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1

Propagation effects in the quantum description of collective recoil lasing  

NASA Astrophysics Data System (ADS)

The free electron laser and collective atomic recoil laser (CARL) are examples of collective recoil lasing, where exponential amplification of a radiation field occurs simultaneously with self-bunching of an ensemble of particles (electrons in the case of the FEL and atoms in the case of the CARL). In this paper, we discuss quantum and propagation effects using a model where the particle dynamics are described quantum-mechanically in terms of a matter-wave field, which evolves self-consistently with the radiation field. The model shows that the scattered radiation evolves superradiantly both in the case where the particle ensemble is short compared to the cooperation length of the system, and where the ensemble is long compared to the cooperation length. In both short and long pulse cases there exist a classical and quantum regime of superradiant emission. For short samples in both quantum and classical regimes the superradiant pulse has a low peak intensity and is said to exhibit 'weak' superradiance. For long pulses in both quantum and classical regimes of evolution, the dynamics at the rear edge of the sample is dominated by propagation. This produces a 'strong' superradiant pulse with much higher peak intensity than that predicted by 'mean-field' or 'steady-state' models in which propagation effects are neglected.

Bonifacio, R.; Piovella, N.; Robb, G. R. M.; Cola, M. M.

2005-08-01

2

Quantum recoil and Bohm diffusion  

SciTech Connect

It is argued that the inclusion of the Bohm potential in quantum fluid equations is equivalent to inclusion of a nonrelativistic form of the quantum recoil in plasma kinetic theory. The Bohm term is incorrect when applied to waves with phase speed greater than the speed of light.

Melrose, D. B.; Mushtaq, A. [School of Physics, University of Sydney, Sydney, New South Wales 2006 (Australia)

2009-09-15

3

A quantum model for collective recoil lasing  

NASA Astrophysics Data System (ADS)

Free Electron Laser (FEL) and Collective Atomic Recoil Laser (CARL) are described by the same model of classical equations for properly defined scaled variables. These equations are extended to the quantum domain describing the particle's motion by a Schrödinger equation coupled to a self-consistent radiation field. The model depends on a single collective parameter bar rho which represents the maximum number of photons emitted per particle. We demonstrate that the classical model is recovered in the limit bar rho >> 1, in which the Wigner function associated to the Schrödinger equation obeys to the classical Vlasov equation. On the contrary, for bar rho <= 1, a new quantum regime is obtained in which both FELs and CARLs behave as a two-state system coupled to the self-consistent radiation field and described by Maxwell-Bloch equations.

Bonifacio, R.; Cola, M. M.; Piovella, N.; Robb, G. R. M.

2005-01-01

4

Quantum effects in the collective light scattering by coherent atomic recoil in a Bose-Einstein condensate  

NASA Astrophysics Data System (ADS)

We extend the semiclassical model of the collective atomic recoil laser (CARL) to include the quantum mechanical description of the center-of-mass motion of the atoms in a Bose-Einstein condensate (BEC). We show that when the average atomic momentum is less than the recoil momentum ? q?, the CARL equations reduce to the Maxwell-Bloch equations for two momentum levels. In the conservative regime (no radiation losses), the quantum model depends on a single collective parameter, ?, that can be interpreted as the average number of photons scattered per atom in the classical limit. When ??1, the semiclassical CARL regime is recovered, with many momentum levels populated at saturation. On the contrary, when ??1, the average momentum oscillates between zero and ? q?, and a periodic train of 2 ? hyperbolic secant pulses is emitted. In the dissipative regime (large radiation losses) and in a suitable quantum limit, a sequential superfluorescence scattering occurs, in which after each process atoms emit a ? hyperbolic secant pulse and populate a lower momentum state. These results describe the regular arrangement of the momentum pattern observed in recent experiments of superradiant Rayleigh scattering from a BEC.

Piovella, N.; Gatelli, M.; Bonifacio, R.

2001-07-01

5

Effects of atomic diffraction on the collective atomic recoil laser  

NASA Astrophysics Data System (ADS)

We formulate a wave-atom-optics theory of the collective atomic recoil laser (CARL) where the atomic center-of-mass motion is treated quantum mechanically. By comparing the predictions of this theory with those of the ray-atom-optics theory, which treats the center-of-mass atomic motion classically, we show that for the case of a far off-resonant pump laser the ray-optics model fails to predict the linear response of the CARL when the temperature is of the order of the recoil temperature or less. This is due to the fact that in this temperature regime one can no longer ignore the effects of matter-wave diffraction on the atomic center-of-mass motion.

Moore, M. G.; Meystre, P.

1998-10-01

6

Recoil effects in a bag model  

SciTech Connect

We attempt to resolve a recent dispute regarding the size, as well as the proper formulation, of recoil corrections to baryon magnetic moments in a bag model. It is demonstrated that the overall center-of-the-system (OCS) motion, when factored out properly to yield the momentum-conservation delta-functions, cannot give rise to additional and sizable recoil corrections as addressed by Betz and Goldflam and independently by Guichon. Thus, the only contribution due to baryon recoil comes from the spinor rotation of the constituent quarks.

Gattone, A.O.; Hwang, W.P.

1984-11-15

7

Recoil effects in valence band photoemission of organic solids.  

PubMed

Recoil effects in valence band X-ray photoelectron spectroscopy (XPS) are studied for both abb-trifluorostyrene and styrene molecular crystal systems. The gradual changes of XPS spectra excited by several photon energies are theoretically investigated within the tight-binding approximation and harmonic approximation of lattice vibrations and have been explained in terms of not only atomic mass but also atomic orbital (AO) population. The recoil effect of valence band photoemission strongly depends on the population and partial photoionization cross section (PICS) of AOs as well as the masses of composite atoms. In abb-trifluorostyrene F 2p dominant bands show the recoil shift close to free F atom recoil shift, and C 2s dominant bands show that to free C atom recoil shift, whereas the mixed bands of C and F give rise to the peak asymmetries due to their different recoil shifts. For these systems, hydrogen contribution is negligibly small which is in contrast to our previous results for the crystals composed of small organic molecules. We also discuss some potential uses of the recoil shifts for these systems. PMID:23441983

Shang, Ming-Hui; Fujikawa, Takashi; Ueno, Nobuo

2013-04-01

8

Accounting for Recoil Effects in Geochronometers: A New Model Approach  

NASA Astrophysics Data System (ADS)

A number of geologically important chronometers are affected by, or owe their utility to, the "recoil effect". This effect describes the physical displacement of a nuclide due to energetic nuclear processes such as radioactive alpha decay (as in the case of various parent-daughter pairs in the uranium-series decay chains, and Sm-Nd), as well as neutron irradiation (in the case of the methodology for the 40Ar/39Ar dating method). The broad range of affected geochronometers means that the recoil effect can impact a wide range of dating method applications in the geosciences, including but not limited to: Earth surface processes, paleoclimate, volcanic processes, and cosmochemistry and planetary evolution. In particular, the recoil effect can have a notable impact on the use of fine grains (silt- and clay-sized particles) for geochronometric dating purposes. This is because recoil-induced loss of a nuclide from the surfaces of a grain can create an isotopically-depleted outer rind, and for small grains, this depleted rind can be volumetrically significant. When this recoil loss is measurable and occurs in a known time-dependent fashion, it can usefully serve as the basis for chronometers (such as the U-series comminution age method); in other cases recoil loss from fine particles creates an unwanted deviation from expected isotope values (such as for the Ar-Ar method). To improve both the accuracy and precision of ages inferred from geochronometric systems that involve the recoil of a key nuclide from small domains, it is necessary to quantify the magnitude of the recoil loss of that particular nuclide. It is also necessary to quantitatively describe the effect of geological processes that can alter the outer surface of grains, and hence the isotopically-depleted rind. Here we present a new mathematical and numerical model that includes two main features that enable enhanced accuracy and precision of ages determined from geochronometers. Since the surface area of the dated grain is a major control on the magnitude of recoil loss, the first feature is the ability to calculate recoil effects on isotopic compositions for realistic, complex grain shapes and surface roughnesses. This is useful because natural grains may have irregular shapes that do not conform to simple geometric descriptions. Perhaps more importantly, the surface area over which recoiled nuclides are lost can be significantly underestimated when grain surface roughness is not accounted for, since the recoil distances can be of similar characteristic lengthscales to surface roughness features. The second key feature is the ability to incorporate dynamical geologic processes affecting grain surfaces in natural settings, such as dissolution and crystallization. We describe the model and its main components, and point out implications for the geologically-relevant chronometers mentioned above.

Lee, V. E.; Huber, C.

2012-12-01

9

Nuclear recoil effects in antiprotonic and muonic atoms  

SciTech Connect

Relativistic nuclear recoil effects are studied for antiprotonic and muonic atoms. The generalization of the Breit-Pauli Hamiltonian including vacuum polarization is presented. Previous treatments are corrected, and the result for the 2S{sub 12}-2P{sub 12} splitting in muonic hydrogen is updated.

Veitia, Andrzej; Pachucki, Krzysztof [Institute of Theoretical Physics, Warsaw University, Hoz-dota 69, 00-681 Warsaw (Poland)

2004-04-01

10

Classical and quantum regimes in the collective atomic recoil laser from a Bose-Einstein condensate  

NASA Astrophysics Data System (ADS)

A collective atomic recoil laser (CARL) realized with a Bose-Einstein condensate offers the possibility to investigate new effects in the coherent interaction between optical and matter waves. This paper discusses some aspects of the nonlinear evolution of scattered radiation and the matter-wave field in the high-Q cavity and superradiant CARL regimes.

Piovella, N.; Cola, M.; Bonifacio, R.

2004-06-01

11

Collective atomic recoil lasing including friction and diffusion effects  

NASA Astrophysics Data System (ADS)

We extend the collective atomic recoil lasing (CARL) model including the effects of friction and diffusion forces acting on the atoms due to the presence of optical molasses fields. The results from this model are consistent with those from a recent experiment by Kruse et al. [

Phys. Rev. Lett. 91, 183601 (2003)
]. In particular, we obtain a threshold condition above which collective backscattering occurs. Using a nonlinear analysis we show that the backscattered field and the bunching evolve to a steady state, in contrast to the nonstationary behavior of the standard CARL model. For a proper choice of the parameters, this steady state can be superfluorescent.

Robb, G. R.; Piovella, N.; Ferraro, A.; Bonifacio, R.; Courteille, Ph. W.; Zimmermann, C.

2004-04-01

12

Propagation effects in a collective atomic recoil laser  

NASA Astrophysics Data System (ADS)

We present a theoretical investigation of propagation effects in a collective atomic recoil laser (CARL) operating in the FEL limit. We consider the cases where the system evolves while in free space and while enclosed in a ring cavity. In the case where no cavity is present, we show that the scattered radiation consists of soliton-like superfluorescent pulses. In the case of a 'good' cavity we arrive analytically at a condition to neglect propagation effects. This condition implies that in order to use the so-called mean field approximation, the condition {(? L) }/{l {3}/{2}c}?0, T ? 0 must be satisfied with {(Tl c}/{(? L) {2}/{3}} finite where lc is the cooperation length of the system, T is the transmission coefficient of the mirrors, L and ? are the sample length and cavity length respectively. We confirm the validity of this condition using a numerical analysis and provide a simple physical interpretation. In the mean field limit, we show that if the cavity linewidth is greater than the spectral width of the pulse emitted by the sample, the emission remains superfluorescent and is not sensitive to the presence of the cavity. We also show that in the opposite case the emission is sensitive to the cavity parameters and no longer superfluorescent.

Bonifacio, R.; De Salvo, L.; Robb, G. R. M.

1997-02-01

13

Reactive and inelastic hydrogen + deuterium collisions: Classical recoil, quantum interference, and the tug-of-war mechanism  

NASA Astrophysics Data System (ADS)

Differential cross sections (DCSs) are presented for reactive and inelastic H + D2 collisions over a wide range of collision energies and product quantum states. A mixture of HBr and D2 is expanded into a vacuum chamber; a laser photolyzes HBr to initiate the collision process. Three-dimensional ion imaging is employed to detect HD/D2 products that have been quantum state selected by resonance enhanced multiphoton ionization. The construction of the imaging instrument and a novel application of two-color Doppler-free ionization are described. Reactively scattered HD(v' = 1, j') products are mostly back scattered, and the DCS contains a single peak; the dependence of the DCS on the collision energy over the range 1.48 ? Ecoll ? 1.94 eV is very weak. This behavior is consistent with the direct recoil mechanism that is known to be dominant. For HD( v' = 1, j' = 1, 2) at collision energies Ecoll ? 1.72 eV, a bimodal feature is observed, which may be caused by indirect scattering from the conical intersection. For HD( v' = 3, j = 0), there are three major peaks whose widths and centers vary rapidly with the collision energy. Recent quantum mechanical (QM) calculations attributed this behavior to the interference between nearside and farside pathways. New and existing QM calculations accurately reproduce the measured DCSs for reactive scattering; the experiments presented here corroborate the theoretical predictions to a much higher level of detail compared with previous measurements. Inelastically scattered D2(v' = 1-4, j') products are mostly forward scattered. This observation is contrary to the commonly accepted wisdom that collisions capable of transferring a large amount of energy into vibration occur at low impact parameters and are back scattered. We compare our results with quasi-classical trajectory calculations and suggest that the forward scattering can be explained by a tug-of-war mechanism in which attractive forces dominate the inelastic scattering process. Many inelastic trajectories recross the reaction barrier, and we find evidence of quantum interference effects for D2(v' = 3, j' ? 2) that may be related to those observed for the HD( v' = 3, j' = 0) reactive channel.

Goldberg, Noah Tribe

14

Quantum effects in electron beam pumped GaAs  

SciTech Connect

Propagation of waves in nano-sized GaAs semiconductor induced by electron beam are investigated. A dispersion relation is derived by using quantum hydrodynamics equations including the electrons and holes quantum recoil effects, exchange-correlation potentials, and degenerate pressures. It is found that the propagating modes are instable and strongly depend on the electron beam parameters, as well as the quantum recoil effects and degenerate pressures. The instability region shrinks with the increase of the semiconductor number density. The instability arises because of the energetic electron beam produces electron-hole pairs, which do not keep in phase with the electrostatic potential arising from the pair plasma.

Yahia, M. E. [Faculty of Engineering, The British University in Egypt (BUE), El-Shorouk City, Cairo (Egypt) [Faculty of Engineering, The British University in Egypt (BUE), El-Shorouk City, Cairo (Egypt); National Institute of Laser Enhanced Sciences (NILES), Cairo University (Egypt); Azzouz, I. M. [National Institute of Laser Enhanced Sciences (NILES), Cairo University (Egypt)] [National Institute of Laser Enhanced Sciences (NILES), Cairo University (Egypt); Moslem, W. M. [Department of Physics, Faculty of Science, Port Said University, Port Said (Egypt)] [Department of Physics, Faculty of Science, Port Said University, Port Said (Egypt)

2013-08-19

15

Quantum effects in electron beam pumped GaAs  

NASA Astrophysics Data System (ADS)

Propagation of waves in nano-sized GaAs semiconductor induced by electron beam are investigated. A dispersion relation is derived by using quantum hydrodynamics equations including the electrons and holes quantum recoil effects, exchange-correlation potentials, and degenerate pressures. It is found that the propagating modes are instable and strongly depend on the electron beam parameters, as well as the quantum recoil effects and degenerate pressures. The instability region shrinks with the increase of the semiconductor number density. The instability arises because of the energetic electron beam produces electron-hole pairs, which do not keep in phase with the electrostatic potential arising from the pair plasma.

Yahia, M. E.; Azzouz, I. M.; Moslem, W. M.

2013-08-01

16

Exploring relativistic many-body recoil effects in highly charged ions.  

PubMed

The relativistic recoil effect has been the object of experimental investigations using highly charged ions at the Heidelberg electron beam ion trap. Its scaling with the nuclear charge Z boosts its contribution to a measurable level in the magnetic-dipole (M1) transitions of B- and Be-like Ar ions. The isotope shifts of 36Ar versus 40Ar have been detected with sub-ppm accuracy, and the recoil effect contribution was extracted from the 1s(2)2s(2)2p 2P(1/2) - 2P(3/2) transition in Ar13+ and the 1s(2)2s2p 3P1-3P2 transition in Ar14+. The experimental isotope shifts of 0.00123(6) nm (Ar13+) and 0.00120(10) nm (Ar14+) are in agreement with our present predictions of 0.00123(5) nm (Ar13+) and 0.00122(5) nm (Ar14+) based on the total relativistic recoil operator, confirming that a thorough understanding of correlated relativistic electron dynamics is necessary even in a region of intermediate nuclear charges. PMID:17025810

Orts, R Soria; Harman, Z; López-Urrutia, J R Crespo; Artemyev, A N; Bruhns, H; Martínez, A J González; Jentschura, U D; Keitel, C H; Lapierre, A; Mironov, V; Shabaev, V M; Tawara, H; Tupitsyn, I I; Ullrich, J; Volotka, A V

2006-09-01

17

Isotopic disequilibrium of uranium: alpha-recoil damage and preferential solution effects  

SciTech Connect

Preferential loss of uranium-234 relative to uranium-238 from rocks into solutions has long been attributed to recoiling alpha-emitting nuclei. Direct evidence has been obtained for two mechanisms, first, recoil ejection from grains, and now release by natural etching of alpha-recoil tracks. The observations have implications for radon emanation and for the storage of alpha-emitting radioactive waste.

Fleischer, R.L.

1980-02-29

18

Photon statistics and quantum fluctuations in a Collective Atomic Recoil Laser (CARL)  

NASA Astrophysics Data System (ADS)

We present a complete quantum mechanical treatment of the exponential instability of CARL. We show that the Glauber P function, in general, is the one that results from a superposition of a coherent probe field and the spontaneous emission chaotic field. In particular, if no probe is present the photon statistics during the exponential growth is that of a chaotic thermal field.

Bonifacio, Rodolfo

1998-01-01

19

The alpha-recoil effects of uranium in the Oklo reactor  

NASA Astrophysics Data System (ADS)

A series of acid-leaching experiments have been carried out on a sample of uranium ore from reactor zone number 10 of the Oklo mines in Gabon. Anomalously high U-234/U-238 ratios were observed accompanied by modestly increased U-235/U-238 ratios in uranium fractions. These results, which can be interpreted as being due to the alpha-recoil effects of U-238 and Pu-239, provide a convenient way of calculating the conversion factor (the fraction of uranium atoms converted to plutonium) of the natural reactors from radiochemical data, obviating the necessity for mass-spectrometric measurements.

Sheng, Z. Z.; Kuroda, P. K.

1984-12-01

20

Quantum zeno effect  

Microsoft Academic Search

Misra and Sudarshan pointed out, based on the quantum measurement theory, that repeated measurements lead to a slowing down of the transition, which they called the quantum Zeno effect. Recently, Itano, Heinzen, Bollinger and Wineland have reported that they succeeded in observing that effect. We show that the results of Itano et al. can be recovered through conventional quantum mechanics

T. Petrosky; S. Tasaki; I. Prigogine

1990-01-01

21

Concept of Gamma-Ray Lasing Assisted by Nuclear Recoil Effect.  

National Technical Information Service (NTIS)

This report results from a contract tasking MIREA Technical University as follows: The contractor will develop an analytical and quantitatively proven treatment of how to incorporate the nuclear recoil phenomenon into the nuclear gamma-ray lasing process,...

L. A. Rivlin

1999-01-01

22

Calculation of recoil ion effective track lengths in neutron-radiation-induced nucleation  

SciTech Connect

A theoretical model was developed to predict the amount of nucleation that occurs as a result of neutron interactions in superheated liquids. The model utilizes nuclear cross-section data, charged-particle linear energy transfer information, and computations of critical bubble nucleation energy to generate the number of bubbles formed in superheated liquid droplet ('bubble') neutron detectors exposed to neutron fluxes of specified intensity and energy. Previous experimental attempts to relate effective (energy-depositing) ion track length L to critical bubble radius r[sub c] using a dimensionless coefficient were unsuccessful. The formulation of a new coefficient b, equal to the ratio of effective ion track length L to the seed bubble radius r[sub o] is now proposed. By parameterizing the value of b within the model, the least-squares best value of b was determined to be 4.3 for both high-and low-energy [sup 252]Cf neutrons. Thus, the effective recoil ion track length in radiation-induced nucleation can be determined if the seed bubble radius is known.

Harper, M.J. (United States Naval Academy, Annapolis, MD (United States))

1993-06-01

23

Effect of recoiled O on damage regrowth and electrical properties of through-oxide implanted Si  

SciTech Connect

High dose (4 to 7.5 x 10/sup 15/ cm/sup -2/) As implantations into p-type (100) Si have been carried out through a screen-oxide of thicknesses less than or equal to 775A and without screen oxide. The effect of recoiled O on damage annealing and electrical properties of the implanted layers has been investigated using a combination of the following techniques: TEM, RBS/MeV He/sup +/ channeling, SIMS and Hall measurements in conjunction with chemical stripping and sheet resistivity measurements. The TEM results show that there is a dramatically different annealing behavior of the implantation damage for the through oxide implants (Case I) as compared to implants into bare silicon (Case II). Comparison of the structural defect profiles with O distributions obtained by SIMS demonstrated that retardation in the secondary damage growth in Case I can be directly related with the presence of O. Weak-beam TEM showed that a high density of fine defect clusters (less than or equal to 50A) were present both in Case I and Case II. The electrical profiles showed only 30% of the total As to be electrically active. The structural and electrical results have been explained by a model that entails As-O, Si-O and As-As complex formation and their interaction with the dislocations.

Sadana, D.K.; Wu, N.R.; Washburn, J.; Current, M.; Morgan, A.; Reed, D.; Maenpaa, M.

1982-10-01

24

Temperature Dependence and Recoil-free Fraction Effects in Olivines Across the Mg-Fe Solid Solution  

NASA Technical Reports Server (NTRS)

Olivine and pyroxene are the major ferromagnesian minerals in most meteorite types and in mafic igneous rocks that are dominant at the surface of the Earth. It is probable that they are the major mineralogical components at the surface of any planetary body that has undergone differentiation processes. In situ mineralogical studies of the rocks and soils on Mars suggest that olivine is a widespread mineral on that planet s surface (particularly at the Gusev site) and that it has been relatively unaffected by alteration. Thus an understanding of the characteristics of Mossbauer spectra of olivine is of great importance in interpreting MER results. However, variable temperature Mossbauer spectra of olivine, which are needed to quantify recoil-free fraction effects and to understand the temperature dependence of olivine spectra, are lacking in the literature. Thus, we present here a study of the temperature dependence and recoil-free fraction of a series of synthetic olivines.

Sklute, E. C.; Rothstein, Y.; Dyar, M. D.; Schaefer, M. W.; Menzies, O. N.; Bland, P. A.; Berry, F. J.

2005-01-01

25

Alpha-recoil in U–Pb geochronology: effective sample size matters  

Microsoft Academic Search

Displacement of the daughter isotope by a-recoil results in an open system on the nanoscale. For a heterogeneous distribution of U and Th, this redistribution of intermediate and stable daughter isotopes results in subvolumes with a deficit of Pb and others with an excess of Pb. Whether such heterogeneities affect the analyzed U–Pb system depends on: (1) the volume of

Rolf L. Romer

2003-01-01

26

Doppler broadening and collision effects in a collective atomic recoil laser  

NASA Astrophysics Data System (ADS)

We outline the basic physics of CARL in the cold and warm beam limits showing that recoil gain and self bunching can occur with very different features and intensities depending on the relevance of the velocity spead. In the cold beam limit we find the well known high gain FEL regime, whereas in the warm beam limit one has a small gain regime described by the derivative of the thermal velocity distribution.

Bonifacio, R.; Verkerk, P.

1996-02-01

27

Effects of post-Newtonian spin alignment on the distribution of black-hole recoils  

NASA Astrophysics Data System (ADS)

Recent numerical relativity simulations have shown that the final black hole produced in a binary merger can recoil with a velocity as large as 5000km/s. Because of enhanced gravitational-wave emission in the so-called “hang-up” configurations, this maximum recoil occurs when the black-hole spins are partially aligned with the orbital angular momentum. We revisit our previous statistical analysis of post-Newtonian evolutions of black-hole binaries in the light of these new findings. We demonstrate that despite these new configurations with enhanced recoil velocities, spin alignment during the post-Newtonian stage of the inspiral will still significantly suppress (or enhance) kick magnitudes when the initial spin of the more massive black hole is more (or less) closely aligned with the orbital angular momentum than that of the smaller hole. We present a preliminary study of how this post-Newtonian spin alignment affects the ejection probabilities of supermassive black holes from their host galaxies with astrophysically motivated mass ratio and initial spin distributions. We find that spin alignment suppresses (enhances) ejection probabilities by ˜40% (20%) for an observationally motivated mass-dependent galactic escape velocity, and by an even greater amount for a constant escape velocity of 1000km/s. Kick suppression is thus at least a factor two more efficient than enhancement.

Berti, Emanuele; Kesden, Michael; Sperhake, Ulrich

2012-06-01

28

Recoil effects of a motional scatterer on single-photon scattering in one dimension  

PubMed Central

The scattering of a single photon with sufficiently high energy can cause a recoil of a motional scatterer. We study its backaction on the photon's coherent transport in one dimension by modeling the motional scatterer as a two-level system, which is trapped in a harmonic potential. While the reflection spectrum is of a single peak in the Lamb-Dicke limit, multi-peaks due to phonon excitations can be observed in the reflection spectrum as the trap becomes looser or the mass of the two-level system becomes smaller.

Li, Qiong; Xu, D. Z.; Cai, C. Y.; Sun, C. P.

2013-01-01

29

Quantum effects in biology  

Microsoft Academic Search

The idea that quantum-mechanical phenomena can play nontrivial roles in biology has fascinated researchers for a century. Here we review some examples of such effects, including light-harvesting in photosynthesis, vision, electron- and proton-tunneling, olfactory sensing, and magnetoreception. We examine how experimental tests have aided this field in recent years and discuss the importance of developing new experimental probes for future

Graham R. Fleming; Gregory D. Scholes; Yuan-Chung Cheng

2011-01-01

30

Quantum Zeno effect: Quantum shuffling and Markovianity  

NASA Astrophysics Data System (ADS)

The behavior displayed by a quantum system when it is perturbed by a series of von Neumann measurements along time is analyzed. Because of the similarity between this general process with giving a deck of playing cards a shuffle, here it is referred to as quantum shuffling, showing that the quantum Zeno and anti-Zeno effects emerge naturally as two time limits. Within this framework, a connection between the gradual transition from anti-Zeno to Zeno behavior and the appearance of an underlying Markovian dynamics is found. Accordingly, although a priori it might result counterintuitive, the quantum Zeno effect corresponds to a dynamical regime where any trace of knowledge on how the unperturbed system should evolve initially is wiped out (very rapid shuffling). This would explain why the system apparently does not evolve or decay for a relatively long time, although it eventually undergoes an exponential decay. By means of a simple working model, conditions characterizing the shuffling dynamics have been determined, which can be of help to understand and to devise quantum control mechanisms in a number of processes from the atomic, molecular and optical physics.

