consideration reflectivity characteristics of the integrating sphere used for the measurements. 3. Reference and Sample measurement using direct excitation and indirect excitation. 4. Quantum Yield calculation using Direct and Indirect excitation. Direct excitation is when the sample is facing directly the excitation beam, which would be the normal measurement setup. However, because we use an integrating sphere, a portion of the emitted photons resulting from the sample fluorescence are reflected by the integrating sphere and will re-excite the sample, so we need to take into consideration indirect excitation. This is accomplished by measuring the sample placed in the port facing the emission monochromator, calculating indirect quantum yield and correcting the direct quantum yield calculation. 5. Corrected quantum yield calculation. 6. Chromaticity coordinates calculation using Report Generator program. The Hitachi F-7000 Quantum Yield Measurement System offer advantages for this application, as follows: High sensitivity (S/N ratio 800 or better RMS). Signal is the Raman band of water measured under the following conditions: Ex wavelength 350 nm, band pass Ex and Em 5 nm, response 2 sec), noise is measured at the maximum of the Raman peak. High sensitivity allows measurement of samples even with low quantum yield. Using this system we have measured quantum yields as low as 0.1 for a sample of salicylic acid and as high as 0.8 for a sample of magnesium tungstate. Highly accurate measurement with a dynamic range of 6 orders of magnitude allows for measurements of both sharp scattering peaks with high intensity, as well as broad fluorescence peaks of low intensity under the same conditions. High measuring throughput and reduced light exposure to the sample, due to a high scanning speed of up to 60,000 nm/minute and automatic shutter function. Measurement of quantum yield over a wide wavelength range from 240 to 800 nm. Accurate quantum yield measurements are the result of collecting instrument spectral response and integrating sphere correction factors before measuring the sample. Large selection of calculated parameters provided by dedicated and easy to use software. During this video we will measure sodium salicylate in powder form which is known to have a quantum yield value of 0.4 to 0.5.

Verifiable fault tolerance in measurement-based quantum computation

NASA Astrophysics Data System (ADS)

Fujii, Keisuke; Hayashi, Masahito

2017-09-01

Quantum systems, in general, cannot be simulated efficiently by a classical computer, and hence are useful for solving certain mathematical problems and simulating quantum many-body systems. This also implies, unfortunately, that verification of the output of the quantum systems is not so trivial, since predicting the output is exponentially hard. As another problem, the quantum system is very delicate for noise and thus needs an error correction. Here, we propose a framework for verification of the output of fault-tolerant quantum computation in a measurement-based model. In contrast to existing analyses on fault tolerance, we do not assume any noise model on the resource state, but an arbitrary resource state is tested by using only single-qubit measurements to verify whether or not the output of measurement-based quantum computation on it is correct. Verifiability is equipped by a constant time repetition of the original measurement-based quantum computation in appropriate measurement bases. Since full characterization of quantum noise is exponentially hard for large-scale quantum computing systems, our framework provides an efficient way to practically verify the experimental quantum error correction.

Absolute detection efficiencies of low energy H, H -, H +, H 2+ and H 3+ incident on a multichannel plate detector

NASA Astrophysics Data System (ADS)

Peko, B. L.; Stephen, T. M.

2000-12-01

Measured absolute detection efficiencies are presented for H, H - and H n+ ( n=1,2,3) impacting a commercially available, dual multichannel plate (MCP) electron multiplier at kinetic energies ranging from 30 to 1000 eV. Measurements involving isotopic substitutions (D, D -, D n+) and Ar + are also presented. In addition, atomic hydrogen detection efficiencies relative to those of H + and H - are given, as they may have a more universal application. For the three charge states, H, H + and H -, the absolute detection efficiencies are markedly different at low energies and converge to a nearly uniform value of ˜70% with increasing projectile energy. The energy dependence is strongest for H +, varying nearly three orders of magnitude over the energy range studied, and weakest for H -, varying by less than one order of magnitude. In general, for the low energy positive ions at a given energy, the lighter the incident particle mass, the greater the probability of its detection.

An Efficient Quantum Somewhat Homomorphic Symmetric Searchable Encryption

NASA Astrophysics Data System (ADS)

Sun, Xiaoqiang; Wang, Ting; Sun, Zhiwei; Wang, Ping; Yu, Jianping; Xie, Weixin

2017-04-01

In 2009, Gentry first introduced an ideal lattices fully homomorphic encryption (FHE) scheme. Later, based on the approximate greatest common divisor problem, learning with errors problem or learning with errors over rings problem, FHE has developed rapidly, along with the low efficiency and computational security. Combined with quantum mechanics, Liang proposed a symmetric quantum somewhat homomorphic encryption (QSHE) scheme based on quantum one-time pad, which is unconditional security. And it was converted to a quantum fully homomorphic encryption scheme, whose evaluation algorithm is based on the secret key. Compared with Liang's QSHE scheme, we propose a more efficient QSHE scheme for classical input states with perfect security, which is used to encrypt the classical message, and the secret key is not required in the evaluation algorithm. Furthermore, an efficient symmetric searchable encryption (SSE) scheme is constructed based on our QSHE scheme. SSE is important in the cloud storage, which allows users to offload search queries to the untrusted cloud. Then the cloud is responsible for returning encrypted files that match search queries (also encrypted), which protects users' privacy.

Broadband Light Collection Efficiency Enhancement of Carbon Nanotube Excitons Coupled to Metallo-Dielectric Antenna Arrays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shayan, Kamran; Rabut, Claire; Kong, Xiaoqing

The realization of on-chip quantum networks ideally requires lossless interfaces between photons and solid-state quantum emitters. We propose and demonstrate on-chip arrays of metallo-dielectric antennas (MDA) that are tailored toward efficient and broadband light collection from individual embedded carbon nanotube quantum emitters by trapping air gaps on chip that form cavity modes. Scalable implementation is realized by employing polymer layer dry-transfer techniques that avoid solvent incompatibility issues, as well as a planar design that avoids solid-immersion lenses. Cryogenic measurements demonstrate 7-fold enhanced exciton intensity when compared to emitters located on bare wafers, corresponding to a light collection efficiency (LCE) upmore » to 92% in the best case (average LCE of 69%) into a narrow output cone of +/-15 degrees that enables a priori fiber-to-chip butt coupling. The demonstrated MDA arrays are directly compatible with other quantum systems, particularly 2D materials, toward enabling efficient on-chip quantum light sources or spin-photon interfaces requiring unity light collection, both at cryogenic or room temperature.« less

Corrugated Quantum Well Infrared Photodetector Focal Plane Array Test Results

NASA Technical Reports Server (NTRS)

Goldberg, A.; Choi, K. K.; Das, N. C.; La, A.; Jhabvala, M.

1999-01-01

The corrugated quantum-well infrared photodetector (C-QWIP) uses total internal reflection to couple normal incident light into the optically active quantum wells. The coupling efficiency has been shown to be relatively independent of the pixel size and wavelength thus making the C-QWIP a candidate for detectors over the entire infrared spectrum. The broadband coupling efficiency of the C-QWIP makes it an ideal candidate for multiwavelength detectors. We fabricated and tested C-QWIP focal plane arrays (FPAs) with cutoff wavelengths of 11.2 and 16.2 micrometers. Each FPA has 256 x 256 pixels that are bump-bonded to a direct injection readout circuit. Both FPAs provided infrared imagery with good aesthetic attributes. For the 11.2-micrometers FPA, background-limited performance (BLIP) was observed at 60 K with f/3 optics. For the 16.2-micrometers FPA, BLIP was observed at 38 K. Besides the reduction of dark current in C-QWIP structures, the measured internal quantum efficiency (eta) remains to be high. The values for responsivity and quantum efficiency obtained from the FPA results agree well with those measured for single devices.

Stability and lifetime testing of photomultiplier detectors for the Earth observing system SOLSTICE program

NASA Astrophysics Data System (ADS)

Hadler, Joshua A.; van de Kop, Toni; Drake, Virginia A.; McClintock, William E.; Murphy, John; Rodgers, Paul

1998-10-01

The primary objective of the Earth Observing System (EOS) Solar Stellar Irradiance Comparison Experiment (SOLSTICE) is to accurately measure the absolute value of the solar UV irradiance at the top of the earth's atmosphere for a minimum mission lifetime of 5 years. To meet this objective, SOLSTICE employs a unique design to determine changes in instrument performance by routinely observing a series of early-type stars and comparing the irradiances directly with the solar value. Although the comparison techniques allows us to track instrument performance, the success of the SOLSTICE experiment depends upon photomultiplier detectors which have graceful degradation properties. Therefore, we have established a laboratory program to evaluate the characteristics of photomultiplier tubes which are exposed to long term fluxes similar to those we expected to encounter in flight. Three types of Hamamatsu photomultiplier tubes were tested as candidates for use in the EOS-SOLSTICE project. The results of these studies: pulse height distribution; quantum efficiency; surface maps,; and lifetime analysis are presented in this paper.

Hierarchy of Efficiently Computable and Faithful Lower Bounds to Quantum Discord

NASA Astrophysics Data System (ADS)

Piani, Marco

2016-08-01

Quantum discord expresses a fundamental nonclassicality of correlations that is more general than entanglement, but that, in its standard definition, is not easily evaluated. We derive a hierarchy of computationally efficient lower bounds to the standard quantum discord. Every nontrivial element of the hierarchy constitutes by itself a valid discordlike measure, based on a fundamental feature of quantum correlations: their lack of shareability. Our approach emphasizes how the difference between entanglement and discord depends on whether shareability is intended as a static property or as a dynamical process.

Secure Multiparty Quantum Computation for Summation and Multiplication.

PubMed

Shi, Run-hua; Mu, Yi; Zhong, Hong; Cui, Jie; Zhang, Shun

2016-01-21

As a fundamental primitive, Secure Multiparty Summation and Multiplication can be used to build complex secure protocols for other multiparty computations, specially, numerical computations. However, there is still lack of systematical and efficient quantum methods to compute Secure Multiparty Summation and Multiplication. In this paper, we present a novel and efficient quantum approach to securely compute the summation and multiplication of multiparty private inputs, respectively. Compared to classical solutions, our proposed approach can ensure the unconditional security and the perfect privacy protection based on the physical principle of quantum mechanics.

Secure Multiparty Quantum Computation for Summation and Multiplication

PubMed Central

Shi, Run-hua; Mu, Yi; Zhong, Hong; Cui, Jie; Zhang, Shun

2016-01-01

As a fundamental primitive, Secure Multiparty Summation and Multiplication can be used to build complex secure protocols for other multiparty computations, specially, numerical computations. However, there is still lack of systematical and efficient quantum methods to compute Secure Multiparty Summation and Multiplication. In this paper, we present a novel and efficient quantum approach to securely compute the summation and multiplication of multiparty private inputs, respectively. Compared to classical solutions, our proposed approach can ensure the unconditional security and the perfect privacy protection based on the physical principle of quantum mechanics. PMID:26792197

Efficient Variational Quantum Simulator Incorporating Active Error Minimization

NASA Astrophysics Data System (ADS)

Li, Ying; Benjamin, Simon C.

2017-04-01

One of the key applications for quantum computers will be the simulation of other quantum systems that arise in chemistry, materials science, etc., in order to accelerate the process of discovery. It is important to ask the following question: Can this simulation be achieved using near-future quantum processors, of modest size and under imperfect control, or must it await the more distant era of large-scale fault-tolerant quantum computing? Here, we propose a variational method involving closely integrated classical and quantum coprocessors. We presume that all operations in the quantum coprocessor are prone to error. The impact of such errors is minimized by boosting them artificially and then extrapolating to the zero-error case. In comparison to a more conventional optimized Trotterization technique, we find that our protocol is efficient and appears to be fundamentally more robust against error accumulation.

Ultrafast Room-Temperature Single Photon Emission from Quantum Dots Coupled to Plasmonic Nanocavities.

PubMed

Hoang, Thang B; Akselrod, Gleb M; Mikkelsen, Maiken H

2016-01-13

Efficient and bright single photon sources at room temperature are critical components for quantum information systems such as quantum key distribution, quantum state teleportation, and quantum computation. However, the intrinsic radiative lifetime of quantum emitters is typically ∼10 ns, which severely limits the maximum single photon emission rate and thus entanglement rates. Here, we demonstrate the regime of ultrafast spontaneous emission (∼10 ps) from a single quantum emitter coupled to a plasmonic nanocavity at room temperature. The nanocavity integrated with a single colloidal semiconductor quantum dot produces a 540-fold decrease in the emission lifetime and a simultaneous 1900-fold increase in the total emission intensity. At the same time, the nanocavity acts as a highly efficient optical antenna directing the emission into a single lobe normal to the surface. This plasmonic platform is a versatile geometry into which a variety of other quantum emitters, such as crystal color centers, can be integrated for directional, room-temperature single photon emission rates exceeding 80 GHz.

Efficient tomography of a quantum many-body system

NASA Astrophysics Data System (ADS)

Lanyon, B. P.; Maier, C.; Holzäpfel, M.; Baumgratz, T.; Hempel, C.; Jurcevic, P.; Dhand, I.; Buyskikh, A. S.; Daley, A. J.; Cramer, M.; Plenio, M. B.; Blatt, R.; Roos, C. F.

2017-12-01

Quantum state tomography is the standard technique for estimating the quantum state of small systems. But its application to larger systems soon becomes impractical as the required resources scale exponentially with the size. Therefore, considerable effort is dedicated to the development of new characterization tools for quantum many-body states. Here we demonstrate matrix product state tomography, which is theoretically proven to allow for the efficient and accurate estimation of a broad class of quantum states. We use this technique to reconstruct the dynamical state of a trapped-ion quantum simulator comprising up to 14 entangled and individually controlled spins: a size far beyond the practical limits of quantum state tomography. Our results reveal the dynamical growth of entanglement and describe its complexity as correlations spread out during a quench: a necessary condition for future demonstrations of better-than-classical performance. Matrix product state tomography should therefore find widespread use in the study of large quantum many-body systems and the benchmarking and verification of quantum simulators and computers.

Quantum junction solar cells.

PubMed

Tang, Jiang; Liu, Huan; Zhitomirsky, David; Hoogland, Sjoerd; Wang, Xihua; Furukawa, Melissa; Levina, Larissa; Sargent, Edward H

2012-09-12

Colloidal quantum dot solids combine convenient solution-processing with quantum size effect tuning, offering avenues to high-efficiency multijunction cells based on a single materials synthesis and processing platform. The highest-performing colloidal quantum dot rectifying devices reported to date have relied on a junction between a quantum-tuned absorber and a bulk material (e.g., TiO(2)); however, quantum tuning of the absorber then requires complete redesign of the bulk acceptor, compromising the benefits of facile quantum tuning. Here we report rectifying junctions constructed entirely using inherently band-aligned quantum-tuned materials. Realizing these quantum junction diodes relied upon the creation of an n-type quantum dot solid having a clean bandgap. We combine stable, chemically compatible, high-performance n-type and p-type materials to create the first quantum junction solar cells. We present a family of photovoltaic devices having widely tuned bandgaps of 0.6-1.6 eV that excel where conventional quantum-to-bulk devices fail to perform. Devices having optimal single-junction bandgaps exhibit certified AM1.5 solar power conversion efficiencies of 5.4%. Control over doping in quantum solids, and the successful integration of these materials to form stable quantum junctions, offers a powerful new degree of freedom to colloidal quantum dot optoelectronics.

Integrability versus Thermalizability in Isolated Quantum Systems

NASA Astrophysics Data System (ADS)

Olshanii, Maxim

2012-02-01

The purpose of this presentation is to assess the status of our understanding of the transition from integrability to thermalizability in isolated quantum systems. In Classical Mechanics, the boundary stripe between the two is relatively sharp: its integrability edge is marked by the appearance of finite Lyapunov's exponents that further converge to a unique value when the ergodicity edge is reached. Classical ergodicity is a universal property: if a system is ergodic, then every observable attains its microcanonical value in the infinite time average over the trajectory. On the contrary, in Quantum Mechanics, Lyapunov's exponents are always zero. Furthermore, since quantum dynamics necessarily invokes coherent superpositions of eigenstates of different energy, projectors to the eigenstates become more relevant; those in turn never thermalize. All of the above indicates that in quantum many-body systems, (a) the integrability-thermalizability transition is smooth, and (b) the degree of thermalizability is not absolute like in classical mechanics, but it is relative to the class of observables of interest. In accordance with these observations, we propose a concrete measure of the degree of quantum thermalizability, consistent with the expected empirical manifestations of it. As a practical application of this measure, we devise a unified recipe for choosing an optimal set of conserved quantities to govern the after-relaxation values of observables, in both integrable quantum systems and in quantum systems in between integrable and thermalizable.

Observation of vacuum-enhanced electron spin resonance of optically levitated nanodiamonds

NASA Astrophysics Data System (ADS)

Li, Tongcang; Hoang, Thai; Ahn, Jonghoon; Bang, Jaehoon

Electron spins of diamond nitrogen-vacancy (NV) centers are important quantum resources for nanoscale sensing and quantum information. Combining such NV spin systems with levitated optomechanical resonators will provide a hybrid quantum system for many novel applications. Here we optically levitate a nanodiamond and demonstrate electron spin control of its built-in NV centers in low vacuum. We observe that the strength of electron spin resonance (ESR) is enhanced when the air pressure is reduced. To better understand this novel system, we also investigate the effects of trap power and measure the absolute internal temperature of levitated nanodiamonds with ESR after calibration of the strain effect. Our results show that optical levitation of nanodiamonds in vacuum not only can improve the mechanical quality of its oscillation, but also enhance the ESR contrast, which pave the way towards a novel levitated spin-optomechanical system for studying macroscopic quantum mechanics. The results also indicate potential applications of NV centers in gas sensing.

Alleviation of efficiency droop in InGaN/GaN multiple quantum well light-emitting diodes with trapezoidal quantum barriers

NASA Astrophysics Data System (ADS)

Kim, Sang-Jo; Lee, Kwang Jae; Park, Seong-Ju

2018-06-01

We numerically investigated the effects of trapezoidal quantum barriers (QBs) on efficiency droop in InGaN/GaN multiple quantum well (MQW) light-emitting diodes (LEDs). Simulations showed that the electrostatic field in QWs of LEDs with trapezoidal barriers is reduced because of the reduced sheet charge density at the QW-QB interface caused by the thin GaN layer in trapezoidal QBs. Additionally, the InGaN grading region in trapezoidal QBs suppresses hot carrier transport and this enhances efficient carrier injection into the QWs. The electroluminescence intensity of an LED with trapezoidal QBs is increased by 10.2% and 6.7% at 245 A cm‑2 when compared with the intensities of LEDs with square-type GaN barriers and multilayer barriers, respectively. The internal quantum efficiency (IQE) droop of an LED with trapezoidal QBs is 16% at 300 A cm‑2, while LEDs with square-type GaN barriers and multilayer barriers have IQE droop of 31% and 24%, respectively. This IQE droop alleviation in LEDs with trapezoidal QBs is attributed to the reduced energy band bending, efficient hole injection, and more uniform hole distribution in the MQWs that results from reduction of the piezoelectric field by the trapezoidal QBs. These results indicate that the trapezoidal QB in MQWs is promising for enhanced efficiency in high-power GaN-based LEDs.

Detection of Biochemical Pathogens, Laser Stand-off Spectroscopy, Quantum Coherence, and Many Body Quantum Optics

DTIC Science & Technology

2012-02-24

AND SUBTITLE Detection of Biochemical Pathogens, Laser Stand-off Spectroscopy, Quantum Coherence, and Many Body Quantum Optics 6. AUTHORS Marian O...Maximum 200 words) Results of our earlier research in the realm of quantum optics were extended in order to solve the challenging technical problems of...efficient methods of generating UV light via quantum coherence. 14. SUBJECT TERMS Quantum coherence, quantum optics, lasers 15. NUMBER OF PAGES 15

Entropy and the Shelf Model: A Quantum Physical Approach to a Physical Property

ERIC Educational Resources Information Center

Jungermann, Arnd H.

2006-01-01

In contrast to most other thermodynamic data, entropy values are not given in relation to a certain--more or less arbitrarily defined--zero level. They are listed in standard thermodynamic tables as absolute values of specific substances. Therefore these values describe a physical property of the listed substances. One of the main tasks of…

Efficient quantum dialogue without information leakage

NASA Astrophysics Data System (ADS)

Yin, Ai-Han; Tang, Zhi-Hui; Chen, Dong

2015-02-01

A two-step quantum dialogue scheme is put forward with a class of three-qubit W state and quantum dense coding. Each W state can carry three bits of secret information and the measurement result is encrypted without information leakage. Furthermore, we utilize the entangle properties of W state and decoy photon checking technique to realize three-time channel detection, which can improve the efficiency and security of the scheme.