Sanz, A. S.; Sanz-Sanz, C.; González-Lezana, T.; Roncero, O.; Miret-Artés, S.

2012-04-01

31

Effective Constraints for Quantum Systems  

Microsoft Academic Search

An effective formalism for quantum constrained systems is presented which allows manageable derivations of solutions and observables, including a treatment of physical reality conditions without requiring full knowledge of the physical inner product. Instead of a state equation from a constraint operator, an infinite system of constraint functions on the quantum phase space of expectation values and moments of states

Martin Bojowald; Barbara Sandhöfer; Aureliano Skirzewski; Artur Tsobanjan

2009-01-01

32

Photon recoil momentum in dispersive media.  

PubMed

A systematic shift of the photon recoil momentum due to the index of refraction of a dilute gas of atoms has been observed. The recoil frequency was determined with a two-pulse light grating interferometer using near-resonant laser light. The results show that the recoil momentum of atoms caused by the absorption of a photon is n variant Planck's k, where n is the index of refraction of the gas and k is the vacuum wave vector of the photon. This systematic effect must be accounted for in high-precision atom interferometry with light gratings. PMID:15904272

Campbell, Gretchen K; Leanhardt, Aaron E; Mun, Jongchul; Boyd, Micah; Streed, Erik W; Ketterle, Wolfgang; Pritchard, David E

2005-05-01

33

Photon Recoil Momentum in Dispersive Media  

SciTech Connect

A systematic shift of the photon recoil momentum due to the index of refraction of a dilute gas of atoms has been observed. The recoil frequency was determined with a two-pulse light grating interferometer using near-resonant laser light. The results show that the recoil momentum of atoms caused by the absorption of a photon is n({Dirac_h}/2{pi})k, where n is the index of refraction of the gas and k is the vacuum wave vector of the photon. This systematic effect must be accounted for in high-precision atom interferometry with light gratings.

Campbell, Gretchen K.; Leanhardt, Aaron E.; Mun, Jongchul; Boyd, Micah; Streed, Erik W.; Ketterle, Wolfgang; Pritchard, David E. [MIT-Harvard Center for Ultracold Atoms, Research Laboratory of Electronics and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

2005-05-06

34

Quantum Wipe Effect  

NASA Astrophysics Data System (ADS)

We consider a model of a spin system under the influence of decoherence such that a system coupled with a dissipating environmental system consisting of either spins or bosonic modes. The dissipation of an environment is governed by a certain probability with which an environmental system localized around a principal system dissipates into a larger bath and a thermal environmental system instead migrates into the place. A certain threshold on the probability is found in the growth of decoherence in a principal system. A larger as well as a smaller dissipation probability than the threshold results in smaller decoherence. This finding is utilized to elucidate a spin relaxation theory of a magnetic resonance spectrometer. In particular, a seamless description of transverse relaxation and motional narrowing is possible. We also numerically evaluate the dynamics of coherence useful for quantum information processing. The bang-bang control and anti-Zeno effect in entanglement and the Oppenheim-Horodecki nonclassical correlation are investigated in the model of spin-boson coupling.

Saitoh, Akira; Rahimi, Robabeh; Nakahara, Mikio

2010-11-01

35

Transport of Radioactive Material by Alpha Recoil  

SciTech Connect

The movement of high-specific-activity radioactive particles (i.e., alpha recoil) has been observed and studied since the early 1900s. These studies have been motivated by concerns about containment of radioactivity and the protection of human health. Additionally, studies have investigated the potential advantage of alpha recoil to effect separations of various isotopes. This report provides a review of the observations and results of a number of the studies.

Icenhour, A.S.

2005-05-19

36

Transport of Radioactive Material by Alpha Recoil  

Microsoft Academic Search

The movement of high-specific-activity radioactive particles (i.e., alpha recoil) has been observed and studied since the early 1900s. These studies have been motivated by concerns about containment of radioactivity and the protection of human health. Additionally, studies have investigated the potential advantage of alpha recoil to effect separations of various isotopes. This report provides a review of the observations and

A. S. Icenhour

2005-01-01

37

The recoil shadow anisotropy method  

NASA Astrophysics Data System (ADS)

The Recoil Shadow Anisotropy Method (RSAM) is a new experimental method for identifying isomers in the nanosecond range and measuring their half-lives. This method can be applied to experiments performed with thin targets and ?-ray multidetector arrays including collimated composite detectors and does not require any additional device. It uses the shadow effect imposed by the collimators on the different elements of composite detectors for ?-rays emitted by recoiling nuclei. RSAM was developed for the clover detectors of the Eurogam-2 array and tested using several data sets obtained with this array. A number of known isomers with half-lives lying between 0.9 and 18 ns in 194Hg, 191Au, 148Gd, 149Gd, 193Pb and 194Pb have been successfully re-measured, proving the ability of RSAM for lifetime measurements.

Gueorguieva, E.; Kaci, M.; Schück, C.; Minkova, A.; Vieu, Ch.; Correia, J. J.; Dionisio, J. S.

2001-12-01

38

Quantum Chaos and Effective Thermalization  

NASA Astrophysics Data System (ADS)

We demonstrate effective equilibration for unitary quantum dynamics under conditions of classical chaos. Focusing on the paradigmatic example of the Dicke model, we show how a constructive description of the thermalization process is facilitated by the Glauber Q or Husimi function, for which the evolution equation turns out to be of Fokker-Planck type. The equation describes a competition of classical drift and quantum diffusion in contractive and expansive directions. By this mechanism the system follows a “quantum smoothened” approach to equilibrium, which avoids the notorious singularities inherent to classical chaotic flows.

Altland, Alexander; Haake, Fritz

2012-02-01

39

Quantum chaos and effective thermalization.  

PubMed

We demonstrate effective equilibration for unitary quantum dynamics under conditions of classical chaos. Focusing on the paradigmatic example of the Dicke model, we show how a constructive description of the thermalization process is facilitated by the Glauber Q or Husimi function, for which the evolution equation turns out to be of Fokker-Planck type. The equation describes a competition of classical drift and quantum diffusion in contractive and expansive directions. By this mechanism the system follows a "quantum smoothened" approach to equilibrium, which avoids the notorious singularities inherent to classical chaotic flows. PMID:22401203

Altland, Alexander; Haake, Fritz

2012-02-17

40

The HERMES recoil detector  

NASA Astrophysics Data System (ADS)

For the final running period of HERA, a recoil detector was installed at the HERMES experiment to improve measurements of hard exclusive processes in charged-lepton nucleon scattering. Here, deeply virtual Compton scattering is of particular interest as this process provides constraints on generalised parton distributions that give access to the total angular momenta of quarks within the nucleon. The HERMES recoil detector was designed to improve the selection of exclusive events by a direct measurement of the four-momentum of the recoiling particle. It consisted of three components: two layers of double-sided silicon strip sensors inside the HERA beam vacuum, a two-barrel scintillating fibre tracker, and a photon detector. All sub-detectors were located inside a solenoidal magnetic field with a field strength of 1T. The recoil detector was installed in late 2005. After the commissioning of all components was finished in September 2006, it operated stably until the end of data taking at HERA end of June 2007. The present paper gives a brief overview of the physics processes of interest and the general detector design. The recoil detector components, their calibration, the momentum reconstruction of charged particles, and the event selection are described in detail. The paper closes with a summary of the performance of the detection system.

Airapetian, A.; Aschenauer, E. C.; Belostotski, S.; Borisenko, A.; Bowles, J.; Brodski, I.; Bryzgalov, V.; Burns, J.; Capitani, G. P.; Carassiti, V.; Ciullo, G.; Clarkson, A.; Contalbrigo, M.; De Leo, R.; De Sanctis, E.; Diefenthaler, M.; Di Nezza, P.; Düren, M.; Ehrenfried, M.; Guler, H.; Gregor, I. M.; Hartig, M.; Hill, G.; Hoek, M.; Holler, Y.; Hristova, I.; Jo, H. S.; Kaiser, R.; Keri, T.; Kisselev, A.; Krause, B.; Krauss, B.; Lagamba, L.; Lehmann, I.; Lenisa, P.; Lu, S.; Lu, X.-G.; Lumsden, S.; Mahon, D.; Martinez de la Ossa, A.; Murray, M.; Mussgiller, A.; Nowak, W.-D.; Naryshkin, Y.; Osborne, A.; Pappalardo, L. L.; Perez-Benito, R.; Petrov, A.; Pickert, N.; Prahl, V.; Protopopescu, D.; Reinecke, M.; Riedl, C.; Rith, K.; Rosner, G.; Rubacek, L.; Ryckbosch, D.; Salomatin, Y.; Schnell, G.; Seitz, B.; Shearer, C.; Shutov, V.; Statera, M.; Steijger, J. J. M.; Stenzel, H.; Stewart, J.; Stinzing, F.; Trzcinski, A.; Tytgat, M.; Vandenbroucke, A.; Van Haarlem, Y.; Van Hulse, C.; Varanda, M.; Veretennikov, D.; Vilardi, I.; Vikhrov, V.; Vogel, C.; Yaschenko, S.; Ye, Z.; Yu, W.; Zeiler, D.; Zihlmann, B.

2013-05-01

41

Theory of multi-electron recoil effects on x-ray lineshapes of metals  

SciTech Connect

Within the change of self-consistent field approximation, x-ray spectra can be considerably richer in many-electron phenomena than once suspected. With the finite number of electrons method, these spectra can be evaluated for realistic electron-hole interactions in free electron metals. Preliminary results indicate that metals with band structure can also be treated this way. However, theories of final-state interactions in metals await the reliable determinations of the screened potential of a core hole in a metal and realistic avaluation of the effects of electron-electron interactions. (GHT)

Dow, J. D.; Swarts, C. A.; Bowen, M. A.; Mehreteab, E.; Satpathy, S. S.

1980-01-01

42

Quantum Annealing and Quantum Fluctuation Effect in Frustrated Ising Systems  

NASA Astrophysics Data System (ADS)

Quantum annealing method has been widely attracted attention in statistical physics and information science since it is expected to be a powerful method to obtain the best solution of optimization problem as well as simulated annealing. The quantum annealing method was incubated in quantum statistical physics. This is an alternative method of the simulated annealing which is well-adopted for many optimization problems. In the simulated annealing, we obtain a solution of optimization problem by decreasing temperature (thermal fluctuation) gradually. In the quantum annealing, in contrast, we decrease quantum field (quantum fluctuation) gradually and obtain a solution. In this paper we review how to implement quantum annealing and show some quantum fluctuation effects in frustrated Ising spin systems.

Tanaka, Shu; Tamura, Ryo

2013-09-01

43

Comparison of quantum confinement effects between quantum wires and dots  

SciTech Connect

Dimensionality is an important factor to govern the electronic structures of semiconductor nanocrystals. The quantum confinement energies in one-dimensional quantum wires and zero-dimensional quantum dots are quite different. Using large-scale first-principles calculations, we systematically study the electronic structures of semiconductor (including group IV, III-V, and II-VI) surface-passivated quantum wires and dots. The band-gap energies of quantum wires and dots have the same scaling with diameter for a given material. The ratio of band-gap-increases between quantum wires and dots is material-dependent, and slightly deviates from 0.586 predicted by effective-mass approximation. Highly linear polarization of photoluminescence in quantum wires is found. The degree of polarization decreases with the increasing temperature and size.

Li, Jingbo; Wang, Lin-Wang

2004-03-30

44

Biological Effect of Lead-212 Localized in the Nucleus of Mammalian Cells: Role of Recoil Energy in the Radiotoxicity of Internal Alpha-Particle Emitters1  

PubMed Central

The radiochemical dipyrrolidinedithiocarbamato-212Pb(II) [212Pb(PDC)2] is synthesized and its effects on colony formation in cultured Chinese hamster V79 cells are investigated. The cellular uptake, biological retention, subcellular distribution and cytotoxicity of the radiocompound are determined. The 212Pb is taken up quickly by the cells, reaching saturation levels in 1.25 h. When the cells are washed, the intracellular activity is retained with a biological half-life of 11.6 h. Gamma-ray spectroscopy indicates that the 212Pb daughters (212Bi, 212Po and 208Tl) are in secular equilibrium within the cell. About 72% of the cellular activity localizes in the cell nucleus, of which 35% is bound specifically to nuclear DNA. The mean cellular uptake required to achieve 37% survival is 0.35 mBq of 212Pb per cell, which delivers a dose of 1.0 Gy to the cell nucleus when the recoil energy of 212Bi and 212Po decays is ignored and 1.7 Gy when recoil is included. The corresponding RBE values compared to acute external 137Cs ? rays at 37% survival are 4.0 and 2.3, respectively. The chemical Pb(PDC)2 is not chemotoxic at the concentrations used in this study. Because the ?-particle emitter 212Pb decays to the ?-particle-emitting daughters 212Bi and 212Po, these studies provide information on the biological effects of ?-particle decays that occur in the cell nucleus. Our earlier studies with cells of the same cell line using 210Po (emits 5.3 MeV ? particle) localized predominantly in the cytoplasm resulted in an RBE of 6. These earlier results for 210Po, along with the present results for 212Pb, suggest that the recoil energy associated with the 212Bi and 212Po daughter nuclei plays little or no role in imparting biological damage to critical targets in the cell nucleus.

Azure, Michael T.; Archer, Ronald D.; Sastry, Kandula S. R.; Rao, Dandamudi V.; Howell, Roger W.

2012-01-01

45

Correlation Effects in Quantum Crystals  

Microsoft Academic Search

Correlation effects in the quantum crystals He3 and He4 are studied in detail. The single-particle wave function is obtained in the harmonic effective-field approximation; the parameters of the harmonic-oscillator potential are determined self-consistently from the two-body correlation function and the bare interatomic potential. We determine the two-body correlation function by solving numerically an equation derived by decoupling the three-body correlation

C. Ebner; C. C. Sung

1971-01-01

46

Theory of a collective atomic recoil laser  

NASA Astrophysics Data System (ADS)

We perform a study of a collective atomic recoil laser (CARL) that goes beyond the initial growth period. The study is based on a theory that treats both internal and external degrees of atomic freedom quantum mechanically but regards the laser light as a classical field obeying Maxwell's equations. We introduce the concepts of momentum families and diffraction groups and organize the matter wave equations in terms of diffraction groups. The steady-state lasing conditions are discussed in connection with the probe gain in the recoil-induced resonances. The nontrivial steady states and the linear stability analysis of the steady states are both carried out by the method of two-dimensional continued fractions. Both stable and unstable nontrivial steady states are calculated and discussed in the context of regarding the CARL as multiwave mixing involving many modes of matter waves and two optical fields.

Ling, H. Y.; Pu, H.; Baksmaty, L.; Bigelow, N. P.

2001-05-01

47

Nuclear Quantum Effects in Water  

NASA Astrophysics Data System (ADS)

A path-integral Car-Parrinello molecular dynamics simulation of liquid water and ice is performed. It is found that the inclusion of nuclear quantum effects systematically improves the agreement of first-principles simulations of liquid water with experiment. In addition, the proton momentum distribution is computed utilizing a recently developed open path-integral molecular dynamics methodology. It is shown that these results are in good agreement with experimental data.

Morrone, Joseph A.; Car, Roberto

2008-07-01

48

The Quantum Hall Effect Revisited  

NASA Astrophysics Data System (ADS)

Experiments shown here reveal inflection points of the Hall resistivity at half-integer filling factors 5/2 and 7/2 which become more pronounced with increasing current and finally lead to half-integer plateau like structures. These features contradict the edge-state picture of the quantum Hall effect (QHE) and also the disorder picture of the QHE, which cannot explain a gap directly in the middle of a Landau level. We present a novel approach to the quantum Hall effect, which allows us to calculate the electronic transport in a highly non-uniform Hall field, which is present in two opposite corners of a Hall bar, the hot-spots. Precisely in one corner electrons are injected into the device and we derive the local density of states there. We obtain a self-consistent equation for the current-voltage relation through the Ohmic contact and thus a computable theory of the quantum Hall effect, which predicts a unique modulation and splitting of Landau levels caused by the presence of a high electric field exactly in line with the experimental observations.

Kramer, Tobias; Heller, E. J.; Parrott, R. E.; Liang, C.-T.; Huang, C. F.; Chen, K. Y.; Lin, L.-H.; Wu, J.-Y.; Lin, S.-D.

2009-03-01

49

Quantum gravity effects on space-time  

Microsoft Academic Search

General relativity promotes space-time to a physical, dynamical object subject to equations of motion. Quantum gravity, accordingly, must provide a quantum framework for space-time, applicable on the smallest distance scales. Just like generic states in quantum mechanics, quantum space-time structures may be highly counter-intuitive. But if low-energy effects can be extracted, they shed considerable light on the implications to be

Martin Bojowald

2010-01-01

50

Sonic Rarefaction Wave Low Recoil Gun.  

National Technical Information Service (NTIS)

A principal challenge faced by the U.S. Army TACOM-ARDEC Benet Laboratories in the design of armaments for lightweight future fighting vehicles with lethality overmatch is mitigating the deleterious effects of large caliber cannon recoil. The sonic RArefa...

E. Kathe R. Dillon

2002-01-01

51

Quantum Interference Effects for the Electronic Fluctuations in Quantum Dots  

NASA Astrophysics Data System (ADS)

For the main quantum interference term of coherent electronic transport, we study the effect of temperature, perpendicular and/or parallel magnetic fields, spin-orbit coupling and tunneling rates in both metallic grains and mesoscopic heterostructures. We show that the Zeeman effects determines a crucial way to characterize the quantum interference phenomena of the noise for anisotropic systems (mesoscopic heterostructures), qualitatively distinct from those observed in isotropic structures (metallic grains).

Ramos, J. G. G. S.; Barbosa, A. L. R.; Hussein, M. S.

2014-06-01

52

The Effect of Dopant Dose Loss during Annealing on Heavily Doped Surface Layers Obtained by Recoil Implantation of Antimony in Silicon  

NASA Astrophysics Data System (ADS)

The aim of our investigation is focused on studying the effect of dopant dose loss during annealing treatments on heavily doped surface layers, obtained by recoil implantation of antimony in silicon. We are interested particularly by the increase of sheet resistance consequently to the shallow junctions obtained at the surface of substrate and the contribution of the dopant dose loss phenomenon following the high concentration of impurities at the surface. In this work, we report some quantitative data concerning the dopant loss at the surface of silicon implanted and its dependence with annealing treatments. Electrical measurements associated with Rutherford backscattering (RBS) technical analysis showed interesting values of sheet resistance compared with classical ion implantation and despite dopant dose loss phenomenon.

Mesli, M. N.; Benbahi, B.; Bouafia, H.; Belmekki, M.; Abidri, B.; Hiadsi, S.

2013-08-01

53

Quantum Gravity Effect on Neutrino Oscillation  

NASA Astrophysics Data System (ADS)

The quantum gravity may have strong consequence for neutrino oscillation phenemomenon over a large distance.We found a significant modification of neutrino oscillation due to quantum gravity effects. Quantum gravity (Planck scale effects) leads to an effective S U(2) L ×U(1) invariant dimension-5 Lagrangian involving, neutrino and Higgs fields. On symmetry breaking, this operator gives rise to correction to the neutrino masses and mixing. The gravitational interaction (M X =M p l ) demands that the element of this perturbation matrix should be independent of flavor indices. In this paper, we study the quantum gravity effects on neutrino oscillation, namely modified dispersion relation for neutrino oscillations parameter.

Koranga, Bipin Singh; Narayan, Mohan

2014-05-01

54

Stimulated Brillouin scattering in semiconductors: Quantum effects  

NASA Astrophysics Data System (ADS)

Present work is an attempt to find the influence of quantum effects on the Stimulated Brillouin Scattering in semiconductor plasmas using quantum hydrodynamic model. Third-order Brillouin susceptibility arising due to induced nonlinear current density in an n-type semiconductor crystal has been determined using coupled mode analysis. Effect of Bohm potential on the Brillouin gain coefficient is studied through the quantum corrections in classical hydrodynamic equations. It is found that the Bohm potential in the electron dynamics enhances the Brillouin gain. Reduction in the threshold pump intensity of the said process has been realized as a consequence of inclusion of quantum correction term.

Vanshpal, Ravi; Dubey, Swati; Ghosh, S.

2013-06-01

55

Quantum optics of a quantum dot: Local-field effects  

SciTech Connect

The role of local fields in quantum electrodynamics of isolated quantum dot (QD) has been analyzed. The system is modeled as a strongly confined in space two-level quantum oscillator illuminated by quantum light. Relation between local and acting fields in QD has been derived in the dipole approximation from the integral Maxwell equations for electromagnetic field operators. A formalism of the electromagnetic field quantization in electrically small scatterers has been developed. As a result, Hamiltonian of the system has been formulated in terms of the acting field with a separate term responsible for the effect of depolarization. Schroedinger equation with that Hamiltonian has been solved in linear approximation. Interaction of QD with different quantum states of light, such as Fock states, coherent states, Fock qubits, entangled states, has been analyzed. It has been shown that the local-fields induce a fine structure of the QD absorption (emission) spectrum: instead of a single line with the frequency corresponding to the exciton transition, a doublet appears with one component shifted to the blue (red). The value of the shift depends only on the geometrical and electronic properties of QD while the intensities of components are completely determined by the quantum light statistics. It has been demonstrated that in the limiting cases of classical light and single-photon state the doublet is reduced to a singlet shifted in the former case and unshifted in the latter one. A physical interpretation of the predicted effect has been proposed. Possible ways of experimental observation of the effect has been discussed together with the potentiality of its utilization in the quantum information processing.

Slepyan, G.Ya.; Maksimenko, S.A.; Hoffmann, A.; Bimberg, D. [Institute of Nuclear Problems, Belarus State University, Bobruiskaya 11, 220050 Minsk (Belarus); Institut fuer Festkoerperphysik, Technische Universitaet Berlin, Hardenbergstrasse 36, 10623 Berlin (Germany)

2002-12-01

56

Photon Landau damping of electron plasma waves with photon recoil  

SciTech Connect

Photon Landau damping of electron plasma waves with relativistic phase velocity is described, using a photon kinetic theory where photon recoil is taken into account. An exact form of the wave kinetic equation is used. Kinetic and fluid regimes of photon beam instabilities are discussed. Diffusion in the photon momentum space is derived and a quasilinear wave kinetic equation is established. In the present approach, photon recoil effects associated with the emission or absorption of plasmons are included. The neglect of recoil, which is equivalent to using the geometric optics approximation, reduces the present results to those already existing in the literature.

Mendonca, J. T.; Serbeto, A. [CFP and CFIF, Instituto Superior Tecnico, Av. Rovisco Pais 1, 1049-001 Lisbon (Portugal); Instituto de Fisica, Universidade Federal Fulminense, BR-24210-340 Niteroi, RJ (Brazil)

2006-10-15

57

Dynamic quantum Kerr effect in circuit quantum electrodynamics  

NASA Astrophysics Data System (ADS)

In the dispersive regime of circuit quantum electrodynamics (QED), where the qubit and resonator frequencies differ slightly, photons in the resonator exhibit induced frequency and phase shifts. The qubit-state dependent phase shift is usually measured by monitoring the resonator transmission spectrum at fixed qubit-resonator detuning. In this static scheme, the phase shift can only be monitored in the far-detuned, linear dispersion regime, in order to avoid measurement-induced demolition of the quantum state. By using a dynamic procedure to adiabatically drive the qubit frequency, here we are able to explore the dispersive interaction over a much broader range, and we further monitor the interaction using resonator Wigner tomography. Exotic non-linear effects on different photon states, e.g., Fock states, coherent states and Schrodinger cat states, are thereby directly revealed. Correspondingly, we demonstrate a quantum Kerr effect in the dynamic framework in circuit QED.

Yin, Yi; Wang, Haohua; Mariantoni, Matteo; Barends, Rami; Bialczak, Radoslaw C.; Chen, Yu; Lenander, Mike; Kelly, Julian; Lucero, Erik; Megrant, Anthony; O'Malley, Peter; Sank, Daniel; Wenner, Jim; White, Ted; Cleland, Andrew; Martinis, John

2012-02-01

58

Collective atomic recoil lasing  

NASA Astrophysics Data System (ADS)

A cloud of ultra-cold atoms is loaded into the attractive potential of a light wave that is generated by two counter-propagating modes of a high-finesse ring resonator. The two modes are coupled by the atoms due to coherent Rayleigh scattering and generate a potential which acts back on the motion of the atoms. This feedback leads to a new frequency component and can be described in terms of the long time proposed collective atomic recoil laser (CARL). This model is investigated experimentally and extended by introducing an optical friction force acting on the atoms. This allows for steady state operation of the CARL. Furthermore, it leads to a threshold behaviour of the CARL that translates into a novel type of phase transition: while passing the threshold the initially homogeneous atomic distribution is bunched in space and velocity. With this behaviour the system turns out to acquire some of the main features of the so-called Kuramoto model which provides a very general description of a network of limit cycle oscillators.

Zimmermann, Claus; Kruse, Dietmar; von Cube, Christoph; Slama, Sebastian; Deh, Benjamin; Courteille, Philippe

2004-06-01

59

Recoil Based Fuel Breeding Fuel Structure  

SciTech Connect

Nuclear transmutation reactions are based on the absorption of a smaller particle as neutron, proton, deuteron, alpha, etc. The resulting compound nucleus gets out of its initial lattice mainly by taking the recoil, also with help from its sudden change in chemical properties. The recoil implantation is used in correlation with thin and ultra thin materials mainly for producing radiopharmaceuticals and ultra-thin layer radioactive tracers. In nuclear reactors, the use of nano-particulate pellets could facilitate the recoil implantation for breeding, transmutation and partitioning purposes. Using enriched {sup 238}U or {sup 232}Th leads to {sup 239}Pu and {sup 233}U production while using other actinides as {sup 240}Pu, {sup 241}Am etc. leads to actinide burning. When such a lattice is immersed into a radiation resistant fluid (water, methanol, etc.), the recoiled product is transferred into the flowing fluid and removed from the hot area using a concentrator/purifier, preventing the occurrence of secondary transmutation reactions. The simulation of nuclear collision and energy transfer shows that the impacted nucleus recoils in the interstitial space creating a defect or lives small lattices. The defect diffuses, and if no recombination occurs it stops at the lattices boundaries. The nano-grains are coated in thin layer to get a hydrophilic shell to be washed by the collection liquid the particle is immersed in. The efficiency of collection depends on particle magnitude and nuclear reaction channel parameters. For {sup 239}Pu the direct recoil extraction rate is about 70% for {sup 238}UO{sub 2} grains of 5 nm diameters and is brought up to 95% by diffusion due to {sup 239}Neptunium incompatibility with Uranium dioxide lattice. Particles of 5 nm are hard to produce so a structure using particles of 100 nm have been tested. The particles were obtained by plasma sputtering in oxygen atmosphere. A novel effect as nano-cluster radiation damage robustness and cluster amplified defects rejection will be discussed. The advantage of the method and device is its ability of producing small amount of isotopic materials easy to separate, using the nuclear reactors, with higher yield than the accelerator based methods and requiring less chemistry. (author)

Popa-Simil, Liviu [R and D, LAVM LLC., Los Alamos, NM, 87544 (United States)

2008-07-01

60

Nuclear quantum effects in water  

NASA Astrophysics Data System (ADS)

In this work, a path integral Car-Parrinello molecular dynamicsootnotetextCPMD V3.11 Copyright IBM Corp 1990-2006, Copyright MPI fuer Festkoerperforschung Stuttgart 1997-2001. simulation of liquid water is performed. It is found that the inclusion of nuclear quantum effects systematically improves the agreement of first-principles simulations of liquid water with experiment. In addition, the proton momentum distribution is computed utilizing a recently developed ``open'' path integral molecular dynamics methodologyootnotetextJ.A. Morrone, V. Srinivasan, D. Sebastiani, R. Car J. Chem. Phys. 126 234504 (2007).. It is shown that these results, which are consistent with our computations of the liquid structure, are in good agreement with neutron Compton scattering dataootnotetextG.F. Reiter, J.C. Li, J. Mayers, T. Abdul-Redah, P. Platzman Braz. J. Phys. 34 142 (2004).. The remaining discrepancies between experiment and the present results are indicative of some degree of over-binding in the hydrogen bond network, likely engendered by the use of semi-local approximations to density functional theory in order to describe the electronic structure.

Morrone, Joseph; Car, Roberto

2008-03-01

61

A mesoscopic quantum gravity effect  

NASA Astrophysics Data System (ADS)

We explore the symmetry reduced form of a non-perturbative solution to the constraints of quantum gravity corresponding to quantum de Sitter space. The system has a remarkably precise analogy with the non-relativistic formulation of a particle falling in a constant gravitational field that we exploit in our analysis. We find that the solution reduces to de Sitter space in the semi-classical limit, but the uniquely quantum features of the solution have peculiar property. Namely, the unambiguous quantum structures are neither of Planck scale nor of cosmological scale. Instead, we find a periodicity in the volume of the universe whose period, using the observed value of the cosmological constant, is on the order of the volume of the proton.

Randono, Andrew

2010-08-01

62

Quantum Size Effects in Semimetals and Semiconductors.  

National Technical Information Service (NTIS)

The basic facilities for the thin film compound semiconductor program have been developed. Results were obtained in the areas of transport properties of bismuth and indium antimonide films, the theory of quantum size effects, insulating barriers with InSb...

J. R. Sites, C. W. Wilmsen

1974-01-01

63

Theory of Fractional Quantum Hall Effect.  

National Technical Information Service (NTIS)

A theory of the Fractional Quantum Hall Effect is constructed based on magnetic flux fractionization, which lead to instability of the system against selfcompression. A theorem is proved stating that arbitrary potentials fail to lift a specific degeneracy...

I. Z. Kostadinov

1985-01-01

64

Hartman effect and dissipative quantum systems  

NASA Astrophysics Data System (ADS)

The dwell time for dissipative quantum system is shown to increase with barrier width. It clearly precludes Hartman effect for dissipative systems. Here calculation has been done for inverted parabolic potential barrier.

Bhattacharya, Samyadeb; Roy, Sisir

2013-05-01

65

Effective constraints for relativistic quantum systems  

SciTech Connect

Determining the physical Hilbert space is often considered the most difficult but crucial part of completing the quantization of a constrained system. In such a situation it can be more economical to use effective constraint methods, which are extended here to relativistic systems as they arise for instance in quantum cosmology. By sidestepping explicit constructions of states, such tools allow one to arrive much more feasibly at results for physical observables at least in semiclassical regimes. Several questions discussed recently regarding effective equations and state properties in quantum cosmology, including the spreading of states and quantum backreaction, are addressed by the examples studied here.

Bojowald, Martin; Tsobanjan, Artur [Institute for Gravitation and the Cosmos, Pennsylvania State University, 104 Davey Lab, University Park, Pennsylvania 16802 (United States)

2009-12-15

66

Effect algebras and unsharp quantum logics  

Microsoft Academic Search

The effects in a quantum-mechanical system form a partial algebra and a partially ordered set which is the prototypical example of the effect algebras discussed in this paper. The relationships among effect algebras and such structures as orthoalgebras and orthomodular posets are investigated, as are morphisms and group- valued measures (or charges) on effect algebras. It is proved that there

D. J. Foulis; M. K. Bennett

1994-01-01

67

Quantum magnetoelectric effect in iron garnet  

NASA Astrophysics Data System (ADS)

The magnetoelectric response and its quantum relaxation phenomenon have been investigated for a single crystal of yttrium iron garnet. The electric-dipole moments, built in by excess localized electrons forming Fe2+ sites, never freeze even at the lowest temperature and relax through a quantum tunneling process. Application of magnetic field enhances the dielectric relaxation strength and gives rise to a large magnetocapacitance effect ( ˜13% at 10 K with 0.5 T). We show that this magnetically tunable quantum paraelectricity is associated with the Fe2+ -based magnetoelectric centers in which the electric polarization depends on the magnetization vector via the spin-orbit coupling.

Yamasaki, Yuichi; Kohara, Yuki; Tokura, Yoshinori

2009-10-01

68

Anomalous decoherence effect in a quantum bath.  

PubMed

Decoherence of quantum objects in noisy environments is important in quantum sciences and technologies. It is generally believed that different processes coupled to the same noise source have similar decoherence behaviors and stronger noises cause faster decoherence. Here we show that in a quantum bath, the case can be the opposite. We predict that the multitransition of a nitrogen-vacancy center spin-1 in diamond can have longer coherence time than the single transitions, even though the former suffers twice stronger noises from the nuclear spin bath than the latter. This anomalous decoherence effect is due to manipulation of the bath evolution via flips of the center spin. PMID:21699338

Zhao, Nan; Wang, Zhen-Yu; Liu, Ren-Bao

2011-05-27

69

Suppressing Hawking radiation by quantum Zeno effect  

NASA Astrophysics Data System (ADS)

We present evidence that quantum Zeno effect, otherwise working only for microscopic systems, may also work for large black holes (BH's). The expectation that a BH geometry should behave classically at time intervals larger than the Planck time tPl indicates that the quantum process of measurement of classical degrees of freedom takes time of the order of tPl. Since BH has only a few classical degrees of freedom, such a fast measurement makes a macroscopic BH strongly susceptible to the quantum Zeno effect, which repeatedly collapses the quantum state to the initial one, the state before the creation of Hawking quanta. By this mechanism, Hawking radiation from a BH of mass M is strongly suppressed by a factor of the order of mPl/M.

Nikoli?, Hrvoje

2014-06-01

70

Coherent quantum effects through dispersive bosonic media  

SciTech Connect

The coherent evolution of two qubits mediated by a set of bosonic field modes is investigated. By assuming a specific asymmetric encoding of the quantum states in the internal levels of the qubits, we show that entangling quantum gates can be realized, with high fidelity, even when a large number of mediating modes is involved. The effect of losses and imperfections on the gates' operation is also considered in detail.

Ye Saiyun [Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom); Department of Physics, Fuzhou University, Fuzhou 350002 (China); Yang Zhenbiao; Zheng Shibiao [Department of Physics, Fuzhou University, Fuzhou 350002 (China); Serafini, Alessio [Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom)

2010-07-15

71

Possible observational effects of loop quantum cosmology  

SciTech Connect

In this paper, we consider realistic model of inflation embedded in the framework of loop quantum cosmology. Phase of inflation is preceded here by the phase of a quantum bounce. We show how parameters of inflation depend on the initial conditions established in the contracting, prebounce phase. Our investigations indicate that phase of the bounce easily sets proper initial conditions for the inflation. Subsequently, we study observational effects that might arise due to the quantum gravitational modifications. We perform preliminary observational constraints for the Barbero-Immirzi parameter {gamma}, critical density {rho}{sub c}, and parameter {lambda}. In the next step, we study effects on power spectrum of perturbations. We calculate spectrum of perturbations from the bounce and from the joined bounce+inflation phase. Based on these studies, we indicate a possible way to relate quantum cosmological models with the astronomical observations. Using the Sachs-Wolfe approximation, we calculate the spectrum of the superhorizontal CMB anisotropies. We show that quantum cosmological effects can, in the natural way, explain suppression of the low CMB multipoles. We show that fine-tuning is not required here, and the model is consistent with observations. We also analyze other possible probes of the quantum cosmologies and discuss perspectives of their implementation.

Mielczarek, Jakub [Astronomical Observatory, Jagiellonian University, 30-244 Cracow, Orla 171 (Poland) and Laboratoire de Physique Subatomique et de Cosmologie, 53, avenue des Martyrs, 38026 Grenoble cedex (France)

2010-03-15

72

The Effects of Lateral Diffusion of Recoil Photoelectrons in Gen.II Image Intensifiers on the Performance of the ACE\\/CRIS Scintillating Optical Fiber Trajectory Detector  

Microsoft Academic Search

It has been observed in Gen. II image intensifiers that a certain fraction of the photoelectrons emitted from the photocathode strike the glass matrix of the front micro-channel plate. These photoelectrons recoil with a distribution of lateral momenta, resulting in a diffusion of the electrons from their original incident position. When used with scintillating fibers, this can result in an

Jennifer Fues; W. R. Binns; Paul L. Hink; Kim Slavis; D. H. Kaplan

1996-01-01

73

Effective Potential and Effective Hamiltonian in Quantum Statistical Mechanics.  

National Technical Information Service (NTIS)

An overview on the theoretic formalism and up to date applications in quantum condensed matter physics of the effective potential and effective hamiltonian methods is given. The main steps of their unified derivation by the so-called pure-quantum self-con...

A. Cuccoli R. Giachetti V. Tognetti R. Vaia P. Verrucchi

1995-01-01

74

Recoil Separators for Nuclear Astrophysics  

NASA Astrophysics Data System (ADS)

Hydrogen and helium capture reactions are important in many astrophysical environments. Measurements in inverse kinematics using recoil separators have demonstrated a particularly sensitive technique for studying low-yield capture reactions.(M. S. Smith, C. E. Rolfs, and C. A. Barnes, Nucl. Instrum. Meth. Phys. Res. A306) (1991) 233. This approach allows a low background rate to be achieved with a high detection efficiency (about 50%) for the particles of interest using a device with only modest acceptance. Recoil separators using a variety of ion-optic configurations have been installed at numerous accelerator facilities in the past decade and have been used to measure, for example, alpha capture reactions using stable beams(D. Rogalla et al.), Eur. Phys. J. 6 (1999) 471. and proton capture reactions using radioactive ion beams.(S. Bishop et al.), Phys. Rev. Lett. 90 (2003) 162501. Measurements in inverse kinematics are the only viable means for studying reactions on short-lived nuclei that are crucial for understanding stellar explosions, and a recoil separator optimized for the measurement of capture reactions with radioactive ion beams figures prominently into the design of the low energy experimental area at the Rare Isotope Accelerator (RIA). The operational requirements for such a device will be outlined, and recoil separator designs and characteristics will be presented.

Blackmon, J. C.

2004-10-01

75

Macroscopic Effects of Quantum Entanglement  

NASA Astrophysics Data System (ADS)

It is commonly believed that for the understanding of the behaviour of large, macroscopic, objects there is no need to invoke any genuine quantum entanglement - Einstein's ``spooky action at a distance.'' We show that this belief is fundamentally mistaken and that entanglement is crucial to correctly describe some macroscopic properties of solids. We demonstrate that macroscopic thermodynamical properties - such as internal energy, heat capacity or magnetic susceptibility - can detect quantum entanglement in solids in the thermodynamical limit even at moderately high temperatures. We identify the parameter regions (critical values of magnetic field and temperature) within which entanglement is witnessed by these thermodynamical quantities. Finally, we demonstrate that two different experiments performed in 1963 and in 2000 clearly and conclusively indicate that entanglement exits in macroscopic samples of Cooper Nitrate at temperatures below 5 Kelvin. We interpret our results as indicating that entanglement may play a broad generic role in macroscopic phenomena.

Brukner, Caslav; Vedral, Vlatko; Zeilinger, Anton

2005-03-01

76

Quantum hydrodynamics approach to the research of quantum effects and vorticity evolution in spin quantum plasmas  

NASA Astrophysics Data System (ADS)

In this paper, we explain a magneto quantum hydrodynamics (MQHD) method for the study of the quantum evolution of a system of spinning fermions in an external electromagnetic field. The fundamental equations of microscopic quantum hydrodynamics (the momentum balance equation and the magnetic moment density equation) are derived from the many-particle microscopic Schrödinger equation with a spin-spin and Coulomb modified Hamiltonian. Using the developed approach, an extended vorticity evolution equation for the quantum spinning plasma is derived. The effects of the new spin forces and spin-spin interaction contributions on the motion of fermions, the evolution of the magnetic moment density, and vorticity generation are predicted. The influence of the intrinsic spin of electrons on whistler mode turbulence is investigated. The results can be used for theoretical studies of spinning many-particle systems, especially dense quantum plasmas in compact astrophysical objects, plasmas in semiconductors, and micro-mechanical systems, in quantum X-ray free-electron lasers.

Trukhanova, M., Iv.

2013-11-01

77

Berkeley Experiments on Superfluid Macroscopic Quantum Effects  

SciTech Connect

This paper provides a brief history of the evolution of the Berkeley experiments on macroscopic quantum effects in superfluid helium. The narrative follows the evolution of the experiments proceeding from the detection of single vortex lines to vortex photography to quantized circulation in 3He to Josephson effects and superfluid gyroscopes in both 4He and 3He.

Packard, Richard [Physics Department, University of California, Berkeley, CA 94720 (United States)

2006-09-07

78

Effective Equations of Motion for Quantum Systems  

Microsoft Academic Search

In many situations, one can approximate the behavior of a quantum system, i.e. a wave function subject to a partial differential equation, by effective classical equations which are ordinary differential equations. A general method and geometrical picture are developed and shown to agree with effective action results, commonly derived through path integration, for perturbations around a harmonic oscillator ground state.

Martin Bojowald; Aureliano Skirzewski

2006-01-01

79

Effective constraints of loop quantum gravity  

SciTech Connect

Within a perturbative cosmological regime of loop quantum gravity corrections to effective constraints are computed. This takes into account all inhomogeneous degrees of freedom relevant for scalar metric modes around flat space and results in explicit expressions for modified coefficients and of higher order terms. It also illustrates the role of different scales determining the relative magnitude of corrections. Our results demonstrate that loop quantum gravity has the correct classical limit, at least in its sector of cosmological perturbations around flat space, in the sense of perturbative effective theory.

Bojowald, Martin; Kagan, Mikhail; Hernandez, Hector H.; Skirzewski, Aureliano [Institute for Gravitational Physics and Geometry, Pennsylvania State University, 104 Davey Lab, University Park, Pennsylvania 16802 (United States); Max-Planck-Institut fuer Gravitationsphysik, Albert-Einstein-Institut, Am Muehlenberg 1, D-14476 Potsdam (Germany)

2007-03-15

80

The Effects of Lateral Diffusion of Recoil Photoelectrons in Gen.II Image Intensifiers on the Performance of the ACE/CRIS Scintillating Optical Fiber Trajectory Detector  

NASA Astrophysics Data System (ADS)

It has been observed in Gen. II image intensifiers that a certain fraction of the photoelectrons emitted from the photocathode strike the glass matrix of the front micro-channel plate. These photoelectrons recoil with a distribution of lateral momenta, resulting in a diffusion of the electrons from their original incident position. When used with scintillating fibers, this can result in an error in the assignment of the particular fiber associated with the event. Data have been analyzed from a calibration of the ACE/CRIS Scintillating Optical Fiber Trajectory Detector using 155Mev/nucleon He, Li, C, N, O, Ne, and Ar obtained at the Michigan State University National Superconducting Synchrotron Laboratory. The probability of a fiber misassignment due to the lateral diffusion of recoil photoelectrons will be presented as a function of the particle's incident angle and charge.

Fues, Jennifer; Binns, W. R.; Hink, Paul L.; Slavis, Kim; Kaplan, D. H.

1996-05-01

81

Large Quantum Gravity Effects in Unexpected Domains  

NASA Astrophysics Data System (ADS)

In quantum gravity, the three fundamental constants, c, G, hbar provide us with a new scale. It is generally assumed that the quantum effects are important only in situations where the space-time curvature is large, of the order of this Planck scale. However, one can envisage situations in which physical fields have Planckian frequencies but such low amplitudes that the curvature is small. Can one trust classical or semi-classical theory in such domains? To probe this question, we will consider an exactly soluble model: three dimensional gravity coupled to Maxwell fields, assuming axi-symmetry. The quantum fluctuations in the geometry turn out to be very large unless the number and the frequency of photons satisfy the inequality N (hbar G?)^2 << 1. Thus, even when an electromagnetic wave of Planckian frequency has such low amplitude that the expectation value of the number of photons is just one, the quantum uncertainties in the metric are so large that classical and semi-classical approximations fail. This is a purely `coulombic' effect, unrelated to gravitons. It arises because non-linearities of Einstein's equations magnify the tiny fluctuations in the Maxwell field to huge uncertainties in the geometry. These results also hold for certain sectors of four dimensional quantum gravity but are absent for linarized gravity coupled to matter.

Ashtekar, Abhay

1997-04-01

82

Room-Temperature Quantum Hall Effect in Graphene  

Microsoft Academic Search

The quantum Hall effect (QHE), one example of a quantum phenomenon that occurs on a truly macroscopic scale, has attracted intense interest since its discovery in 1980 and has helped elucidate many important aspects of quantum physics. It has also led to the establishment of a new metrological standard, the resistance quantum. Disappointingly, however, the QHE has been observed only

K. S. Novoselov; Philip Kim; Zhigang Jiang; Horst Stormer; Yuanbo Zhang; Sergey Morozov; G. S. Boebinger; P. Kim; A. K. Geim

2007-01-01

83

Effects depolarizing quantum channels on BB84 and SARG04 quantum cryptography  

NASA Astrophysics Data System (ADS)

We have studied experimentally the effect of a depolarizing quantum channel on polarization-encode weak pulse BB84 and SARG04 quantum cryptography. Experimental results show that, in real world conditions in which channel depolarization cannot be ignored, BB84 is more robust than SARG04 on the effect of the depolarizing quantum channel.

Jeong, Youn-Chang; Kim, Yong-Su; Kim, Yoon-Ho

2010-08-01

84

Neutrino-recoil induced desorption  

Microsoft Academic Search

Nuclear decay induced [sup 37]Cl ion desorption from the electron capture decay [sup 37]Ar[r arrow][sup 37]Cl+[nu] is reported for the first time. A mixture of one part [sup 36]Ar and [similar to]5[times]10[sup [minus]5] parts [sup 37]Ar ([sup 36\\/37]Ar) is physisorbed on a gold-plated Si wafer kept at 16 K under ultrahigh vacuum conditions. The time of flight (TOF) of recoiled

L. Zhu; R. Avci; G. J. Lapeyre; M. M. Hindi; R. L. Kozub; S. J. Robinson

1994-01-01

85

Effective constraints of loop quantum gravity  

Microsoft Academic Search

Within a perturbative cosmological regime of loop quantum gravity corrections to effective constraints are computed. This takes into account all inhomogeneous degrees of freedom relevant for scalar metric modes around flat space and results in explicit expressions for modified coefficients and of higher order terms. It also illustrates the role of different scales determining the relative magnitude of corrections. Our

Martin Bojowald; Hector H. Hernandez; Mikhail Kagan; Aureliano Skirzewski

2006-01-01

86

Effective constraints of loop quantum gravity  

Microsoft Academic Search

Within a perturbative cosmological regime of loop quantum gravity corrections to effective constraints are computed. This takes into account all inhomogeneous degrees of freedom relevant for scalar metric modes around flat space and results in explicit expressions for modified coefficients and of higher order terms. It also illustrates the role of different scales determining the relative magnitude of corrections. Our

Martin Bojowald; Mikhail Kagan; Hector H. Hernández; Aureliano Skirzewski

2007-01-01

87

Theory of Fractional Quantum Hall Effect.  

National Technical Information Service (NTIS)

A theory of the fractional quantum Hall effect is constructed by introducing 3-particle interactions breaking the symmetry for nu =1/3 according to a degeneracy theorem proved here. An order parameter is introduced and a gap in the single particle spectru...

I. Z. Kostadinov

1984-01-01

88

Significant Quantum Effects in Hydrogen Activation  

PubMed Central

Dissociation of molecular hydrogen is an important step in a wide variety of chemical, biological, and physical processes. Due to the light mass of hydrogen, it is recognized that quantum effects are often important to its reactivity. However, understanding how quantum effects impact the reactivity of hydrogen is still in its infancy. Here, we examine this issue using a well-defined Pd/Cu(111) alloy that allows the activation of hydrogen and deuterium molecules to be examined at individual Pd atom surface sites over a wide range of temperatures. Experiments comparing the uptake of hydrogen and deuterium as a function of temperature reveal completely different behavior of the two species. The rate of hydrogen activation increases at lower sample temperature, whereas deuterium activation slows as the temperature is lowered. Density functional theory simulations in which quantum nuclear effects are accounted for reveal that tunneling through the dissociation barrier is prevalent for H2 up to ?190 K and for D2 up to ?140 K. Kinetic Monte Carlo simulations indicate that the effective barrier to H2 dissociation is so low that hydrogen uptake on the surface is limited merely by thermodynamics, whereas the D2 dissociation process is controlled by kinetics. These data illustrate the complexity and inherent quantum nature of this ubiquitous and seemingly simple chemical process. Examining these effects in other systems with a similar range of approaches may uncover temperature regimes where quantum effects can be harnessed, yielding greater control of bond-breaking processes at surfaces and uncovering useful chemistries such as selective bond activation or isotope separation.

2014-01-01

89

Significant quantum effects in hydrogen activation.  

PubMed

Dissociation of molecular hydrogen is an important step in a wide variety of chemical, biological, and physical processes. Due to the light mass of hydrogen, it is recognized that quantum effects are often important to its reactivity. However, understanding how quantum effects impact the reactivity of hydrogen is still in its infancy. Here, we examine this issue using a well-defined Pd/Cu(111) alloy that allows the activation of hydrogen and deuterium molecules to be examined at individual Pd atom surface sites over a wide range of temperatures. Experiments comparing the uptake of hydrogen and deuterium as a function of temperature reveal completely different behavior of the two species. The rate of hydrogen activation increases at lower sample temperature, whereas deuterium activation slows as the temperature is lowered. Density functional theory simulations in which quantum nuclear effects are accounted for reveal that tunneling through the dissociation barrier is prevalent for H2 up to ?190 K and for D2 up to ?140 K. Kinetic Monte Carlo simulations indicate that the effective barrier to H2 dissociation is so low that hydrogen uptake on the surface is limited merely by thermodynamics, whereas the D2 dissociation process is controlled by kinetics. These data illustrate the complexity and inherent quantum nature of this ubiquitous and seemingly simple chemical process. Examining these effects in other systems with a similar range of approaches may uncover temperature regimes where quantum effects can be harnessed, yielding greater control of bond-breaking processes at surfaces and uncovering useful chemistries such as selective bond activation or isotope separation. PMID:24684530

Kyriakou, Georgios; Davidson, Erlend R M; Peng, Guowen; Roling, Luke T; Singh, Suyash; Boucher, Matthew B; Marcinkowski, Matthew D; Mavrikakis, Manos; Michaelides, Angelos; Sykes, E Charles H

2014-05-27

90

Gravitation: global formulation and quantum effects  

NASA Astrophysics Data System (ADS)

A non-integrable phase-factor global approach to gravitation is developed by using the similarity of teleparallel gravity to electromagnetism. The phase shifts of both the COW and the gravitational Aharonov Bohm effects are obtained. It is then shown, by considering a simple slit experiment, that in the classical limit the global approach yields the same result as the gravitational Lorentz force equation of teleparallel gravity. It represents, therefore, the quantum mechanical version of the classical description provided by the gravitational Lorentz force equation. As teleparallel gravity can be formulated independently of the equivalence principle, it will consequently require no generalization of this principle at the quantum level.

Aldrovandi, R.; Pereira, J. G.; Vu, K. H.

2004-01-01

91

Unconventional Integer Quantum Hall Effect in Graphene  

Microsoft Academic Search

Monolayer graphite films, or graphene, have quasiparticle excitations that\\u000acan be described by 2+1 dimensional Dirac theory. We demonstrate that this\\u000aproduces an unconventional form of the quantized Hall conductivity $\\\\sigma_{xy}\\u000a= - (2 e^2\\/h)(2n+1)$ with $n=0,1,...$, that notably distinguishes graphene from\\u000aother materials where the integer quantum Hall effect was observed. This\\u000aunconventional quantization is caused by the quantum

V. P. Gusynin; S. G. Sharapov

2005-01-01

92

Strong dipolar effects in a quantum ferrofluid.  