Heralded high-efficiency quantum repeater with atomic ensembles assisted by faithful single-photon transmission

NASA Astrophysics Data System (ADS)

Li, Tao; Deng, Fu-Guo

2015-10-01

Quantum repeater is one of the important building blocks for long distance quantum communication network. The previous quantum repeaters based on atomic ensembles and linear optical elements can only be performed with a maximal success probability of 1/2 during the entanglement creation and entanglement swapping procedures. Meanwhile, the polarization noise during the entanglement distribution process is harmful to the entangled channel created. Here we introduce a general interface between a polarized photon and an atomic ensemble trapped in a single-sided optical cavity, and with which we propose a high-efficiency quantum repeater protocol in which the robust entanglement distribution is accomplished by the stable spatial-temporal entanglement and it can in principle create the deterministic entanglement between neighboring atomic ensembles in a heralded way as a result of cavity quantum electrodynamics. Meanwhile, the simplified parity-check gate makes the entanglement swapping be completed with unity efficiency, other than 1/2 with linear optics. We detail the performance of our protocol with current experimental parameters and show its robustness to the imperfections, i.e., detuning and coupling variation, involved in the reflection process. These good features make it a useful building block in long distance quantum communication.

Heralded high-efficiency quantum repeater with atomic ensembles assisted by faithful single-photon transmission.

PubMed

Li, Tao; Deng, Fu-Guo

2015-10-27

Quantum repeater is one of the important building blocks for long distance quantum communication network. The previous quantum repeaters based on atomic ensembles and linear optical elements can only be performed with a maximal success probability of 1/2 during the entanglement creation and entanglement swapping procedures. Meanwhile, the polarization noise during the entanglement distribution process is harmful to the entangled channel created. Here we introduce a general interface between a polarized photon and an atomic ensemble trapped in a single-sided optical cavity, and with which we propose a high-efficiency quantum repeater protocol in which the robust entanglement distribution is accomplished by the stable spatial-temporal entanglement and it can in principle create the deterministic entanglement between neighboring atomic ensembles in a heralded way as a result of cavity quantum electrodynamics. Meanwhile, the simplified parity-check gate makes the entanglement swapping be completed with unity efficiency, other than 1/2 with linear optics. We detail the performance of our protocol with current experimental parameters and show its robustness to the imperfections, i.e., detuning and coupling variation, involved in the reflection process. These good features make it a useful building block in long distance quantum communication.

Heralded high-efficiency quantum repeater with atomic ensembles assisted by faithful single-photon transmission

PubMed Central

Li, Tao; Deng, Fu-Guo

2015-01-01

Quantum repeater is one of the important building blocks for long distance quantum communication network. The previous quantum repeaters based on atomic ensembles and linear optical elements can only be performed with a maximal success probability of 1/2 during the entanglement creation and entanglement swapping procedures. Meanwhile, the polarization noise during the entanglement distribution process is harmful to the entangled channel created. Here we introduce a general interface between a polarized photon and an atomic ensemble trapped in a single-sided optical cavity, and with which we propose a high-efficiency quantum repeater protocol in which the robust entanglement distribution is accomplished by the stable spatial-temporal entanglement and it can in principle create the deterministic entanglement between neighboring atomic ensembles in a heralded way as a result of cavity quantum electrodynamics. Meanwhile, the simplified parity-check gate makes the entanglement swapping be completed with unity efficiency, other than 1/2 with linear optics. We detail the performance of our protocol with current experimental parameters and show its robustness to the imperfections, i.e., detuning and coupling variation, involved in the reflection process. These good features make it a useful building block in long distance quantum communication. PMID:26502993

Quantitative photoabsorption and fluorescence spectroscopy of benzene, naphthalene, and some derivatives at 106-295 nm

NASA Technical Reports Server (NTRS)

Suto, Masako; Wang, Xiuyan; Shan, Jun; Lee, L. C.

1992-01-01

Photoabsorption and fluorescence cross sections of benzene, (o-, m-, p-) xylenes, naphthalene, 1-methylnaphthalene, and 2-ethylnaphthalene in the gas phase are measured at 106-295 nm using synchrotron radiation as a light source. Fluorescences are observed from the photoexcitation of benzene and xylenes at 230-280 nm and from naphthalene and its derivatives at 190-295 nm. The absolute fluorescence cross section is determined by calibration with respect to the emission intensity of the NO(A-X) system, for which the fluorescence quantum yield is equal to 1. To cross-check the current calibration method, the quantum yield of the SO2(C-X) system at 220-230 nm was measured since it is about equal to 1. The current quantum-yield data are compared with previously published values measured by different methods.

Experimental quantum computing without entanglement.

PubMed

Lanyon, B P; Barbieri, M; Almeida, M P; White, A G

2008-11-14

Deterministic quantum computation with one pure qubit (DQC1) is an efficient model of computation that uses highly mixed states. Unlike pure-state models, its power is not derived from the generation of a large amount of entanglement. Instead it has been proposed that other nonclassical correlations are responsible for the computational speedup, and that these can be captured by the quantum discord. In this Letter we implement DQC1 in an all-optical architecture, and experimentally observe the generated correlations. We find no entanglement, but large amounts of quantum discord-except in three cases where an efficient classical simulation is always possible. Our results show that even fully separable, highly mixed, states can contain intrinsically quantum mechanical correlations and that these could offer a valuable resource for quantum information technologies.

Symmetric Blind Information Reconciliation for Quantum Key Distribution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kiktenko, Evgeniy O.; Trushechkin, Anton S.; Lim, Charles Ci Wen

Quantum key distribution (QKD) is a quantum-proof key-exchange scheme which is fast approaching the communication industry. An essential component in QKD is the information reconciliation step, which is used for correcting the quantum-channel noise errors. The recently suggested blind-reconciliation technique, based on low-density parity-check codes, offers remarkable prospectives for efficient information reconciliation without an a priori quantum bit error rate estimation. We suggest an improvement of the blind-information-reconciliation protocol promoting a significant increase in the efficiency of the procedure and reducing its interactivity. Finally, the proposed technique is based on introducing symmetry in operations of parties, and the consideration ofmore » results of unsuccessful belief-propagation decodings.« less

Symmetric Blind Information Reconciliation for Quantum Key Distribution

DOE PAGES

Kiktenko, Evgeniy O.; Trushechkin, Anton S.; Lim, Charles Ci Wen; ...

2017-10-27

Quantum key distribution (QKD) is a quantum-proof key-exchange scheme which is fast approaching the communication industry. An essential component in QKD is the information reconciliation step, which is used for correcting the quantum-channel noise errors. The recently suggested blind-reconciliation technique, based on low-density parity-check codes, offers remarkable prospectives for efficient information reconciliation without an a priori quantum bit error rate estimation. We suggest an improvement of the blind-information-reconciliation protocol promoting a significant increase in the efficiency of the procedure and reducing its interactivity. Finally, the proposed technique is based on introducing symmetry in operations of parties, and the consideration ofmore » results of unsuccessful belief-propagation decodings.« less

Symmetric Blind Information Reconciliation for Quantum Key Distribution

NASA Astrophysics Data System (ADS)

Kiktenko, E. O.; Trushechkin, A. S.; Lim, C. C. W.; Kurochkin, Y. V.; Fedorov, A. K.

2017-10-01

Quantum key distribution (QKD) is a quantum-proof key-exchange scheme which is fast approaching the communication industry. An essential component in QKD is the information reconciliation step, which is used for correcting the quantum-channel noise errors. The recently suggested blind-reconciliation technique, based on low-density parity-check codes, offers remarkable prospectives for efficient information reconciliation without an a priori quantum bit error rate estimation. We suggest an improvement of the blind-information-reconciliation protocol promoting a significant increase in the efficiency of the procedure and reducing its interactivity. The proposed technique is based on introducing symmetry in operations of parties, and the consideration of results of unsuccessful belief-propagation decodings.

Absolute ion detection efficiencies of microchannel plates and funnel microchannel plates for multi-coincidence detection

NASA Astrophysics Data System (ADS)

Fehre, K.; Trojanowskaja, D.; Gatzke, J.; Kunitski, M.; Trinter, F.; Zeller, S.; Schmidt, L. Ph. H.; Stohner, J.; Berger, R.; Czasch, A.; Jagutzki, O.; Jahnke, T.; Dörner, R.; Schöffler, M. S.

2018-04-01

Modern momentum imaging techniques allow for the investigation of complex molecules in the gas phase by detection of several fragment ions in coincidence. For these studies, it is of great importance that the single-particle detection efficiency ɛ is as high as possible, as the overall efficiency scales with ɛn, i.e., the power of the number of detected particles. Here we present measured absolute detection efficiencies for protons of several micro-channel plates (MCPs), including efficiency enhanced "funnel MCPs." Furthermore, the relative detection efficiency for two-, three-, four-, and five-body fragmentation of CHBrClF has been examined. The "funnel" MCPs exhibit an efficiency of approximately 90%, gaining a factor of 24 (as compared to "normal" MCPs) in the case of a five-fold ion coincidence detection.

Photodetectors for scintillator proportionality measurement

NASA Astrophysics Data System (ADS)

Moses, William W.; Choong, Woon-Seng; Hull, Giulia; Payne, Steve; Cherepy, Nerine; Valentine, John D.

2009-10-01

We evaluate photodetectors for use in a Compton Coincidence apparatus designed for measuring scintillator proportionality. There are many requirements placed on the photodetector in these systems, including active area, linearity, and the ability to accurately measure low light levels (which implies high quantum efficiency and high signal-to-noise ratio). Through a combination of measurement and Monte Carlo simulation, we evaluate a number of potential photodetectors, especially photomultiplier tubes and hybrid photodetectors. Of these, we find that the most promising devices available are photomultiplier tubes with high (˜50%) quantum efficiency, although hybrid photodetectors with high quantum efficiency would be preferable.

Internal quantum efficiency and tunable colour temperature in monolithic white InGaN/GaN LED

NASA Astrophysics Data System (ADS)

Titkov, Ilya E.; Yadav, Amit; Zerova, Vera L.; Zulonas, Modestas; Tsatsulnikov, Andrey F.; Lundin, Wsevolod V.; Sakharov, Alexey V.; Rafailov, Edik U.

2014-03-01

Internal Quantum Efficiency (IQE) of two-colour monolithic white light emitting diode (LED) was measured by temperature dependant electro-luminescence (TDEL) and analysed with modified rate equation based on ABC model. External, internal and injection efficiencies of blue and green quantum wells were analysed separately. Monolithic white LED contained one green InGaN QW and two blue QWs being separated by GaN barrier. This paper reports also the tunable behaviour of correlated colour temperature (CCT) in pulsed operation mode and effect of self-heating on device performance.

Nano-patterned superconducting surface for high quantum efficiency cathode

DOEpatents

Hannon, Fay; Musumeci, Pietro

2017-03-07

A method for providing a superconducting surface on a laser-driven niobium cathode in order to increase the effective quantum efficiency. The enhanced surface increases the effective quantum efficiency by improving the laser absorption of the surface and enhancing the local electric field. The surface preparation method makes feasible the construction of superconducting radio frequency injectors with niobium as the photocathode. An array of nano-structures are provided on a flat surface of niobium. The nano-structures are dimensionally tailored to interact with a laser of specific wavelength to thereby increase the electron yield of the surface.

Tailoring the Energy Landscape in Quasi-2D Halide Perovskites Enables Efficient Green-Light Emission.

PubMed

Quan, Li Na; Zhao, Yongbiao; García de Arquer, F Pelayo; Sabatini, Randy; Walters, Grant; Voznyy, Oleksandr; Comin, Riccardo; Li, Yiying; Fan, James Z; Tan, Hairen; Pan, Jun; Yuan, Mingjian; Bakr, Osman M; Lu, Zhenghong; Kim, Dong Ha; Sargent, Edward H

2017-06-14

Organo-metal halide perovskites are a promising platform for optoelectronic applications in view of their excellent charge-transport and bandgap tunability. However, their low photoluminescence quantum efficiencies, especially in low-excitation regimes, limit their efficiency for light emission. Consequently, perovskite light-emitting devices are operated under high injection, a regime under which the materials have so far been unstable. Here we show that, by concentrating photoexcited states into a small subpopulation of radiative domains, one can achieve a high quantum yield, even at low excitation intensities. We tailor the composition of quasi-2D perovskites to direct the energy transfer into the lowest-bandgap minority phase and to do so faster than it is lost to nonradiative centers. The new material exhibits 60% photoluminescence quantum yield at excitation intensities as low as 1.8 mW/cm 2 , yielding a ratio of quantum yield to excitation intensity of 0.3 cm 2 /mW; this represents a decrease of 2 orders of magnitude in the excitation power required to reach high efficiency compared with the best prior reports. Using this strategy, we report light-emitting diodes with external quantum efficiencies of 7.4% and a high luminescence of 8400 cd/m 2 .

Quantum optics with nanowires (Conference Presentation)

NASA Astrophysics Data System (ADS)

Zwiller, Val

2017-02-01

Nanowires offer new opportunities for nanoscale quantum optics; the quantum dot geometry in semiconducting nanowires as well as the material composition and environment can be engineered with unprecedented freedom to improve the light extraction efficiency. Quantum dots in nanowires are shown to be efficient single photon sources, in addition because of the very small fine structure splitting, we demonstrate the generation of entangled pairs of photons from a nanowire. By doping a nanowire and making ohmic contacts on both sides, a nanowire light emitting diode can be obtained with a single quantum dot as the active region. Under forward bias, this will act as an electrically pumped source of single photons. Under reverse bias, an avalanche effect can multiply photocurrent and enables the detection of single photons. Another type of nanowire under study in our group is superconducting nanowires for single photon detection, reaching efficiencies, time resolution and dark counts beyond currently available detectors. We will discuss our first attempts at combining semiconducting nanowire based single photon emitters and superconducting nanowire single photon detectors on a chip to realize integrated quantum circuits.

Transcending the slow bimolecular recombination in lead-halide perovskites for electroluminescence

PubMed Central

Xing, Guichuan; Wu, Bo; Wu, Xiangyang; Li, Mingjie; Du, Bin; Wei, Qi; Guo, Jia; Yeow, Edwin K. L.; Sum, Tze Chien; Huang, Wei

2017-01-01

The slow bimolecular recombination that drives three-dimensional lead-halide perovskites' outstanding photovoltaic performance is conversely a fundamental limitation for electroluminescence. Under electroluminescence working conditions with typical charge densities lower than 1015 cm−3, defect-states trapping in three-dimensional perovskites competes effectively with the bimolecular radiative recombination. Herein, we overcome this limitation using van-der-Waals-coupled Ruddlesden-Popper perovskite multi-quantum-wells. Injected charge carriers are rapidly localized from adjacent thin few layer (n≤4) multi-quantum-wells to the thick (n≥5) multi-quantum-wells with extremely high efficiency (over 85%) through quantum coupling. Light emission originates from excitonic recombination in the thick multi-quantum-wells at much higher decay rate and efficiency than bimolecular recombination in three-dimensional perovskites. These multi-quantum-wells retain the simple solution processability and high charge carrier mobility of two-dimensional lead-halide perovskites. Importantly, these Ruddlesden-Popper perovskites offer new functionalities unavailable in single phase constituents, permitting the transcendence of the slow bimolecular recombination bottleneck in lead-halide perovskites for efficient electroluminescence. PMID:28239146

Transcending the slow bimolecular recombination in lead-halide perovskites for electroluminescence.

PubMed

Xing, Guichuan; Wu, Bo; Wu, Xiangyang; Li, Mingjie; Du, Bin; Wei, Qi; Guo, Jia; Yeow, Edwin K L; Sum, Tze Chien; Huang, Wei

2017-02-27

The slow bimolecular recombination that drives three-dimensional lead-halide perovskites' outstanding photovoltaic performance is conversely a fundamental limitation for electroluminescence. Under electroluminescence working conditions with typical charge densities lower than 10 15  cm -3 , defect-states trapping in three-dimensional perovskites competes effectively with the bimolecular radiative recombination. Herein, we overcome this limitation using van-der-Waals-coupled Ruddlesden-Popper perovskite multi-quantum-wells. Injected charge carriers are rapidly localized from adjacent thin few layer (n≤4) multi-quantum-wells to the thick (n≥5) multi-quantum-wells with extremely high efficiency (over 85%) through quantum coupling. Light emission originates from excitonic recombination in the thick multi-quantum-wells at much higher decay rate and efficiency than bimolecular recombination in three-dimensional perovskites. These multi-quantum-wells retain the simple solution processability and high charge carrier mobility of two-dimensional lead-halide perovskites. Importantly, these Ruddlesden-Popper perovskites offer new functionalities unavailable in single phase constituents, permitting the transcendence of the slow bimolecular recombination bottleneck in lead-halide perovskites for efficient electroluminescence.

Brightly Luminescent and Color-Tunable Colloidal CH3NH3PbX3 (X = Br, I, Cl) Quantum Dots: Potential Alternatives for Display Technology.

PubMed

Zhang, Feng; Zhong, Haizheng; Chen, Cheng; Wu, Xian-gang; Hu, Xiangmin; Huang, Hailong; Han, Junbo; Zou, Bingsuo; Dong, Yuping

2015-04-28

Organometal halide perovskites are inexpensive materials with desirable characteristics of color-tunable and narrow-band emissions for lighting and display technology, but they suffer from low photoluminescence quantum yields at low excitation fluencies. Here we developed a ligand-assisted reprecipitation strategy to fabricate brightly luminescent and color-tunable colloidal CH3NH3PbX3 (X = Br, I, Cl) quantum dots with absolute quantum yield up to 70% at room temperature and low excitation fluencies. To illustrate the photoluminescence enhancements in these quantum dots, we conducted comprehensive composition and surface characterizations and determined the time- and temperature-dependent photoluminescence spectra. Comparisons between small-sized CH3NH3PbBr3 quantum dots (average diameter 3.3 nm) and corresponding micrometer-sized bulk particles (2-8 μm) suggest that the intense increased photoluminescence quantum yield originates from the increase of exciton binding energy due to size reduction as well as proper chemical passivations of the Br-rich surface. We further demonstrated wide-color gamut white-light-emitting diodes using green emissive CH3NH3PbBr3 quantum dots and red emissive K2SiF6:Mn(4+) as color converters, providing enhanced color quality for display technology. Moreover, colloidal CH3NH3PbX3 quantum dots are expected to exhibit interesting nanoscale excitonic properties and also have other potential applications in lasers, electroluminescence devices, and optical sensors.

Enhancing the photon-extraction efficiency of site-controlled quantum dots by deterministically fabricated microlenses

NASA Astrophysics Data System (ADS)

Kaganskiy, Arsenty; Fischbach, Sarah; Strittmatter, André; Rodt, Sven; Heindel, Tobias; Reitzenstein, Stephan

2018-04-01

We report on the realization of scalable single-photon sources (SPSs) based on single site-controlled quantum dots (SCQDs) and deterministically fabricated microlenses. The fabrication process comprises the buried-stressor growth technique complemented with low-temperature in-situ electron-beam lithography for the integration of SCQDs into microlens structures with high yield and high alignment accuracy. The microlens-approach leads to a broadband enhancement of the photon-extraction efficiency of up to (21 ± 2)% and a high suppression of multi-photon events with g (2)(τ = 0) < 0.06 without background subtraction. The demonstrated combination of site-controlled growth of QDs and in-situ electron-beam lithography is relevant for arrays of efficient SPSs which, can be applied in photonic quantum circuits and advanced quantum computation schemes.

Spectral difference Lanczos method for efficient time propagation in quantum control theory

NASA Astrophysics Data System (ADS)

Farnum, John D.; Mazziotti, David A.

2004-04-01

Spectral difference methods represent the real-space Hamiltonian of a quantum system as a banded matrix which possesses the accuracy of the discrete variable representation (DVR) and the efficiency of finite differences. When applied to time-dependent quantum mechanics, spectral differences enhance the efficiency of propagation methods for evolving the Schrödinger equation. We develop a spectral difference Lanczos method which is computationally more economical than the sinc-DVR Lanczos method, the split-operator technique, and even the fast-Fourier-Transform Lanczos method. Application of fast propagation is made to quantum control theory where chirped laser pulses are designed to dissociate both diatomic and polyatomic molecules. The specificity of the chirped laser fields is also tested as a possible method for molecular identification and discrimination.

Quantum and quasiclassical dynamics of the multi-channel H + H2S reaction.

PubMed

Qi, Ji; Lu, Dandan; Song, Hongwei; Li, Jun; Yang, Minghui

2017-03-28

The prototypical multi-channel reaction H + H 2 S → H 2 + SH/H + H 2 S has been investigated using the full-dimensional quantum scattering and quasi-classical trajectory methods to unveil the underlying competition mechanism between different product channels and the mode specificity. This reaction favors the abstraction channel over the exchange channel. For both channels, excitations in the two stretching modes promote the reaction with nearly equal efficiency and are more efficient than the bending mode excitation. However, they are all less efficient than the translational energy. In addition, the experimentally observed non-Arrhenius temperature dependence of the thermal rate constants is reasonably reproduced by the quantum dynamics calculations, confirming that the non-Arrhenius behavior is caused by the pronounced quantum tunneling.

Fast, efficient error reconciliation for quantum cryptography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Buttler, W.T.; Lamoreaux, S.K.; Torgerson, J.R.