PubMed

Symmetry-breaking interactions have a crucial role in many areas of physics, ranging from classical ferrofluids to superfluid (3)He and d-wave superconductivity. For superfluid quantum gases, a variety of new physical phenomena arising from the symmetry-breaking interaction between electric or magnetic dipoles are expected. Novel quantum phases in optical lattices, such as chequerboard or supersolid phases, are predicted for dipolar bosons. Dipolar interactions can also enrich considerably the physics of quantum gases with internal degrees of freedom. Arrays of dipolar particles could be used for efficient quantum information processing. Here we report the realization of a chromium Bose-Einstein condensate with strong dipolar interactions. By using a Feshbach resonance, we reduce the usual isotropic contact interaction, such that the anisotropic magnetic dipole-dipole interaction between 52Cr atoms becomes comparable in strength. This induces a change of the aspect ratio of the atom cloud; for strong dipolar interactions, the inversion of ellipticity during expansion (the usual 'smoking gun' evidence for a Bose-Einstein condensate) can be suppressed. These effects are accounted for by taking into account the dipolar interaction in the superfluid hydrodynamic equations governing the dynamics of the gas, in the same way as classical ferrofluids can be described by including dipolar terms in the classical hydrodynamic equations. Our results are a first step in the exploration of the unique properties of quantum ferrofluids. PMID:17687319

Lahaye, Thierry; Koch, Tobias; Fröhlich, Bernd; Fattori, Marco; Metz, Jonas; Griesmaier, Axel; Giovanazzi, Stefano; Pfau, Tilman

2007-08-01

93

Quantum effects in biological electron transfer.  

PubMed

Over recent decades, quantum effects such as coherent electronic energy transfers, electron and hydrogen tunneling have been uncovered in biological processes. In this Perspective, we highlight some of the main conceptual and methodological tools employed in the field to investigate electron tunneling in proteins, with a particular emphasis on the methodologies we are currently developing. In particular, we describe our recent contributions to the development of a mixed quantum-classical framework aimed at describing physical systems lying at the border between the quantum and semi-classical worlds. We present original results obtained by combining our approach with constrained Density Functional Theory calculations. Moving to coarser levels of description, we summarize our latest findings on electron transfer between two redox proteins, thereby showing the stabilization of inter-protein, water-mediated, electron-transfer pathways. PMID:22434318

de la Lande, Aurélien; Babcock, Nathan S; Rezá?, Jan; Lévy, Bernard; Sanders, Barry C; Salahub, Dennis R

2012-05-01

94

Electron-exchange and quantum screening effects on the collisional entanglement fidelity in degenerate quantum plasmas  

NASA Astrophysics Data System (ADS)

The influence of electron-exchange and quantum screening on the collisional entanglement fidelity for the elastic electron–ion collision is investigated in degenerate quantum plasmas. The effective Shukla–Eliasson potential and the partial wave method are used to obtain the collisional entanglement fidelity in quantum plasmas as a function of the electron-exchange parameter, Fermi energy, plasmon energy and collision energy. The results show that the quantum screening effect enhances the entanglement fidelity in quantum plasmas. However, it is found that the electron-exchange effect strongly suppresses the collisional entanglement fidelity. Hence, we have found that the influence of the electron-exchange reduces the transmission of quantum information in quantum plasmas. In addition, it is found that, although the entanglement fidelity decreases with an increase of the Fermi energy, it increases with increasing plasmon energy in degenerate quantum plasmas.

Hong, Woo-Pyo; Jung, Young-Dae

2014-06-01

95

A programmable quantum current standard from the Josephson and the quantum Hall effects  

NASA Astrophysics Data System (ADS)

We propose a way to realize a programmable quantum current standard (PQCS) from the Josephson voltage standard and the quantum Hall resistance standard (QHR) exploiting the multiple connection technique provided by the quantum Hall effect (QHE) and the exactness of the cryogenic current comparator. The PQCS could lead to breakthroughs in electrical metrology like the realization of a programmable quantum current source, a quantum ampere-meter, and a simplified closure of the quantum metrological triangle. Moreover, very accurate universality tests of the QHE could be performed by comparing PQCS based on different QHRs.

Poirier, W.; Lafont, F.; Djordjevic, S.; Schopfer, F.; Devoille, L.

2014-01-01

96

Enhancing the sensitivity of recoil-beta tagging  

NASA Astrophysics Data System (ADS)

Tagging with ?-particles at the focal plane of a recoil separator has been shown to be an effective technique for the study of exotic proton-rich nuclei. This article describes three new pieces of apparatus used to greatly improve the sensitivity of the recoil-beta tagging technique. These include a highly-pixelated double-sided silicon strip detector, a plastic phoswich detector for discriminating high-energy ?-particles, and a charged-particle veto box. The performance of these new detectors is described and characterised, and the resulting improvements are discussed.

Henderson, J.; Ruotsalainen, P.; Jenkins, D. G.; Scholey, C.; Auranen, K.; Davies, P. J.; Grahn, T.; Greenlees, P. T.; Henry, T. W.; Herzá?, A.; Jakobsson, U.; Joshi, P.; Julin, R.; Juutinen, S.; Konki, J.; Leino, M.; Lotay, G.; Nichols, A. J.; Obertelli, A.; Pakarinen, J.; Partanen, J.; Peura, P.; Rahkila, P.; Sandzelius, M.; Sarén, J.; Sorri, J.; Stolze, S.; Uusitalo, J.; Wadsworth, R.

2013-04-01

97

Loop Quantum Gravity Effective Matter Dynamics  

NASA Astrophysics Data System (ADS)

The cosmological character of Gamma-Ray-Bursts 1 (GRBs), short and intense bursts of 100 keV - 1 MeV photons and 105 - 109 GeV neutrinos 2, makes it plausible to probe quantum gravity -which is expected to become important near Planck scale: EQG ˜ EP : = ? {\\hbar c5 /G} ? 1019 {GeV}. To see why one can look at -for instance- dispersion relations for photons in a space endowed with a structure required by an underlying quantum gravity theory3, say c2 {bar p2} /E2 = 1 + ? E/EQG + {O} (E/EQG )2 with ? a parameter of order one, E the energy and vec p the spatial momentum of the photon. The result is a speed v/c = (1/c)? E/? p = 1 - ? E/EQG + {O} (E/EQG )2 , and a retardation time w.r.t. to speed c propagation: ?t ? ?(E/EQG)(L/c), L being the distance traveled. With E ? 0.20MeV, L ? 1010ly, one gets ?t ? 10-5s. This can be contrasted with the time resolution of GRBs ?t ? 10-3s. Indeed, effective dispersion relations might have observable imprints of physics at Planck scale and may be other aspects of quantum gravity can be probed7. Here we point out how non perturbative quantum general relativity can yield such effective dispersion relations either for photons or neutrinosa...

Alfaro, J.; Morales-Tecotl, H. A.; Urrutia, L. F.

2002-12-01

98

Quantum fluid model of coherent stimulated radiation by a dense relativistic cold electron beam  

NASA Astrophysics Data System (ADS)

Using a quantum fluid model, the linear dispersion relation for FEL pumped by a short wavelength laser wiggler is deduced. Subsequently, a new quantum corrected resonance condition is obtained. It is shown that, in the limit of low energy electron beam and low frequency pump, the quantum recoil effect can be neglected, recovering the classical FEL resonance condition, ks=4kw?2. On the other hand, for short wavelength and high energy electron beam, the quantum recoil effect becomes strong and the resonance condition turns into ks=2kw/\\slgrc?3/2, with \\slgrc being the reduced Compton wavelength. As a result, a set of nonlinear coupled equations, which describes the quantum FEL dynamics as a three-wave interaction, is obtained. Neglecting wave propagation effects, this set of equations is solved numerically and results are presented.

Monteiro, L. F.; Serbeto, A.; Tsui, K. H.; Mendonça, J. T.; Galva~o, R. M. O.

2013-07-01

99

Quantum fluid model of coherent stimulated radiation by a dense relativistic cold electron beam  

SciTech Connect

Using a quantum fluid model, the linear dispersion relation for FEL pumped by a short wavelength laser wiggler is deduced. Subsequently, a new quantum corrected resonance condition is obtained. It is shown that, in the limit of low energy electron beam and low frequency pump, the quantum recoil effect can be neglected, recovering the classical FEL resonance condition, k{sub s}=4k{sub w}?{sup 2}. On the other hand, for short wavelength and high energy electron beam, the quantum recoil effect becomes strong and the resonance condition turns into k{sub s}=2?(k{sub w}/?{sub c})?{sup 3/2}, with ?{sub c} being the reduced Compton wavelength. As a result, a set of nonlinear coupled equations, which describes the quantum FEL dynamics as a three-wave interaction, is obtained. Neglecting wave propagation effects, this set of equations is solved numerically and results are presented.

Monteiro, L. F.; Serbeto, A.; Tsui, K. H. [Instituto de Física, Universidade Federal Fluminense, Campus da Praia Vermelha, Niterói, RJ 24210-346 (Brazil)] [Instituto de Física, Universidade Federal Fluminense, Campus da Praia Vermelha, Niterói, RJ 24210-346 (Brazil); Mendonça, J. T.; Galvão, R. M. O. [Instituto de Física, Universidade de São Paulo, São Paulo, SP 05508-090 (Brazil)] [Instituto de Física, Universidade de São Paulo, São Paulo, SP 05508-090 (Brazil)

2013-07-15

100

Effective equations for isotropic quantum cosmology including matter  

Microsoft Academic Search

Effective equations often provide powerful tools to develop a systematic understanding of detailed properties of a quantum system. This is especially helpful in quantum cosmology where several conceptual and technical difficulties associated with the full quantum equations can be avoided in this way. Here, effective equations for Wheeler-DeWitt and loop quantizations of spatially flat, isotropic cosmological models sourced by a

Martin Bojowald; Hector Hernández; Aureliano Skirzewski

2007-01-01

101

Reentrant Quantum Hall Effect at Low Fields  

NASA Astrophysics Data System (ADS)

Several recent experiments, on various semiconductor heterostructures, have shown that an insulating phase at zero field can undergo a phase transition to the quantum Hall effect phase in an applied magnetic field.(see for example, H. W. Jiang, C. E. Johnson, K. L. Wang, and S. T. Hannahs, Phys. Rev. Lett. 71, 1439 (1993).) To understand this phenomena, we have studied the evolution of the quantum Hall effect at low fields.(I. Glozman, C. E. Johnson, and H. W. Jiang, Phys. Rev. Lett. 74, 594 (1995).) We found that the chemical potential of the lowest delocalized-state band not only deviates from the host Landau level center, but also "floats up" above the Fermi level as B goes to zero. In the region where the floating of delocalized states is observed, we have also found that the position of the conductivity minimum in the density - field plane to be strongly path-dependent. This path dependence has, in fact, given us information to quantitatively link the floating to Landau level mixing.(I. Glozman, C. E. Johnson, and H. W. Jiang, Phys. Rev. B 52, R14348 (1995).) The similar studies have been extended to the fractional quantum Hall effect regime.(L. W. Wong, H. W. Jiang, and W. J. Schaff, Phys. Rev. B54, Dec. 15, in press (1996).) The potential floating of the delocalized states of composite-fermions in a vanishing effective field will be discussed.

Jiang, H. W.

1997-03-01

102

On the effective hydrodynamics of the fractional quantum Hall effect  

NASA Astrophysics Data System (ADS)

We present here a classical hydrodynamic model of a two-dimensional fluid which has many properties of the fractional quantum Hall effect (FQHE). This model incorporates the FQHE relation between the vorticity and density of the fluid and exhibits the Hall viscosity and Hall conductivity found in FQHE liquids. We describe the relation of the model to the Chern-Simons-Ginzburg-Landau theory of FQHE and show how Laughlin's wavefunction is annihilated by the quantum velocity operator.

Abanov, Alexander G.

2013-07-01

103

Quantum field-effect directional coupler  

NASA Astrophysics Data System (ADS)

A new quantum-effect electronic device is proposed which consists of two one-dimensional electron waveguides which, over a certain interaction length, come in close proximity to each other so that coherent quantum mechanical tunneling can take place between them. The degree of coupling between the two waveguides is controlled by modulating, through the field-effect action of a gate, the height of the potential energy barrier which separates them. If an electron wave packet is injected into this device through one of the waveguides, then the probability density of the electron wave function will oscillate back and forth between the two waveguides as the packet advances. The gate voltage can be adjusted to achieve complete electron transfer at either of the two waveguides at the output of the device. The device, therefore, behaves as a current switch. First-order calculations indicate that this device can be fabricated with state-of-the-art nanolithography.

del Alamo, Jesus A.; Eugster, Cristopher C.

1990-01-01

104

Quantum Zeno Effect and Parametric Resonance in Mesoscopic Physics  

NASA Astrophysics Data System (ADS)

As a realization of the quantum Zeno effect, we consider electron tunneling between two quantum dots with one of the dots coupled to a quantum point contact detector. The coupling leads to decoherence and to the suppression of tunneling. When the detector is driven with an ac voltage, a parametric resonance occurs which strongly counteracts decoherence. We propose a novel experiment with which it is possible to observe both the quantum Zeno effect and the parametric resonance in electric transport.

Hackenbroich, G.; Rosenow, B.; Weidenmüller, H. A.

1998-12-01

105

Finite temperature effects in quantum field theory  

Microsoft Academic Search

We consider quantum electrodynamics at finite temperatures. By making use of the real time formalism we compute, on the one-loop level, the finite-temperature correction to the mass of the electron and to the anomalous magnetic moment aeth. The gauge-invariant correction to the electron mass is found to be a ten percent effect at a temperature of the order of 2×1010

G. Peressutti; B.-S. Skagerstam

1982-01-01

106

Quantum Spin Hall Effect in Graphene  

Microsoft Academic Search

We study the effects of spin orbit interactions on the low energy electronic\\u000astructure of a single plane of graphene. We find that in an experimentally\\u000aaccessible low temperature regime the symmetry allowed spin orbit potential\\u000aconverts graphene from an ideal two dimensional semimetallic state to a quantum\\u000aspin Hall insulator. This novel electronic state of matter is gapped in

C. L. Kane; E. J. Mele

2005-01-01

107

Joule-Thomson Effect and Quantum Statistics  

Microsoft Academic Search

IN view of the numerous physical and astro-physical applications of the new quantum statistics it may be worth while to investigate the Joule-Thomson effect for a gas obeying Fermi-Dirac or Bose-Einstein statistics. The calculation is simple and runs on the usual lines. The results obtained are quite interesting. It is found that for a degenerate gas, degenerate in the sense

D. S. Kothari; B. N. Srivasava

1937-01-01

108

The pinning effect in quantum dots  

NASA Astrophysics Data System (ADS)

The pinning effect is studied in a Gaussian quantum dot using the improved Wigner-Brillouin perturbation theory (IWBPT) in the presence of electron-phonon interaction. The electron ground state plus one phonon state is degenerate with the electron in the first excited state. The electron-phonon interaction lifts the degeneracy and the first excited states get pinned to the ground state plus one phonon state as we increase the confinement frequency.

Monisha, P. J.; Mukhopadhyay, Soma

2014-04-01

109

Grand unification and enhanced quantum gravitational effects.  

PubMed

In grand unified theories with large numbers of fields, renormalization effects significantly modify the scale at which quantum gravity becomes strong. This in turn can modify the boundary conditions for coupling constant unification, if higher dimensional operators induced by gravity are taken into consideration. We show that the generic size of, and the uncertainty in, these effects from gravity can be larger than the two-loop corrections typically considered in renormalization group analyses of unification. In some cases, gravitational effects of modest size can render unification impossible. PMID:18999739

Calmet, Xavier; Hsu, Stephen D H; Reeb, David

2008-10-24

110

Evidence for mirror dark matter from the CDMS low energy electron recoil spectrum  

SciTech Connect

We point out that mirror dark matter predicts low-energy (E{sub R} < or approx. 2 keV) electron recoils from mirror electron scattering as well as nuclear recoils from mirror ion scattering. The former effect is examined and applied to the recently released low-energy electron recoil data from the CDMS Collaboration. We speculate that the sharp rise in electron recoils seen in CDMS below 2 keV might be due to mirror electron scattering and show that the parameters suggested by the data are roughly consistent with the mirror dark matter explanation of the annual modulation signal observed in the DAMA/Libra and DAMA/NaI experiments. Thus, the CDMS data offer tentative evidence supporting the mirror dark matter explanation of the DAMA experiments, which can be more rigorously checked by future low-energy electron recoil measurements.

Foot, R. [School of Physics, University of Melbourne, Victoria 3010 (Australia)

2009-11-01

111

Investigation of potential profile effects in quantum dot and onion-like quantum dot-quantum well on optical properties  

NASA Astrophysics Data System (ADS)

This paper investigates GaAs/AlGaAs modified quantum dot nanocrystal and GaAs/AlGaAs/GaAs/AlGaAs quantum dot-quantum well heteronanocrystal. These quantum dots have been analyzed by the finite element numerical methods. Simulations carried out for state n=1, l=0, and m=0 which are original, orbital, and magnetic state of quantum numbers. The effects of variation in radius layers such as total radius, GaAs core, shell and AlGaAs barriers radius on the wavelength and emission coefficient are studied. For the best time, it has also investigated the effect of mole fraction on emission coefficient. Meanwhile, one of the problems in biological applications is alteration of the emission wavelength of a quantum dot by changing in its dimension. This problem will be resolved by changing in potential profile.

Elyasi, P.; SalmanOgli, A.

2014-05-01

112

Epitaxial silicide formation on recoil-implanted substrates  

SciTech Connect

An epitaxy-on-recoil-implanted-substrate (ERIS) technique is presented. A disordered surface layer, generated by forward recoil implantation of {approx}0.7-3x10{sup 15} cm{sup -2} of oxygen during Ar plasma etching of surface oxide, is shown to facilitate the subsequent epitaxial growth of {approx}25-35-nm-thick CoSi{sub 2} layers on Si(100). The dependence of the epitaxial fraction of the silicide on the recoil-implantation parameters is studied in detail. A reduction in the silicide reaction rate due to recoil-implanted oxygen is shown to be responsible for the observed epitaxial formation, similar to mechanisms previously observed for interlayer-mediated growth techniques. Oxygen is found to remain inside the fully reacted CoSi{sub 2} layer, likely in the form of oxide precipitates. The presence of these oxide precipitates, with only a minor effect on the sheet resistance of the silicide layer, has a surprisingly beneficial effect on the thermal stability of the silicide layers. The agglomeration of ERIS-grown silicide layers on polycrystalline Si is significantly suppressed, likely from a reduced diffusivity due to oxygen in the grain boundaries. The implications of the present technique for the processing of deep submicron devices are discussed.

Hashimoto, Shin; Egashira, Kyoko; Tanaka, Tomoya; Etoh, Ryuji; Hata, Yoshifumi; Tung, R. T. [Corporate Manufacturing and Development Division, Semiconductor Company, Matsushita Electric Industrial Co., Ltd., Kyoto 617-8520 (Japan); Department of Physics, Brooklyn College, City University of New York, Brooklyn, New York 11210 (United States)

2005-01-15

113

Channeling patterns recorded using radioactive recoil atoms  

Microsoft Academic Search

Differences in the penetration of Rn-220 recoil atoms injected from a Ra-224 point source into single crystals of Si, SiO2 and KCl were used to record patterns showing directions and planes along which the recoil atoms channeled deeper into the crystal.

C. Jech

1972-01-01

114

Quantum and Collective Effects in Information Processing and Communication.  

National Technical Information Service (NTIS)

The original aim of this MURI was to combine an experimental effort to develop tools to manipulate quantum coherence in the solid state. based on metallic wires, quantum point contacts, and the quantum Hall effect, with theoretical efforts aimed at unders...

C. M. Marcus

1999-01-01

115

Spin-orbit force, recoil corrections, and possible BB¯* and DD¯* molecular states  

NASA Astrophysics Data System (ADS)

In the framework of the one-boson exchange model, we have calculated the effective potentials between two heavy mesons BB¯* and DD¯* from the t- and u-channel ?-, ?-, ?-, ?-, and ?-meson exchanges with four kinds of quantum number: I=0, JPC=1++; I =0, JPC=1+-; I =1, JPC=1++; I =1, JPC=1+-. We keep the recoil corrections to the BB¯* and DD¯* systems up to O(1/M2). The spin-orbit force appears at O(1/M), which turns out to be important for the very loosely bound molecular states. Our numerical results show that the momentum-related corrections are unfavorable to the formation of the molecular states in the I =0, JPC=1++ and I =1, JPC=1+- channels in the DD¯* system.

Zhao, Lu; Ma, Li; Zhu, Shi-Lin

2014-05-01

116

Excitons in the Fractional Quantum Hall Effect  

SciTech Connect

Quasiparticles of charge 1/m in the Fractional Quantum Hall Effect form excitons, which are collective excitations physically similar to the transverse magnetoplasma oscillations of a Wigner crystal. A variational exciton wavefunction which shows explicitly that the magnetic length is effectively longer for quasiparticles than for electrons is proposed. This wavefunction is used to estimate the dispersion relation of these excitons and the matrix elements to generate them optically out of the ground state. These quantities are then used to describe a type of nonlinear conductivity which may occur in these systems when they are relatively clean.

Laughlin, R.B.

1984-09-01

117

Recoil Experiments Using a Compressed Air Cannon  

NASA Astrophysics Data System (ADS)

Ping-Pong vacuum cannons, potato guns, and compressed air cannons are popular and dramatic demonstrations for lecture and lab.1-3 Students enjoy them for the spectacle, but they can also be used effectively to teach physics. Recently we have used a student-built compressed air cannon as a laboratory activity to investigate impulse, conservation of momentum, and kinematics. It is possible to use the cannon, along with the output from an electronic force plate, as the basis for many other experiments in the laboratory. In this paper, we will discuss the recoil experiment done by our students in the lab and also mention a few other possibilities that this apparatus could be used for.

Taylor, Brett

2006-12-01

118

The Collective Atomic Recoil Laser  

NASA Astrophysics Data System (ADS)

An ensemble of periodically ordered atoms coherently scatters the light of an incident laser beam. The scattered and the incident light may interfere and give rise to a light intensity modulation and thus to optical dipole forces which, in turn, emphasize the atomic ordering. This positive feedback is at the origin of the collective atomic recoil laser (CARL). We demonstrate this dynamics using ultracold atoms confined by dipole forces in a unidirectionally pumped far red-detuned high-finesse optical ring cavity. Under the influence of an additional dissipative force exerted by an optical molasses the atoms, starting from an unordered distribution, spontaneously form a density grating moving at constant velocity. Additionally, steady state lasing is observed in the reverse direction if the pump laser power exceeds a certain threshold. We compare the dynamics of the atomic trajectories to the behavior of globally coupled oscillators, which exhibit phase transitions from incoherent to coherent states if the coupling strength exceeds a critical value.

Courteille, Ph. W.; von Cube, C.; Deh, B.; Kruse, D.; Ludewig, A.; Slama, S.; Zimmermann, C.

2005-05-01

119

Gravitational Recoil: Signatures on the Massive Black Hole Population  

NASA Astrophysics Data System (ADS)

In the last stages of a black hole merger, the binary can experience a recoil due to asymmetric emission of gravitational radiation. Recent numerical relativity simulations suggest that the recoil velocity can be as high as a few thousands kilometers per second for particular configurations. We consider here the effect of a worst case scenario for orbital and phase configurations on the hierarchical evolution of the massive black hole (MBH) population. The orbital configuration and spin orientation in the plane is chosen to be the one yielding the highest possible kick. Masses and spin magnitudes are instead derived self-consistently from the MBH evolutionary models. If seeds form early, for example, as remnants of the first stars, almost the totality of the first few generation of binaries are ejected. The fraction of lost binaries decreases at later times due to a combination of the binary mass ratio distribution becoming shallower, and the deepening of the hosts' potential wells. If seeds form at later times, in more massive halos, then the retention rate is much higher. We show that the gravitational recoil does not pose a threat to the evolution of the MBH population that we observe locally in either case, although high-mass seeds seem to be favored. The gravitational recoil is instead a real hazard for (1) MBHs in biased halos at high redshift, where mergers are more common and the potential wells still relatively shallow. Similarly, it is very challenging to retain (2) MBHs merging in star clusters.

Volonteri, Marta

2007-07-01

120

The effect of measurements, randomly distributed in time, on quantum systems: stochastic quantum Zeno effect  

NASA Astrophysics Data System (ADS)

The manifestation of measurements, randomly distributed in time, on the evolution of quantum systems are analyzed in detail. The set of randomly distributed measurements (RDM) is modeled within the renewal theory, in which the distribution is characterized by the probability density function (PDF) W(t) of times t between successive events (measurements). The evolution of the quantum system affected by the RDM is shown to be described by the density matrix satisfying the stochastic Liouville equation. This equation is applied to the analysis of the RDM effect on the evolution of a two-level system for different types of RDM statistics, corresponding to different PDFs W(t). Obtained general results are illustrated as applied to the cases of the Poissonian (W(t) \\sim \\,e^{-w_r t}) and anomalous (W(t) ~ 1/t1 + ?, ? <= 1) RDM statistics. In particular, specific features of the quantum and inverse Zeno effects, resulting from the RDM, are thoroughly discussed.

Shushin, A. I.

2011-02-01

121

Quantum Numbers of Textured Hall Effect Quasiparticles  

NASA Astrophysics Data System (ADS)

We propose a class of variational wave functions with slow variation in spin and charge density and simple vortex structure at infinity, which properly generalize both the Laughlin quasiparticles and baby Skyrmions. We argue, on the basis of these wave functions and a spin-statistics relation in the relevant effective field theory, that the spin of the corresponding quasiparticle has a fractional part related in a universal fashion to the properties of the bulk state. We propose a direct experimental test of this claim. We show that certain spin-singlet quantum Hall states can be understood as arising from primary polarized states by Skyrmion condensation.

Nayak, Chetan; Wilczek, Frank

1996-11-01

122

Integer quantum Hall effect in trilayer graphene.  

PubMed

By using high-magnetic fields (up to 60 T), we observe compelling evidence of the integer quantum Hall effect in trilayer graphene. The magnetotransport fingerprints are similar to those of the graphene monolayer, except for the absence of a plateau at a filling factor of ?=2. At a very low filling factor, the Hall resistance vanishes due to the presence of mixed electron and hole carriers induced by disorder. The measured Hall resistivity plateaus are well reproduced theoretically, using a self-consistent Hartree calculations of the Landau levels and assuming an ABC stacking order of the three layers. PMID:22026788

Kumar, A; Escoffier, W; Poumirol, J M; Faugeras, C; Arovas, D P; Fogler, M M; Guinea, F; Roche, S; Goiran, M; Raquet, B

2011-09-16

123

Magnetic quantum ratchet effect in graphene.  

PubMed

A periodically driven system with spatial asymmetry can exhibit a directed motion facilitated by thermal or quantum fluctuations. This so-called ratchet effect has fascinating ramifications in engineering and natural sciences. Graphene is nominally a symmetric system. Driven by a periodic electric field, no directed electric current should flow. However, if the graphene has lost its spatial symmetry due to its substrate or adatoms, an electronic ratchet motion can arise. We report an experimental demonstration of such an electronic ratchet in graphene layers, proving the underlying spatial asymmetry. The orbital asymmetry of the Dirac fermions is induced by an in-plane magnetic field, whereas the periodic driving comes from terahertz radiation. The resulting magnetic quantum ratchet transforms the a.c. power into a d.c. current, extracting work from the out-of-equilibrium electrons driven by undirected periodic forces. The observation of ratchet transport in this purest possible two-dimensional system indicates that the orbital effects may appear and be substantial in other two-dimensional crystals such as boron nitride, molybdenum dichalcogenides and related heterostructures. The measurable orbital effects in the presence of an in-plane magnetic field provide strong evidence for the existence of structure inversion asymmetry in graphene. PMID:23334170

Drexler, C; Tarasenko, S A; Olbrich, P; Karch, J; Hirmer, M; Müller, F; Gmitra, M; Fabian, J; Yakimova, R; Lara-Avila, S; Kubatkin, S; Wang, M; Vajtai, R; Ajayan, P M; Kono, J; Ganichev, S D

2013-02-01

124

Jet extinction from nonperturbative quantum gravity effects  

NASA Astrophysics Data System (ADS)

The infrared-ultraviolet properties of quantum gravity suggest on very general grounds that hard short distance scattering processes are highly suppressed for center of mass scattering energies beyond the fundamental Planck scale. If this scale is not too far above the electroweak scale, these nonperturbative quantum gravity effects could be manifest as an extinction of high transverse momentum jets at the LHC. To model these effects, we implement an extinction Monte Carlo modification of the PYTHIA event generator based on a Veneziano form factor with a large absorptive branch cut modification of hard QCD scattering processes. Using this we illustrate the leading effects of extinction on the inclusive jet transverse momentum spectrum at the LHC. We estimate that an extinction mass scale of up to roughly half the center of mass beam collision energy could be probed with high statistics data. Experimental searches at the LHC for jet extinction would be complementary to ongoing searches for the related phenomenon of excess production of high multiplicity final states.

Kilic, Can; Lath, Amitabh; Rose, Keith; Thomas, Scott

2014-01-01

125

Quantum 1/f effect in spin decoherence rates and quantum computing  

NASA Astrophysics Data System (ADS)

The quantum 1/f effect is a fundamental new aspect of quantum mechanics, quantum electrodynamics, and quantum field theory in general, with practical importance in most high-technology applications. It is based on the reaction of material currents to their spontaneous emission of infra-quanta such as photons, gravitons, transversal phonons, spin waves, etc. It is the result of decoherence of entangled states of particles and their spontaneous bremsstrahlung, a consequence of infrared-divergent interactions between particles and their field. It is the quantum manifestation of classical turbulence and it represents the most fundamental form of quantum chaos. It is described by the simple universal formula of conventional and coherent quantum 1/f noise, important in engineering, science and technology. It provides a new physical meaning to the notion of ``constant current,'' in time and space, similar to the 1937 definition of elastic processes by Bloch and Nordsieck. Finally, it is an interesting aspect of the concrete way in which matter generates its forms of existence, for instance time and space. Quantum 1/f spin decoherence rates, known to severely limit the performance of quantum computers, are shown here to be also affected by the quantum 1/f effect. Indeed, the elementary spin-flip process has a bremsstrahlung amplitude, leading to a non-stationary state with 1/f quantum fluctuations, and a disentangled system of non-localized low-frequency photons with negative conditional entropy. Thus, decoherence is due to the entangled system's interaction with the rest of the world, as is its quantum 1/f fluctuation which can be expressed in qubits. Increasing the spin-excess n is one way to reduce these fluctuations. In general, we find that both decoherence and its quantum 1/f noise could be controlled by better insulating the system in a new way. .

Handel, Peter H.

2001-06-01

126

Non-Markovian effect on the quantum discord  

SciTech Connect

We study the non-Markovian effect on the dynamics of the quantum discord by exactly solving a model consisting of two independent qubits subject to two zero-temperature non-Markovian reservoirs, respectively. Considering the two qubits initially prepared in Bell-like or extended Werner-like states, we show that there is no occurrence of the sudden death, but only instantaneous disappearance of the quantum discord at some time points, in comparison to the entanglement sudden death in the same range of the parameters of interest. This implies that the quantum discord is more useful than the entanglement to describe the quantum correlation involved in quantum systems.

Wang Bo; Xu Zhenyu [Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071 (China); Graduate School of the Chinese Academy of Sciences, Beijing 100049 (China); Chen Zeqian; Feng Mang [Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071 (China)

2010-01-15

127

Approximate inclusion of quantum effects in transition path sampling.  

PubMed

We propose a method for incorporating nuclear quantum effects in transition path sampling studies of systems that consist of a few degrees of freedom that must be treated quantum mechanically, while the rest are classical-like. We used the normal mode centroid method to describe the quantum subsystem, which is a method that is not CPU intensive but still reasonably accurate. We applied this mixed centroid/classical transition path sampling method to a model system that has nontrivial quantum behavior, and showed that it can capture the correct quantum dynamical features. PMID:20001028

Antoniou, Dimitri; Schwartz, Steven D

2009-12-14

128

Gas powered fluid gun with recoil mitigation  

DOEpatents

A gas powered fluid gun for propelling a stream or slug of a fluid at high velocity toward a target. Recoil mitigation is provided that reduces or eliminates the associated recoil forces, with minimal or no backwash. By launching a quantity of water in the opposite direction, net momentum forces are reduced or eliminated. Examples of recoil mitigation devices include a cone for making a conical fluid sheet, a device forming multiple impinging streams of fluid, a cavitating venturi, one or more spinning vanes, or an annular tangential entry/exit.

Grubelich, Mark C; Yonas, Gerold

2013-11-12

129

Recoiling DNA molecule: simulation and experiment  

NASA Astrophysics Data System (ADS)

Single molecule DNA experiments often generate data from force versus extension measurements involving the tethering of a microsphere to one end of a single DNA molecule while the other is attached to a substrate. We show that the persistence length of single DNA molecules can also be measured based on the recoil dynamics of these DNA-microsphere complexes if appropriate corrections are made to the friction coefficient of the microsphere in the vicinity of the substrate. Comparison between computer simulated recoil curves, generated from the corresponding Langevin equation, and experimental recoils are used to assure the validity of data analysis.

Neto, José Coelho; Dickman, Ronald; Mesquita, O. N.

2005-01-01

130

The microscopic nature of localization in the quantum Hall effect  

Microsoft Academic Search

The quantum Hall effect arises from the interplay between localized and extended states that form when electrons, confined to two dimensions, are subject to a perpendicular magnetic field. The effect involves exact quantization of all the electronic transport properties owing to particle localization. In the conventional theory of the quantum Hall effect, strong-field localization is associated with a single-particle drift

S. Ilani; J. Martin; E. Teitelbaum; J. H. Smet; D. Mahalu; V. Umansky; A. Yacoby

2004-01-01

131

Magnetic field effects on quantum ring excitons  

SciTech Connect

We study the effect of magnetic field and geometric confinement on excitons confined to a quantum ring. We use analytical matrix elements of the Coulomb interaction and diagonalize numerically the effective-mass Hamiltonian of the problem. To explore the role of different boundary conditions, we investigate the quantum ring structure with a parabolic confinement potential, which allows the wave functions to be expressed in terms of center of mass and relative degrees of freedom of the exciton. On the other hand, wave functions expressed in terms of Bessel functions for electron and hole are used for a hard-wall confinement potential. The binding energy and electron--hole separation of the exciton are calculated as function of the width of the ring and the strength of an external magnetic field. The linear optical susceptibility as a function of magnetic fields is also discussed. We explore the Coulomb electron--hole correlation and magnetic confinement for several ring width and size combinations. The Aharanov--Bohm oscillations of exciton characteristics predicted for one-dimensional rings are found to not be present in these finite-width systems.

Song, Jakyoung; Ulloa, Sergio E.

2001-03-15

132

Guiding effect of quantum wells in semiconductor lasers  

SciTech Connect

The guiding effect of InGaAs quantum wells in GaAs- and InP-based semiconductor lasers has been studied theoretically and experimentally. The results demonstrate that such waveguides can be effectively used in laser structures with a large refractive index difference between the quantum well material and semiconductor matrix and a large number of quantum wells (e.g. in InP-based structures). (semiconductor lasers. physics and technology)

Aleshkin, V Ya; Dikareva, Natalia V; Dubinov, A A; Zvonkov, B N; Karzanova, Maria V; Kudryavtsev, K E; Nekorkin, S M; Yablonskii, A N

2013-05-31

133

Ensemble density functional theory of the fractional quantum Hall effect  

NASA Astrophysics Data System (ADS)

We develop an ensemble density functional theory for the fractional quantum Hall effect using a local density approximation. Model calculations for edge reconstructions of a spin-polarized quantum dot give results in good agreement with semiclassical and Hartree-Fock calculations, and with small system numerical diagonalizations. This establishes the usefulness of density functional theory to study the fractional quantum Hall effect, which opens up the possibility of studying inhomogeneous systems with many more electrons than has heretofore been possible.

Heinonen, O.; Lubin, M. I.; Johnson, M. D.

1995-11-01

134

Focus on quantum effects and noise in biomolecules  

Microsoft Academic Search

The role of quantum mechanics in biological organisms has been a fundamental question of twentieth-century biology. It is only now, however, with modern experimental techniques, that it is possible to observe quantum mechanical effects in bio-molecular complexes directly. Indeed, recent experiments have provided evidence that quantum effects such as wave-like motion of excitonic energy flow, delocalization and entanglement can be

G. R. Fleming; S. F. Huelga; M. B. Plenio

2011-01-01

135

Optimal tunneling enhances the quantum photovoltaic effect in double quantum dots  

NASA Astrophysics Data System (ADS)

We investigate the quantum photovoltaic effect in double quantum dots by applying the nonequilibrium quantum master equation. A drastic suppression of the photovoltaic current is observed near the open circuit voltage, which leads to a large filling factor. We find that there always exists an optimal inter-dot tunneling that significantly enhances the photovoltaic current. Maximal output power will also be obtained around the optimal inter-dot tunneling. Moreover, the open circuit voltage behaves approximately as the product of the eigen-level gap and the Carnot efficiency. These results suggest a great potential for double quantum dots as efficient photovoltaic devices.

Wang, Chen; Ren, Jie; Cao, Jianshu

2014-04-01

136

Fractional quantum Hall effect in optical lattices  

NASA Astrophysics Data System (ADS)

We analyze a recently proposed method to create fractional quantum Hall (FQH) states of atoms confined in optical lattices [A. Sørensen , Phys. Rev. Lett. 94, 086803 (2005)]. Extending the previous work, we investigate conditions under which the FQH effect can be achieved for bosons on a lattice with an effective magnetic field and finite on-site interaction. Furthermore, we characterize the ground state in such systems by calculating Chern numbers which can provide direct signatures of topological order and explore regimes where the characterization in terms of wave-function overlap fails. We also discuss various issues which are relevant for the practical realization of such FQH states with ultracold atoms in an optical lattice, including the presence of a long-range dipole interaction which can improve the energy gap and stabilize the ground state. We also investigate a detection technique based on Bragg spectroscopy to probe these systems in an experimental realization.

Hafezi, M.; Sørensen, A. S.; Demler, E.; Lukin, M. D.

2007-08-01

137

Strong infrared effects in quantum gravity  

SciTech Connect

Another consequence is that the graviton`s on-shell self-energy is negative and infrared divergent at one loop, thereby inducing a negative infrared divergence in the two-loop vacuum energy. We analyze these effects in the context of causal evolution from an initial patch of one Hubble volume which begins inflation at finite times in one of the homogeneous and isotropic Fock states of free QCG. Up to some tedious but probably manageable tensor algebra we show that quantum infrared effects exert an ever increasing drag on the background`s expansion for as long as perturbation theory remains valid. A rough estimate of the relaxation time is easily consistent with enough inflation to solve the smoothness problem. {copyright} 1995 Academic Press, Inc.

Tsamis, N.C. [Department of Physics, University of Crete, Heraklion, Crete 71409, Greece and Theory Group, FO.R.T.H., Heraklion, Crete 71110 (Greece)] [Department of Physics, University of Crete, Heraklion, Crete 71409, Greece and Theory Group, FO.R.T.H., Heraklion, Crete 71110 (Greece); Woodard, R.P. [Department of Physics, University of Floride, Gainesville, Florida 32611 (United States)] [Department of Physics, University of Floride, Gainesville, Florida 32611 (United States)

1995-02-15

138

Effects of depolarizing quantum channels on BB84 and SARG04 quantum cryptography protocols  

NASA Astrophysics Data System (ADS)

We report experimental studies on the effect of the depolarizing quantum channel on weak-pulse BB84 and SARG04 quantum cryptography. The experimental results show that, in real world conditions in which channel depolarization cannot be ignored, BB84 should perform better than SARG04 under the most general eavesdropping attack.

Jeong, Y.-C.; Kim, Y.-S.; Kim, Y.-H.

2011-08-01

139

Transverse effects in nonlinear and quantum optics  

NASA Astrophysics Data System (ADS)

The transverse structure of an optical field can carry a large amount of information. Such a simple concept is the basis for important technologies such as imaging and photolithography. However, some effects in nature will effectively destroy any useful transverse structure the field may possess. In this thesis, both desirable and undesirable transverse optical effects will be studied. The ultimate limit to the amount of energy that may be usefully transmitted through a medium in a laser beam is imposed by the nonlinear response of the medium. This nonlinearity can be a thermal effect for continuous-wave or long-pulse lasers, while for short-pulse lasers will tend to be an electronic or molecular effect. Whenever the intensity-nonlinearity product is too large, the transverse structure of the beam will be so greatly distorted as to make the beam essentially useless. This beam degradation is discussed in the thesis for both the continuous-wave thermal case as well as for the short-pulse case, known as laser beam filamentation. The undesirable effect of filamentation is a single-beam four-wave mixing effect. Similar physical processes exist for two-beam four-wave mixing. In the two-beam case, however, there is reason to believe that the generated transverse structure may possess very useful properties for applications in quantum optics. Such effects are explored in this thesis. After discussing physical effects that can alter the transverse structure of a beam, two applications of the use of transverse structure to carry information are also explored. The first of these is coincidence imaging. This is a technique for generating an image of an object with photons that do not directly interact with the object. Experiments were performed to compare the quality of the technique when done using classical versus quantum methods. The second application of transverse effects that is developed is a new method for generating lithographic patterns with super-resolution. The method is shown theoretically for any level of resolution improvement, and is demonstrated experimentally for up to a factor of three improvement over the traditionally accepted limit.

Bentley, Sean J.

140

Quantum interference effects in degenerate systems. Spontaneous and stimulated radiation  

Microsoft Academic Search

We study the effect of quantum interference on the structure and properties of spontaneous and stimulated transitions in a degenerate V-type three-level atom with an arbitrary total momentum of each state. Explicit expressions for the factors in the terms of the relaxation operator and stimulated transition operator with account of quantum interference effects are obtained. It has been demonstrated that

A. A. Panteleev; Vl. K. Roerich

2004-01-01

141

Effective equations for isotropic quantum cosmology including matter  

SciTech Connect

Effective equations often provide powerful tools to develop a systematic understanding of detailed properties of a quantum system. This is especially helpful in quantum cosmology where several conceptual and technical difficulties associated with the full quantum equations can be avoided in this way. Here, effective equations for Wheeler-DeWitt and loop quantizations of spatially flat, isotropic cosmological models sourced by a massive or interacting scalar are derived and studied. The resulting systems are remarkably different from that given for a free, massless scalar. This has implications for the coherence of evolving states and the realization of a bounce in loop quantum cosmology.

Bojowald, Martin; Hernandez, Hector; Skirzewski, Aureliano [Institute for Gravitation and the Cosmos, Pennsylvania State University, 104 Davey Lab, University Park, Pennsylvania 16802 (United States); Universidad Autonoma de Chihuahua, Facultad de Ingenieria, Nuevo Campus Universitario, Chihuahua 31125 (Mexico); Centro de Fisica Fundamental, Universidad de los Andes, Merida 5101 (Venezuela)

2007-09-15

142

Dilution effects in two-dimensional quantum orbital systems.  

PubMed

Interacting orbital degrees of freedom in a Mott insulator are essentially directional and frustrated. In this Letter, the effect of dilution in a quantum-orbital system with this kind of interaction is studied by analyzing a minimal orbital model which we call the two-dimensional quantum compass model. We find that the decrease of the ordering temperature due to dilution is stronger than that in spin models, but it is also much weaker than that of the classical model. The difference between the classical and the quantum-orbital systems arises from the enhancement of the effective dimensionality due to quantum fluctuations. PMID:17678040

Tanaka, Takayoshi; Ishihara, Sumio

2007-06-22

143

Dilution Effects in Two-Dimensional Quantum Orbital Systems  

NASA Astrophysics Data System (ADS)

Interacting orbital degrees of freedom in a Mott insulator are essentially directional and frustrated. In this Letter, the effect of dilution in a quantum-orbital system with this kind of interaction is studied by analyzing a minimal orbital model which we call the two-dimensional quantum compass model. We find that the decrease of the ordering temperature due to dilution is stronger than that in spin models, but it is also much weaker than that of the classical model. The difference between the classical and the quantum-orbital systems arises from the enhancement of the effective dimensionality due to quantum fluctuations.

Tanaka, Takayoshi; Ishihara, Sumio

2007-06-01

144

Addressing Coulomb's singularity, nanoparticle recoil and Johnson's noise  

NASA Astrophysics Data System (ADS)

Recent experiments prompt rethinking of the basics of elastic and inelastic electron scattering in electron microscopy. Standard approximations of elastic scattering largely based Bragg's law seem less clearly relevant when individual columns or even single atoms are probed. Phase shift analysis of atomic scattering can provide some checks and insights. The dielectric theory of aloof beam interactions is severely tested by observations of nanoparticle recoil but may be capable of explaining de-coherence effects induced by thermal fluctuations.

Howie, Archie

2014-06-01

145

Continuous and pulsed quantum zeno effect.  

PubMed

Continuous and pulsed quantum Zeno effects were observed using a 87Rb Bose-Einstein condensate. Oscillations between two ground hyperfine states of a magnetically trapped condensate, externally driven at a transition rate omega(R), were suppressed by destructively measuring the population in one of the states with resonant light. The suppression of the transition rate in the two-level system was quantified for pulsed measurements with a time interval deltat between pulses and continuous measurements with a scattering rate gamma. We observe that the continuous measurements exhibit the same suppression in the transition rate as the pulsed measurements when gammadeltat=3.60(0.43), in agreement with the predicted value of 4. Increasing the measurement rate suppressed the transition rate down to 0.005 omega(R). PMID:17280408

Streed, Erik W; Mun, Jongchul; Boyd, Micah; Campbell, Gretchen K; Medley, Patrick; Ketterle, Wolfgang; Pritchard, David E

2006-12-31

146

On Quantum Effects in a Theory of Biological Evolution  

PubMed Central

We construct a descriptive toy model that considers quantum effects on biological evolution starting from Chaitin's classical framework. There are smart evolution scenarios in which a quantum world is as favorable as classical worlds for evolution to take place. However, in more natural scenarios, the rate of evolution depends on the degree of entanglement present in quantum organisms with respect to classical organisms. If the entanglement is maximal, classical evolution turns out to be more favorable.

Martin-Delgado, M. A.

2012-01-01

147

A recoil resilient lumen support, design, fabrication and mechanical evaluation  

NASA Astrophysics Data System (ADS)

Stents are artificial implants that provide scaffolding to a cavity inside the body. This paper presents a new luminal device for reducing the mechanical failure of stents due to recoil, which is one of the most important issues in stenting. This device, which we call a recoil-resilient ring (RRR), is utilized standalone or potentially integrated with existing stents to address the problem of recoil. The proposed structure aims to minimize the need for high-pressure overexpansion that can induce intra-luminal trauma and excess growth of vascular tissue causing later restenosis. The RRR is an overlapped open ring with asymmetrical sawtooth structures that are intermeshed. These teeth can slide on top of each other, while the ring is radially expanded, but interlock step-by-step so as to keep the final expanded state against compressional forces that normally cause recoil. The RRRs thus deliver balloon expandability and, when integrated with a stent, bring both radial rigidity and longitudinal flexibility to the stent. The design of the RRR is investigated through finite element analysis (FEA), and then the devices are fabricated using micro-electro-discharge machining of 200-µm-thick Nitinol sheet. The standalone RRR is balloon expandable in vitro by 5-7 Atm in pressure, which is well within the recommended in vivo pressure ranges for stenting procedures. FEA compression tests indicate 13× less reduction of the cross-sectional area of the RRR compared with a typical stainless steel stent. These results also show perfect elastic recovery of the RRR after removal of the pressure compared to the remaining plastic deformations of the stainless steel stent. On the other hand, experimental loading tests show that the fabricated RRRs have 2.8× radial stiffness compared to a two-column section of a commercial stent while exhibiting comparable elastic recovery. Furthermore, testing of in vitro expansion in a mock artery tube shows around 2.9% recoil, approximately 5-11× smaller than the recoil reported for commercial stents. These experimental results demonstrate the effectiveness of the device design for the targeted luminal support and stenting applications.

Mehdizadeh, Arash; Ali, Mohamed Sultan Mohamed; Takahata, Kenichi; Al-Sarawi, Said; Abbott, Derek

2013-06-01

148

Kondo effects in triangular triple quantum dots  

NASA Astrophysics Data System (ADS)

We study the conductance through a triangular triple quantum dot, which is connected to two noninteracting leads, using the numerical renormalization group (NRG). It is found that the system shows a variety of Kondo effects depending on the filling of the triangle. The SU(4) Kondo effect occurs at half-filling, and a sharp conductance dip due to a phase lapse appears in the gate-voltage dependence. Furthermore, when four electrons occupy the three sites on average, a local S=1 moment, which is caused by the Nagaoka mechanism, is induced along the triangle. The temperature dependence of the entropy and spin susceptibility of the triangle shows that this moment is screened by the conduction electrons via two separate stages at different temperatures. The two-terminal and four-terminal conductances show a clear difference at the gate voltages, where the SU(4) or the S=1 Kondo effects occur[1]. We will also discuss effects of deformations of the triangular configuration, caused by the inhomogeneity in the inter-dot couplings and in the gate voltages. [4pt] [1] T.Numata, Y.Nisikawa, A.Oguri, and A.C.Hewson: arXiv:0808.3496.

Oguri, Akira; Numata, Takahide; Nisikawa, Yunori; Hewson, A. C.

2009-03-01

149

Recoil-ion and electron momentum spectroscopy: reaction-microscopes  

NASA Astrophysics Data System (ADS)

Recoil-ion and electron momentum spectroscopy is a rapidly developing technique that allows one to measure the vector momenta of several ions and electrons resulting from atomic or molecular fragmentation. In a unique combination, large solid angles close to 4pi and superior momentum resolutions around a few per cent of an atomic unit (a.u.) are typically reached in state-of-the art machines, so-called reaction-microscopes. Evolving from recoil-ion and cold target recoil-ion momentum spectroscopy (COLTRIMS), reaction-microscopes—the `bubble chambers of atomic physics'—mark the decisive step forward to investigate many-particle quantum-dynamics occurring when atomic and molecular systems or even surfaces and solids are exposed to time-dependent external electromagnetic fields. This paper concentrates on just these latest technical developments and on at least four new classes of fragmentation experiments that have emerged within about the last five years. First, multi-dimensional images in momentum space brought unprecedented information on the dynamics of single-photon induced fragmentation of fixed-in-space molecules and on their structure. Second, a break-through in the investigation of high-intensity short-pulse laser induced fragmentation of atoms and molecules has been achieved by using reaction-microscopes. Third, for electron and ion-impact, the investigation of two-electron reactions has matured to a state such that the first fully differential cross sections (FDCSs) are reported. Fourth, comprehensive sets of FDCSs for single ionization of atoms by ion-impact, the most basic atomic fragmentation reaction, brought new insight, a couple of surprises and unexpected challenges to theory at keV to GeV collision energies. In addition, a brief summary on the kinematics is provided at the beginning. Finally, the rich future potential of the method is briefly envisaged.

Ullrich, J.; Moshammer, R.; Dorn, A.; Dörner, R.; Schmidt, L. Ph H.; Schmidt-Böcking, H.

2003-09-01

150

Recoiling from a Kick in the Head-On Case  

NASA Technical Reports Server (NTRS)

Recoil "kicks" induced by gravitational radiation are expected in the inspiral and merger of black holes. Recently the numerical relativity community has begun to measure the significant kicks found when both unequal masses and spins are considered. Because understanding the cause and magnitude of each component of this kick may be complicated in inspiral simulations, we consider these effects in the context of a simple test problem. We study recoils from collisions of binaries with initially head-on trajectories, starting with the simplest case of equal masses with no spin; adding spin and varying the mass ratio, both separately and jointly. We find spin-induced recoils to be significant even in head-on configurations. Additionally, it appears that the scaling of transverse kicks with spins is consistent with post-Newtonian (PN) theory, even though the kick is generated in the nonlinear merger interaction, where PN theory should not apply. This suggests that a simple heuristic description might be effective in the estimation of spin-kicks.