2003-05-01

We describe an error-reconciliation protocol, which we call Winnow, based on the exchange of parity and Hamming's 'syndrome' for N-bit subunits of a large dataset. The Winnow protocol was developed in the context of quantum-key distribution and offers significant advantages and net higher efficiency compared to other widely used protocols within the quantum cryptography community. A detailed mathematical analysis of the Winnow protocol is presented in the context of practical implementations of quantum-key distribution; in particular, the information overhead required for secure implementation is one of the most important criteria in the evaluation of a particular error-reconciliation protocol. The increasemore » in efficiency for the Winnow protocol is largely due to the reduction in authenticated public communication required for its implementation.« less

A variational eigenvalue solver on a photonic quantum processor

PubMed Central

Peruzzo, Alberto; McClean, Jarrod; Shadbolt, Peter; Yung, Man-Hong; Zhou, Xiao-Qi; Love, Peter J.; Aspuru-Guzik, Alán; O’Brien, Jeremy L.

2014-01-01

Quantum computers promise to efficiently solve important problems that are intractable on a conventional computer. For quantum systems, where the physical dimension grows exponentially, finding the eigenvalues of certain operators is one such intractable problem and remains a fundamental challenge. The quantum phase estimation algorithm efficiently finds the eigenvalue of a given eigenvector but requires fully coherent evolution. Here we present an alternative approach that greatly reduces the requirements for coherent evolution and combine this method with a new approach to state preparation based on ansätze and classical optimization. We implement the algorithm by combining a highly reconfigurable photonic quantum processor with a conventional computer. We experimentally demonstrate the feasibility of this approach with an example from quantum chemistry—calculating the ground-state molecular energy for He–H+. The proposed approach drastically reduces the coherence time requirements, enhancing the potential of quantum resources available today and in the near future. PMID:25055053

A space-efficient quantum computer simulator suitable for high-speed FPGA implementation

NASA Astrophysics Data System (ADS)

Frank, Michael P.; Oniciuc, Liviu; Meyer-Baese, Uwe H.; Chiorescu, Irinel

2009-05-01

Conventional vector-based simulators for quantum computers are quite limited in the size of the quantum circuits they can handle, due to the worst-case exponential growth of even sparse representations of the full quantum state vector as a function of the number of quantum operations applied. However, this exponential-space requirement can be avoided by using general space-time tradeoffs long known to complexity theorists, which can be appropriately optimized for this particular problem in a way that also illustrates some interesting reformulations of quantum mechanics. In this paper, we describe the design and empirical space/time complexity measurements of a working software prototype of a quantum computer simulator that avoids excessive space requirements. Due to its space-efficiency, this design is well-suited to embedding in single-chip environments, permitting especially fast execution that avoids access latencies to main memory. We plan to prototype our design on a standard FPGA development board.

Quantum storage of a photonic polarization qubit in a solid.

PubMed

Gündoğan, Mustafa; Ledingham, Patrick M; Almasi, Attaallah; Cristiani, Matteo; de Riedmatten, Hugues

2012-05-11

We report on the quantum storage and retrieval of photonic polarization quantum bits onto and out of a solid state storage device. The qubits are implemented with weak coherent states at the single photon level, and are stored for a predetermined time of 500 ns in a praseodymium doped crystal with a storage and retrieval efficiency of 10%, using the atomic frequency comb scheme. We characterize the storage by using quantum state tomography, and find that the average conditional fidelity of the retrieved qubits exceeds 95% for a mean photon number μ=0.4. This is significantly higher than a classical benchmark, taking into account the poissonian statistics and finite memory efficiency, which proves that our crystal functions as a quantum storage device for polarization qubits. These results extend the storage capabilities of solid state quantum light matter interfaces to polarization encoding, which is widely used in quantum information science.

In vitro evaluation of heat and moisture exchangers designed for spontaneously breathing tracheostomized patients.

PubMed

Brusasco, Claudia; Corradi, Francesco; Vargas, Maria; Bona, Margherita; Bruno, Federica; Marsili, Maria; Simonassi, Francesca; Santori, Gregorio; Severgnini, Paolo; Kacmarek, Robert M; Pelosi, Paolo

2013-11-01

Heat and moisture exchangers (HMEs) are commonly used in chronically tracheostomized spontaneously breathing patients, to condition inhaled air, maintain lower airway function, and minimize the viscosity of secretions. Supplemental oxygen (O2) can be added to most HMEs designed for spontaneously breathing tracheostomized patients. We tested the efficiency of 7 HMEs designed for spontaneously breathing tracheostomized patients, in a normothermic model, at different minute ventilations (VE) and supplemental O2 flows. HME efficiency was evaluated using an in vitro lung model at 2 VE (5 and 15 L/min) and 4 supplemental O2 flows (0, 3, 6, and 12 L/min). Wet and dry temperatures of the inspiratory flow were measured, and absolute humidity was calculated. In addition, HME efficiency at 0, 12, and 24 h use was evaluated, as well as resistance to flow at 0 and 24 h. The progressive increase in O2 flow from 0 to 12 L/min was associated with a reduction in temperature and absolute humidity. Under the same conditions, this effect was greater at lower VE. The HME with the best performance provided an absolute humidity of 26 mg H2O/L and a temperature of 27.8 °C. No significant changes in efficiency or resistance were detected during the 24 h evaluation. The efficiency of HMEs in terms of temperature and absolute humidity is significantly affected by O2 supplementation and V(E).

Efficient 3He/4He separation in a nanoporous graphenylene membrane.

PubMed

Qu, Yuanyuan; Li, Feng; Zhao, Mingwen

2017-08-16

Helium-3 is a precious noble gas, which is essential in many advanced technologies such as cryogenics, isotope labeling and nuclear weapons. The current imbalance of 3 He demand and supply shortage leads to the search for an efficient membrane with high performance for 3 He separation. In this study, based on first-principles calculations, we demonstrated that highly efficient 3 He harvesting can be achieved in a nanoporous graphenylene membrane with industrially-acceptable selectivity and permeance. The quantum tunneling effect leads to 3 He harvesting with high efficiency via kinetic sieving. Both the quantum tunneling effect and zero-point energy (ZPE) determine the 3 He/ 4 He separation via thermally-driven equilibrium sieving, where the ZPE effect dominates efficient 3 He/ 4 He separation between two reservoirs. The quantum effects revealed in this work suggest that the nanoporous graphenylene membrane is promising for efficient 3 He harvesting that can be exploited for industrial applications.

Anomalous gain in an isotopically mixed CO2 laser and application to absolute wavelength calibration

NASA Technical Reports Server (NTRS)

Hewagama, Tilak; Oppenheim, Uri P.; Mumma, Michael J.

1991-01-01

Measurements are reported on a grating-tuned CO2 laser, containing an isotropic mixture of O-16C-12O-16, O-16C-12O-18, and O-18C-12O-18. The P6 and R14 lines of O-16C-12O-16 were found to have anomalously high intensities. These anomalies are produced by the near coincidence of the transition frequencies in two distinct isotopes, permitting them to act as a single indistinguishable population. These two lines can be used to identify the rotational quantum numbers in the P and R branch spectra, thereby permitting absolute wavelength calibration to be achieved.

Pure sources and efficient detectors for optical quantum information processing

NASA Astrophysics Data System (ADS)

Zielnicki, Kevin

Over the last sixty years, classical information theory has revolutionized the understanding of the nature of information, and how it can be quantified and manipulated. Quantum information processing extends these lessons to quantum systems, where the properties of intrinsic uncertainty and entanglement fundamentally defy classical explanation. This growing field has many potential applications, including computing, cryptography, communication, and metrology. As inherently mobile quantum particles, photons are likely to play an important role in any mature large-scale quantum information processing system. However, the available methods for producing and detecting complex multi-photon states place practical limits on the feasibility of sophisticated optical quantum information processing experiments. In a typical quantum information protocol, a source first produces an interesting or useful quantum state (or set of states), perhaps involving superposition or entanglement. Then, some manipulations are performed on this state, perhaps involving quantum logic gates which further manipulate or entangle the intial state. Finally, the state must be detected, obtaining some desired measurement result, e.g., for secure communication or computationally efficient factoring. The work presented here concerns the first and last stages of this process as they relate to photons: sources and detectors. Our work on sources is based on the need for optimized non-classical states of light delivered at high rates, particularly of single photons in a pure quantum state. We seek to better understand the properties of spontaneous parameteric downconversion (SPDC) sources of photon pairs, and in doing so, produce such an optimized source. We report an SPDC source which produces pure heralded single photons with little or no spectral filtering, allowing a significant rate enhancement. Our work on detectors is based on the need to reliably measure single-photon states. We have focused on optimizing the detection efficiency of visible light photon counters (VLPCs), a single-photon detection technology that is also capable of resolving photon number states. We report a record-breaking quantum efficiency of 91 +/- 3% observed with our detection system. Both sources and detectors are independently interesting physical systems worthy of study, but together they promise to enable entire new classes and applications of information based on quantum mechanics.

High-quantum efficiency, long-lived luminescing refractory oxides

DOEpatents

Chen, Y.; Gonzalez, R.; Summers, G.P.

A crystal having a high-quantum efficiency and a long period of luminescence is formed of MgO or CaO and possessing a concentration ratio of H/sup -/ ions to F centers in the range of about 0.05 to about 10.

GaN ultraviolet p-i-n photodetectors with enhanced deep ultraviolet quantum efficiency

NASA Astrophysics Data System (ADS)

Wang, Guosheng; Xie, Feng; Wang, Jun; Guo, Jin

2017-10-01

GaN ultraviolet (UV) p-i-n photodetectors (PDs) with a thin p-AlGaN/GaN contact layer are designed and fabricated. The PD exhibits a low dark current density of˜7 nA/cm2 under -5 V, and a zero-bias peak responsivity of ˜0.16 A/W at 360 nm, which corresponds to a maximum quantum efficiency of 55%. It is found that, in the wavelength range between 250 and 365 nm, the PD with thin p-AlGaN/GaN contact layer exhibits enhanced quantum efficiency especially in a deep-UV wavelength range, than that of the control PD with conventional thin p-GaN contact layer. The improved quantum efficiency of the PD with thin p-AlGaN/GaN contact layer in the deep-UV wavelength range is mainly attributed to minority carrier reflecting properties of thin p-AlGaN/GaN heterojunction which could reduce the surface recombination loss of photon-generated carriers and improve light current collection efficiency.

Quantum versus classical dynamics in the optical centrifuge

NASA Astrophysics Data System (ADS)

Armon, Tsafrir; Friedland, Lazar

2017-09-01

The interplay between classical and quantum-mechanical evolution in the optical centrifuge (OC) is discussed. The analysis is based on the quantum-mechanical formalism starting from either the ground state or a thermal ensemble. Two resonant mechanisms are identified, i.e., the classical autoresonance and the quantum-mechanical ladder climbing, yielding different dynamics and rotational excitation efficiencies. The rotating-wave approximation is used to analyze the two resonant regimes in the associated dimensionless two-parameter space and calculate the OC excitation efficiency. The results show good agreement between numerical simulations and theory and are relevant to existing experimental setups.

Fluorescent porous silicon biological probes with high quantum efficiency and stability.

PubMed

Tu, Chang-Ching; Chou, Ying-Nien; Hung, Hsiang-Chieh; Wu, Jingda; Jiang, Shaoyi; Lin, Lih Y

2014-12-01

We demonstrate porous silicon biological probes as a stable and non-toxic alternative to organic dyes or cadmium-containing quantum dots for imaging and sensing applications. The fluorescent silicon quantum dots which are embedded on the porous silicon surface are passivated with carboxyl-terminated ligands through stable Si-C covalent bonds. The porous silicon bio-probes have shown photoluminescence quantum yield around 50% under near-UV excitation, with high photochemical and thermal stability. The bio-probes can be efficiently conjugated with antibodies, which is confirmed by a standard enzyme-linked immunosorbent assay (ELISA) method.

Entanglement enhances cooling in microscopic quantum refrigerators.

PubMed

Brunner, Nicolas; Huber, Marcus; Linden, Noah; Popescu, Sandu; Silva, Ralph; Skrzypczyk, Paul

2014-03-01

Small self-contained quantum thermal machines function without external source of work or control but using only incoherent interactions with thermal baths. Here we investigate the role of entanglement in a small self-contained quantum refrigerator. We first show that entanglement is detrimental as far as efficiency is concerned-fridges operating at efficiencies close to the Carnot limit do not feature any entanglement. Moving away from the Carnot regime, we show that entanglement can enhance cooling and energy transport. Hence, a truly quantum refrigerator can outperform a classical one. Furthermore, the amount of entanglement alone quantifies the enhancement in cooling.

Femtosecond Laser--Pumped Source of Entangled Photons for Quantum Cryptography Applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pan, D.; Donaldson, W.; Sobolewski, R.

2007-07-31

We present an experimental setup for generation of entangled-photon pairs via spontaneous parametric down-conversion, based on the femtosecond-pulsed laser. Our entangled-photon source utilizes a 76-MHz-repetition-rate, 100-fs-pulse-width, mode-locked, ultrafast femtosecond laser, which can produce, on average, more photon pairs than a cw laser of an equal pump power. The resulting entangled pairs are counted by a pair of high-quantum-efficiency, single-photon, silicon avalanche photodiodes. Our apparatus is intended as an efficient source/receiver system for the quantum communications and quantum cryptography applications.

Minimized state complexity of quantum-encoded cryptic processes

NASA Astrophysics Data System (ADS)

Riechers, Paul M.; Mahoney, John R.; Aghamohammadi, Cina; Crutchfield, James P.

2016-05-01

The predictive information required for proper trajectory sampling of a stochastic process can be more efficiently transmitted via a quantum channel than a classical one. This recent discovery allows quantum information processing to drastically reduce the memory necessary to simulate complex classical stochastic processes. It also points to a new perspective on the intrinsic complexity that nature must employ in generating the processes we observe. The quantum advantage increases with codeword length: the length of process sequences used in constructing the quantum communication scheme. In analogy with the classical complexity measure, statistical complexity, we use this reduced communication cost as an entropic measure of state complexity in the quantum representation. Previously difficult to compute, the quantum advantage is expressed here in closed form using spectral decomposition. This allows for efficient numerical computation of the quantum-reduced state complexity at all encoding lengths, including infinite. Additionally, it makes clear how finite-codeword reduction in state complexity is controlled by the classical process's cryptic order, and it allows asymptotic analysis of infinite-cryptic-order processes.

Tuning Single Quantum Dot Emission with a Micromirror.

PubMed

Yuan, Gangcheng; Gómez, Daniel; Kirkwood, Nicholas; Mulvaney, Paul

2018-02-14

The photoluminescence of single quantum dots fluctuates between bright (on) and dark (off) states, also termed fluorescence intermittency or blinking. This blinking limits the performance of quantum dot-based devices such as light-emitting diodes and solar cells. However, the origins of the blinking remain unresolved. Here, we use a movable gold micromirror to determine both the quantum yield of the bright state and the orientation of the excited state dipole of single quantum dots. We observe that the quantum yield of the bright state is close to unity for these single QDs. Furthermore, we also study the effect of a micromirror on blinking, and then evaluate excitation efficiency, biexciton quantum yield, and detection efficiency. The mirror does not modify the off-time statistics, but it does change the density of optical states available to the quantum dot and hence the on times. The duration of the on times can be lengthened due to an increase in the radiative recombination rate.

Thermal Quantum Correlations in Photosynthetic Light-Harvesting Complexes

NASA Astrophysics Data System (ADS)

Mahdian, M.; Kouhestani, H.

2015-08-01

Photosynthesis is one of the ancient biological processes, playing crucial role converting solar energy to cellular usable currency. Environmental factors and external perturbations has forced nature to choose systems with the highest efficiency and performance. Recent theoretical and experimental studies have proved the presence of quantum properties in biological systems. Energy transfer systems like Fenna-Matthews-Olson (FMO) complex shows quantum entanglement between sites of Bacteriophylla molecules in protein environment and presence of decoherence. Complex biological systems implement more truthful mechanisms beside chemical-quantum correlations to assure system's efficiency. In this study we investigate thermal quantum correlations in FMO protein of the photosynthetic apparatus of green sulfur bacteria by quantum discord measure. The results confirmed existence of remarkable quantum correlations of of BChla pigments in room temperature. This results approve involvement of quantum correlation mechanisms for information storage and retention in living organisms that could be useful for further evolutionary studies. Inspired idea of this study is potentially interesting to practice by the same procedure in genetic data transfer mechanisms.

Topics in quantum cryptography, quantum error correction, and channel simulation

NASA Astrophysics Data System (ADS)

Luo, Zhicheng

In this thesis, we mainly investigate four different topics: efficiently implementable codes for quantum key expansion [51], quantum error-correcting codes based on privacy amplification [48], private classical capacity of quantum channels [44], and classical channel simulation with quantum side information [49, 50]. For the first topic, we propose an efficiently implementable quantum key expansion protocol, capable of increasing the size of a pre-shared secret key by a constant factor. Previously, the Shor-Preskill proof [64] of the security of the Bennett-Brassard 1984 (BB84) [6] quantum key distribution protocol relied on the theoretical existence of good classical error-correcting codes with the "dual-containing" property. But the explicit and efficiently decodable construction of such codes is unknown. We show that we can lift the dual-containing constraint by employing the non-dual-containing codes with excellent performance and efficient decoding algorithms. For the second topic, we propose a construction of Calderbank-Shor-Steane (CSS) [19, 68] quantum error-correcting codes, which are originally based on pairs of mutually dual-containing classical codes, by combining a classical code with a two-universal hash function. We show, using the results of Renner and Koenig [57], that the communication rates of such codes approach the hashing bound on tensor powers of Pauli channels in the limit of large block-length. For the third topic, we prove a regularized formula for the secret key assisted capacity region of a quantum channel for transmitting private classical information. This result parallels the work of Devetak on entanglement assisted quantum communication capacity. This formula provides a new family protocol, the private father protocol, under the resource inequality framework that includes the private classical communication without the assisted secret keys as a child protocol. For the fourth topic, we study and solve the problem of classical channel simulation with quantum side information at the receiver. Our main theorem has two important corollaries: rate-distortion theory with quantum side information and common randomness distillation. Simple proofs of achievability of classical multi-terminal source coding problems can be made via a unified approach using the channel simulation theorem as building blocks. The fully quantum generalization of the problem is also conjectured with outer and inner bounds on the achievable rate pairs.

Quantum chemical study of the inhibition of the corrosion of mild steel in H2SO4 by some antibiotics.

PubMed

Eddy, Nnabuk O; Ibok, Udo J; Ebenso, Eno E; El Nemr, Ahmed; El Ashry, El Sayed H

2009-09-01

The inhibition efficiency of some antibiotics against mild steel corrosion was studied using weight loss and quantum chemical techniques. Values of inhibition efficiency obtained from weight loss measurements correlated strongly with theoretical values obtained through semi empirical calculations. High correlation coefficients were also obtained between inhibition efficiency of the antibiotics and some quantum chemical parameters, including frontier orbital (E (HOMO) and E (LUMO)), dipole moment, log P, TNC and LSER parameters (critical volume and dipolar-polarisability factor), which indicated that these parameters affect the inhibition efficiency of the compounds. It was also found that quantitative structure activity relation can be used to adequately predict the inhibition effectiveness of these compounds.

Experimental Realization of High-Efficiency Counterfactual Computation.

PubMed

Kong, Fei; Ju, Chenyong; Huang, Pu; Wang, Pengfei; Kong, Xi; Shi, Fazhan; Jiang, Liang; Du, Jiangfeng

2015-08-21

Counterfactual computation (CFC) exemplifies the fascinating quantum process by which the result of a computation may be learned without actually running the computer. In previous experimental studies, the counterfactual efficiency is limited to below 50%. Here we report an experimental realization of the generalized CFC protocol, in which the counterfactual efficiency can break the 50% limit and even approach unity in principle. The experiment is performed with the spins of a negatively charged nitrogen-vacancy color center in diamond. Taking advantage of the quantum Zeno effect, the computer can remain in the not-running subspace due to the frequent projection by the environment, while the computation result can be revealed by final detection. The counterfactual efficiency up to 85% has been demonstrated in our experiment, which opens the possibility of many exciting applications of CFC, such as high-efficiency quantum integration and imaging.

Experimental Realization of High-Efficiency Counterfactual Computation

NASA Astrophysics Data System (ADS)

Kong, Fei; Ju, Chenyong; Huang, Pu; Wang, Pengfei; Kong, Xi; Shi, Fazhan; Jiang, Liang; Du, Jiangfeng

2015-08-01

Counterfactual computation (CFC) exemplifies the fascinating quantum process by which the result of a computation may be learned without actually running the computer. In previous experimental studies, the counterfactual efficiency is limited to below 50%. Here we report an experimental realization of the generalized CFC protocol, in which the counterfactual efficiency can break the 50% limit and even approach unity in principle. The experiment is performed with the spins of a negatively charged nitrogen-vacancy color center in diamond. Taking advantage of the quantum Zeno effect, the computer can remain in the not-running subspace due to the frequent projection by the environment, while the computation result can be revealed by final detection. The counterfactual efficiency up to 85% has been demonstrated in our experiment, which opens the possibility of many exciting applications of CFC, such as high-efficiency quantum integration and imaging.