Choi, Dae-Il; Kelly, Bernard J.; Boggs, William D.; Baker, John G.; Centrella, Joan; Van Meter, James

2007-01-01

151

Quantum size effects in classical hadrodynamics  

SciTech Connect

The author discusses future directions in the development of classical hydrodynamics for extended nucleons, corresponding to nucleons of finite size interacting with massive meson fields. This new theory provides a natural covariant microscopic approach to relativistic nucleus-nucleus collisions that includes automatically spacetime nonlocality and retardation, nonequilibrium phenomena, interactions among all nucleons, and particle production. The present version of the theory includes only the neutral scalar ({sigma}) and neutral vector ({omega}) meson fields. In the future, additional isovector pseudoscalar ({pi}{sup +}, {pi}{sup {minus}}, {pi}{sup 0}), isovector vector ({rho}{sup +}, {rho}{sup {minus}}, {rho}{sup 0}), and neutral pseudoscalar ({eta}) meson fields should be incorporated. Quantum size effects should be included in the equations of motion by use of the spreading function of Moniz and Sharp, which generates an effective nucleon mass density smeared out over a Compton wavelength. However, unlike the situation in electrodynamics, the Compton wavelength of the nucleon is small compared to its radius, so that effects due to the intrinsic size of the nucleon dominate.

Nix, J.R.

1994-03-01

152

Radiation effects in Si-Ge quantum size structure (Review)  

SciTech Connect

The article is dedicated to the review and analysis of the effects and processes occurring in Si-Ge quantum size semiconductor structures upon particle irradiation including ion implantation. Comparisons to bulk materials are drawn. The reasons of the enhanced radiation hardness of superlattices and quantum dots are elucidated. Some technological applications of the radiation treatment are reviewed.

Sobolev, N. A., E-mail: sobolev@ua.pt [Universidade de Aveiro, Departamento de Fisica and I3N (Portugal)

2013-02-15

153

Dilution Effects in Two-Dimensional Quantum Orbital Systems  

Microsoft Academic Search

Interacting orbital degrees of freedom in a Mott insulator are essentially directional and frustrated. In this Letter, the effect of dilution in a quantum-orbital system with this kind of interaction is studied by analyzing a minimal orbital model which we call the two-dimensional quantum compass model. We find that the decrease of the ordering temperature due to dilution is stronger

Takayoshi Tanaka; Sumio Ishihara

2007-01-01

154

Effect of violation of quantum mechanics on neutrino oscillation  

NASA Astrophysics Data System (ADS)

The effect of quantum mechanics violation due to quantum gravity on neutrino oscillation is investigated. It is found that the mechanism introduced by Ellis, Hagelin, Nanopoulos, and Srednicki through the modification of the Liouville equation can affect neutrino oscillation behavior and may be taken as a new solution of the solar neutrino problem.

Liu, Yong; Hu, Liangzhong; Ge, Mo-Lin

1997-11-01

155

Oscillatory quantum screening effects on the transition bremsstrahlung radiation in quantum plasmas  

SciTech Connect

The oscillatory screening effects on the transition bremsstrahlung radiation due to the polarization interaction between the electron and shielding cloud are investigated in dense quantum plasmas. The impact-parameter analysis with the modified Debye-Hueckel potential is applied to obtain the bremsstrahlung radiation cross section as a function of the quantum wave number, impact parameter, photon energy, and projectile energy. The results show that the oscillatory quantum screening effect strongly suppresses the transition bremsstrahlung radiation spectrum in dense quantum plasmas. It is also found that the oscillatory quantum screening effect is more significant near the maximum peak of the bremsstrahlung radiation cross section. In addition, the maximum peak of the bremsstrahlung radiation cross section is getting close to the center of the shielding cloud as increasing quantum wave number. It is interesting to note that the range of the bremsstrahlung photon energy would be broadened with an increase of the oscillatory screening effect. It is also found that the oscillatory screening effects on the transition bremsstrahlung spectrum decreases with increasing projectile energy.

Jung, Young-Dae [Department of Applied Physics, Hanyang University, Ansan, Kyunggi-Do 426-791, South Korea and Department of Electrical and Computer Engineering, MC 0407, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0407 (United States)

2011-06-15

156

Quantum Spin Hall Effect in Inverted Type II Semiconductors  

SciTech Connect

The quantum spin Hall (QSH) state is a topologically non-trivial state of quantum matter which preserves time-reversal symmetry; it has an energy gap in the bulk, but topologically robust gapless states at the edge. Recently, this novel effect has been predicted and observed in HgTe quantum wells. In this work we predict a similar effect arising in Type-II semiconductor quantum wells made from InAs/GaSb/AlSb. Because of a rare band alignment the quantum well band structure exhibits an 'inverted' phase similar to CdTe/HgTe quantum wells, which is a QSH state when the Fermi level lies inside the gap. Due to the asymmetric structure of this quantum well, the effects of inversion symmetry breaking and inter-layer charge transfer are essential. By standard self-consistent calculations, we show that the QSH state persists when these corrections are included, and a quantum phase transition between the normal insulator and the QSH phase can be electrically tuned by the gate voltage.

Liu, Chaoxing; /Tsinghua U., Beijing /Stanford U., Phys. Dept.; Hughes, Taylor L.; Qi, Xiao-Liang; /Stanford U., Phys. Dept.; Wang, Kang; /UCLA; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

2010-03-19

157

Oscillation and recoil of single and consecutively printed droplets.  

PubMed

In this study, the recoil and oscillation of single and consecutively printed drops on substrates of different wettabilities are examined using a high speed camera. The results show that, for a droplet impact on a dry surface at Weber number ~ O (1), both inertia and capillary effects are important in the initial spreading regime before the droplet starts to oscillate. For a substrate of higher wettability, drop oscillation decays faster due to a stronger viscous dissipation over a longer oscillation path parallel to the substrate. It is also found that when a drop impacts on a sessile drop sitting on a hydrophobic substrate, the combined drop recoil twice resulted from the coalescence of the two drops, whereas no recoil is observed for the impact of a single drop on a dry surface under the same condition. Furthermore, a single-degree-of-freedom vibration model for the height oscillation of single and combined drops on a hydrophobic substrate is established. For the condition considered, the model predictions match well with the experiments. The results also show the extent to which the increase in the liquid viscosity facilitates oscillation damping and the quantitative extension of the oscillation time of a combined drop compared to a single drop. PMID:23360081

Yang, Xin; Chhasatia, Viral H; Sun, Ying

2013-02-19

158

Quantum Zeno effect rationalizes the phonon bottleneck in semiconductor quantum dots.  

PubMed

Quantum confinement can dramatically slow down electron-phonon relaxation in nanoclusters. Known as the phonon bottleneck, the effect remains elusive. Using a state-of-the-art time-domain ab initio approach, we model the observed bottleneck in CdSe quantum dots and show that it occurs under quantum Zeno conditions. Decoherence in the electronic subsystem, induced by elastic electron-phonon scattering, should be significantly faster than inelastic scattering. Achieved with multiphonon relaxation, the phonon bottleneck is broken by Auger processes and structural defects, rationalizing experimental difficulties. PMID:23683182

Kilina, Svetlana V; Neukirch, Amanda J; Habenicht, Bradley F; Kilin, Dmitri S; Prezhdo, Oleg V

2013-05-01

159

From quantum confinement to quantum Hall effect in graphene nanostructures  

NASA Astrophysics Data System (ADS)

We study the evolution of the two-terminal conductance plateaus with a magnetic field for armchair graphene nanoribbons (GNRs) and graphene nanoconstrictions (GNCs). For GNRs, the conductance plateaus of (2e2)/(h) at zero magnetic field evolve smoothly to the quantum Hall regime, where the plateaus in conductance at even multiples of (2e2)/(h) disappear. It is shown that the relation between the energy and magnetic field does not follow the same behavior as in “bulk” graphene, reflecting the different electronic structure of a GNR. For the nanoconstrictions we show that the conductance plateaus do not have the same sharp behavior in zero magnetic field as in a GNR, which reflects the presence of backscattering in such structures. Our results show good agreement with recent experiments on high-quality graphene nanoconstrictions. The behavior with the magnetic field for a GNC shows some resemblance to the one for a GNR but now depends also on the length of the constriction. By analyzing the evolution of the conductance plateaus in the presence of the magnetic field we can obtain the width of the structures studied and show that this is a powerful experimental technique in the study of the electronic and structural properties of narrow structures.

Guimarães, M. H. D.; Shevtsov, O.; Waintal, X.; van Wees, B. J.

2012-02-01

160

Quantum theory of the Borrmann effect  

NASA Astrophysics Data System (ADS)

In the phenomenon of diffraction of an electromagnetic wave in a lattice, the phase relations between the transmitted wave and the diffracted wave are fundamental. A vector can be written that describes the quantum state of the radiation in the above-mentioned case, and the photoelectric absorption cross section can be computed. It will be proved that the way the dynamical theory of x-ray diffraction deals with absorption is not correct because it does not consider the interference between the ? and ? rays; this phenomenon causes the failure of the dynamical theory in the explication of the Borrmann effect, which will be explained by means of a theory proposed herein. In addition, a new phenomenon is described that is not expected by the dynamical theory, the coherent scattering of photons from the ? ray to the ? ray; such a phenomenon is the real origin of the ?-ray extinction in the crystal and a quite anomalous expression for the extinction depth is found that is inversely proportional to the incident intensity.

Biagini, M.

1990-10-01

161

Octet Quantum Hall Effect in Graphene Bilayers  

NASA Astrophysics Data System (ADS)

Interaction driven integer quantum Hall effects are anticipated [1]in graphene bilayers because of the near-degeneracy of eight Landau levels which appear near the neutral system Fermi level at filling factors between ?=-4 and ?=4. The bilayer graphene octet exhibtits a wide variety of broken symmetry states, with Ising, XY and Heisenberg character which can be controlled by an external field which creates an electric potential difference between the two layers. Because of the peculiarities of the bilayer graphene electronic structure states with n=0 and n=1 orbital character are degenerate. I will explain predictions that an intra-Landau-level cyclotron resonance signal will appear at some odd-integer filling factors, accompanied by collective modes which are nearly gapless and have approximate k^3/2 dispersion. This talk will be based on work performed in collaboration with Yafis Barlas, Rene Cote, Kentaro Nomura, and Jules Lambert. [4pt] [1] Y. Barlas et al. , Phys. Rev. Lett. 101, 097601(2008).

MacDonald, Allan H.

2009-03-01

162

Nuclear spin effects in semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

The interaction of an electronic spin with its nuclear environment, an issue known as the central spin problem, has been the subject of considerable attention due to its relevance for spin-based quantum computation using semiconductor quantum dots. Independent control of the nuclear spin bath using nuclear magnetic resonance techniques and dynamic nuclear polarization using the central spin itself offer unique possibilities for manipulating the nuclear bath with significant consequences for the coherence and controlled manipulation of the central spin. Here we review some of the recent optical and transport experiments that have explored this central spin problem using semiconductor quantum dots. We focus on the interaction between 104-106 nuclear spins and a spin of a single electron or valence-band hole. We also review the experimental techniques as well as the key theoretical ideas and the implications for quantum information science.

Chekhovich, E. A.; Makhonin, M. N.; Tartakovskii, A. I.; Yacoby, A.; Bluhm, H.; Nowack, K. C.; Vandersypen, L. M. K.

2013-06-01

163

Stark effect in parabolic quantum dot  

Microsoft Academic Search

We theoretically investigate the optical properties of the exciton confined in parabolic quantum-dot , with and without electric field, by means of perturbative-variational method. The quantum-dot size enhances the 1s eigenvalue ahd oscillator strength . In smaller dot the relative extension of the exciton wave function is equal to the size of the dot . The 1s exciton bihding energy

S. JAZIRI; G. BASTARD; R. BENNACEUR

1993-01-01

164

Electronic states and curved surface effect of silicon quantum dots  

NASA Astrophysics Data System (ADS)

The calculation results show that the bonding energy and electronic states of silicon quantum dots (Si QDs) are different on various curved surfaces (CS), for example, a Si-O-Si bridge bond on curved surface provides the localized levels in band gap and its bonding energy is shallower than that on facet. Curved surface breaks symmetrical shape of silicon quantum dots on which some bonds can produce localized electronic states in band gap. The red-shifting of photoluminescence spectra on smaller silicon quantum dots can be explained by CS effect. In CS effect, surface curvature is determined by the shape of Si QDs or silicon nanostructures, which is independent of their sizes. The CS effect has the interesting fundamental physical properties in nanophysics as that of quantum confinement effect.

Huang, Wei-Qi; Huang, Zhong-Mei; Cheng, Han-Qiong; Miao, Xin-Jian; Shu, Qin; Liu, Shi-Rong; Qin, Chao-Jian

2012-10-01

165

Fractional quantum Hall effect in the absence of Landau levels  

PubMed Central

It is well known that the topological phenomena with fractional excitations, the fractional quantum Hall effect, will emerge when electrons move in Landau levels. Here we show the theoretical discovery of the fractional quantum Hall effect in the absence of Landau levels in an interacting fermion model. The non-interacting part of our Hamiltonian is the recently proposed topologically non-trivial flat-band model on a checkerboard lattice. In the presence of nearest-neighbouring repulsion, we find that at 1/3 filling, the Fermi-liquid state is unstable towards the fractional quantum Hall effect. At 1/5 filling, however, a next-nearest-neighbouring repulsion is needed for the occurrence of the 1/5 fractional quantum Hall effect when nearest-neighbouring repulsion is not too strong. We demonstrate the characteristic features of these novel states and determine the corresponding phase diagram.

Sheng, D.N.; Gu, Zheng-Cheng; Sun, Kai; Sheng, L.

2011-01-01

166

Critical Current in the Integral Quantum Hall Effect.  

National Technical Information Service (NTIS)

A multiparticle theory of the Integral Quantum Hall Effect (IQHE) was constructed operating with pairs wave function as an order parameter. The IQHE is described with bosonic macroscopic states while the fractional QHE with fermionic ones. The calculation...

I. Z. Kostadinov

1985-01-01

167

Complex scattering dynamics and the quantum Hall effects  

SciTech Connect

We review both classical and quantum potential scattering in two dimensions in a magnetic field, with applications to the quantum Hall effect. Classical scattering is complex, due to the approach of scattering states to an infinite number of dynamically bound states. Quantum scattering follows the classical behavior rather closely, exhibiting sharp resonances in place of the classical bound states. Extended scatterers provide a quantitative explanation for the breakdown of the QHE at a comparatively small Hall voltage as seen by Kawaji et al., and possibly for noise effects.

Trugman, S.A.

1994-12-16

168

Electron-exchange and quantum screening effects on the Thomson scattering process in quantum Fermi plasmas  

SciTech Connect

The influence of the electron-exchange and quantum screening on the Thomson scattering process is investigated in degenerate quantum Fermi plasmas. The Thomson scattering cross section in quantum plasmas is obtained by the plasma dielectric function and fluctuation-dissipation theorem as a function of the electron-exchange parameter, Fermi energy, plasmon energy, and wave number. It is shown that the electron-exchange effect enhances the Thomson scattering cross section in quantum plasmas. It is also shown that the differential Thomson scattering cross section has a minimum at the scattering angle ?=?/2. It is also found that the Thomson scattering cross section increases with an increase of the Fermi energy. In addition, the Thomson scattering cross section is found to be decreased with increasing plasmon energy.

Lee, Gyeong Won [Department of Applied Physics, Hanyang University, Ansan, Kyunggi-Do 426-791 (Korea, Republic of)] [Department of Applied Physics, Hanyang University, Ansan, Kyunggi-Do 426-791 (Korea, Republic of); Jung, Young-Dae [Department of Applied Physics, Hanyang University, Ansan, Kyunggi-Do 426-791 (Korea, Republic of) [Department of Applied Physics, Hanyang University, Ansan, Kyunggi-Do 426-791 (Korea, Republic of); Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, 110 Eighth Street, Troy, New York 12180-3590 (United States)

2013-06-15

169

Quantum nondemolition photon detection in circuit QED and the quantum Zeno effect  

NASA Astrophysics Data System (ADS)

We analyze the detection of itinerant photons using a quantum nondemolition measurement. An important example is the dispersive detection of microwave photons in circuit quantum electrodynamics, which can be realized via the nonlinear interaction between photons inside a superconducting transmission line resonator. We show that the back action due to the continuous measurement imposes a limit on the detector efficiency in such a scheme. We illustrate this using a setup where signal photons have to enter a cavity in order to be detected dispersively. In this approach, the measurement signal is the phase shift imparted to an intense beam passing through a second cavity mode. The restrictions on the fidelity are a consequence of the quantum Zeno effect, and we discuss both analytical results and quantum trajectory simulations of the measurement process.

Helmer, Ferdinand; Mariantoni, Matteo; Solano, Enrique; Marquardt, Florian

2009-05-01

170

Recoil-proton polarization in high-energy deuteron photodisintegration with circularly polarized photons.  

PubMed

We measured the angular dependence of the three recoil-proton polarization components in two-body photodisintegration of the deuteron at a photon energy of 2 GeV. These new data provide a benchmark for calculations based on quantum chromodynamics. Two of the five existing models have made predictions of polarization observables. Both explain the longitudinal polarization transfer satisfactorily. Transverse polarizations are not well described, but suggest isovector dominance. PMID:17501566

Jiang, X; Arrington, J; Benmokhtar, F; Camsonne, A; Chen, J P; Choi, S; Chudakov, E; Cusanno, F; Deur, A; Dutta, D; Garibaldi, F; Gaskell, D; Gayou, O; Gilman, R; Glashauser, C; Hamilton, D; Hansen, O; Higinbotham, D W; Holt, R J; de Jager, C W; Jones, M K; Kaufman, L J; Kinney, E R; Kramer, K; Lagamba, L; de Leo, R; Lerose, J; Lhuillier, D; Lindgren, R; Liyanage, N; McCormick, K; Meziani, Z-E; Michaels, R; Moffit, B; Monaghan, P; Nanda, S; Paschke, K D; Perdrisat, C F; Punjabi, V; Qattan, I A; Ransome, R D; Reimer, P E; Reitz, B; Saha, A; Schulte, E C; Sheyor, R; Slifer, K; Solvignon, P; Sulkosky, V; Urciuoli, G M; Voutier, E; Wang, K; Wijesooriya, K; Wojtsekhowski, B; Zhu, L

2007-05-01

171

Intrinsic Spin Hall Effect Induced by Quantum Phase Transition in HgCdTe Quantum Wells  

SciTech Connect

Spin Hall effect can be induced both by the extrinsic impurity scattering and by the intrinsic spin-orbit coupling in the electronic structure. The HgTe/CdTe quantum well has a quantum phase transition where the electronic structure changes from normal to inverted. We show that the intrinsic spin Hall effect of the conduction band vanishes on the normal side, while it is finite on the inverted side. This difference gives a direct mechanism to experimentally distinguish the intrinsic spin Hall effect from the extrinsic one.

Yang, Wen; Chang, Kai; /Beijing, Inst. Semiconductors; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

2010-03-19

172

Spin blockade of quantum cellular automata effects in a few electron triple quantum dot  

NASA Astrophysics Data System (ADS)

It has been previously demonstrated, employing charge detection techniques, that quantum cellular automata (QCA) processes exist in the vicinity of quadruple degeneracy points in both ring and serial arrangements of lateral triple quantum dots. The effect is primarily an electrostatic one. In this paper, we report on transport measurements through a triple dot potential and study experimentally the interplay between these QCA phenomena and the Pauli (spin) blockade effect. We demonstrate experimentally that the interaction between these processes leads to a higher order and indirect form of spin blockade in which the QCA effect itself is blockaded.

Gaudreau, L.; Sachrajda, A. S.; Studenikin, S. A.; Zawadzki, P.; Kam, A.

2008-03-01

173

Proton recoil scintillator neutron rem meter  

DOEpatents

A neutron rem meter utilizing proton recoil and thermal neutron scintillators to provide neutron detection and dose measurement. In using both fast scintillators and a thermal neutron scintillator the meter provides a wide range of sensitivity, uniform directional response, and uniform dose response. The scintillators output light to a photomultiplier tube that produces an electrical signal to an external neutron counter.

Olsher, Richard H. (Los Alamos, NM); Seagraves, David T. (Los Alamos, NM)

2003-01-01

174

Scattering and recoiling imaging code (SARIC)  

NASA Astrophysics Data System (ADS)

A new classical ion trajectory simulation program based on the binary collision approximation has been developed in order to support the results of time-of-flight scattering and recoiling spectrometry (TOF-SARS) and scattering and recoiling imaging spectrometry (SARIS). The code was designed to provide information directly related to the TOF-SARS and SARIS measurements and to operate efficiently on small personal computers. The calculation uses the Ziegler-Biersack-Littmark (ZBL) universal screening function or the Moliére screening function to simulate the three-dimensional motion of atomic particles and includes simultaneous collisions involving several atoms. For TOF-SARS, the program calculates the energy and time-of-flight distributions of scattered and recoiled particles, polar (incident) angle ?-scans, and azimuthal angle ?-scans. For SARIS, the program provides images of the scattering and recoiling intensities in polar exit angle and azimuthal angle (?, ?)-space. A two-dimensional reliability factor ( R) has been developed in order to obtain a quantitative comparison of experimental and simulated images. Examples of simulations are presented for Ni{100}, {110} and {111} surfaces and a Pt{111} surface. The R-factor is used to quantitatively compare the simulated Pt{111} image to an experimentally emulated image.

Bykov, V.; Kim, C.; Sung, M. M.; Boyd, K. J.; Todorov, S. S.; Rabalais, J. W.

175

Nuclear Recoil Background Evaluation for WIMP Searches  

Microsoft Academic Search

Nuclear recoils produced by neutrons, alphas and neutrinos as they scatter from target nuclei are important sources of background which must be considered in WIMP searches. PMTs and other detector components may contribute neutrons which generate a source of background. Alphas on the surface of the vessel can also be a serious issue for some of the experiments. And, neutrino-induced

Dongming Mei; Andrew Hime; Christina Keller; Zhongbao Yin

2007-01-01

176

Effects of symmetry breaking in finite quantum systems  

NASA Astrophysics Data System (ADS)

The review considers the peculiarities of symmetry breaking and symmetry transformations and the related physical effects in finite quantum systems. Some types of symmetry in finite systems can be broken only asymptotically. However, with a sufficiently large number of particles, crossover transitions become sharp, so that symmetry breaking happens similarly to that in macroscopic systems. This concerns, in particular, global gauge symmetry breaking, related to Bose-Einstein condensation and superconductivity, or isotropy breaking, related to the generation of quantum vortices, and the stratification in multicomponent mixtures. A special type of symmetry transformation, characteristic only for finite systems, is the change of shape symmetry. These phenomena are illustrated by the examples of several typical mesoscopic systems, such as trapped atoms, quantum dots, atomic nuclei, and metallic grains. The specific features of the review are: (i) the emphasis on the peculiarities of the symmetry breaking in finite mesoscopic systems; (ii) the analysis of common properties of physically different finite quantum systems; (iii) the manifestations of symmetry breaking in the spectra of collective excitations in finite quantum systems. The analysis of these features allows for the better understanding of the intimate relation between the type of symmetry and other physical properties of quantum systems. This also makes it possible to predict new effects by employing the analogies between finite quantum systems of different physical nature.

Birman, J. L.; Nazmitdinov, R. G.; Yukalov, V. I.

2013-05-01

177

Optical recoil of asymmetric nano-optical antenna  

NASA Astrophysics Data System (ADS)

We propose nano-optical antennas with asymmetric radiation patterns as light-driven mechanical recoil force generators. Directional antennas are found to generate recoil force efficiently when driven in the spectral proximity of their resonances. It is also shown that the recoil force is equivalent to the Poynting vector integrated over a closed sphere containing the antenna structures.

Song, Jung-Hwan; Shin, Jonghwa; Lim, Hee-Jin; Lee, Yong-Hee

2011-08-01

178

Electromagnetic manipulation for the anti-Zeno effect in an engineered quantum tunneling process  

SciTech Connect

We investigate the anti-Zeno phenomenon as well as the quantum Zeno effect for the irreversible quantum tunneling from a quantum dot to a ring array of quantum dots. By modeling the total system with the Anderson-Fano-Lee model, it is found that the transition from the quantum Zeno to the quantum anti-Zeno effect can happen by adjusting magnetic flux and gate voltage.

Zhou Lan [Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing, 100080 (China); Department of Physics, Hunan Normal University, Changsha 410081 (China); Hu, F. M. [Department of Mathematics, Capital Normal University, Beijing, 100037 (China); Lu Jing [Department of Physics, Hunan Normal University, Changsha 410081 (China); Sun, C. P. [Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing, 100080 (China)

2006-09-15

179

Low energy quantum gravity from the effective average action  

SciTech Connect

Within the effective average action approach to quantum gravity, we recover the low-energy effective action as derived in the effective field theory framework by studying the flow of possibly nonlocal form factors that appear in the curvature expansion of the effective average action. We restrict to the one-loop flow where progress can be made with the aid of the nonlocal heat kernel expansion. We discuss the possible physical implications of the scale-dependent low-energy effective action through the analysis of the quantum corrections to the Newtonian potential.

Satz, A.; Mazzitelli, F. D. [Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Univ. de Buenos Aires and Instituto de Fisica de Buenos Aires, CONICET Ciudad Universitaria, Pabellon 1, 1428 Buenos Aires (Argentina); Codello, A. [Institut fuer Physik, Johannes Gutenberg-Universitaet, Mainz Staudingerweg 7, D-55099 Mainz (Germany)

2010-10-15

180

Quantum effects improve the energy efficiency of feedback control.  

PubMed

The laws of thermodynamics apply equally well to quantum systems as to classical systems, and because of this, quantum effects do not change the fundamental thermodynamic efficiency of isothermal refrigerators or engines. We show that, despite this fact, quantum mechanics permits measurement-based feedback control protocols that are more thermodynamically efficient than their classical counterparts. As part of our analysis, we perform a detailed accounting of the thermodynamics of unitary feedback control and elucidate the sources of inefficiency in measurement-based and coherent feedback. PMID:24827219

Horowitz, Jordan M; Jacobs, Kurt

2014-04-01

181

Quantum effects improve the energy efficiency of feedback control  

NASA Astrophysics Data System (ADS)

The laws of thermodynamics apply equally well to quantum systems as to classical systems, and because of this, quantum effects do not change the fundamental thermodynamic efficiency of isothermal refrigerators or engines. We show that, despite this fact, quantum mechanics permits measurement-based feedback control protocols that are more thermodynamically efficient than their classical counterparts. As part of our analysis, we perform a detailed accounting of the thermodynamics of unitary feedback control and elucidate the sources of inefficiency in measurement-based and coherent feedback.