Flexible deep-ultraviolet light-emitting diodes for significant improvement of quantum efficiencies by external bending

NASA Astrophysics Data System (ADS)

Shervin, Shahab; Oh, Seung Kyu; Park, Hyun Jung; Lee, Keon-Hwa; Asadirad, Mojtaba; Kim, Seung-Hwan; Kim, Jeomoh; Pouladi, Sara; Lee, Sung-Nam; Li, Xiaohang; Kwak, Joon Seop; Ryou, Jae-Hyun

2018-03-01

We report a new route to improve quantum efficiencies of AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) using mechanical flexibility of recently developed bendable thin-film structures. Numerical studies show that electronic band structures of AlGaN heterostructures and resulting optical and electrical characteristics of the devices can be significantly modified by external bending through active control of piezoelectric polarization. Internal quantum efficiency is enhanced higher than three times, when the DUV LEDs are moderately bent with concave curvatures. Furthermore, an efficiency droop at high injection currents is mitigated and turn-on voltage of diodes decreases with the same bending condition. The concept of bendable DUV LEDs with a controlled external strain can provide a new path for high-output-power and high-efficiency devices.

An integrated approach to realizing high-performance liquid-junction quantum dot sensitized solar cells

PubMed Central

McDaniel, Hunter; Fuke, Nobuhiro; Makarov, Nikolay S.; Pietryga, Jeffrey M.; Klimov, Victor I.

2013-01-01

Solution-processed semiconductor quantum dot solar cells offer a path towards both reduced fabrication cost and higher efficiency enabled by novel processes such as hot-electron extraction and carrier multiplication. Here we use a new class of low-cost, low-toxicity CuInSexS2−x quantum dots to demonstrate sensitized solar cells with certified efficiencies exceeding 5%. Among other material and device design improvements studied, use of a methanol-based polysulfide electrolyte results in a particularly dramatic enhancement in photocurrent and reduced series resistance. Despite the high vapour pressure of methanol, the solar cells are stable for months under ambient conditions, which is much longer than any previously reported quantum dot sensitized solar cell. This study demonstrates the large potential of CuInSexS2−x quantum dots as active materials for the realization of low-cost, robust and efficient photovoltaics as well as a platform for investigating various advanced concepts derived from the unique physics of the nanoscale size regime. PMID:24322379

Density-functional theory simulation of large quantum dots

NASA Astrophysics Data System (ADS)

Jiang, Hong; Baranger, Harold U.; Yang, Weitao

2003-10-01

Kohn-Sham spin-density functional theory provides an efficient and accurate model to study electron-electron interaction effects in quantum dots, but its application to large systems is a challenge. Here an efficient method for the simulation of quantum dots using density-function theory is developed; it includes the particle-in-the-box representation of the Kohn-Sham orbitals, an efficient conjugate-gradient method to directly minimize the total energy, a Fourier convolution approach for the calculation of the Hartree potential, and a simplified multigrid technique to accelerate the convergence. We test the methodology in a two-dimensional model system and show that numerical studies of large quantum dots with several hundred electrons become computationally affordable. In the noninteracting limit, the classical dynamics of the system we study can be continuously varied from integrable to fully chaotic. The qualitative difference in the noninteracting classical dynamics has an effect on the quantum properties of the interacting system: integrable classical dynamics leads to higher-spin states and a broader distribution of spacing between Coulomb blockade peaks.

High charge-carrier mobility enables exploitation of carrier multiplication in quantum-dot films

PubMed Central

Sandeep, C. S. Suchand; Cate, Sybren ten; Schins, Juleon M.; Savenije, Tom J.; Liu, Yao; Law, Matt; Kinge, Sachin; Houtepen, Arjan J.; Siebbeles, Laurens D. A.

2013-01-01

Carrier multiplication, the generation of multiple electron–hole pairs by a single photon, is of great interest for solar cells as it may enhance their photocurrent. This process has been shown to occur efficiently in colloidal quantum dots, however, harvesting of the generated multiple charges has proved difficult. Here we show that by tuning the charge-carrier mobility in quantum-dot films, carrier multiplication can be optimized and may show an efficiency as high as in colloidal dispersion. Our results are explained quantitatively by the competition between dissociation of multiple electron–hole pairs and Auger recombination. Above a mobility of ~1 cm2 V−1 s−1, all charges escape Auger recombination and are quantitatively converted to free charges, offering the prospect of cheap quantum-dot solar cells with efficiencies in excess of the Shockley–Queisser limit. In addition, we show that the threshold energy for carrier multiplication is reduced to twice the band gap of the quantum dots. PMID:23974282

Structural Investigation of Cesium Lead Halide Perovskites for High-Efficiency Quantum Dot Light-Emitting Diodes.

PubMed

Le, Quyet Van; Kim, Jong Beom; Kim, Soo Young; Lee, Byeongdu; Lee, Dong Ryeol

2017-09-07

We have investigated the effect of reaction temperature of hot-injection method on the structural properties of CsPbX 3 (X: Br, I, Cl) perovskite nanocrystals (NCs) using small- and wide-angle X-ray scattering. It is confirmed that the size of the NCs decreased as the reaction temperature decreased, resulting in stronger quantum confinement. The cubic-phase perovskite NCs formed despite the fact that the reaction temperatures increased from 140 to 180 °C; however, monodispersive NC cubes that are required for densely packing self-assembly film were formed only at lower temperatures. From the X-ray scattering measurements, the spin-coated film from more monodispersive perovskite nanocubes synthesized at lower temperatures resulted in more preferred orientation. This dense-packing perovskite film with preferred orientation yielded efficient light-emitting diode (LED) performance. Thus the dense-packing structure of NC assemblies formed after spin-coating should be considered for high-efficient LEDs based on perovskite quantum dots in addition to quantum confinement effect of the quantum dots.

Can quantum coherent solar cells break detailed balance?

NASA Astrophysics Data System (ADS)

Kirk, Alexander P.

2015-07-01

Carefully engineered coherent quantum states have been proposed as a design attribute that is hypothesized to enable solar photovoltaic cells to break the detailed balance (or radiative) limit of power conversion efficiency by possibly causing radiative recombination to be suppressed. However, in full compliance with the principles of statistical mechanics and the laws of thermodynamics, specially prepared coherent quantum states do not allow a solar photovoltaic cell—a quantum threshold energy conversion device—to exceed the detailed balance limit of power conversion efficiency. At the condition given by steady-state open circuit operation with zero nonradiative recombination, the photon absorption rate (or carrier photogeneration rate) must balance the photon emission rate (or carrier radiative recombination rate) thus ensuring that detailed balance prevails. Quantum state transitions, entropy-generating hot carrier relaxation, and photon absorption and emission rate balancing are employed holistically and self-consistently along with calculations of current density, voltage, and power conversion efficiency to explain why detailed balance may not be violated in solar photovoltaic cells.

Purely organic electroluminescent material realizing 100% conversion from electricity to light

PubMed Central

Kaji, Hironori; Suzuki, Hajime; Fukushima, Tatsuya; Shizu, Katsuyuki; Suzuki, Katsuaki; Kubo, Shosei; Komino, Takeshi; Oiwa, Hajime; Suzuki, Furitsu; Wakamiya, Atsushi; Murata, Yasujiro; Adachi, Chihaya

2015-01-01

Efficient organic light-emitting diodes have been developed using emitters containing rare metals, such as platinum and iridium complexes. However, there is an urgent need to develop emitters composed of more abundant materials. Here we show a thermally activated delayed fluorescence material for organic light-emitting diodes, which realizes both approximately 100% photoluminescence quantum yield and approximately 100% up-conversion of the triplet to singlet excited state. The material contains electron-donating diphenylaminocarbazole and electron-accepting triphenyltriazine moieties. The typical trade-off between effective emission and triplet-to-singlet up-conversion is overcome by fine-tuning the highest occupied molecular orbital and lowest unoccupied molecular orbital distributions. The nearly zero singlet–triplet energy gap, smaller than the thermal energy at room temperature, results in an organic light-emitting diode with external quantum efficiency of 29.6%. An external quantum efficiency of 41.5% is obtained when using an out-coupling sheet. The external quantum efficiency is 30.7% even at a high luminance of 3,000 cd m−2. PMID:26477390

Positive Wigner functions render classical simulation of quantum computation efficient.

PubMed

Mari, A; Eisert, J

2012-12-07

We show that quantum circuits where the initial state and all the following quantum operations can be represented by positive Wigner functions can be classically efficiently simulated. This is true both for continuous-variable as well as discrete variable systems in odd prime dimensions, two cases which will be treated on entirely the same footing. Noting the fact that Clifford and Gaussian operations preserve the positivity of the Wigner function, our result generalizes the Gottesman-Knill theorem. Our algorithm provides a way of sampling from the output distribution of a computation or a simulation, including the efficient sampling from an approximate output distribution in the case of sampling imperfections for initial states, gates, or measurements. In this sense, this work highlights the role of the positive Wigner function as separating classically efficiently simulable systems from those that are potentially universal for quantum computing and simulation, and it emphasizes the role of negativity of the Wigner function as a computational resource.

Development of a unique laboratory standard: Indium gallium arsenide detector for the 500-1700 nm spectral region

NASA Technical Reports Server (NTRS)

1987-01-01

A planar (5 mm diameter) indium gallium arsenide detector having a high (greater than 50 pct) quantum efficiency from the visible into the infrared spectrum (500 to 1700 nm) was fabricated. Quantum efficiencies as high as 37 pct at 510 nm, 58 pct at 820 nm and 62 pct at 1300 nm and 1550 nm were measured. A planar InP/InGaAs detector structure was also fabricated using vapor phase epitaxy to grow device structures with 0, 0.2, 0.4 and 0.6 micrometer thick InP caps. Quantum efficiency was studied as a function of cap thickness. Conventional detector structures were also used by completely etching off the InP cap after zinc diffusion. Calibrated quantum efficiencies were measured. Best results were obtained with devices whose caps were completely removed by etching. Certain problems still remain with these detectors including non-uniform shunt resistance, reproducibility, contact resistance and narrow band anti-reflection coatings.

One-dimensional organic lead halide perovskites with efficient bluish white-light emission

NASA Astrophysics Data System (ADS)

Yuan, Zhao; Zhou, Chenkun; Tian, Yu; Shu, Yu; Messier, Joshua; Wang, Jamie C.; van de Burgt, Lambertus J.; Kountouriotis, Konstantinos; Xin, Yan; Holt, Ethan; Schanze, Kirk; Clark, Ronald; Siegrist, Theo; Ma, Biwu

2017-01-01

Organic-inorganic hybrid metal halide perovskites, an emerging class of solution processable photoactive materials, welcome a new member with a one-dimensional structure. Herein we report the synthesis, crystal structure and photophysical properties of one-dimensional organic lead bromide perovskites, C4N2H14PbBr4, in which the edge sharing octahedral lead bromide chains [PbBr4 2-]∞ are surrounded by the organic cations C4N2H14 2+ to form the bulk assembly of core-shell quantum wires. This unique one-dimensional structure enables strong quantum confinement with the formation of self-trapped excited states that give efficient bluish white-light emissions with photoluminescence quantum efficiencies of approximately 20% for the bulk single crystals and 12% for the microscale crystals. This work verifies once again that one-dimensional systems are favourable for exciton self-trapping to produce highly efficient below-gap broadband luminescence, and opens up a new route towards superior light emitters based on bulk quantum materials.

Enhancing the quantum efficiency of InGaN yellow-green light-emitting diodes by growth interruption

DOE Office of Scientific and Technical Information (OSTI.GOV)

Du, Chunhua; Ma, Ziguang; Zhou, Junming

2014-08-18

We studied the effect of multiple interruptions during the quantum well growth on emission-efficiency enhancement of InGaN-based yellow-green light emitting diodes on c-plane sapphire substrate. The output power and dominant wavelength at 20 mA are 0.24 mW and 556.3 nm. High resolution x-ray diffraction, photoluminescence, and electroluminescence measurements demonstrate that efficiency enhancement could be partially attributed to crystal quality improvement of the active region resulted from reduced In clusters and relevant defects on the surface of InGaN layer by introducing interruptions. The less tilted energy band in the quantum well is also caused by the decrease of In-content gradient along c-axis resultedmore » from In segregation during the interruptions, which increases spatial overlap of electron-hole wavefunction and thus the internal quantum efficiency. The latter also leads to smaller blueshift of dominant wavelength with current increasing.« less

One-dimensional organic lead halide perovskites with efficient bluish white-light emission

PubMed Central

Yuan, Zhao; Zhou, Chenkun; Tian, Yu; Shu, Yu; Messier, Joshua; Wang, Jamie C.; van de Burgt, Lambertus J.; Kountouriotis, Konstantinos; Xin, Yan; Holt, Ethan; Schanze, Kirk; Clark, Ronald; Siegrist, Theo; Ma, Biwu

2017-01-01

Organic-inorganic hybrid metal halide perovskites, an emerging class of solution processable photoactive materials, welcome a new member with a one-dimensional structure. Herein we report the synthesis, crystal structure and photophysical properties of one-dimensional organic lead bromide perovskites, C4N2H14PbBr4, in which the edge sharing octahedral lead bromide chains [PbBr4 2−]∞ are surrounded by the organic cations C4N2H14 2+ to form the bulk assembly of core-shell quantum wires. This unique one-dimensional structure enables strong quantum confinement with the formation of self-trapped excited states that give efficient bluish white-light emissions with photoluminescence quantum efficiencies of approximately 20% for the bulk single crystals and 12% for the microscale crystals. This work verifies once again that one-dimensional systems are favourable for exciton self-trapping to produce highly efficient below-gap broadband luminescence, and opens up a new route towards superior light emitters based on bulk quantum materials. PMID:28051092

One-dimensional organic lead halide perovskites with efficient bluish white-light emission.

PubMed

Yuan, Zhao; Zhou, Chenkun; Tian, Yu; Shu, Yu; Messier, Joshua; Wang, Jamie C; van de Burgt, Lambertus J; Kountouriotis, Konstantinos; Xin, Yan; Holt, Ethan; Schanze, Kirk; Clark, Ronald; Siegrist, Theo; Ma, Biwu

2017-01-04

Organic-inorganic hybrid metal halide perovskites, an emerging class of solution processable photoactive materials, welcome a new member with a one-dimensional structure. Herein we report the synthesis, crystal structure and photophysical properties of one-dimensional organic lead bromide perovskites, C 4 N 2 H 14 PbBr 4 , in which the edge sharing octahedral lead bromide chains [PbBr 4   2- ] ∞ are surrounded by the organic cations C 4 N 2 H 14   2+ to form the bulk assembly of core-shell quantum wires. This unique one-dimensional structure enables strong quantum confinement with the formation of self-trapped excited states that give efficient bluish white-light emissions with photoluminescence quantum efficiencies of approximately 20% for the bulk single crystals and 12% for the microscale crystals. This work verifies once again that one-dimensional systems are favourable for exciton self-trapping to produce highly efficient below-gap broadband luminescence, and opens up a new route towards superior light emitters based on bulk quantum materials.

Strong plasmonic enhancement of biexciton emission: controlled coupling of a single quantum dot to a gold nanocone antenna

DOE PAGES

Matsuzaki, Korenobu; Vassant, Simon; Liu, Hsuan-Wei; ...

2017-02-14

Multiexcitonic transitions and emission of several photons per excitation comprise a very attractive feature of semiconductor quantum dots for optoelectronics applications. However, these higher-order radiative processes are usually quenched in colloidal quantum dots by Auger and other nonradiative decay channels. To increase the multiexcitonic quantum efficiency, several groups have explored plasmonic enhancement, so far with moderate results. By controlled positioning of individual quantum dots in the near field of gold nanocone antennas, we enhance the radiative decay rates of monoexcitons and biexcitons by 109 and 100 folds at quantum efficiencies of 60 and 70%, respectively, in very good agreement withmore » the outcome of numerical calculations. We discuss the implications of our work for future fundamental and applied research in nano-optics.« less

Phosphor-Free Apple-White LEDs with Embedded Indium-Rich Nanostructures Grown on Strain Relaxed Nano-epitaxy GaN.

PubMed

Soh, C B; Liu, W; Yong, A M; Chua, S J; Chow, S Y; Tripathy, S; Tan, R J N

2010-08-01

Phosphor-free apple-white light emitting diodes have been fabricated using a dual stacked InGaN/GaN multiple quantum wells comprising of a lower set of long wavelength emitting indium-rich nanostructures incorporated in multiple quantum wells with an upper set of cyan-green emitting multiple quantum wells. The light-emitting diodes were grown on nano-epitaxially lateral overgrown GaN template formed by regrowth of GaN over SiO(2) film patterned with an anodic aluminum oxide mask with holes of 125 nm diameter and a period of 250 nm. The growth of InGaN/GaN multiple quantum wells on these stress relaxed low defect density templates improves the internal quantum efficiency by 15% for the cyan-green multiple quantum wells. Higher emission intensity with redshift in the PL peak emission wavelength is obtained for the indium-rich nanostructures incorporated in multiple quantum wells. The quantum wells grown on the nano-epitaxially lateral overgrown GaN has a weaker piezoelectric field and hence shows a minimal peak shift with application of higher injection current. An enhancement of external quantum efficiency is achieved for the apple-white light emitting diodes grown on the nano-epitaxially lateral overgrown GaN template based on the light -output power measurement. The improvement in light extraction efficiency, η(extraction,) was found to be 34% for the cyan-green emission peak and 15% from the broad long wavelength emission with optimized lattice period.

Phosphor-Free Apple-White LEDs with Embedded Indium-Rich Nanostructures Grown on Strain Relaxed Nano-epitaxy GaN

NASA Astrophysics Data System (ADS)

Soh, C. B.; Liu, W.; Yong, A. M.; Chua, S. J.; Chow, S. Y.; Tripathy, S.; Tan, R. J. N.

2010-11-01

Phosphor-free apple-white light emitting diodes have been fabricated using a dual stacked InGaN/GaN multiple quantum wells comprising of a lower set of long wavelength emitting indium-rich nanostructures incorporated in multiple quantum wells with an upper set of cyan-green emitting multiple quantum wells. The light-emitting diodes were grown on nano-epitaxially lateral overgrown GaN template formed by regrowth of GaN over SiO2 film patterned with an anodic aluminum oxide mask with holes of 125 nm diameter and a period of 250 nm. The growth of InGaN/GaN multiple quantum wells on these stress relaxed low defect density templates improves the internal quantum efficiency by 15% for the cyan-green multiple quantum wells. Higher emission intensity with redshift in the PL peak emission wavelength is obtained for the indium-rich nanostructures incorporated in multiple quantum wells. The quantum wells grown on the nano-epitaxially lateral overgrown GaN has a weaker piezoelectric field and hence shows a minimal peak shift with application of higher injection current. An enhancement of external quantum efficiency is achieved for the apple-white light emitting diodes grown on the nano-epitaxially lateral overgrown GaN template based on the light -output power measurement. The improvement in light extraction efficiency, ηextraction, was found to be 34% for the cyan-green emission peak and 15% from the broad long wavelength emission with optimized lattice period.

Efficient Multi-Dimensional Simulation of Quantum Confinement Effects in Advanced MOS Devices

NASA Technical Reports Server (NTRS)

Biegel, Bryan A.; Rafferty, Conor S.; Ancona, Mario G.; Yu, Zhi-Ping

2000-01-01

We investigate the density-gradient (DG) transport model for efficient multi-dimensional simulation of quantum confinement effects in advanced MOS devices. The formulation of the DG model is described as a quantum correction to the classical drift-diffusion model. Quantum confinement effects are shown to be significant in sub-100nm MOSFETs. In thin-oxide MOS capacitors, quantum effects may reduce gate capacitance by 25% or more. As a result, the inclusion or quantum effects in simulations dramatically improves the match between C-V simulations and measurements for oxide thickness down to 2 nm. Significant quantum corrections also occur in the I-V characteristics of short-channel (30 to 100 nm) n-MOSFETs, with current drive reduced by up to 70%. This effect is shown to result from reduced inversion charge due to quantum confinement of electrons in the channel. Also, subthreshold slope is degraded by 15 to 20 mV/decade with the inclusion of quantum effects via the density-gradient model, and short channel effects (in particular, drain-induced barrier lowering) are noticeably increased.

Density of Trap States and Auger-mediated Electron Trapping in CdTe Quantum-Dot Solids.

PubMed

Boehme, Simon C; Azpiroz, Jon Mikel; Aulin, Yaroslav V; Grozema, Ferdinand C; Vanmaekelbergh, Daniël; Siebbeles, Laurens D A; Infante, Ivan; Houtepen, Arjan J

2015-05-13

Charge trapping is an ubiquitous process in colloidal quantum-dot solids and a major limitation to the efficiency of quantum dot based devices such as solar cells, LEDs, and thermoelectrics. Although empirical approaches led to a reduction of trapping and thereby efficiency enhancements, the exact chemical nature of the trapping mechanism remains largely unidentified. In this study, we determine the density of trap states in CdTe quantum-dot solids both experimentally, using a combination of electrochemical control of the Fermi level with ultrafast transient absorption and time-resolved photoluminescence spectroscopy, and theoretically, via density functional theory calculations. We find a high density of very efficient electron traps centered ∼0.42 eV above the valence band. Electrochemical filling of these traps increases the electron lifetime and the photoluminescence quantum yield by more than an order of magnitude. The trapping rate constant for holes is an order of magnitude lower that for electrons. These observations can be explained by Auger-mediated electron trapping. From density functional theory calculations we infer that the traps are formed by dicoordinated Te atoms at the quantum dot surface. The combination of our unique experimental determination of the density of trap states with the theoretical modeling of the quantum dot surface allows us to identify the trapping mechanism and chemical reaction at play during charge trapping in these quantum dots.

Generation of Antibunched Light by Excited Molecules in a Microcavity Trap

NASA Technical Reports Server (NTRS)

DeMartini, F.; DiGiuseppe, G.; Marrocco, M.

1996-01-01

The active microcavity is adopted as an efficient source of non-classical light. By this device, excited by a mode-locked laser at a rate of 100 MHz, single-photons are generated over a single field mode with a nonclassical sub-poissonian distribution. The process of adiabatic recycling within a multi-step Franck-Condon molecular optical-pumping mechanism, characterized in our case by a quantum efficiency very close to one, implies a pump self-regularization process leading to a striking n-squeezing effect. By a replication of the basic single-atom excitation process a beam of quantum photon (Fock states) can be created. The new process represents a significant advance in the modern fields of basic quantum-mechanical investigation, quantum communication and quantum cryptography.

The Experimental Demonstration of High Efficiency Interaction-free Measurement for Quantum Counterfactual-like Communication.

PubMed

Liu, Chao; Liu, Jinhong; Zhang, Junxiang; Zhu, Shiyao

2017-09-07

We present an interaction-free measurement with quantum Zeno effect and a high efficiency η = 74.6% ± 0.15%. As a proof-of-principle demonstration, this measurement can be used to implement a quantum counterfactual-like communication protocol. Instead of a single photon state, we use a coherent light as the input source and show that the output agrees with the proposed quantum counterfactual communication protocol according to Salih et al. Although the counterfactuality is not achieved due to the presence of a few photons in the public channel, we show that the signal light is nearly absent in the public channel, which exhibits a proof-of-principle quantum counterfactual-like property of communication.

Ultrabroadband Two-Dimensional Coherent Optical Spectrometer for Directed Energy Trapping in Quantum Dynamical Systems

DTIC Science & Technology

2015-12-04

in the 2DFT spectrum. 9 Figure 8. Comparison of 2DFT spectra. Absolute-value 2DFT spectra of (a) IR-144 cyanine dye ( ) and (b) LH2 ...a subset of the Hadamard- encoded measurements [10% (819 spatial masks) for IR-144 and 35% (2867 spatial masks) for LH2 ]. Diagonal peaks arise from

Quantum cryptography to satellites for global secure key distribution

NASA Astrophysics Data System (ADS)

Rarity, John G.; Gorman, Philip M.; Knight, Paul; Wallace, Kotska; Tapster, Paul R.

2017-11-01

We have designed and built a free space secure key exchange system using weak laser pulses with polarisation modulation by acousto-optic switching. We have used this system to exchange keys over a 1.2km ground range with absolute security. Building from this initial result we analyse the feasibility of exchanging keys to a low earth orbit satellite.

Practical system for the generation of pulsed quantum frequency combs.

PubMed

Roztocki, Piotr; Kues, Michael; Reimer, Christian; Wetzel, Benjamin; Sciara, Stefania; Zhang, Yanbing; Cino, Alfonso; Little, Brent E; Chu, Sai T; Moss, David J; Morandotti, Roberto

2017-08-07

The on-chip generation of large and complex optical quantum states will enable low-cost and accessible advances for quantum technologies, such as secure communications and quantum computation. Integrated frequency combs are on-chip light sources with a broad spectrum of evenly-spaced frequency modes, commonly generated by four-wave mixing in optically-excited nonlinear micro-cavities, whose recent use for quantum state generation has provided a solution for scalable and multi-mode quantum light sources. Pulsed quantum frequency combs are of particular interest, since they allow the generation of single-frequency-mode photons, required for scaling state complexity towards, e.g., multi-photon states, and for quantum information applications. However, generation schemes for such pulsed combs have, to date, relied on micro-cavity excitation via lasers external to the sources, being neither versatile nor power-efficient, and impractical for scalable realizations of quantum technologies. Here, we introduce an actively-modulated, nested-cavity configuration that exploits the resonance pass-band characteristic of the micro-cavity to enable a mode-locked and energy-efficient excitation. We demonstrate that the scheme allows the generation of high-purity photons at large coincidence-to-accidental ratios (CAR). Furthermore, by increasing the repetition rate of the excitation field via harmonic mode-locking (i.e. driving the cavity modulation at harmonics of the fundamental repetition rate), we managed to increase the pair production rates (i.e. source efficiency), while maintaining a high CAR and photon purity. Our approach represents a significant step towards the realization of fully on-chip, stable, and versatile sources of pulsed quantum frequency combs, crucial for the development of accessible quantum technologies.

Neural-Network Quantum States, String-Bond States, and Chiral Topological States

NASA Astrophysics Data System (ADS)

Glasser, Ivan; Pancotti, Nicola; August, Moritz; Rodriguez, Ivan D.; Cirac, J. Ignacio

2018-01-01

Neural-network quantum states have recently been introduced as an Ansatz for describing the wave function of quantum many-body systems. We show that there are strong connections between neural-network quantum states in the form of restricted Boltzmann machines and some classes of tensor-network states in arbitrary dimensions. In particular, we demonstrate that short-range restricted Boltzmann machines are entangled plaquette states, while fully connected restricted Boltzmann machines are string-bond states with a nonlocal geometry and low bond dimension. These results shed light on the underlying architecture of restricted Boltzmann machines and their efficiency at representing many-body quantum states. String-bond states also provide a generic way of enhancing the power of neural-network quantum states and a natural generalization to systems with larger local Hilbert space. We compare the advantages and drawbacks of these different classes of states and present a method to combine them together. This allows us to benefit from both the entanglement structure of tensor networks and the efficiency of neural-network quantum states into a single Ansatz capable of targeting the wave function of strongly correlated systems. While it remains a challenge to describe states with chiral topological order using traditional tensor networks, we show that, because of their nonlocal geometry, neural-network quantum states and their string-bond-state extension can describe a lattice fractional quantum Hall state exactly. In addition, we provide numerical evidence that neural-network quantum states can approximate a chiral spin liquid with better accuracy than entangled plaquette states and local string-bond states. Our results demonstrate the efficiency of neural networks to describe complex quantum wave functions and pave the way towards the use of string-bond states as a tool in more traditional machine-learning applications.

Efficient single photon detection by quantum dot resonant tunneling diodes.

PubMed

Blakesley, J C; See, P; Shields, A J; Kardynał, B E; Atkinson, P; Farrer, I; Ritchie, D A

2005-02-18

We demonstrate that the resonant tunnel current through a double-barrier structure is sensitive to the capture of single photoexcited holes by an adjacent layer of quantum dots. This phenomenon could allow the detection of single photons with low dark count rates and high quantum efficiencies. The magnitude of the sensing current may be controlled via the thickness of the tunnel barriers. Larger currents give improved signal to noise and allow sub-mus photon time resolution.

Improved tests of extra-dimensional physics and thermal quantum field theory from new Casimir force measurements

NASA Astrophysics Data System (ADS)

Decca, R. S.; Fischbach, E.; Klimchitskaya, G. L.; Krause, D. E.; López, D.; Mostepanenko, V. M.

2003-12-01

We report new constraints on extra-dimensional models and other physics beyond the standard model based on measurements of the Casimir force between two dissimilar metals for separations in the range 0.2 1.2 μm. The Casimir force between a Au-coated sphere and a Cu-coated plate of a microelectromechanical torsional oscillator was measured statically with an absolute error of 0.3 pN. In addition, the Casimir pressure between two parallel plates was determined dynamically with an absolute error of ≈0.6 mPa. Within the limits of experimental and theoretical errors, the results are in agreement with a theory that takes into account the finite conductivity and roughness of the two metals. The level of agreement between experiment and theory was then used to set limits on the predictions of extra-dimensional physics and thermal quantum field theory. It is shown that two theoretical approaches to the thermal Casimir force which predict effects linear in temperature are ruled out by these experiments. Finally, constraints on Yukawa corrections to Newton’s law of gravity are strengthened by more than an order of magnitude in the range 56 330 nm.

Thermal Entanglement in XXZ Heisenberg Model for Coupled Spin-Half and Spin-One Triangular Cell

NASA Astrophysics Data System (ADS)

Najarbashi, Ghader; Balazadeh, Leila; Tavana, Ali

2018-01-01

In this paper, we investigate the thermal entanglement of two-spin subsystems in an ensemble of coupled spin-half and spin-one triangular cells, (1/2, 1/2, 1/2), (1/2, 1, 1/2), (1, 1/2, 1) and (1, 1, 1) with the XXZ anisotropic Heisenberg model subjected to an external homogeneous magnetic field. We adopt the generalized concurrence as the measure of entanglement which is a good indicator of the thermal entanglement and the critical points in the mixed higher dimensional spin systems. We observe that in the near vicinity of the absolute zero, the concurrence measure is symmetric with respect to zero magnetic field and changes abruptly from a non-null to null value for a critical magnetic field that can be signature of a quantum phase transition at finite temperature. The analysis of concurrence versus temperature shows that there exists a critical temperature, that depends on the type of the interaction, i.e. ferromagnetic or antiferromagnetic, the anisotropy parameter and the strength of the magnetic field. Results show that the pairwise thermal entanglement depends on the third spin which affects the maximum value of the concurrence at absolute zero and at quantum critical points.

Cohesive energy and structural parameters of binary oxides of groups IIA and IIIB from diffusion quantum Monte Carlo

DOE PAGES

Santana, Juan A.; Krogel, Jaron T.; Kent, Paul R. C.; ...

2016-05-03

We have applied the diffusion quantum Monte Carlo (DMC) method to calculate the cohesive energy and the structural parameters of the binary oxides CaO, SrO, BaO, Sc 2O 3, Y 2O 3 and La 2O 3. The aim of our calculations is to systematically quantify the accuracy of the DMC method to study this type of metal oxides. The DMC results were compared with local and semi-local Density Functional Theory (DFT) approximations as well as with experimental measurements. The DMC method yields cohesive energies for these oxides with a mean absolute deviation from experimental measurements of 0.18(2) eV, while withmore » local and semi-local DFT approximations the deviation is 3.06 and 0.94 eV, respectively. For lattice constants, the mean absolute deviation in DMC, local and semi-local DFT approximations, are 0.017(1), 0.07 and 0.05 , respectively. In conclusion, DMC is highly accurate method, outperforming the local and semi-local DFT approximations in describing the cohesive energies and structural parameters of these binary oxides.« less

Spectral purity and tunability of terahertz quantum cascade laser sources based on intracavity difference-frequency generation

PubMed Central

Consolino, Luigi; Jung, Seungyong; Campa, Annamaria; De Regis, Michele; Pal, Shovon; Kim, Jae Hyun; Fujita, Kazuue; Ito, Akio; Hitaka, Masahiro; Bartalini, Saverio; De Natale, Paolo; Belkin, Mikhail A.; Vitiello, Miriam Serena

2017-01-01

Terahertz sources based on intracavity difference-frequency generation in mid-infrared quantum cascade lasers (THz DFG-QCLs) have recently emerged as the first monolithic electrically pumped semiconductor sources capable of operating at room temperature across the 1- to 6-THz range. Despite tremendous progress in power output, which now exceeds 1 mW in pulsed and 10 μW in continuous-wave regimes at room temperature, knowledge of the major figure of merits of these devices for high-precision spectroscopy, such as spectral purity and absolute frequency tunability, is still lacking. By exploiting a metrological grade system comprising a terahertz frequency comb synthesizer, we measure, for the first time, the free-running emission linewidth (LW), the tuning characteristics, and the absolute center frequency of individual emission lines of these sources with an uncertainty of 4 × 10−10. The unveiled emission LW (400 kHz at 1-ms integration time) indicates that DFG-QCLs are well suited to operate as local oscillators and to be used for a variety of metrological, spectroscopic, communication, and imaging applications that require narrow-LW THz sources. PMID:28879235

Coupling of individual quantum emitters to channel plasmons.

PubMed

Bermúdez-Ureña, Esteban; Gonzalez-Ballestero, Carlos; Geiselmann, Michael; Marty, Renaud; Radko, Ilya P; Holmgaard, Tobias; Alaverdyan, Yury; Moreno, Esteban; García-Vidal, Francisco J; Bozhevolnyi, Sergey I; Quidant, Romain

2015-08-07

Efficient light-matter interaction lies at the heart of many emerging technologies that seek on-chip integration of solid-state photonic systems. Plasmonic waveguides, which guide the radiation in the form of strongly confined surface plasmon-polariton modes, represent a promising solution to manipulate single photons in coplanar architectures with unprecedented small footprints. Here we demonstrate coupling of the emission from a single quantum emitter to the channel plasmon polaritons supported by a V-groove plasmonic waveguide. Extensive theoretical simulations enable us to determine the position and orientation of the quantum emitter for optimum coupling. Concomitantly with these predictions, we demonstrate experimentally that 42% of a single nitrogen-vacancy centre emission efficiently couples into the supported modes of the V-groove. This work paves the way towards practical realization of efficient and long distance transfer of energy for integrated solid-state quantum systems.

Organic Light Emitting Devices and Materials Integrated with Active Matrix Backplanes for Flexible Displays

DTIC Science & Technology

2006-11-01

fabricated. Of the molecules, the fac- Ir(dfppy)(dfppz)2 compound had the blue-est emission with the highest quantum efficiency . Phosphorescent...phosphorescent lifetimes, high quantum efficiencies and good stability. The emission color can be readily tuned from blue/green to red by judicious... electroluminescent efficiency as a function of current density plotted against the luminance. Fig. 3 Illustration of an

Silicon Photonics: Challenges and Future

DTIC Science & Technology

2007-01-01

process or phonon assisted. It directly impacts the internal quantum efficiency through the relationship : ηi = (1+ (τrad/τ non-rad ))-1 There are...linear cavity approach, the reported differential quantum efficiency is currently low. The measured characteristic temperature (To), is lower than...rule changes • package design 4.1.2 Inter-chip interconnects There is a requirement on the circuit card to transfer data more efficiently between

Reduction of CO2 to C1 products and fuel

USGS Publications Warehouse

Mill, T.; Ross, D.

2002-01-01

Photochemical semiconductor processes readily reduced CO2 to a broad range of C1 products. However the intrinsic and solar efficiencies for the processes were low. Improved quantum efficiencies could be realized utilizing quantum-sized particles, but at the expense of using less of the visible solar spectrum. Conversely, semiconductors with small bandgaps used more of the visible solar spectrum at the expense of quantum efficiency. Thermal reduction of CO2 with Fe(II) was thermodynamically favored for forming many kinds of organic compounds and occurred readily with olivine and other Fe(II) minerals above 200??C to form higher alkanes and alkenes. No added hydrogen was required.

Environment-assisted Quantum Critical Effect for Excitation Energy Transfer in a LH2-type Trimer

NASA Astrophysics Data System (ADS)

Xu, Lan; Xu, Bo

2015-10-01

In this article, we are investigating excitation energy transfer (EET) in a basic unit cell of light-harvesting complex II (LH2), named a LH2-type trimer. Calculation of energy transfer efficiency (ETE) in the framework of non-Markovian environment is also implemented. With these achievements, we theoretically predict the environment-assisted quantum critical effect, where ETE exhibits a sudden change at the critical point of quantum phase transition (QPT) for the LH2-type trimer. It is found that highly efficient EET with nearly unit efficiency may occur in the vicinity of the critical point of QPT.

High-efficiency reconciliation for continuous variable quantum key distribution

NASA Astrophysics Data System (ADS)

Bai, Zengliang; Yang, Shenshen; Li, Yongmin

2017-04-01

Quantum key distribution (QKD) is the most mature application of quantum information technology. Information reconciliation is a crucial step in QKD and significantly affects the final secret key rates shared between two legitimate parties. We analyze and compare various construction methods of low-density parity-check (LDPC) codes and design high-performance irregular LDPC codes with a block length of 106. Starting from these good codes and exploiting the slice reconciliation technique based on multilevel coding and multistage decoding, we realize high-efficiency Gaussian key reconciliation with efficiency higher than 95% for signal-to-noise ratios above 1. Our demonstrated method can be readily applied in continuous variable QKD.

The DUV Stability of Superlattice-Doped CMOS Detector Arrays

NASA Technical Reports Server (NTRS)

Hoenk, M. E.; Carver, A. G.; Jones, T.; Dickie, M.; Cheng, P.; Greer, H. F.; Nikzad, S.; Sgro, J.; Tsur, S.

2013-01-01

JPL and Alacron have recently developed a high performance, DUV camera with a superlattice doped CMOS imaging detector. Supperlattice doped detectors achieve nearly 100% internal quantum efficiency in the deep and far ultraviolet, and a single layer, Al2O3 antireflection coating enables 64% external quantum efficiency at 263nm. In lifetime tests performed at Applied Materials using 263 nm pulsed, solid state and 193 nm pulsed excimer laser, the quantum efficiency and dark current of the JPL/Alacron camera remained stable to better than 1% precision during long-term exposure to several billion laser pulses, with no measurable degradation, no blooming and no image memory at 1000 fps.

General method for extracting the quantum efficiency of dispersive qubit readout in circuit QED

NASA Astrophysics Data System (ADS)

Bultink, C. C.; Tarasinski, B.; Haandbæk, N.; Poletto, S.; Haider, N.; Michalak, D. J.; Bruno, A.; DiCarlo, L.

2018-02-01

We present and demonstrate a general three-step method for extracting the quantum efficiency of dispersive qubit readout in circuit QED. We use active depletion of post-measurement photons and optimal integration weight functions on two quadratures to maximize the signal-to-noise ratio of the non-steady-state homodyne measurement. We derive analytically and demonstrate experimentally that the method robustly extracts the quantum efficiency for arbitrary readout conditions in the linear regime. We use the proven method to optimally bias a Josephson traveling-wave parametric amplifier and to quantify different noise contributions in the readout amplification chain.

Radiation and quantum chemical studies of chalcone derivatives.

PubMed

Gaikwad, P; Priyadarsini, K I; Naumov, S; Rao, B S M

2010-08-05

The reactions of oxidizing radicals ((*)OH, Br(2)(*-), and SO(4)(*-)) with -OH-, -CH(3)-, or -NH(2)-substituted indole chalcones and hydroxy benzenoid chalcones were studied by radiation and quantum chemical methods. The (*)OH radical was found to react by addition at diffusion-controlled rates (k = 1.1-1.7 x 10(10) dm(3) mol(-1) s(-1)), but Br(2)(*-) radical reacted by 2 orders of magnitude lower. Quantum chemical calculations at the B3LYP/6-31+G(d,p) level of theory have shown that the (C2-OH)(*), (C11-OH)(*), and (C10-OH)(*) adducts of the indole chalcones and the (C7-OH)(*) and (C8-OH)(*) adducts of the hydroxy benzenoid chalcones are more stable with DeltaH = -39 to -28 kcal mol(-1) and DeltaG = -32 to -19 kcal mol(-1). This suggests that (*)OH addition to the alpha,beta-unsaturated bond is a major reaction channel in both types of chalcones and is barrierless. The stability and lack of dehydration of the (*)OH adducts arise from two factors: strong frontier orbital interaction due to the low energy gap between interacting orbitals and the negligible Coulombic repulsion due to small absolute values of Mulliken charges. The transient absorption spectrum measured in the (*)OH radical reaction with all the indole chalcone derivatives exhibited a maximum at 390 nm, which is in excellent agreement with the computed value (394 nm). The formation of three phenolic products under steady-state radiolysis is in line with the three stable (*)OH adducts predicted by theory. Independent of the substituent, identical spectra (lambda(max) = 330-360 and approximately 580 nm) were obtained on one-electron oxidation of the three indole chalcones. MO calculations predict the deprotonation from the -NH group is more efficient than from the substituent due to the larger electron density on the N1 atom forming the chalcone indolyl radical. Its reduction potential was determined to be 0.56 V from the ABTS(*-)/ABTS(2-) couple. In benzenoid chalcones, the (*)OH adduct spectrum is characterized by a peak at 270 nm and a broad maximum centered in the range 430-450 nm with an intense bleaching at 340 nm. The spectrum formed by electron transfer in these derivatives with lambda(max) = 280 and 380 nm (epsilon(280) = 5000 dm(3) mol(-1) cm(-1) and epsilon(380) = 700 dm(3) mol(-1) cm(-1)) was assigned to its phenoxyl radical. Our pulse radiolysis experiments in combination with quantum chemical calculations demonstrate that chalcones are efficient scavengers of damaging oxyl radicals.

Robust Timing Synchronization for Aviation Communications, and Efficient Modulation and Coding Study for Quantum Communication

NASA Technical Reports Server (NTRS)

Xiong, Fugin

2003-01-01

One half of Professor Xiong's effort will investigate robust timing synchronization schemes for dynamically varying characteristics of aviation communication channels. The other half of his time will focus on efficient modulation and coding study for the emerging quantum communications.

Photon-number-resolving SSPDs with system detection efficiency over 50% at telecom range

NASA Astrophysics Data System (ADS)

Zolotov, P.; Divochiy, A.; Vakhtomin, Yu.; Moshkova, M.; Morozov, P.; Seleznev, V.; Smirnov, K.