Horowitz, Jordan M.; Jacobs, Kurt

2014-04-01

182

Effective Hamiltonian for the hybrid double quantum dot qubit  

NASA Astrophysics Data System (ADS)

Quantum dot hybrid qubits formed from three electrons in double quantum dots represent a promising compromise between high speed and simple fabrication for solid state implementations of single-qubit and two-qubits quantum logic ports. We derive the Schrieffer-Wolff effective Hamiltonian that describes in a simple and intuitive way the qubit by combining a Hubbard-like model with a projector operator method. As a result, the Hubbard-like Hamiltonian is transformed in an equivalent expression in terms of the exchange coupling interactions between pairs of electrons. The effective Hamiltonian is exploited to derive the dynamical behavior of the system and its eigenstates on the Bloch sphere to generate qubits operation for quantum logic ports. A realistic implementation in silicon and the coupling of the qubit with a detector are discussed.

Ferraro, E.; De Michielis, M.; Mazzeo, G.; Fanciulli, M.; Prati, E.

2014-05-01

183

Dissipative quantum transport in macromolecules: Effective field theory approach  

NASA Astrophysics Data System (ADS)

We introduce an atomistic approach to the dissipative quantum dynamics of charged or neutral excitations propagating through macromolecular systems. Using the Feynman-Vernon path integral formalism, we analytically trace out from the density matrix the atomic coordinates and the heat bath degrees of freedom. This way we obtain an effective field theory which describes the real-time evolution of the quantum excitation and is fully consistent with the fluctuation-dissipation relation. The main advantage of the field-theoretic approach is that it allows us to avoid using the Keldysh contour formulation. This simplification makes it straightforward to derive Feynman diagrams to analytically compute the effects of the interaction of the propagating quantum excitation with the heat bath and with the molecular atomic vibrations. For illustration purposes, we apply this formalism to investigate the loss of quantum coherence of holes propagating through a poly(3-alkylthiophene) polymer.

Schneider, E.; a Beccara, S.; Faccioli, P.

2013-08-01

184

Quantum transport: From effective mass approximation to full band  

NASA Astrophysics Data System (ADS)

To study dissipative quantum transport in ultra-scaled devices, we first solve the Pauli Master Equation using the Effective Mass Approximation, followed by solving ballistic quantum transport using the full band structure determined from the empirical pseudopotential method. We study the geometry induced quantum access resistance, evaluate the influence of non-polar phonon scattering, and calculate impurity scattering in devices such as n-i-n resistor, Double-Barrier Resonant Tunneling Diode, Double-Gate Field Effect Transistors. We calculate band structure and the complex band structure of Silicon Nanowires, develop open boundary conditions for full band quantum transport using the empirical pseudopotential method, and perform atomistic modeling of Silicon Nanowire structures to study electron transport characteristics.

Fu, Bo

185

Non-Markovian effect on the quantum discord  

Microsoft Academic Search

We study the non-Markovian effect on the dynamics of the quantum discord by exactly solving a model consisting of two independent qubits subject to two zero-temperature non-Markovian reservoirs, respectively. Considering the two qubits initially prepared in Bell-like or extended Werner-like states, we show that there is no occurrence of the sudden death, but only instantaneous disappearance of the quantum discord

Bo Wang; Zhen-Yu Xu; Ze-Qian Chen; Mang Feng

2010-01-01

186

Theory of Non-Adiabatic Optical Effects in Quantum Dots  

Microsoft Academic Search

Quantum dots continue to be an area of intense scientific activity, because they have a number of advantages as the `building blocks' for advanced semiconductor devices with three-dimensional band-structure engineering. Considerable effort is being devoted to the investigation of effects due to the exciton-phonon interaction on the optical properties of quantum dots. Our theory of photoluminescence and Raman scattering in

J. T. Devreese

2002-01-01

187

Quantum Electrodynamics Effects in Heavy Ions and Atoms  

NASA Astrophysics Data System (ADS)

Quantum electrodynamics theory of heavy ions and atoms is considered. The current status of calculations of the binding energies, the hyperfine splitting and g factor values in heavy few-electron ions is reviewed. The theoretical predictions are compared with available experimental data. A special attention is focused on tests of quantum electrodynamics in strong electromagnetic fields and on determination of the fundamental constants. Recent progress in calculations of the parity nonconservation effects with heavy atoms and ions is also reported.

Shabaev, V. M.; Andreev, O. V.; Bondarev, A. I.; Glazov, D. A.; Kozhedub, Y. S.; Maiorova, A. V.; Plunien, G.; Tupitsyn, I. I.; Volotka, A. V.

2011-05-01

188

Quantum effects on the singularity of the Gowdy cosmology  

NASA Astrophysics Data System (ADS)

Quantum effects on the initial singularity of the Gowdy T(-cubed) x R cosmology are studied. This is done by calculating the expectation values of the curvature invariant operator in suitable quantum states. It is found that eigenstates of 'particle' number do not introduce inhomogeneities into the model whereas linear combinations of these states such as the coherent states do. It is also found that the classical singularity persists.

Husain, Viqar

1987-11-01

189

Quantum effects in cosmological models with singularities  

NASA Astrophysics Data System (ADS)

The vacuum expectation values of the energy-momentum tensor of quantized scalar and spinor fields in a de Sitter space of the first kind are calculated. Limiting cases of the obtained exact expressions are considered. It is noted that the de Sitter space is a self-consistent solution of the Einstein equations with allowance for quantum vacuum fluctuations of massless fields.

Mamaev, S. G.

1981-01-01

190

near zero recoil in and beyond the Standard Model  

NASA Astrophysics Data System (ADS)

We compute the normalization of the form factor entering the decay amplitude by using numerical simulations of QCD on the lattice. From our study with dynamical light quarks, and by employing the maximally twisted Wilson quark action, we obtain in the continuum limit . We also compute the scalar and tensor form factors in the region near zero recoil and find , , for . The latter results are useful for searching the effects of physics beyond the Standard Model in decays. Our results for the similar form factors relevant to the non-strange case indicate that the method employed here can be used to achieve the precision determination of the decay amplitude as well.

Atoui, Mariam; Morénas, Vincent; Be?irevi?, Damir; Sanfilippo, Francesco

2014-05-01

191

Singularity free gravitational collapse in an effective dynamical quantum spacetime  

NASA Astrophysics Data System (ADS)

We model the gravitational collapse of heavy massive shells including its main quantum corrections. Among these corrections, quantum improvements coming from Quantum Einstein Gravity are taken into account, which provides us with an effective quantum spacetime. Likewise, we consider dynamical Hawking radiation by modeling its back-reaction once the horizons have been generated. Our results point towards a picture of gravitational collapse in which the collapsing shell reaches a minimum non-zero radius (whose value depends on the shell initial conditions) with its mass only slightly reduced. Then, there is always a rebound after which most (or all) of the mass evaporates in the form of Hawking radiation. Since the mass never concentrates in a single point, no singularity appears.

Torres, R.; Fayos, F.

2014-06-01

192

Entanglement switching via the Kondo effect in triple quantum dots  

NASA Astrophysics Data System (ADS)

We consider a triple quantum dot system in a triangular geometry with one of the dots connected to metallic leads. Using Wilson's numerical renormalization group method, we investigate quantum entanglement and its relation to the thermodynamic and transport properties in the regime where each of the dots is singly occupied on average, but with non-negligible charge fluctuations. It is shown that even in the regime of significant charge fluctuations the formation of the Kondo singlets induces switching between separable and perfectly entangled states. The quantum phase transition between unentangled and entangled states is analyzed quantitatively and the corresponding phase diagram is explained by exactly solvable spin model. In the framework of an effective model we also explain smearing of the entanglement transition for cases when the symmetry of the triple quantum dot system is relaxed.

Tooski, S. B.; Bu?ka, Bogdan R.; Žitko, Rok; Ramšak, Anton

2014-06-01

193

Size and shape effects in electromagnetic response of quantum dots and quantum dot arrays  

Microsoft Academic Search

Size and shape effects in electromagnetic response of quantum dots (QDs) such as depolarization shift of the exciton resonance and fine structure of the gain band are considered on the basis of a unified concept of light confinement. We show that at sufficiently large oscillator strength of the transition, QD behaves itself as a microcavity and excitation of cavity eigenmodes

S. A Maksimenko; G. Ya Slepyan; V. P Kalosha; N. N Ledentsov; A Hoffmann; D Bimberg

2001-01-01

194

The Theory of the Quantum Hall Effect  

Microsoft Academic Search

Laughlin's theory of fractional charges is worked out in detail for small charges from 1\\/3 till 1\\/101. There is a small deviation between computed values and those obtained from the closed form expression. The ground state energy crosses that of the charge-density waves. We develop a theory of fractional charges by using the quantum mechanics of angular momentum. We find

Keshav N. Shrivastava

2008-01-01

195

Molecular Dynamics Simulation Methods including Quantum Effects  

Microsoft Academic Search

\\u000a The progress of computational chemistry in the treatment of liquid systems is outlined, and the combination of the statistical\\u000a methods (in particular molecular dynamics) with quantum mechanics as the main foundation of this progress is emphasised. The\\u000a difficulties of experimental studies of liquid systems without having obtained sophisticated theoretical models describing\\u000a the structural entities and the dynamical behaviour of these

THOMAS S. HOFER; BERNHARD R. RANDOLF; BERND M. RODE

196

Aging effects in free quantum Brownian motion  

Microsoft Academic Search

The two-time correlation function Cxx(t,t?) of the displacement x(t)?x(t0) of a free quantum Brownian particle with respect to its position at a given time t0 is calculated analytically in the framework of the Caldeira and Leggett ohmic dissipation model. As a result, at any temperature T,Cxx(t,t?) exhibits aging, i.e. it depends explicitly on both times t and t? and not

Noëlle Pottier; Alain Mauger

2000-01-01

197

High-Efficiency Quantum Interrogation Measurements via the Quantum Zeno Effect  

SciTech Connect

The phenomenon of quantum interrogation allows one to optically detect the presence of an absorbing object, without the measuring light interacting with it. In an application of the quantum Zeno effect, the object inhibits the otherwise coherent evolution of the light, such that the probability that an interrogating photon is absorbed can in principle be arbitrarily small. We have implemented this technique, achieving efficiencies of up to 73% , and consequently exceeding the 50% theoretical maximum of the original ''interaction-free'' measurement proposal. We have also predicted and experimentally verified a previously unsuspected dependence on loss. (c) 1999 The American Physical Society.

Kwiat, P. G. [Physics Division, P-23, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Physics Division, P-23, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); White, A. G. [Physics Division, P-23, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Physics Division, P-23, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Mitchell, J. R. [Physics Division, P-23, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)] [Physics Division, P-23, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Nairz, O. [Institute for Experimental Physics, University of Innsbruck, Innsbruck 6020, (Austria)] [Institute for Experimental Physics, University of Innsbruck, Innsbruck 6020, (Austria); Weihs, G. [Institute for Experimental Physics, University of Innsbruck, Innsbruck 6020, (Austria)] [Institute for Experimental Physics, University of Innsbruck, Innsbruck 6020, (Austria); Weinfurter, H. [Institute for Experimental Physics, University of Innsbruck, Innsbruck 6020, (Austria)] [Institute for Experimental Physics, University of Innsbruck, Innsbruck 6020, (Austria); Zeilinger, A. [Institute for Experimental Physics, University of Innsbruck, Innsbruck 6020, (Austria)] [Institute for Experimental Physics, University of Innsbruck, Innsbruck 6020, (Austria)

1999-12-06

198

Molecular Recoiling in Polymer Thin Film Dewetting  

NASA Astrophysics Data System (ADS)

The molecular recoiling force stemming from nonequilibrium chain conformation was found to play a very important role in the dewetting stability of polymer thin films. Correct measurements and inclusion of this molecular force into thermodynamic consideration are crucial for analyzing dewetting phenomena and nanoscale polymer chain physics. This force was measured using a simple method based on contour relaxation at the incipient dewetting holes. The recoiling stress was found to increase dramatically with molecular weight and decreasing film thickness. The corresponding forces were calculated to be in the range from 9.0 to 28.2mN/m, too large to be neglected when compared to the dispersive forces (˜10mN/m) commonly operative in thin polymer films.

Yang, M. H.; Hou, S. Y.; Chang, Y. L.; Yang, A. C.-M.

2006-02-01

199

Quantum Zeno and anti-Zeno effects on quantum and classical correlations  

SciTech Connect

In this paper we study the possibility of modifying the dynamics of both quantum correlations, such as entanglement and discord, and classical correlations of an open bipartite system by means of the quantum Zeno effect. We consider two qubits coupled to a common boson reservoir at zero temperature. This model describes, for example, two atoms interacting with a quantized mode of a lossy cavity. We show that when the frequencies of the two atoms are symmetrically detuned from that of the cavity mode, oscillations between the Zeno and anti-Zeno regimes occur. We also calculate analytically the time evolution of both classical correlations and quantum discord, and we compare the Zeno dynamics of entanglement with the Zeno dynamics of classical correlations and discord.

Francica, F.; Plastina, F. [Dipartimento di Fisica, Universita della Calabria, I-87036 Arcavacata di Rende (Italy); INFN-Gruppo Collegato di Cosenza, Cosenza (Italy); Maniscalco, S. [Turku Centre for Quantum Physics, Department of Physics and Astronomy, University of Turku, FIN-20014 Turun yliopisto (Finland)

2010-11-15

200

Effective potential approach to the quantum scattering of solitons  

Microsoft Academic Search

Systems of solitons are approximately described in terms of a finite number of ``effective degrees of freedom'' interacting via ``effective potentials''. These are reconstructed, principally from knowledge of solutions to the classical field equations, by a procedure involving the sometric mapping of a sector of the field theoretical Hilbert space onto the Hilbert space of non-relativistic point particles. The quantum

P. Vinciarelli

1976-01-01

201

Ratchet effects in graphene and quantum wells with lateral superlattice  

NASA Astrophysics Data System (ADS)

Theoretical and experimental studies on the ratchet effects in graphene and in quantum wells with a lateral superlattice excited by alternating electric fields of terahertz frequency range are presented. We discuss the Seebeck ratchet effect and helicity driven photocurrents and show that the photocurrent generation is based on the combined action of a spatially periodic in-plane potential and a spatially modulated light.

Golub, L. E.; Nalitov, A. V.; Ivchenko, E. L.; Olbrich, P.; Kamann, J.; Eroms, J.; Weiss, D.; Ganichev, S. D.

2013-12-01

202

Residual-Impurity Effects in Directional Solidification: Long-Lasting Recoil of the Front and Nucleation-Growth of Gas Bubbles  

Microsoft Academic Search

Directional-solidification experiments are often perturbed by the nucleation of gas bubbles and other residual-impurity effects. We present a detailed experimental study of these phenomena in the system CBr{4}-C2Cl6 directionally solidified in thin films. As is usual in this type of experiments, we use zone-refined and outgased products, but do not fill and seal the samples under vacuum. We study the

Silvère Akamatsu; Gabriel Faivre

1996-01-01

203

Focus on quantum effects and noise in biomolecules  

NASA Astrophysics Data System (ADS)

The role of quantum mechanics in biological organisms has been a fundamental question of twentieth-century biology. It is only now, however, with modern experimental techniques, that it is possible to observe quantum mechanical effects in bio-molecular complexes directly. Indeed, recent experiments have provided evidence that quantum effects such as wave-like motion of excitonic energy flow, delocalization and entanglement can be seen even in complex and noisy biological environments (Engel et al 2007 Nature 446 782; Collini et al 2010 Nature 463 644; Panitchayangkoon et al 2010 Proc. Natl Acad. Sci. USA 107 12766). Motivated by these observations, theoretical work has highlighted the importance of an interplay between environmental noise and quantum coherence in such systems (Mohseni et al 2008 J. Chem. Phys. 129 174106; Plenio and Huelga 2008 New J. Phys. 10 113019; Olaya-Castro et al 2008 Phys. Rev. B 78 085115; Rebentrost et al 2009 New J. Phys. 11 033003; Caruso et al 2009 J. Chem. Phys. 131 105106; Ishizaki and Fleming 2009 J. Chem. Phys. 130 234111). All of this has led to a surge of interest in the exploration of quantum effects in biological systems in order to understand the possible relevance of non-trivial quantum features and to establish a potential link between quantum coherence and biological function. These studies include not only exciton transfer across light harvesting complexes, but also the avian compass (Ritz et al 2000 Biophys. J. 78 707), and the olfactory system (Turin 1996 Chem. Sens. 21 773; Chin et al 2010 New J. Phys. 12 065002). These examples show that the full understanding of the dynamics at bio-molecular length (10 Å) and timescales (sub picosecond) in noisy biological systems can uncover novel phenomena and concepts and hence present a fertile ground for truly multidisciplinary research.

Fleming, G. R.; Huelga, S. F.; Plenio, M. B.

2011-11-01

204

Dynamical quantum Hall effect in the parameter space  

PubMed Central

Geometric phases in quantum mechanics play an extraordinary role in broadening our understanding of fundamental significance of geometry in nature. One of the best known examples is the Berry phase [M.V. Berry (1984), Proc. Royal. Soc. London A, 392:45], which naturally emerges in quantum adiabatic evolution. So far the applicability and measurements of the Berry phase were mostly limited to systems of weakly interacting quasi-particles, where interference experiments are feasible. Here we show how one can go beyond this limitation and observe the Berry curvature, and hence the Berry phase, in generic systems as a nonadiabatic response of physical observables to the rate of change of an external parameter. These results can be interpreted as a dynamical quantum Hall effect in a parameter space. The conventional quantum Hall effect is a particular example of the general relation if one views the electric field as a rate of change of the vector potential. We illustrate our findings by analyzing the response of interacting spin chains to a rotating magnetic field. We observe the quantization of this response, which we term the rotational quantum Hall effect.

Gritsev, V.; Polkovnikov, A.

2012-01-01

205

Quantum effects and nonlocality in strongly coupled plasmonic nanowire dimers.  

PubMed

Using a fully quantum mechanical approach we study the optical response of a strongly coupled metallic nanowire dimer for variable separation widths of the junction between the nanowires. The translational invariance of the system allows to apply the time-dependent density functional theory (TDDFT) for nanowires of diameters up to 10 nm which is the largest size considered so far in quantum modeling of plasmonic dimers. By performing a detailed analysis of the optical extinction, induced charge densities, and near fields, we reveal the major nonlocal quantum effects determining the plasmonic modes and field enhancement in the system. These effects consist mainly of electron tunneling between the nanowires at small junction widths and dynamical screening. The TDDFT results are compared with results from classical electromagnetic calculations based on the local Drude and non-local hydrodynamic descriptions of the nanowire permittivity, as well as with results from a recently developed quantum corrected model. The latter provides a way to include quantum mechanical effects such as electron tunneling in standard classical electromagnetic simulations. We show that the TDDFT results can be thus retrieved semi-quantitatively within a classical framework. We also discuss the shortcomings of classical non-local hydrodynamic approaches. Finally, the implications of the actual position of the screening charge density at the gap interfaces are discussed in connection with plasmon ruler applications at subnanometric distances. PMID:24216954

Teperik, Tatiana V; Nordlander, Peter; Aizpurua, Javier; Borisov, Andrei G

2013-11-01

206

Effective critical points in finite quantum phase transitional systems  

SciTech Connect

Properties of quantum phase transitional systems in atomic nuclei are explored within the context of the interacting boson model 1 for both first and second order systems. A traditionally experimental approach is used to search for the effective finite-size critical point as a function of system size and angular momentum by studying derivatives of observables across the phase transition region. The effects of angular momentum on quantum phase transitions are investigated, and properties of first order phase transitions within the Casten triangle are examined.

Williams, E.; Casperson, R. J.; Werner, V. [A. W. Wright Nuclear Structure Laboratory, Yale University, New Haven, Connecticut 06520 (United States)

2010-11-15

207

Quantum-electrodynamics corrections in pionic hydrogen  

NASA Astrophysics Data System (ADS)

We investigate all pure quantum-electrodynamics corrections to the np?1s, n=2-4 transition energies of pionic hydrogen larger than 1meV, which requires an accurate evaluation of all relevant contributions up to order ?5. These values are needed to extract an accurate strong interaction shift from experiment. Many small effects, such as second-order and double vacuum polarization contribution, proton and pion self-energies, finite size and recoil effects are included with exact mass dependence. Our final value differs from previous calculations by up to ?11ppm for the 1s state, while a recent experiment aims at a 4ppm accuracy.

Schlesser, S.; Le Bigot, E.-O.; Indelicato, P.; Pachucki, K.

2011-07-01

208

Fractional quantum Hall effect in AlAs quantum wells: Role of valley degree of freedom  

NASA Astrophysics Data System (ADS)

When interacting two-dimensional electrons are placed in a large perpendicular magnetic field, to minimize their energy, they capture an even number of flux quanta and create new particles called composite fermions (CFs). These complex electron-flux-bound states offer an elegant explanation for the fractional quantum Hall effect. Thanks to the flux attachment, the effective field vanishes at half-filled Landau levels (?= 1/2 and 3/2) and CFs exhibit Fermi-liquid-like properties, similar to their zero-field electron counterparts. Here, we study a two-dimensional electron system in AlAs quantum wells where the electrons occupy two conduction band valleys with anisotropic Fermi contours and strain-tunable occupation. We address a fundamental question whether the anisotropy of the electron effective mass and Fermi surface is transferred to the CFs formed around filling factors ?= 1/2 and 3/2. Similar to their electron counter parts, CFs also exhibit anisotropic transport, suggesting an anisotropy of CF effective mass and Fermi surface. We also study quantum Hall ferromagnetism for fractional quantum Hall states formed at ?= 1/3 and 5/3 as a function of valley splitting. Within the framework of the CF theory, electronic fractional filling factors ?= 1/3 and 5/3 are equivalent to the integer filling factor p= 1 of CFs. Reminiscent of the quantum Hall ferromagnetism observed at ?= 1, we report persistent fractional quantum Hall states at filling factors ?= 1/3 and 5/3 when the two valleys are degenerate. However, the comparison of the energy gaps measured at ?= 1/3 and 5/3 to the available theory developed for single-valley, two-spin systems reveals that the gaps and their rates of rise with strain are much smaller than predicted.[4pt] [1] ``Transference of Transport Anisotropy to Composite Fermions,'' T. Gokmen, M. Padmanabhan, and M. Shayegan, Nature Physics 6, 621-624 (2010).[4pt] [2] `Ferromagnetic Fractional Quantum Hall States in a Valley-Degenerate Two-Dimensional Electron System,'' M. Padmanabhan, T. Gokmen, and M. Shayegan, Phys. Rev. Lett. 104, 016805 (2010).

Gokmen, Tayfun

2013-03-01

209

Collective Atomic Recoil Lasing and Superradiant Rayleigh Scattering in a high-Q ring cavity  

NASA Astrophysics Data System (ADS)

Cold atoms in optical high-Q cavities are an ideal model system for long-range interacting particles. The position of two arbitrary atoms is, independent on their distance, coupled by the back-scattering of photons within the cavity. This mutual coupling can lead to collective instability and self-organization of a cloud of cold atoms interacting with the cavity fields. This phenomenon (CARL, i.e. Collective Atomic Recoil Lasing) has been discussed theoretically for years, but was observed only recently in our lab. The CARL-effect is closely linked to superradiant Rayleigh scattering, which has been intensely studied with Bose-Einstein condensates in free space. By adding a resonator the coherence time of the system, in which the instability occurs, can be strongly enhanced. This enables us to observe cavity-enhanced superradiance with both Bose-Einstein condensates and thermal clouds and allows us to close the discussion about the role of quantum statistics in superradiant scattering.

Slama, Sebastian; Krenz, Gordon; Bux, Simone; Zimmermann, Claus; Courteille, Philippe W.

2008-01-01

210

Microscopic Properties of the Fractional Quantum Hall Effect  

NASA Astrophysics Data System (ADS)

The fractional quantum Hall effect occurs when an extremely clean 2-dimensional fermion gas is subject to a magnetic field. This simple set of circumstances creates phenomena, such as edge reconstruction and fractional statistics, that remain subjects of experimental study 30 years after the discovery of the fractional quantum Hall effect. This thesis investigates the properties of excitations of the fractional quantum Hall effect. The first set of experiments studies the interaction between fractional quantum Hall quasiparticles and nuclei in a quantum point contact (QPC). Following the application of a DC bias, fractional plateaus in the QPC shift symmetrically about half filling of the lowest Landau level, nu = 1/3, suggesting an interpretation in terms of composite fermions. Mapping the effects from the integer to fractional regimes extends the composite fermion picture to include hyperfine coupling. The second set of experiments studies the tunneling of quasiparticles through an antidot in the integer and fractional quantum Hall effect. In the integer regime, we conclude that oscillations are of the Coulomb type from the scaling of magnetic field period with the number of edges bound to the antidot. Generalizing this picture to the fractional regime, we find (based on magnetic field and gate-voltage periods) at nu = 2/3 a tunneling charge of (2/3)e and a single charged edge. Further unpublished data related to this experiment as well as alternative theoretical explanations are also presented. The third set of experiments investigates the properties of the fractional quantum Hall effect in the lowest Landau level of bilayer graphene using a scanning single-electron transistor. We observe a sequence of states which breaks particle-hole symmetry and instead obeys a nu ? nu + 2 symmetry. This asymmetry highlights the importance of the orbital degeneracy for many-body states in bilayer graphene. The fourth set of experiments investigates the coupling between microwaves and the fractional quantum Hall effect. Reflectometry is used to investigate bulk properties of samples with different electron densities. We observe large changes in the amplitude of the reflected signal at each integer filling factor as well as changes in the capacitance of the system.

Kou, Angela

211

The spin Hall effect in a quantum gas.  