2018-02-01

We used technology of making high-efficiency superconducting single-photon detectors as a basis for improvement of photon-number-resolving devices. By adding optical cavity and using an improved NbN superconducting film, we enhanced previously reported system detection efficiency at telecom range for such detectors. Our results show that implementation of optical cavity helps to develop four-section device with quantum efficiency over 50% at 1.55 µm. Performed experimental studies of detecting multi-photon optical pulses showed irregularities over defining multi-photon through single-photon quantum efficiency.

Inverse Temperature Dependence of Nuclear Quantum Effects in DNA Base Pairs

PubMed Central

2016-01-01

Despite the inherently quantum mechanical nature of hydrogen bonding, it is unclear how nuclear quantum effects (NQEs) alter the strengths of hydrogen bonds. With this in mind, we use ab initio path integral molecular dynamics to determine the absolute contribution of NQEs to the binding in DNA base pair complexes, arguably the most important hydrogen-bonded systems of all. We find that depending on the temperature, NQEs can either strengthen or weaken the binding within the hydrogen-bonded complexes. As a somewhat counterintuitive consequence, NQEs can have a smaller impact on hydrogen bond strengths at cryogenic temperatures than at room temperature. We rationalize this in terms of a competition of NQEs between low-frequency and high-frequency vibrational modes. Extending this idea, we also propose a simple model to predict the temperature dependence of NQEs on hydrogen bond strengths in general. PMID:27195654

Ferromagnetic quantum critical point in the heavy-fermion metal YbNi4(P(1-x)As(x))2.

PubMed

Steppke, Alexander; Küchler, Robert; Lausberg, Stefan; Lengyel, Edit; Steinke, Lucia; Borth, Robert; Lühmann, Thomas; Krellner, Cornelius; Nicklas, Michael; Geibel, Christoph; Steglich, Frank; Brando, Manuel

2013-02-22

Unconventional superconductivity and other previously unknown phases of matter exist in the vicinity of a quantum critical point (QCP): a continuous phase change of matter at absolute zero. Intensive theoretical and experimental investigations on itinerant systems have shown that metallic ferromagnets tend to develop via either a first-order phase transition or through the formation of intermediate superconducting or inhomogeneous magnetic phases. Here, through precision low-temperature measurements, we show that the Grüneisen ratio of the heavy fermion metallic ferromagnet YbNi(4)(P(0.92)As(0.08))(2) diverges upon cooling to T = 0, indicating a ferromagnetic QCP. Our observation that this kind of instability, which is forbidden in d-electron metals, occurs in a heavy fermion system will have a large impact on the studies of quantum critical materials.

Single quantum dot tracking reveals the impact of nanoparticle surface on intracellular state.

PubMed

Zahid, Mohammad U; Ma, Liang; Lim, Sung Jun; Smith, Andrew M

2018-05-08

Inefficient delivery of macromolecules and nanoparticles to intracellular targets is a major bottleneck in drug delivery, genetic engineering, and molecular imaging. Here we apply live-cell single-quantum-dot imaging and tracking to analyze and classify nanoparticle states after intracellular delivery. By merging trajectory diffusion parameters with brightness measurements, multidimensional analysis reveals distinct and heterogeneous populations that are indistinguishable using single parameters alone. We derive new quantitative metrics of particle loading, cluster distribution, and vesicular release in single cells, and evaluate intracellular nanoparticles with diverse surfaces following osmotic delivery. Surface properties have a major impact on cell uptake, but little impact on the absolute cytoplasmic numbers. A key outcome is that stable zwitterionic surfaces yield uniform cytosolic behavior, ideal for imaging agents. We anticipate that this combination of quantum dots and single-particle tracking can be widely applied to design and optimize next-generation imaging probes, nanoparticle therapeutics, and biologics.

Computationally Aided Absolute Stereochemical Determination of Enantioenriched Amines.

PubMed

Zhang, Jun; Gholami, Hadi; Ding, Xinliang; Chun, Minji; Vasileiou, Chrysoula; Nehira, Tatsuo; Borhan, Babak

2017-03-17

A simple and efficient protocol for sensing the absolute stereochemistry and enantiomeric excess of chiral monoamines is reported. Preparation of the sample requires a single-step reaction of the 1,1'-(bromomethylene)dinaphthalene (BDN) with the chiral amine. Analysis of the exciton coupled circular dichroism generated from the BDN-derivatized chiral amine sample, along with comparison to conformational analysis performed computationally, yields the absolute stereochemistry of the parent chiral monoamine.

Efficient energy transfer in light-harvesting systems: Quantum-classical comparison, flux network, and robustness analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu Jianlan; Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, Massachusetts 02139; Liu Fan

2012-11-07

Following the calculation of optimal energy transfer in thermal environment in our first paper [J. L. Wu, F. Liu, Y. Shen, J. S. Cao, and R. J. Silbey, New J. Phys. 12, 105012 (2010)], full quantum dynamics and leading-order 'classical' hopping kinetics are compared in the seven-site Fenna-Matthews-Olson (FMO) protein complex. The difference between these two dynamic descriptions is due to higher-order quantum corrections. Two thermal bath models, classical white noise (the Haken-Strobl-Reineker (HSR) model) and quantum Debye model, are considered. In the seven-site FMO model, we observe that higher-order corrections lead to negligible changes in the trapping time ormore » in energy transfer efficiency around the optimal and physiological conditions (2% in the HSR model and 0.1% in the quantum Debye model for the initial site at BChl 1). However, using the concept of integrated flux, we can identify significant differences in branching probabilities of the energy transfer network between hopping kinetics and quantum dynamics (26% in the HSR model and 32% in the quantum Debye model for the initial site at BChl 1). This observation indicates that the quantum coherence can significantly change the distribution of energy transfer pathways in the flux network with the efficiency nearly the same. The quantum-classical comparison of the average trapping time with the removal of the bottleneck site, BChl 4, demonstrates the robustness of the efficient energy transfer by the mechanism of multi-site quantum coherence. To reconcile with the latest eight-site FMO model which is also investigated in the third paper [J. Moix, J. L. Wu, P. F. Huo, D. F. Coker, and J. S. Cao, J. Phys. Chem. Lett. 2, 3045 (2011)], the quantum-classical comparison with the flux network analysis is summarized in Appendix C. The eight-site FMO model yields similar trapping time and network structure as the seven-site FMO model but leads to a more disperse distribution of energy transfer pathways.« less

Quantum diffusion of H/D on Ni(111)—A partially adiabatic centroid MD study

NASA Astrophysics Data System (ADS)

Hopkinson, A. R.; Probert, M. I. J.

2018-03-01

We present the results of a theoretical study of H/D diffusion on a Ni(111) surface at a range of temperatures, from 250 K to 75 K. The diffusion is studied using both classical molecular dynamics and the partially adiabatic centroid molecular dynamics method. The calculations are performed with the hydrogen (or deuterium) moving in 3D across a static nickel surface using a novel Fourier interpolated potential energy surface which has been parameterized to density functional theory calculations. The results of the classical simulations are that the calculated diffusion coefficients are far too small and with too large a variation with temperature compared with experiment. By contrast, the quantum simulations are in much better agreement with experiment and show that quantum effects in the diffusion of hydrogen are significant at all temperatures studied. There is also a crossover to a quantum-dominated diffusive regime for temperatures below ˜150 K for hydrogen and ˜85 K for deuterium. The quantum diffusion coefficients are found to accurately reproduce the spread in values with temperature, but with an absolute value that is a little high compared with experiment.

Combined-probability space and certainty or uncertainty relations for a finite-level quantum system

NASA Astrophysics Data System (ADS)

Sehrawat, Arun

2017-08-01

The Born rule provides a probability vector (distribution) with a quantum state for a measurement setting. For two settings, we have a pair of vectors from the same quantum state. Each pair forms a combined-probability vector that obeys certain quantum constraints, which are triangle inequalities in our case. Such a restricted set of combined vectors, called the combined-probability space, is presented here for a d -level quantum system (qudit). The combined space is a compact convex subset of a Euclidean space, and all its extreme points come from a family of parametric curves. Considering a suitable concave function on the combined space to estimate the uncertainty, we deliver an uncertainty relation by finding its global minimum on the curves for a qudit. If one chooses an appropriate concave (or convex) function, then there is no need to search for the absolute minimum (maximum) over the whole space; it will be on the parametric curves. So these curves are quite useful for establishing an uncertainty (or a certainty) relation for a general pair of settings. We also demonstrate that many known tight certainty or uncertainty relations for a qubit can be obtained with the triangle inequalities.

Trade-off between bandwidth and efficiency in semipolar (20 2 ¯ 1 ¯) InGaN/GaN single- and multiple-quantum-well light-emitting diodes

NASA Astrophysics Data System (ADS)

Monavarian, M.; Rashidi, A.; Aragon, A. A.; Nami, M.; Oh, S. H.; DenBaars, S. P.; Feezell, D.

2018-05-01

InGaN/GaN light-emitting diodes (LEDs) with large modulation bandwidths are desirable for visible-light communication. Along with modulation speed, the consideration of the internal quantum efficiency (IQE) under operating conditions is also important. Here, we report the modulation characteristics of semipolar (20 2 ¯ 1 ¯ ) InGaN/GaN (LEDs) with single-quantum well (SQW) and multiple-quantum-well (MQW) active regions grown on free-standing semipolar GaN substrates with peak internal quantum efficiencies (IQEs) of 0.93 and 0.73, respectively. The MQW LEDs exhibit on average about 40-80% higher modulation bandwidth, reaching 1.5 GHz at 13 kA/cm2, but about 27% lower peak IQE than the SQW LEDs. We extract the differential carrier lifetimes (DLTs), RC parasitics, and carrier escape lifetimes and discuss their role in the bandwidth and IQE characteristics. A coulomb-enhanced capture process is shown to rapidly reduce the DLT of the MQW LED at high current densities. Auger recombination is also shown to play little role in increasing the speed of the LEDs. Finally, we investigate the trade-offs between the bandwidth and efficiency and introduce the bandwidth-IQE product as a potential figure of merit for optimizing speed and efficiency in InGaN/GaN LEDs.

Splitting efficiency and interference effects in a Cooper pair splitter based on a triple quantum dot with ferromagnetic contacts

NASA Astrophysics Data System (ADS)

Bocian, Kacper; Rudziński, Wojciech; Weymann, Ireneusz

2018-05-01

We theoretically study the spin-resolved subgap transport properties of a Cooper pair splitter based on a triple quantum dot attached to superconducting and ferromagnetic leads. Using the Keldysh Green's function formalism, we analyze the dependence of the Andreev conductance, Cooper pair splitting efficiency, and tunnel magnetoresistance on the gate and bias voltages applied to the system. We show that the system's transport properties are strongly affected by spin dependence of tunneling processes and quantum interference between different local and nonlocal Andreev reflections. We also study the effects of finite hopping between the side quantum dots on the Andreev current. This allows for identifying the optimal conditions for enhancing the Cooper pair splitting efficiency of the device. We find that the splitting efficiency exhibits a nonmonotonic dependence on the degree of spin polarization of the leads and the magnitude and type of hopping between the dots. An almost perfect splitting efficiency is predicted in the nonlinear response regime when the energies of the side quantum dots are tuned to the energies of the corresponding Andreev bound states. In addition, we analyzed features of the tunnel magnetoresistance (TMR) for a wide range of the gate and bias voltages, as well as for different model parameters, finding the corresponding sign changes of the TMR in certain transport regimes. The mechanisms leading to these effects are thoroughly discussed.

The ABC model of recombination reinterpreted: Impact on understanding carrier transport and efficiency droop in InGaN/GaN light emitting diodes

NASA Astrophysics Data System (ADS)

Hopkins, M. A.; Allsopp, D. W. E.; Kappers, M. J.; Oliver, R. A.; Humphreys, C. J.

2017-12-01

The efficiency of light emitting diodes (LEDs) remains a topic of great contemporary interest due to their potential to reduce the amount of energy consumed in lighting. The current consensus is that electrons and holes distribute themselves through the emissive region by a drift-diffusion process which results in a highly non-uniform distribution of the light emission and can reduce efficiency. In this paper, the measured variations in the external quantum efficiency of a range of InGaN/GaN LEDs with different numbers of quantum wells (QWs) are shown to compare closely with the predictions of a revised ABC model, in which it is assumed that the electrically injected electrons and holes are uniformly distributed through the multi-quantum well (MQW) region, or nearly so, and hence carrier recombination occurs equally in all the quantum wells. The implications of the reported results are that drift-diffusion plays a far lesser role in cross-well carrier transport than previously thought; that the dominant cause of efficiency droop is intrinsic to the quantum wells and that reductions in the density of non-radiative recombination centers in the MQW would enable the use of more QWs and thereby reduce Auger losses by spreading carriers more evenly across a wider emissive region.

Simple Atomic Quantum Memory Suitable for Semiconductor Quantum Dot Single Photons

NASA Astrophysics Data System (ADS)

Wolters, Janik; Buser, Gianni; Horsley, Andrew; Béguin, Lucas; Jöckel, Andreas; Jahn, Jan-Philipp; Warburton, Richard J.; Treutlein, Philipp

2017-08-01

Quantum memories matched to single photon sources will form an important cornerstone of future quantum network technology. We demonstrate such a memory in warm Rb vapor with on-demand storage and retrieval, based on electromagnetically induced transparency. With an acceptance bandwidth of δ f =0.66 GHz , the memory is suitable for single photons emitted by semiconductor quantum dots. In this regime, vapor cell memories offer an excellent compromise between storage efficiency, storage time, noise level, and experimental complexity, and atomic collisions have negligible influence on the optical coherences. Operation of the memory is demonstrated using attenuated laser pulses on the single photon level. For a 50 ns storage time, we measure ηe2 e 50 ns=3.4 (3 )% end-to-end efficiency of the fiber-coupled memory, with a total intrinsic efficiency ηint=17 (3 )%. Straightforward technological improvements can boost the end-to-end-efficiency to ηe 2 e≈35 %; beyond that, increasing the optical depth and exploiting the Zeeman substructure of the atoms will allow such a memory to approach near unity efficiency. In the present memory, the unconditional read-out noise level of 9 ×10-3 photons is dominated by atomic fluorescence, and for input pulses containing on average μ1=0.27 (4 ) photons, the signal to noise level would be unity.

Simple Atomic Quantum Memory Suitable for Semiconductor Quantum Dot Single Photons.

PubMed

Wolters, Janik; Buser, Gianni; Horsley, Andrew; Béguin, Lucas; Jöckel, Andreas; Jahn, Jan-Philipp; Warburton, Richard J; Treutlein, Philipp

2017-08-11

Quantum memories matched to single photon sources will form an important cornerstone of future quantum network technology. We demonstrate such a memory in warm Rb vapor with on-demand storage and retrieval, based on electromagnetically induced transparency. With an acceptance bandwidth of δf=0.66  GHz, the memory is suitable for single photons emitted by semiconductor quantum dots. In this regime, vapor cell memories offer an excellent compromise between storage efficiency, storage time, noise level, and experimental complexity, and atomic collisions have negligible influence on the optical coherences. Operation of the memory is demonstrated using attenuated laser pulses on the single photon level. For a 50 ns storage time, we measure η_{e2e}^{50  ns}=3.4(3)% end-to-end efficiency of the fiber-coupled memory, with a total intrinsic efficiency η_{int}=17(3)%. Straightforward technological improvements can boost the end-to-end-efficiency to η_{e2e}≈35%; beyond that, increasing the optical depth and exploiting the Zeeman substructure of the atoms will allow such a memory to approach near unity efficiency. In the present memory, the unconditional read-out noise level of 9×10^{-3} photons is dominated by atomic fluorescence, and for input pulses containing on average μ_{1}=0.27(4) photons, the signal to noise level would be unity.

Efficient Multi-Dimensional Simulation of Quantum Confinement Effects in Advanced MOS Devices

NASA Technical Reports Server (NTRS)

Biegel, Bryan A.; Ancona, Mario G.; Rafferty, Conor S.; Yu, Zhiping

2000-01-01

We investigate the density-gradient (DG) transport model for efficient multi-dimensional simulation of quantum confinement effects in advanced MOS devices. The formulation of the DG model is described as a quantum correction ot the classical drift-diffusion model. Quantum confinement effects are shown to be significant in sub-100nm MOSFETs. In thin-oxide MOS capacitors, quantum effects may reduce gate capacitance by 25% or more. As a result, the inclusion of quantum effects may reduce gate capacitance by 25% or more. As a result, the inclusion of quantum effects in simulations dramatically improves the match between C-V simulations and measurements for oxide thickness down to 2 nm. Significant quantum corrections also occur in the I-V characteristics of short-channel (30 to 100 nm) n-MOSFETs, with current drive reduced by up to 70%. This effect is shown to result from reduced inversion charge due to quantum confinement of electrons in the channel. Also, subthreshold slope is degraded by 15 to 20 mV/decade with the inclusion of quantum effects via the density-gradient model, and short channel effects (in particular, drain-induced barrier lowering) are noticeably increased.

Optoelectronic engineering of colloidal quantum-dot solar cells beyond the efficiency black hole: a modeling approach

NASA Astrophysics Data System (ADS)

Mahpeykar, Seyed Milad; Wang, Xihua

2017-02-01

Colloidal quantum dot (CQD) solar cells have been under the spotlight in recent years mainly due to their potential for low-cost solution-processed fabrication and efficient light harvesting through multiple exciton generation (MEG) and tunable absorption spectrum via the quantum size effect. Despite the impressive advances achieved in charge carrier mobility of quantum dot solids and the cells' light trapping capabilities, the recent progress in CQD solar cell efficiencies has been slow, leaving them behind other competing solar cell technologies. In this work, using comprehensive optoelectronic modeling and simulation, we demonstrate the presence of a strong efficiency loss mechanism, here called the "efficiency black hole", that can significantly hold back the improvements achieved by any efficiency enhancement strategy. We prove that this efficiency black hole is the result of sole focus on enhancement of either light absorption or charge extraction capabilities of CQD solar cells. This means that for a given thickness of CQD layer, improvements accomplished exclusively in optic or electronic aspect of CQD solar cells do not necessarily translate into tangible enhancement in their efficiency. The results suggest that in order for CQD solar cells to come out of the mentioned black hole, incorporation of an effective light trapping strategy and a high quality CQD film at the same time is an essential necessity. Using the developed optoelectronic model, the requirements for this incorporation approach and the expected efficiencies after its implementation are predicted as a roadmap for CQD solar cell research community.

Demonstration of essentiality of entanglement in a Deutsch-like quantum algorithm

NASA Astrophysics Data System (ADS)

Huang, He-Liang; Goswami, Ashutosh K.; Bao, Wan-Su; Panigrahi, Prasanta K.

2018-06-01

Quantum algorithms can be used to efficiently solve certain classically intractable problems by exploiting quantum parallelism. However, the effectiveness of quantum entanglement in quantum computing remains a question of debate. This study presents a new quantum algorithm that shows entanglement could provide advantages over both classical algorithms and quantum algo- rithms without entanglement. Experiments are implemented to demonstrate the proposed algorithm using superconducting qubits. Results show the viability of the algorithm and suggest that entanglement is essential in obtaining quantum speedup for certain problems in quantum computing. The study provides reliable and clear guidance for developing useful quantum algorithms.

Is Efficiency Enough? Towards a New Framework for Carbon Savingsin the California Residential Sector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moezzi, Mithra; Diamond, Rick

2005-10-01

The overall implementation of energy efficiency in the United States is not adequately aligned with the environmental benefits claimed for efficiency, because it does not consider absolute levels of energy use, pollutant emissions, or consumption. In some ways, promoting energy efficiency may even encourage consumption. A more effective basis for environmental policy could be achieved by recognizing the degree and nature of the synchronization between environmental objectives and efficiency. This research seeks to motivate and initiate exploration of alternative ways of defining efficiency or otherwise moderating energy use toward reaching environmental objectives, as applicable to residential electricity use in California.more » The report offers three main recommendations: (1) produce definitions of efficiency that better integrate absolute consumption, (2) attend to the deeper social messages of energy efficiency communications, and (3) develop a more critical perspective on benefits and limitations of energy efficiency for delivering environmental benefits. In keeping with the exploratory nature of this project, the report also identifies ten questions for further investigation.« less

Enhanced photocatalytic H2-production activity of graphene-modified titania nanosheets

NASA Astrophysics Data System (ADS)

Xiang, Quanjun; Yu, Jiaguo; Jaroniec, Mietek

2011-09-01

Graphene-modified TiO2 nanosheets with exposed (001) facets (graphene/TiO2) were prepared by microwave-hydrothermal treatment of graphene oxide (GO) and hydrothermally synthesized TiO2 nanosheets with exposed (001) facets in an ethanol-water solvent. These nanocomposite samples showed high photocatalytic H2-production activity in aqueous solutions containing methanol, as sacrificial reagent, even without Pt co-catalyst. The optimal graphene content was found to be ~1.0 wt%, giving a H2-production rate of 736 μmol h-1 g-1 with a quantum efficiency (QE) of 3.1%, which exceeded the rate observed on pure TiO2 nanosheets by more than 41 times. This high photocatalytic H2-production activity is due to the deposition of TiO2 nanosheets on graphene sheets, which act as an electron acceptor to efficiently separate the photogenerated charge carriers. The observed enhancement in the photocatalytic activity is due to the lower absolute potential of graphene/graphene z.rad- (-0.08 V vs. SHE, pH = 0) in comparison to the conduction band (-0.24 V) of anatase TiO2, meanwhile the aforementioned absolute value is higher than the reduction potential of H+ (0 V), which favors the electron transfer from the conduction band (CB) of TiO2 to graphene sheets and the reduction of H+, thus enhancing photocatalytic H2-production activity. The proposed mechanism for the observed photocatalytic performance of TiO2 nanosheets, modified with a small amount of graphene, was further confirmed by photoluminescence spectroscopy and transient photocurrent response. This work not only shows a possibility for the utilization of low cost graphene sheets as a substitute for noble metals (such as Pt) in the photocatalytic H2-production but also for the first time shows a significant enhancement in the H2-production activity by using metal-free carbon material as an effective co-catalyst.

Continuous-time quantum walks on multilayer dendrimer networks

NASA Astrophysics Data System (ADS)

Galiceanu, Mircea; Strunz, Walter T.

2016-08-01

We consider continuous-time quantum walks (CTQWs) on multilayer dendrimer networks (MDs) and their application to quantum transport. A detailed study of properties of CTQWs is presented and transport efficiency is determined in terms of the exact and average return probabilities. The latter depends only on the eigenvalues of the connectivity matrix, which even for very large structures allows a complete analytical solution for this particular choice of network. In the case of MDs we observe an interplay between strong localization effects, due to the dendrimer topology, and good efficiency from the linear segments. We show that quantum transport is enhanced by interconnecting more layers of dendrimers.

Efficient universal blind quantum computation.

PubMed

Giovannetti, Vittorio; Maccone, Lorenzo; Morimae, Tomoyuki; Rudolph, Terry G

2013-12-06

We give a cheat sensitive protocol for blind universal quantum computation that is efficient in terms of computational and communication resources: it allows one party to perform an arbitrary computation on a second party's quantum computer without revealing either which computation is performed, or its input and output. The first party's computational capabilities can be extremely limited: she must only be able to create and measure single-qubit superposition states. The second party is not required to use measurement-based quantum computation. The protocol requires the (optimal) exchange of O(Jlog2(N)) single-qubit states, where J is the computational depth and N is the number of qubits needed for the computation.

Demonstration of nonreciprocity in a microwave cavity optomechanical circuit

NASA Astrophysics Data System (ADS)

Peterson, Gabriel; Lecocq, Florent; Kotler, Shlomi; Cicak, Katarina; Simmonds, Raymond; Aumentado, Jose; Teufel, John

The ability to engineer nonreciprocal interactions is essential for many applications including quantum signal processing and quantum transduction. While attributes such as high efficiency and low added noise are always beneficial, for quantum applications these metrics are crucial. Here we present recent experimental results on a parametric, nonreciprocal microwave circuit based on the optomechanical interaction between a superconducting microwave resonator and a mechanically compliant vacuum gap capacitor. Unlike standard Faraday-based circulators, this parametric interaction does not require magnetic fields, and the direction of circulation can be controlled dynamically in situ. Looking forward, such devices could enable programmable, high-efficiency connections between disparate nodes of a quantum network.

Electrically tunable spin filtering for electron tunneling between spin-resolved quantum Hall edge states and a quantum dot

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kiyama, H., E-mail: kiyama@meso.t.u-tokyo.ac.jp; Fujita, T.; Teraoka, S.

2014-06-30

Spin filtering with electrically tunable efficiency is achieved for electron tunneling between a quantum dot and spin-resolved quantum Hall edge states by locally gating the two-dimensional electron gas (2DEG) leads near the tunnel junction to the dot. The local gating can change the potential gradient in the 2DEG and consequently the edge state separation. We use this technique to electrically control the ratio of the dot–edge state tunnel coupling between opposite spins and finally increase spin filtering efficiency up to 91%, the highest ever reported, by optimizing the local gating.

Multi-Dimensional Quantum Tunneling and Transport Using the Density-Gradient Model

NASA Technical Reports Server (NTRS)

Biegel, Bryan A.; Yu, Zhi-Ping; Ancona, Mario; Rafferty, Conor; Saini, Subhash (Technical Monitor)

1999-01-01

We show that quantum effects are likely to significantly degrade the performance of MOSFETs (metal oxide semiconductor field effect transistor) as these devices are scaled below 100 nm channel length and 2 nm oxide thickness over the next decade. A general and computationally efficient electronic device model including quantum effects would allow us to monitor and mitigate these effects. Full quantum models are too expensive in multi-dimensions. Using a general but efficient PDE solver called PROPHET, we implemented the density-gradient (DG) quantum correction to the industry-dominant classical drift-diffusion (DD) model. The DG model efficiently includes quantum carrier profile smoothing and tunneling in multi-dimensions and for any electronic device structure. We show that the DG model reduces DD model error from as much as 50% down to a few percent in comparison to thin oxide MOS capacitance measurements. We also show the first DG simulations of gate oxide tunneling and transverse current flow in ultra-scaled MOSFETs. The advantages of rapid model implementation using the PDE solver approach will be demonstrated, as well as the applicability of the DG model to any electronic device structure.

Electronic Two-Transition-Induced Enhancement of Emission Efficiency in Polymer Light-Emitting Diodes

PubMed Central

Chen, Ren-Ai; Wang, Cong; Li, Sheng; George, Thomas F.

2013-01-01

With the development of experimental techniques, effective injection and transportation of electrons is proven as a way to obtain polymer light-emitting diodes (PLEDs) with high quantum efficiency. This paper reveals a valid mechanism for the enhancement of quantum efficiency in PLEDs. When an external electric field is applied, the interaction between a negative polaron and triplet exciton leads to an electronic two-transition process, which induces the exciton to emit light and thus improve the emission efficiency of PLEDs. PMID:28809346

An efficient (t,n) threshold quantum secret sharing without entanglement

NASA Astrophysics Data System (ADS)

Qin, Huawang; Dai, Yuewei

2016-04-01

An efficient (t,n) threshold quantum secret sharing (QSS) scheme is proposed. In our scheme, the Hash function is used to check the eavesdropping, and no particles need to be published. So the utilization efficiency of the particles is real 100%. No entanglement is used in our scheme. The dealer uses the single particles to encode the secret information, and the participants get the secret through measuring the single particles. Compared to the existing schemes, our scheme is simpler and more efficient.

Photovoltaic characteristics of n(+)pp(+) InP solar cells grown by OMVPE

NASA Technical Reports Server (NTRS)

Tyagi, S.; Singh, K.; Bhimnathwala, H.; Ghandhi, S. K.; Borrego, J. M.

1990-01-01

The photovoltaic characteristics of n(+)/p/p(+) homojunction InP solar cells fabricated by organometallic vapor-phase epitaxy (OMVPE) are described. The cells are characterized by I-V, C-V and quantum efficiency measurements, and simulations are used to obtain various device and material parameters. The I-V characteristics show a high recombination rate in the depletion region; this is shown to be independent of the impurity used. It is shown that cadmium is easier to use as an acceptor for the p base and p(+) buffer and is therefore beneficial. The high quantum efficiency of 98 percent at long wavelengths measured in these cells indicates a very good collection efficiency in the base. The short-wavelength quantum efficiency is poor, indicating a high surface recombination.

High-speed and high-efficiency travelling wave single-photon detectors embedded in nanophotonic circuits

PubMed Central

Pernice, W.H.P.; Schuck, C.; Minaeva, O.; Li, M.; Goltsman, G.N.; Sergienko, A.V.; Tang, H.X.

2012-01-01

Ultrafast, high-efficiency single-photon detectors are among the most sought-after elements in modern quantum optics and quantum communication. However, imperfect modal matching and finite photon absorption rates have usually limited their maximum attainable detection efficiency. Here we demonstrate superconducting nanowire detectors atop nanophotonic waveguides, which enable a drastic increase of the absorption length for incoming photons. This allows us to achieve high on-chip single-photon detection efficiency up to 91% at telecom wavelengths, repeatable across several fabricated chips. We also observe remarkably low dark count rates without significant compromise of the on-chip detection efficiency. The detectors are fully embedded in scalable silicon photonic circuits and provide ultrashort timing jitter of 18 ps. Exploiting this high temporal resolution, we demonstrate ballistic photon transport in silicon ring resonators. Our direct implementation of a high-performance single-photon detector on chip overcomes a major barrier in integrated quantum photonics. PMID:23271658

Finite-size effect on optimal efficiency of heat engines.

PubMed

Tajima, Hiroyasu; Hayashi, Masahito

2017-07-01

The optimal efficiency of quantum (or classical) heat engines whose heat baths are n-particle systems is given by the strong large deviation. We give the optimal work extraction process as a concrete energy-preserving unitary time evolution among the heat baths and the work storage. We show that our optimal work extraction turns the disordered energy of the heat baths to the ordered energy of the work storage, by evaluating the ratio of the entropy difference to the energy difference in the heat baths and the work storage, respectively. By comparing the statistical mechanical optimal efficiency with the macroscopic thermodynamic bound, we evaluate the accuracy of the macroscopic thermodynamics with finite-size heat baths from the statistical mechanical viewpoint. We also evaluate the quantum coherence effect on the optimal efficiency of the cycle processes without restricting their cycle time by comparing the classical and quantum optimal efficiencies.

High-quantum efficiency, long-lived luminescing refractory oxides

DOEpatents

Chen, Yok; Gonzalez, Roberto; Summers, Geoffrey P.

1984-01-01

A crystal having a high-quantum efficiency and a long period of luminescence is formed of an oxide selected from the group consisting of magnesium oxide and calcium oxide and possessing a concentration ratio of H.sup.- ions to F centers in the range of about 0.05 to about 10.

An Efficient Multiparty Quantum Secret Sharing Protocol Based on Bell States in the High Dimension Hilbert Space

NASA Astrophysics Data System (ADS)

Gao, Gan; Wang, Li-Ping

2010-11-01

We propose a quantum secret sharing protocol, in which Bell states in the high dimension Hilbert space are employed. The biggest advantage of our protocol is the high source capacity. Compared with the previous secret sharing protocol, ours has the higher controlling efficiency. In addition, as decoy states in the high dimension Hilbert space are used, we needn’t destroy quantum entanglement for achieving the goal to check the channel security.

Local surface plasmon enhanced polarization and internal quantum efficiency of deep ultraviolet emissions from AlGaN-based quantum wells.

PubMed

Zhang, Cai; Tang, Ning; Shang, Liangliang; Fu, Lei; Wang, Weiying; Xu, Fujun; Wang, Xinqiang; Ge, Weikun; Shen, Bo

2017-05-24

We report the enhancement of the polarization and internal quantum efficiency (IQE) of deep-UV LEDs by evaporating Al nanoparticles on the device surface to induce localized surface plasmons (LSPs). The deep-UV LEDs polarization is improved due to part of TM emission turns into TE emission through LSPs coupling. The significantly enhanced IQE is attributed to LSPs coupling, which suppress the participation of delocalized and dissociated excitons to non-radiative recombination process.

Quantum walks of interacting fermions on a cycle graph

PubMed Central

Melnikov, Alexey A.; Fedichkin, Leonid E.

2016-01-01

Quantum walks have been employed widely to develop new tools for quantum information processing recently. A natural quantum walk dynamics of interacting particles can be used to implement efficiently the universal quantum computation. In this work quantum walks of electrons on a graph are studied. The graph is composed of semiconductor quantum dots arranged in a circle. Electrons can tunnel between adjacent dots and interact via Coulomb repulsion, which leads to entanglement. Fermionic entanglement dynamics is obtained and evaluated. PMID:27681057

Deterministic realization of collective measurements via photonic quantum walks.

PubMed

Hou, Zhibo; Tang, Jun-Feng; Shang, Jiangwei; Zhu, Huangjun; Li, Jian; Yuan, Yuan; Wu, Kang-Da; Xiang, Guo-Yong; Li, Chuan-Feng; Guo, Guang-Can

2018-04-12

Collective measurements on identically prepared quantum systems can extract more information than local measurements, thereby enhancing information-processing efficiency. Although this nonclassical phenomenon has been known for two decades, it has remained a challenging task to demonstrate the advantage of collective measurements in experiments. Here, we introduce a general recipe for performing deterministic collective measurements on two identically prepared qubits based on quantum walks. Using photonic quantum walks, we realize experimentally an optimized collective measurement with fidelity 0.9946 without post selection. As an application, we achieve the highest tomographic efficiency in qubit state tomography to date. Our work offers an effective recipe for beating the precision limit of local measurements in quantum state tomography and metrology. In addition, our study opens an avenue for harvesting the power of collective measurements in quantum information-processing and for exploring the intriguing physics behind this power.

Broadband multiresonator quantum memory-interface.

PubMed

Moiseev, S A; Gerasimov, K I; Latypov, R R; Perminov, N S; Petrovnin, K V; Sherstyukov, O N

2018-03-05

In this paper we experimentally demonstrated a broadband scheme of the multiresonator quantum memory-interface. The microwave photonic scheme consists of the system of mini-resonators strongly interacting with a common broadband resonator coupled with the external waveguide. We have implemented the impedance matched quantum storage in this scheme via controllable tuning of the mini-resonator frequencies and coupling of the common resonator with the external waveguide. Proof-of-principal experiment has been demonstrated for broadband microwave pulses when the quantum efficiency of 16.3% was achieved at room temperature. By using the obtained experimental spectroscopic data, the dynamics of the signal retrieval has been simulated and promising results were found for high-Q mini-resonators in microwave and optical frequency ranges. The results pave the way for the experimental implementation of broadband quantum memory-interface with quite high efficiency η > 0.99 on the basis of modern technologies, including optical quantum memory at room temperature.

Experimental statistical signature of many-body quantum interference

NASA Astrophysics Data System (ADS)

Giordani, Taira; Flamini, Fulvio; Pompili, Matteo; Viggianiello, Niko; Spagnolo, Nicolò; Crespi, Andrea; Osellame, Roberto; Wiebe, Nathan; Walschaers, Mattia; Buchleitner, Andreas; Sciarrino, Fabio

2018-03-01

Multi-particle interference is an essential ingredient for fundamental quantum mechanics phenomena and for quantum information processing to provide a computational advantage, as recently emphasized by boson sampling experiments. Hence, developing a reliable and efficient technique to witness its presence is pivotal in achieving the practical implementation of quantum technologies. Here, we experimentally identify genuine many-body quantum interference via a recent efficient protocol, which exploits statistical signatures at the output of a multimode quantum device. We successfully apply the test to validate three-photon experiments in an integrated photonic circuit, providing an extensive analysis on the resources required to perform it. Moreover, drawing upon established techniques of machine learning, we show how such tools help to identify the—a priori unknown—optimal features to witness these signatures. Our results provide evidence on the efficacy and feasibility of the method, paving the way for its adoption in large-scale implementations.

Enhancement of emission efficiency of colloidal CdSe quantum dots on silicon substrate via an ultra-thin layer of aluminum oxide.

PubMed

Patty, K; Sadeghi, S M; Nejat, A; Mao, C-B

2014-04-18

We demonstrate that an ultra-thin layer of aluminum oxide can significantly enhance the emission efficiency of colloidal quantum dots on a Si substrate. For an ensemble of single quantum dots, our results show that this super brightening process can increase the fluorescence of CdSe quantum dots, forming well-resolved spectra, while in the absence of this layer the emission remains mostly at the noise level. We demonstrate that this process can be further enhanced with irradiation of the quantum dots, suggesting a significant photo-induced fluorescence enhancement via considerable suppression of non-radiative decay channels of the quantum dots. We study the impact of the Al oxide thickness on Si and interdot interactions, and discuss the results in terms of photo-induced catalytic properties of the Al oxide and the effects of such an oxide on the Coulomb blockade responsible for suppression of photo-ionization of the quantum dots.

Electro-optic routing of photons from a single quantum dot in photonic integrated circuits

NASA Astrophysics Data System (ADS)

Midolo, Leonardo; Hansen, Sofie L.; Zhang, Weili; Papon, Camille; Schott, Rüdiger; Ludwig, Arne; Wieck, Andreas D.; Lodahl, Peter; Stobbe, Søren

2017-12-01

Recent breakthroughs in solid-state photonic quantum technologies enable generating and detecting single photons with near-unity efficiency as required for a range of photonic quantum technologies. The lack of methods to simultaneously generate and control photons within the same chip, however, has formed a main obstacle to achieving efficient multi-qubit gates and to harness the advantages of chip-scale quantum photonics. Here we propose and demonstrate an integrated voltage-controlled phase shifter based on the electro-optic effect in suspended photonic waveguides with embedded quantum emitters. The phase control allows building a compact Mach-Zehnder interferometer with two orthogonal arms, taking advantage of the anisotropic electro-optic response in gallium arsenide. Photons emitted by single self-assembled quantum dots can be actively routed into the two outputs of the interferometer. These results, together with the observed sub-microsecond response time, constitute a significant step towards chip-scale single-photon-source de-multiplexing, fiber-loop boson sampling, and linear optical quantum computing.

Report of high quantum efficiency photocathode at Milano

DOE Office of Scientific and Technical Information (OSTI.GOV)

Michelato, P.

R D activity on high quantum efficiency alkali antimonide photocathode is in progress at Milano, in the context of the ARES program. Inside a preliminary preparation chamber, Cs[sub 3]Sb layers with qunatum efficiency up to 9% (at [lambda]=543.5 nm) and lifetime of some days has been recently produced on copper, stainless steel and niobium, using a reproducible deposition procedure adapted to the material of the different substrata.

Computing quantum hashing in the model of quantum branching programs

NASA Astrophysics Data System (ADS)

Ablayev, Farid; Ablayev, Marat; Vasiliev, Alexander

2018-02-01

We investigate the branching program complexity of quantum hashing. We consider a quantum hash function that maps elements of a finite field into quantum states. We require that this function is preimage-resistant and collision-resistant. We consider two complexity measures for Quantum Branching Programs (QBP): a number of qubits and a number of compu-tational steps. We show that the quantum hash function can be computed efficiently. Moreover, we prove that such QBP construction is optimal. That is, we prove lower bounds that match the constructed quantum hash function computation.

Impact of Alloy Fluctuations on Radiative and Auger Recombination in InGaN Quantum Wells

NASA Astrophysics Data System (ADS)

Jones, Christina; Teng, Chu-Hsiang; Yan, Qimin; Ku, Pei-Cheng; Kioupakis, Emmanouil

Light-emitting diodes (LEDs) based on indium gallium nitride (InGaN) are important for efficient solid-state lighting (2014 Nobel Prize in Physics). Despite its many successes, InGaN suffers from issues that reduce the efficiency of devices at high power, such as the green gap and efficiency droop. The origin of the droop has been attributed to Auger recombination, mediated by carrier scattering due to phonons and alloy disorder. Additionally, InGaN exhibits atomic-scale composition fluctuations that localize carriers and may affect the efficiency. In this work, we study the effect of local composition fluctuations on the radiative recombination rate, Auger recombination rate, and efficiency of InGaN/GaN quantum wells. We apply k.p calculations to simulate band edges and wave functions of quantum wells with fluctuating alloy distributions based on atom probe tomography data, and we evaluate double and triple overlaps of electron and hole wave functions. We compare results for quantum wells with fluctuating alloy distributions to those with uniform alloy compositions and to published work. Our results demonstrate that alloy-composition fluctuations aggravate the efficiency-droop and green-gap problems and further reduce LED efficiency at high power. We acknowledge the NSF CAREER award DMR-1254314, the NSF Graduate Research Fellowship Program DGE-1256260, and the DOE NERSC facility (DE-AC02-05CH11231).

Optimality of semiquantum nonlocality in the presence of high inconclusive rates

DOE PAGES

Lim, Charles Ci Wen

2016-02-01

Quantum nonlocality is a counterintuitive phenomenon that lies beyond the purview of causal influences. Recently, Bell inequalities have been generalized to the case of quantum inputs, leading to a powerful family of semiquantum Bell inequalities that are capable of detecting any entangled state. We focus on a different problem and investigate how the local indistinguishability of quantum inputs and postselection may affect the requirements to detect semiquantum nonlocality. Moreover, we consider a semiquantum nonlocal game based on locally indistinguishable qubit inputs, and derive its postselected local and quantum bounds by using a connection to the local distinguishability of quantum states.more » Interestingly, we find that the postselected local bound is independent of the measurement efficiency, and the achievable postselected Bell violation increases with decreasing measurement efficiency.« less

Quantum Otto heat engine with three-qubit XXZ model as working substance

NASA Astrophysics Data System (ADS)

Huang, X. L.; Sun, Qi; Guo, D. Y.; Yu, Qian

2018-02-01

A quantum Otto heat engine is established with a three-qubit Heisenberg XXZ model with Dzyaloshinskii-Moriya (DM) interaction under a homogeneous magnetic field as the working substance. The quantum Otto engine is composed of two quantum isochoric processes and two quantum adiabatic processes. Here we have restricted Bc /Bh =Jc /Jh = r in the two adiabatic processes, where r is the adiabatic compression ratio. The work output and efficiency are calculated for our cycle. The possible adiabatic compression ratios and the ratios of work output between our working substance and a single spin under the same external conditions in the Otto cycle are analyzed with different DM interaction parameters and anisotropic parameters. The effects of pairwise entanglements on the heat engine efficiency are discussed.

Enhanced external quantum efficiency in GaN-based vertical-type light-emitting diodes by localized surface plasmons

PubMed Central

Yao, Yung-Chi; Hwang, Jung-Min; Yang, Zu-Po; Haung, Jing-Yu; Lin, Chia-Ching; Shen, Wei-Chen; Chou, Chun-Yang; Wang, Mei-Tan; Huang, Chun-Ying; Chen, Ching-Yu; Tsai, Meng-Tsan; Lin, Tzu-Neng; Shen, Ji-Lin; Lee, Ya-Ju

2016-01-01

Enhancement of the external quantum efficiency of a GaN-based vertical-type light emitting diode (VLED) through the coupling of localized surface plasmon (LSP) resonance with the wave-guided mode light is studied. To achieve this experimentally, Ag nanoparticles (NPs), as the LSP resonant source, are drop-casted on the most top layer of waveguide channel, which is composed of hydrothermally synthesized ZnO nanorods capped on the top of GaN-based VLED. Enhanced light-output power and external quantum efficiency are observed, and the amount of enhancement remains steady with the increase of the injected currents. To understand the observations theoretically, the absorption spectra and the electric field distributions of the VLED with and without Ag NPs decorated on ZnO NRs are determined using the finite-difference time-domain (FDTD) method. The results prove that the observation of enhancement of the external quantum efficiency can be attributed to the creation of an extra escape channel for trapped light due to the coupling of the LSP with wave-guided mode light, by which the energy of wave-guided mode light can be transferred to the efficient light scattering center of the LSP. PMID:26935648

Quantum efficiency harmonic analysis of exciton annihilation in organic light emitting diodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Price, J. S.; Giebink, N. C., E-mail: ncg2@psu.edu

2015-06-29

Various exciton annihilation processes are known to impact the efficiency roll-off of organic light emitting diodes (OLEDs); however, isolating and quantifying their contribution in the presence of other factors such as changing charge balance continue to be a challenge for routine device characterization. Here, we analyze OLED electroluminescence resulting from a sinusoidal dither superimposed on the device bias and show that nonlinearity between recombination current and light output arising from annihilation mixes the quantum efficiency measured at different dither harmonics in a manner that depends uniquely on the type and magnitude of the annihilation process. We derive a series ofmore » analytical relations involving the DC and first harmonic external quantum efficiency that enable annihilation rates to be quantified through linear regression independent of changing charge balance and evaluate them for prototypical fluorescent and phosphorescent OLEDs based on the emitters 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran and platinum octaethylporphyrin, respectively. We go on to show that, in most cases, it is sufficient to calculate the needed quantum efficiency harmonics directly from derivatives of the DC light versus current curve, thus enabling this analysis to be conducted solely from standard light-current-voltage measurement data.« less

Step-by-step magic state encoding for efficient fault-tolerant quantum computation

PubMed Central

Goto, Hayato

2014-01-01

Quantum error correction allows one to make quantum computers fault-tolerant against unavoidable errors due to decoherence and imperfect physical gate operations. However, the fault-tolerant quantum computation requires impractically large computational resources for useful applications. This is a current major obstacle to the realization of a quantum computer. In particular, magic state distillation, which is a standard approach to universality, consumes the most resources in fault-tolerant quantum computation. For the resource problem, here we propose step-by-step magic state encoding for concatenated quantum codes, where magic states are encoded step by step from the physical level to the logical one. To manage errors during the encoding, we carefully use error detection. Since the sizes of intermediate codes are small, it is expected that the resource overheads will become lower than previous approaches based on the distillation at the logical level. Our simulation results suggest that the resource requirements for a logical magic state will become comparable to those for a single logical controlled-NOT gate. Thus, the present method opens a new possibility for efficient fault-tolerant quantum computation. PMID:25511387

Step-by-step magic state encoding for efficient fault-tolerant quantum computation.

PubMed

Goto, Hayato

2014-12-16

Quantum error correction allows one to make quantum computers fault-tolerant against unavoidable errors due to decoherence and imperfect physical gate operations. However, the fault-tolerant quantum computation requires impractically large computational resources for useful applications. This is a current major obstacle to the realization of a quantum computer. In particular, magic state distillation, which is a standard approach to universality, consumes the most resources in fault-tolerant quantum computation. For the resource problem, here we propose step-by-step magic state encoding for concatenated quantum codes, where magic states are encoded step by step from the physical level to the logical one. To manage errors during the encoding, we carefully use error detection. Since the sizes of intermediate codes are small, it is expected that the resource overheads will become lower than previous approaches based on the distillation at the logical level. Our simulation results suggest that the resource requirements for a logical magic state will become comparable to those for a single logical controlled-NOT gate. Thus, the present method opens a new possibility for efficient fault-tolerant quantum computation.

One-norm geometric quantum discord and critical point estimation in the XY spin chain

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, Chang-Cheng; Wang, Yao; Guo, Jin-Liang, E-mail: guojinliang80@163.com

2016-11-15

In contrast with entanglement and quantum discord (QD), we investigate the thermal quantum correlation in terms of Schatten one-norm geometric quantum discord (GQD) in the XY spin chain, and analyze their capabilities in detecting the critical point of quantum phase transition. We show that the one-norm GQD can reveal more properties about quantum correlation between two spins, especially for the long-range quantum correlation at finite temperature. Under the influences of site distance, anisotropy and temperature, one-norm GQD and its first derivative make it possible to detect the critical point efficiently for a general XY spin chain. - Highlights: • Comparingmore » with entanglement and QD, one-norm GQD is more robust versus the temperature. • One-norm GQD is more efficient in characterization of long-range quantum correlation between two distant qubits. • One-norm GQD performs well in highlighting the critical point of QPT at zero or low finite temperature. • One-norm GQD has a number of advantages over QD in detecting the critical point of the spin chain.« less

Deep-UV emission at 219 nm from ultrathin MBE GaN/AlN quantum heterostructures

NASA Astrophysics Data System (ADS)

Islam, S. M.; Protasenko, Vladimir; Lee, Kevin; Rouvimov, Sergei; Verma, Jai; Xing, Huili Grace; Jena, Debdeep

2017-08-01

Deep ultraviolet (UV) optical emission below 250 nm (˜5 eV) in semiconductors is traditionally obtained from high aluminum containing AlGaN alloy quantum wells. It is shown here that high-quality epitaxial ultrathin binary GaN quantum disks embedded in an AlN matrix can produce efficient optical emission in the 219-235 nm (˜5.7-5.3 eV) spectral range, far above the bulk bandgap (3.4 eV) of GaN. The quantum confinement energy in these heterostructures is larger than the bandgaps of traditional semiconductors, made possible by the large band offsets. These molecular beam epitaxy-grown extreme quantum-confinement GaN/AlN heterostructures exhibit an internal quantum efficiency of 40% at wavelengths as short as 219 nm. These observations together with the ability to engineer the interband optical matrix elements to control the direction of photon emission in such binary quantum disk active regions offer unique advantages over alloy AlGaN quantum well counterparts for the realization of deep-UV light-emitting diodes and lasers.

Exciplex-triplet energy transfer: A new method to achieve extremely efficient organic light-emitting diode with external quantum efficiency over 30% and drive voltage below 3 V

NASA Astrophysics Data System (ADS)

Seo, Satoshi; Shitagaki, Satoko; Ohsawa, Nobuharu; Inoue, Hideko; Suzuki, Kunihiko; Nowatari, Hiromi; Yamazaki, Shunpei

2014-04-01

A novel approach to enhance the power efficiency of an organic light-emitting diode (OLED) by employing energy transfer from an exciplex to a phosphorescent emitter is reported. It was found that excitation energy of an exciplex formed between an electron-transporting material with a π-deficient quinoxaline moiety and a hole-transporting material with aromatic amine structure can be effectively transferred to a phosphorescent iridium complex in an emission layer of a phosphorescent OLED. Moreover, such an exciplex formation increases quantum efficiency and reduces drive voltage. A highly efficient, low-voltage, and long-life OLED based on this energy transfer is also demonstrated. This OLED device exhibited extremely high external quantum efficiency of 31% even without any attempt to enhance light outcoupling and also achieved a low drive voltage of 2.8 V and a long lifetime of approximately 1,000,000 h at a luminance of 1,000 cd/m2.

Enhanced Conversion Efficiency of III–V Triple-junction Solar Cells with Graphene Quantum Dots

PubMed Central

Lin, Tzu-Neng; Santiago, Svette Reina Merden S.; Zheng, Jie-An; Chao, Yu-Chiang; Yuan, Chi-Tsu; Shen, Ji-Lin; Wu, Chih-Hung; Lin, Cheng- An J.; Liu, Wei-Ren; Cheng, Ming-Chiang; Chou, Wu-Ching

2016-01-01

Graphene has been used to synthesize graphene quantum dots (GQDs) via pulsed laser ablation. By depositing the synthesized GQDs on the surface of InGaP/InGaAs/Ge triple-junction solar cells, the short-circuit current, fill factor, and conversion efficiency were enhanced remarkably. As the GQD concentration is increased, the conversion efficiency in the solar cell increases accordingly. A conversion efficiency of 33.2% for InGaP/InGaAs/Ge triple-junction solar cells has been achieved at the GQD concentration of 1.2 mg/ml, corresponding to a 35% enhancement compared to the cell without GQDs. On the basis of time-resolved photoluminescence, external quantum efficiency, and work-function measurements, we suggest that the efficiency enhancement in the InGaP/InGaAs/Ge triple-junction solar cells is primarily caused by the carrier injection from GQDs to the InGaP top subcell. PMID:27982073

Robust nonfullerene solar cells approaching unity external quantum efficiency enabled by suppression of geminate recombination.

PubMed

Baran, Derya; Gasparini, Nicola; Wadsworth, Andrew; Tan, Ching Hong; Wehbe, Nimer; Song, Xin; Hamid, Zeinab; Zhang, Weimin; Neophytou, Marios; Kirchartz, Thomas; Brabec, Christoph J; Durrant, James R; McCulloch, Iain

2018-05-25

Nonfullerene solar cells have increased their efficiencies up to 13%, yet quantum efficiencies are still limited to 80%. Here we report efficient nonfullerene solar cells with quantum efficiencies approaching unity. This is achieved with overlapping absorption bands of donor and acceptor that increases the photon absorption strength in the range from about 570 to 700 nm, thus, almost all incident photons are absorbed in the active layer. The charges generated are found to dissociate with negligible geminate recombination losses resulting in a short-circuit current density of 20 mA cm -2 along with open-circuit voltages >1 V, which is remarkable for a 1.6 eV bandgap system. Most importantly, the unique nano-morphology of the donor:acceptor blend results in a substantially improved stability under illumination. Understanding the efficient charge separation in nonfullerene acceptors can pave the way to robust and recombination-free organic solar cells.

Quantum-enhanced Sensing and Efficient Quantum Computation

DTIC Science & Technology

2015-07-27

accuracy. The system was used to improve quantum boson sampling tests. 15. SUBJECT TERMS EOARD, Quantum Information Processing, Transition Edge Sensors...quantum  boson  sampling (QBS) problem are reported in Ref. [7]. To substantially  increase the scale of feasible tests, we developed a new variation

Sub-Shot-Noise Transmission Measurement Enabled by Active Feed-Forward of Heralded Single Photons

NASA Astrophysics Data System (ADS)

Sabines-Chesterking, J.; Whittaker, R.; Joshi, S. K.; Birchall, P. M.; Moreau, P. A.; McMillan, A.; Cable, H. V.; O'Brien, J. L.; Rarity, J. G.; Matthews, J. C. F.

2017-07-01

Harnessing the unique properties of quantum mechanics offers the possibility of delivering alternative technologies that can fundamentally outperform their classical counterparts. These technologies deliver advantages only when components operate with performance beyond specific thresholds. For optical quantum metrology, the biggest challenge that impacts on performance thresholds is optical loss. Here, we demonstrate how including an optical delay and an optical switch in a feed-forward configuration with a stable and efficient correlated photon-pair source reduces the detector efficiency required to enable quantum-enhanced sensing down to the detection level of single photons and without postselection. When the switch is active, we observe a factor of improvement in precision of 1.27 for transmission measurement on a per-input-photon basis compared to the performance of a laser emitting an ideal coherent state and measured with the same detection efficiency as our setup. When the switch is inoperative, we observe no quantum advantage.

Photoconductive gain and quantum efficiency of remotely doped Ge/Si quantum dot photodetectors

NASA Astrophysics Data System (ADS)

Yakimov, A. I.; Kirienko, V. V.; Armbrister, V. A.; Bloshkin, A. A.; Dvurechenskii, A. V.; Shklyaev, A. A.

2016-10-01

We study the effect of quantum dot charging on the mid-infrared photocurrent, optical gain, hole capture probability, and absorption quantum efficiency in remotely delta-doped Ge/Si quantum dot photodetectors. The dot occupation with holes is controlled by varying dot and doping densities. From our investigations of samples doped to contain from about one to nine holes per dot we observe an over 10 times gain enhancement and similar suppression of the hole capture probability with increased carrier population. The data are explained by quenching the capture process and increasing the photoexcited hole lifetime due to formation of the repulsive Coulomb potential of the extra holes inside the quantum dots. The normal incidence quantum efficiency is found to be strongly asymmetric with respect to applied bias polarity. Based on the polarization-dependent absorption measurements it is concluded that, at a positive voltage, when holes move toward the nearest δ-doping plane, photocurrent is originated from the bound-to-continuum transitions of holes between the ground state confined in Ge dots and the extended states of the Si matrix. At a negative bias polarity, the photoresponse is caused by optical excitation to a quasibound state confined near the valence band edge with subsequent tunneling to the Si valence band. In a latter case, the possibility of hole transfer into continuum states arises from the electric field generated by charge distributed between quantum dots and delta-doping planes.

Complexity of the Quantum Adiabatic Algorithm

NASA Astrophysics Data System (ADS)

Hen, Itay

2013-03-01

The Quantum Adiabatic Algorithm (QAA) has been proposed as a mechanism for efficiently solving optimization problems on a quantum computer. Since adiabatic computation is analog in nature and does not require the design and use of quantum gates, it can be thought of as a simpler and perhaps more profound method for performing quantum computations that might also be easier to implement experimentally. While these features have generated substantial research in QAA, to date there is still a lack of solid evidence that the algorithm can outperform classical optimization algorihms. Here, we discuss several aspects of the quantum adiabatic algorithm: We analyze the efficiency of the algorithm on several ``hard'' (NP) computational problems. Studying the size dependence of the typical minimum energy gap of the Hamiltonians of these problems using quantum Monte Carlo methods, we find that while for most problems the minimum gap decreases exponentially with the size of the problem, indicating that the QAA is not more efficient than existing classical search algorithms, for other problems there is evidence to suggest that the gap may be polynomial near the phase transition. We also discuss applications of the QAA to ``real life'' problems and how they can be implemented on currently available (albeit prototypical) quantum hardware such as ``D-Wave One'', that impose serious restrictions as to which type of problems may be tested. Finally, we discuss different approaches to find improved implementations of the algorithm such as local adiabatic evolution, adaptive methods, local search in Hamiltonian space and others.

A Philosophical Approach to Quantum Field Theory

NASA Astrophysics Data System (ADS)

Öttinger, Hans Christian

2018-01-01

Preface; Acknowledgements; 1. Approach to quantum field theory; 2. Scalar field theory; 3. Quantum electrodynamics; 4. Perspectives; Appendix A. An efficient perturbation scheme; Appendix B. Properties of Dirac matrices; Appendix C. Baker-Campbell-Hausdorff formulas; References; Author index; Subject index.

Highly Efficient Light-Emitting Diodes of Colloidal Metal-Halide Perovskite Nanocrystals beyond Quantum Size.

PubMed

Kim, Young-Hoon; Wolf, Christoph; Kim, Young-Tae; Cho, Himchan; Kwon, Woosung; Do, Sungan; Sadhanala, Aditya; Park, Chan Gyung; Rhee, Shi-Woo; Im, Sang Hyuk; Friend, Richard H; Lee, Tae-Woo

2017-07-25

Colloidal metal-halide perovskite quantum dots (QDs) with a dimension less than the exciton Bohr diameter D B (quantum size regime) emerged as promising light emitters due to their spectrally narrow light, facile color tuning, and high photoluminescence quantum efficiency (PLQE). However, their size-sensitive emission wavelength and color purity and low electroluminescence efficiency are still challenging aspects. Here, we demonstrate highly efficient light-emitting diodes (LEDs) based on the colloidal perovskite nanocrystals (NCs) in a dimension > D B (regime beyond quantum size) by using a multifunctional buffer hole injection layer (Buf-HIL). The perovskite NCs with a dimension greater than D B show a size-irrespective high color purity and PLQE by managing the recombination of excitons occurring at surface traps and inside the NCs. The Buf-HIL composed of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) and perfluorinated ionomer induces uniform perovskite particle films with complete film coverage and prevents exciton quenching at the PEDOT:PSS/perovskite particle film interface. With these strategies, we achieved a very high PLQE (∼60.5%) in compact perovskite particle films without any complex post-treatments and multilayers and a high current efficiency of 15.5 cd/A in the LEDs of colloidal perovskite NCs, even in a simplified structure, which is the highest efficiency to date in green LEDs that use colloidal organic-inorganic metal-halide perovskite nanoparticles including perovskite QDs and NCs. These results can help to guide development of various light-emitting optoelectronic applications based on perovskite NCs.

Optimal Power and Efficiency of Quantum Thermoacoustic Micro-cycle Working in 1D Harmonic Trap

NASA Astrophysics Data System (ADS)

E, Qing; Wu, Feng; Yin, Yong; Liu, XiaoWei

2017-10-01

Thermoacoustic engines (including heat engines and refrigerators) are energy conversion devices without moving part. They have great potential in aviation, new energy utilization, power technology, refrigerating and cryogenics. The thermoacoustic parcels, which compose the working fluid of a thermoacoustic engine, oscillate within the sound channel with a temperature gradient. The thermodynamic foundation of a thermoacoustic engine is the thermoacoustic micro-cycle (TAMC). In this paper, the theory of quantum mechanics is applied to the study of the actual thermoacoustic micro-cycle for the first time. A quantum mechanics model of the TAMC working in a 1D harmonic trap, which is named as a quantum thermoacoustic micro-cycle (QTAMC), is established. The QTAMC is composed of two constant force processes connected by two straight line processes. Analytic expressions of the power output and the efficiency for QTAMC have been derived. The effects of the trap width and the temperature amplitude on the power output and the thermal efficiency have been discussed. Some optimal characteristic curves of power output versus efficiency are plotted, and then the optimization region of QTAMC is given in this paper. The results obtained here not only enrich the thermoacoustic theory but also expand the application of quantum thermodynamics.

Quantum computation and analysis of Wigner and Husimi functions: toward a quantum image treatment.

PubMed

Terraneo, M; Georgeot, B; Shepelyansky, D L

2005-06-01

We study the efficiency of quantum algorithms which aim at obtaining phase-space distribution functions of quantum systems. Wigner and Husimi functions are considered. Different quantum algorithms are envisioned to build these functions, and compared with the classical computation. Different procedures to extract more efficiently information from the final wave function of these algorithms are studied, including coarse-grained measurements, amplitude amplification, and measure of wavelet-transformed wave function. The algorithms are analyzed and numerically tested on a complex quantum system showing different behavior depending on parameters: namely, the kicked rotator. The results for the Wigner function show in particular that the use of the quantum wavelet transform gives a polynomial gain over classical computation. For the Husimi distribution, the gain is much larger than for the Wigner function and is larger with the help of amplitude amplification and wavelet transforms. We discuss the generalization of these results to the simulation of other quantum systems. We also apply the same set of techniques to the analysis of real images. The results show that the use of the quantum wavelet transform allows one to lower dramatically the number of measurements needed, but at the cost of a large loss of information.

PsiQuaSP-A library for efficient computation of symmetric open quantum systems.

PubMed

Gegg, Michael; Richter, Marten

2017-11-24

In a recent publication we showed that permutation symmetry reduces the numerical complexity of Lindblad quantum master equations for identical multi-level systems from exponential to polynomial scaling. This is important for open system dynamics including realistic system bath interactions and dephasing in, for instance, the Dicke model, multi-Λ system setups etc. Here we present an object-oriented C++ library that allows to setup and solve arbitrary quantum optical Lindblad master equations, especially those that are permutationally symmetric in the multi-level systems. PsiQuaSP (Permutation symmetry for identical Quantum Systems Package) uses the PETSc package for sparse linear algebra methods and differential equations as basis. The aim of PsiQuaSP is to provide flexible, storage efficient and scalable code while being as user friendly as possible. It is easily applied to many quantum optical or quantum information systems with more than one multi-level system. We first review the basics of the permutation symmetry for multi-level systems in quantum master equations. The application of PsiQuaSP to quantum dynamical problems is illustrated with several typical, simple examples of open quantum optical systems.