PubMed

Electronic properties such as current flow are generally independent of the electron's spin angular momentum, an internal degree of freedom possessed by quantum particles. The spin Hall effect, first proposed 40 years ago, is an unusual class of phenomena in which flowing particles experience orthogonally directed, spin-dependent forces--analogous to the conventional Lorentz force that gives the Hall effect, but opposite in sign for two spin states. Spin Hall effects have been observed for electrons flowing in spin-orbit-coupled materials such as GaAs and InGaAs (refs 2, 3) and for laser light traversing dielectric junctions. Here we observe the spin Hall effect in a quantum-degenerate Bose gas, and use the resulting spin-dependent Lorentz forces to realize a cold-atom spin transistor. By engineering a spatially inhomogeneous spin-orbit coupling field for our quantum gas, we explicitly introduce and measure the requisite spin-dependent Lorentz forces, finding them to be in excellent agreement with our calculations. This 'atomtronic' transistor behaves as a type of velocity-insensitive adiabatic spin selector, with potential application in devices such as magnetic or inertial sensors. In addition, such techniques for creating and measuring the spin Hall effect are clear prerequisites for engineering topological insulators and detecting their associated quantized spin Hall effects in quantum gases. As implemented, our system realizes a laser-actuated analogue to the archetypal semiconductor spintronic device, the Datta-Das spin transistor. PMID:23739329

Beeler, M C; Williams, R A; Jiménez-García, K; LeBlanc, L J; Perry, A R; Spielman, I B

2013-06-13

212

Semi-inclusive deep-inelastic scattering off few-nucleon systems: Tagging the EMC effect and hadronization mechanisms with detection of slow recoiling nuclei  

SciTech Connect

The semi-inclusive deep-inelastic scattering of electrons off {sup 2}H and {sup 3}He with detection of slow protons and deuterons, respectively, i.e., the processes {sup 2}H(e,e{sup '}p)X and {sup 3}He(e,e{sup '}d)X, are calculated within the spectator mechanism, taking into account the final state interaction of the nucleon debris with the detected protons and deuterons. It is shown that by a proper choice of the kinematics the origin of the EMC effect and the details of the interaction between the hadronizing quark and the nuclear medium can be investigated at a level which cannot be reached by inclusive deep-inelastic scattering. A comparison of the results of our calculations, containing no adjustable parameters, with recently available experimental data on the process {sup 2}H(e,e{sup '}p)X shows a good agreement in the backward hemisphere of the emitted nucleons. Theoretical predictions at energies that will be available at the upgraded Thomas Jefferson National Accelerator Facility are presented, and the possibility to investigate the proposed semi-inclusive processes at electron-ion colliders is briefly discussed.

Ciofi degli Atti, C.; Kaptari, L. P. [Department of Physics, University of Perugia, Piazza dell' Universita 1, I-06123 Perugia (Italy) and Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, Via A. Pascoli, I-06123 Perugia (Italy)

2011-04-15

213

Semi-inclusive deep-inelastic scattering off few-nucleon systems: Tagging the EMC effect and hadronization mechanisms with detection of slow recoiling nuclei  

NASA Astrophysics Data System (ADS)

The semi-inclusive deep-inelastic scattering of electrons off H2 and He3 with detection of slow protons and deuterons, respectively, i.e., the processes 2H(e,e'p)X and 3He(e,e'd)X, are calculated within the spectator mechanism, taking into account the final state interaction of the nucleon debris with the detected protons and deuterons. It is shown that by a proper choice of the kinematics the origin of the EMC effect and the details of the interaction between the hadronizing quark and the nuclear medium can be investigated at a level which cannot be reached by inclusive deep-inelastic scattering. A comparison of the results of our calculations, containing no adjustable parameters, with recently available experimental data on the process 2H(e,e'p)X shows a good agreement in the backward hemisphere of the emitted nucleons. Theoretical predictions at energies that will be available at the upgraded Thomas Jefferson National Accelerator Facility are presented, and the possibility to investigate the proposed semi-inclusive processes at electron-ion colliders is briefly discussed.

Ciofi Degli Atti, C.; Kaptari, L. P.

2011-04-01

214

Finite-size effects in the quantum anomalous Hall system  

NASA Astrophysics Data System (ADS)

We theoretically investigate the finite size effect in quantum anomalous Hall (QAH) system. Using Mn-doped HgTe quantum well as an example, we demonstrate that the coupling between the edge states is spin dependent and is related not only to the distance between the edges but also to the doping concentration. Thus with proper tuning of the two, we can get four kinds of transport regimes: quantum spin Hall, QAH, edge conducting, and normal insulator. These transport regimes have distinguishing edge conducting properties while the bulk is insulting. Our results give a general picture of the finite size effect in a QAH system, and are important for the transport experiments in QAH nanomaterials as well as future device applications.

Fu, Hua-Hua; Lü, Jing-Tao; Gao, Jin-Hua

2014-05-01

215

Effects of reservoir squeezing on quantum systems and work extraction.  

PubMed

We establish a quantum Otto engine cycle in which the working substance contacts with squeezed reservoirs during the two quantum isochoric processes. We consider two working substances: (1) a qubit and (2) two coupled qubits. Due to the effects of squeezing, the working substance can be heated to a higher effective temperature, which leads to many interesting features different from the ordinary ones, such as (1) for the qubit as working substance, if we choose the squeezed parameters properly, the positive work can be exported even when T(H) quantum fuel is more efficient than the classical one. PMID:23214736

Huang, X L; Wang, Tao; Yi, X X

2012-11-01

216

Effective Potential and Effective Hamiltonian in Quantum Statistical Mechanics for Condensed Matter Physics.  

National Technical Information Service (NTIS)

An overview on the theoretic formalism and up-to-date applications in quantum condensed matter physics of the effective potential and effective hamiltonian methods is given. The main steps of their unified derivation by the pure-quantum self-consistent ha...

A. Cuccoli V. Tognetti R. Vaia P. Verrucchi

1996-01-01

217

Loss of coherence and memory effects in quantum dynamics Loss of coherence and memory effects in quantum dynamics  

NASA Astrophysics Data System (ADS)

The last years have witnessed fast growing developments in the use of quantum mechanics in technology-oriented and information-related fields, especially in metrology, in the developments of nano-devices and in understanding highly efficient transport processes. The consequent theoretical and experimental outcomes are now driving new experimental tests of quantum mechanical effects with unprecedented accuracies that carry with themselves the concrete possibility of novel technological spin-offs. Indeed, the manifold advances in quantum optics, atom and ion manipulations, spintronics and nano-technologies are allowing direct experimental verifications of new ideas and their applications to a large variety of fields. All of these activities have revitalized interest in quantum mechanics and created a unique framework in which theoretical and experimental physics have become fruitfully tangled with information theory, computer, material and life sciences. This special issue aims to provide an overview of what is currently being pursued in the field and of what kind of theoretical reference frame is being developed together with the experimental and theoretical results. It consists of three sections: 1. Memory effects in quantum dynamics and quantum channels 2. Driven open quantum systems 3. Experiments concerning quantum coherence and/or decoherence The first two sections are theoretical and concerned with open quantum systems. In all of the above mentioned topics, the presence of an external environment needs to be taken into account, possibly in the presence of external controls and/or forcing, leading to driven open quantum systems. The open system paradigm has proven to be central in the analysis and understanding of many basic issues of quantum mechanics, such as the measurement problem, quantum communication and coherence, as well as for an ever growing number of applications. The theory is, however, well-settled only when the so-called Markovian or memoryless, approximation applies. When strong coupling or long environmental relaxation times make memory effects important for a realistic description of the dynamics, new strategies are asked for and the assessment of the general structure of non-Markovian dynamical equations for realistic systems is a crucial issue. The impact of quantum phenomena such as coherence and entanglement in biology has recently started to be considered as a possible source of the high efficiency of certain biological mechanisms, including e.g. light harvesting in photosynthesis and enzyme catalysis. In this effort, the relatively unknown territory of driven open quantum systems is being explored from various directions, with special attention to the creation and stability of coherent structures away from thermal equilibrium. These investigations are likely to advance our understanding of the scope and role of quantum mechanics in living systems; at the same time they provide new ideas for the developments of next generations of devices implementing highly efficient energy harvesting and conversion. The third section concerns experimental studies that are currently being pursued. Multidimensional nonlinear spectroscopy, in particular, has played an important role in enabling experimental detection of the signatures of coherence. Recent remarkable results suggest that coherence—both electronic and vibrational—survive for substantial timescales even in complex biological systems. The papers reported in this issue describe work at the forefront of this field, where researchers are seeking a detailed understanding of the experimental signatures of coherence and its implications for light-induced processes in biology and chemistry.

Benatti, Fabio; Floreanini, Roberto; Scholes, Greg

2012-08-01

218

Quantum mechanical effects on noise properties of nanoelectronic devices: application to Monte Carlo simulation  

Microsoft Academic Search

A discussion about the quantum mechanical effects on noise properties of ballistic (phase-coherent) nanoscale devices is presented. It is shown that quantum noise can be understood in terms of quantum trajectories. This interpretation provides a simple and intuitive explanation of the origin of quantum noise that can be very salutary for nanoelectronic engineers. In particular, an injection model is presented

Xavier Oriols

2003-01-01

219

Nonlocal quantum effects in cosmology: Quantum memory, nonlocal FLRW equations, and singularity avoidance  

NASA Astrophysics Data System (ADS)

We discuss cosmological effects of the quantum loops of massless particles, which lead to temporal nonlocalities in the equations of motion governing the scale factor a(t). For the effects discussed here, loops cause the evolution of a(t) to depend on the memory of the curvature in the past with a weight that scales initially as 1/(t -t'). As one of our primary examples, we discuss the situation with a large number of light particles, such that these effects occur in a region where gravity may still be treated classically. However, we also describe the effect of quantum graviton loops and the full set of Standard Model particles. We show that these effects decrease with time in an expanding phase, leading to classical behavior at late time. In a contracting phase, within our approximations the quantum results can lead to a bouncelike behavior at scales below the Planck mass, avoiding the singularities required classically by the Hawking-Penrose theorems. For conformally invariant fields, such as the Standard Model with a conformally coupled Higgs, this result is purely nonlocal and parameter independent.

Donoghue, John F.; El-Menoufi, Basem Kamal

2014-05-01

220

Anisotropic intrinsic spin Hall effect in quantum wires.  

PubMed

We use numerical simulations to investigate the spin Hall effect in quantum wires in the presence of both Rashba and Dresselhaus spin-orbit coupling. We find that the intrinsic spin Hall effect is highly anisotropic with respect to the orientation of the wire, and that the nature of this anisotropy depends strongly on the electron density and the relative strengths of the Rashba and Dresselhaus spin-orbit couplings. In particular, at low densities, when only one subband of the quantum wire is occupied, the spin Hall effect is strongest for electron momentum along the [N110] axis, which is the opposite of what is expected for the purely 2D case. In addition, when more than one subband is occupied, the strength and anisotropy of the spin Hall effect can vary greatly over relatively small changes in electron density, which makes it difficult to predict which wire orientation will maximize the strength of the spin Hall effect. These results help to illuminate the role of quantum confinement in spin-orbit-coupled systems, and can serve as a guide for future experimental work on the use of quantum wires for spin-Hall-based spintronic applications. PMID:22052818

Cummings, A W; Akis, R; Ferry, D K

2011-11-23

221

Advanced theory of multiple exciton generation effect in quantum dots  

NASA Astrophysics Data System (ADS)

The theoretical aspects of the effect of multiple exciton generation (MEG) in quantum dots (QDs) have been analysed in this work. The statistical theory of MEG in QDs based on Fermi's approach is presented, taking into account the momentum conservation law. According to Fermi this approach should give the ultimate quantum efficiencies of multiple particle generation. The microscopic mechanism of this effect is based on the theory of electronic "shaking". According to this approach, the wave function of "shaking" electrons can be selected as Plato's functions with effective charges depending on the number of generated excitons. From the theory it is known increasing the number of excitons leads to enhancement of the Auger recombination of electrons which results in reduced quantum yields of excitons. The deviation of the averaged multiplicity of the MEG effect from the Poisson law of fluctuations has been investigated on the basis of synergetics approaches. In addition the role of interface electronic states of QDs and ligands has been considered by means of quantum mechanical approaches. The size optimisation of QDs has been performed to maximise the multiplicity of the MEG effect.

Oksengendler, B. L.; Turaeva, N. N.; Rashidova, S. S.

2012-06-01

222

Quantum effects in inhomogeneous cosmological models  

NASA Astrophysics Data System (ADS)

According to recent discoveries, the large-scale universe is highly isotropic and homogeneous. It is pointed out that the Friedman model with a homogeneous and isotropic Robertson-Walker metric provides the best description of the present universe. It is considered to be the main drawback of the model that it assumes a perfectly symmetric state from the beginning. The present investigation is concerned with a possible approach to the problem of making an initially inhomogeneous metric homogeneous. In the inhomogeneous conformally flat and spherically symmetric metric with the Bondi-type energy-momentum tensor, an additional quantum source is considered. Trace anomaly analysis for the massless scalar field makes it possible to calculate the vacuum expectation of the energy tensor for that field.

Siemieniec-Ozieblo, G.

1984-03-01

223

Quantum statistical effects in nuclear reactions, fission, and open quantum systems  

NASA Astrophysics Data System (ADS)

Quantum diffusion equations with time-dependent transport coefficients are derived from generalized non-Markovian Langevin equations. Generalized fluctuation-dissipation relations and analytical formulas for calculating friction and diffusion coefficients in nuclear processes are obtained. The asymptotics of the transport coefficients and of the correlation functions are investigated. The problem of correlation decay in quantum dissipative systems is studied. A comparative analysis of diffusion coefficients for the harmonic and inverted oscillators is performed. The role of quantum statistical effects during passage through a parabolic potential barrier is investigated. Sets of diffusion coefficient assuring the purity of states at any time instant are found in cases of non-Markovian dynamics. The influence of different sets of transport coefficients on the rate of decay from a metastable state is studied in the framework of the master equation for reduced density matrices describing open quantum systems. The approach developed is applied to investigation of fission processes and the processes of projectile-nuclei capture by target nuclei for bombarding energies in the vicinity of the Coulomb barrier. The influence of dissipation and fluctuation on these processes is taken into account in a self-consistent way. The evaporation residue cross sections for asymmetric fusion reactions are calculated from the derived capture probabilities averaged over all orientations of the deformed projectile and target nuclei.

Sargsyan, V. V.; Kanokov, Z.; Adamian, G. G.; Antonenko, N. V.

2010-03-01

224

The Distribution of Recoil Velocities from Merging Black Holes  

NASA Astrophysics Data System (ADS)

We calculate the linear momentum flux from merging black holes (BHs) with arbitrary masses and spin orientations, using the effective-one-body (EOB) model. This model includes an analytic description of the inspiral phase, a short merger, and a superposition of exponentially damped quasi-normal ring-down modes of a Kerr BH. By varying the matching point between inspiral and ring-down, we can estimate the systematic errors generated with this method. Within these confidence limits, we find close agreement with previously reported results from numerical relativity. Using a Monte Carlo implementation of the EOB model, we are able to sample a large volume of BH parameter space and estimate the distribution of recoil velocities. For a range of mass ratios 1<=m1/m2<=10, spin magnitudes of a1,2=0.9, and uniform random spin orientations, we find that a fraction f500=0.12+0.06-0.05 of binaries have recoil velocities greater than 500 km s-1 and that a fraction f1000=0.027+0.021-0.014 of binaries have kicks greater than 1000 km s-1. These velocities likely are capable of ejecting the final BH from its host galaxy. Limiting the sample to comparable-mass binaries with m1/m2<=4, the typical kicks are even larger, with f500=0.31+0.13-0.12 and f1000=0.079+0.062-0.042.

Schnittman, Jeremy D.; Buonanno, Alessandra

2007-06-01

225

Fragility of the fractional quantum spin Hall effect in quantum gases  

NASA Astrophysics Data System (ADS)

We consider the effect of contact interaction in a prototypical quantum spin Hall system of pseudo-spin-1/2 particles. A strong effective magnetic field with opposite directions for the two spin states restricts two-dimensional particle motion to the lowest Landau level. While interaction between same-spin particles leads to incompressible correlated states at fractional filling factors as known from the fractional quantum Hall effect, these states are destabilized by interactions between opposite spin particles. Exact results for two particles with opposite spin reveal a quasi-continuous spectrum of extended states with a large density of states at low energy. This has implications for the prospects of realizing the fractional quantum spin Hall effect in electronic or ultra-cold atom systems. Numerical diagonalization is used to extend the two-particle results to many bosonic particles and trapped systems. The interplay between an external trapping potential and spin-dependent interactions is shown to open up new possibilities for engineering exotic correlated many-particle states with ultra-cold atoms.

Fialko, O.; Brand, J.; Zülicke, U.

2014-02-01

226

The noncommutative geometry of the quantum Hall effect  

Microsoft Academic Search

We give an overview of the Integer Quantum Hall Effect. We propose a mathematical framework using Non-Commutative Geometry as defined by A. Connes. Within this framework, it is proved that the Hall conductivity is quantized and that plateaux occur when the Fermi energy varies in a region of localized states.

J. Bellissard; A. van Elst; H. Schulz-Baldes

1994-01-01

227

On the Possibility of Quantum Gravity Effects at Astrophysical Scales  

NASA Astrophysics Data System (ADS)

The nonperturbative renormalization group flow of quantum Einstein gravity (QEG) is reviewed. It is argued that at large distances there could be strong renormalization effects, including a scale dependence of Newton's constant, which mimic the presence of dark matter at galactic and cosmological scales.

Reuter, Martin; Weyer, Holger

228

Do we Observe Quantum Gravity Effects at Galactic Scales?  

NASA Astrophysics Data System (ADS)

The nonperturbative renormalization group flow of Quantum Einstein Gravity (QEG) is reviewed. It is argued that there could be strong renormalization effects at large distances, in particular a scale dependent Newton constant, which mimic the presence of dark matter at galactic and cosmological scales.

Reuter, M.; Weyer, H.

229

Effect of Quantum Correction in the Bose-Hubbard Model  

SciTech Connect

Effects of quantum correction in the Bose-Hubbard model at finite temperature are investigated for a homogeneous atomic Bose gas in an optical lattice near its superfluid-insulator transition. Starting from a strong coupling limit, higher order quantum corrections due to the hopping interaction is included in a local approximation (a dynamical mean field approximation) of the non-crossing approximation. When the upper or lower Hubbard band approaches zero energy, there appears a shallow band in the middle of the Hubbard gap due to a strong correlation in the system.

Matsumoto, Hideki; Takahashi, Kiyoshi; Ohashi, Yoji [Institute of Physics, University of Tsukuba, Ibaraki 305-8571 (Japan)

2006-09-07

230

Effect of uniform acceleration on multiplayer quantum game  

NASA Astrophysics Data System (ADS)

We investigate the influence of the Unruh effect on three-qubit quantum games. In particular, we interpret the quantum Prisoners’ Dilemma, which is a famous, non-zero sum game both for entangled and unentangled initial states and show that the acceleration of non-inertial frames disturbs the symmetry of the game. Using the various strategies, the novel Nash equilibrium is obtained at infinite acceleration (r = ?/4). As a remarkable point, it is shown that in our three-player system, in contrast to the two-player quantum game in non-inertial frames (see Khan et al 2011 J. Phys. A: Math. Theor. 44 355302), there is not a dominant strategy (even classical strategy) in the game and choosing the quantum strategy by each player can be the dominant strategy depending on the kind of strategy chosen by others. Since the entangled states of particles play an important role in the quantum game, finally we argue that the results of the players depend on the degree of entanglement in the initial state of the game.

Goudarzi, H.; Beyrami, S.

2012-06-01

231

Unification of dynamical decoupling and the quantum Zeno effect  

SciTech Connect

We unify the quantum Zeno effect (QZE) and the 'bang-bang' (BB) decoupling method for suppressing decoherence in open quantum systems: in both cases strong coupling to an external system or apparatus induces a dynamical superselection rule that partitions the open system's Hilbert space into quantum Zeno subspaces. Our unification makes use of von Neumann' s ergodic theorem and avoids making any of the symmetry assumptions usually made in discussions of BB. Thus we are able to generalize the BB to arbitrary fast and strong pulse sequences, requiring no symmetry, and to show the existence of two alternatives to a pulsed BB: continuous decoupling and pulsed measurements. Our unified treatment enables us to derive limits on the efficacy of the BB method: we explicitly show that the inverse QZE implies that the BB can in some cases accelerate, rather than inhibit, decoherence.

Facchi, P.; Pascazio, S. [Dipartimento di Fisica, Universita di Bari I-70126 Bari (Italy); Istituto Nazionale di Fisica Nucleare, Sezione di Bari, I-70126 Bari (Italy); Lidar, D.A. [Chemical Physics Theory Group, Chemistry Department, University of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6 (Canada)

2004-03-01

232

Thermal recoil force, telemetry, and the Pioneer anomaly  

SciTech Connect

Precision navigation of spacecraft requires accurate knowledge of small forces, including the recoil force due to anisotropies of thermal radiation emitted by spacecraft systems. We develop a formalism to derive the thermal recoil force from the basic principles of radiative heat exchange and energy-momentum conservation. The thermal power emitted by the spacecraft can be computed from engineering data obtained from flight telemetry, which yields a practical approach to incorporate the thermal recoil force into precision spacecraft navigation. Alternatively, orbit determination can be used to estimate the contribution of the thermal recoil force. We apply this approach to the Pioneer anomaly using a simulated Pioneer 10 Doppler data set.

Toth, Viktor T.; Turyshev, Slava G. [Ottawa, Ontario K1N 9H5 (Canada); Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109-8099 (United States)

2009-02-15

233

Relativistic x-ray quantum free-electron lasers: a collective Klein-Gordon model  

NASA Astrophysics Data System (ADS)

We present a quantum-relativistic model for the nonlinear interaction between large-amplitude electromagnetic (EM) waves and a quantum plasma. The model is based on a collective Klein-Gordon equation for the relativistic electrons, which is coupled with the Maxwell equations for the EM and electrostatic fields. The model is used to derive a nonlinear dispersion relation for the EM scattering instabilities in a relativistic quantum plasma. With application to the quantum free-electron laser (FEL), a relativistic electron beam is passing through an intense EM wave used as a wiggler to produce coherent tunable radiation. The frequency upshift of the radiation is tuned by the energy of the electron beam. The nonlinear dispersion relation reveals the importance of quantum recoil effects and oblique scattering of the radiation on the gain of the quantum FEL.

Eliasson, Bengt; Kant Shukla, Padma

2012-12-01

234

Neutron electric form factor via recoil polarimetry  

SciTech Connect

The ratio of the electric to the magnetic form factor of the neutron, G_En/G_Mn, was measured via recoil polarimetry from the quasielastic d({pol-e},e'{pol-n)p reaction at three values of Q^2 [viz., 0.45, 1.15 and 1.47 (GeV/c)^2] in Hall C of the Thomas Jefferson National Accelerator Facility. Preliminary data indicate that G_En follows the Galster parameterization up to Q^2 = 1.15 (GeV/c)^2 and appears to rise above the Galster parameterization at Q^2 = 1.47 (GeV/c)^2.

Richard Madey; Andrei Semenov; Simon Taylor; Aram Aghalaryan; Erick Crouse; Glen MacLachlan; Bradley Plaster; Shigeyuki Tajima; William Tireman; Chenyu Yan; Abdellah Ahmidouch; Brian Anderson; Razmik Asaturyan; O. Baker; Alan Baldwin; Herbert Breuer; Roger Carlini; Michael Christy; Steve Churchwell; Leon Cole; Samuel Danagoulian; Donal Day; Mostafa Elaasar; Rolf Ent; Manouchehr Farkhondeh; Howard Fenker; John Finn; Liping Gan; Kenneth Garrow; Paul Gueye; Calvin Howell; Bitao Hu; Mark Jones; James Kelly; Cynthia Keppel; Mahbubul Khandaker; Wooyoung Kim; Stanley Kowalski; Allison Lung; David Mack; D. Manley; Pete Markowitz; Joseph Mitchell; Hamlet Mkrtchyan; Allena Opper; Charles Perdrisat; Vina Punjabi; Brian Raue; Tilmann Reichelt; Joerg Reinhold; Julie Roche; Yoshinori Sato; Wonick Seo; Neven Simicevic; Gregory Smith; Samuel Stepanyan; Vardan Tadevosyan; Liguang Tang; Paul Ulmer; William Vulcan; John Watson; Steven Wells; Frank Wesselmann; Stephen Wood; Chen Yan; Seunghoon Yang; Lulin Yuan; Wei-Ming Zhang; Hong Guo Zhu; Xiaofeng Zhu

2003-05-01

235

Mesoscopic effects in quantum phases of ultracold quantum gases in optical lattices  

NASA Astrophysics Data System (ADS)

We present a wide array of quantum measures on numerical solutions of one-dimensional Bose- and Fermi-Hubbard Hamiltonians for finite-size systems with open boundary conditions. Finite-size effects are highly relevant to ultracold quantum gases in optical lattices, where an external trap creates smaller effective regions in the form of the celebrated “wedding cake” structure and the local density approximation is often not applicable. Specifically, for the Bose-Hubbard Hamiltonian we calculate number, quantum depletion, local von Neumann entropy, generalized entanglement or Q measure, fidelity, and fidelity susceptibility; for the Fermi-Hubbard Hamiltonian we also calculate the pairing correlations, magnetization, charge-density correlations, and antiferromagnetic structure factor. Our numerical method is imaginary time propagation via time-evolving block decimation. As part of our study we provide a careful comparison of canonical versus grand canonical ensembles and Gutzwiller versus entangled simulations. The most striking effect of finite size occurs for bosons: we observe a strong blurring of the tips of the Mott lobes accompanied by higher depletion, and show how the location of the first Mott lobe tip approaches the thermodynamic value as a function of system size.

Carr, L. D.; Wall, M. L.; Schirmer, D. G.; Brown, R. C.; Williams, J. E.; Clark, Charles W.

2010-01-01

236

Mesoscopic effects in quantum phases of ultracold quantum gases in optical lattices  

SciTech Connect

We present a wide array of quantum measures on numerical solutions of one-dimensional Bose- and Fermi-Hubbard Hamiltonians for finite-size systems with open boundary conditions. Finite-size effects are highly relevant to ultracold quantum gases in optical lattices, where an external trap creates smaller effective regions in the form of the celebrated 'wedding cake' structure and the local density approximation is often not applicable. Specifically, for the Bose-Hubbard Hamiltonian we calculate number, quantum depletion, local von Neumann entropy, generalized entanglement or Q measure, fidelity, and fidelity susceptibility; for the Fermi-Hubbard Hamiltonian we also calculate the pairing correlations, magnetization, charge-density correlations, and antiferromagnetic structure factor. Our numerical method is imaginary time propagation via time-evolving block decimation. As part of our study we provide a careful comparison of canonical versus grand canonical ensembles and Gutzwiller versus entangled simulations. The most striking effect of finite size occurs for bosons: we observe a strong blurring of the tips of the Mott lobes accompanied by higher depletion, and show how the location of the first Mott lobe tip approaches the thermodynamic value as a function of system size.

Carr, L. D.; Schirmer, D. G. [Department of Physics, Colorado School of Mines, Golden, Colorado 80401 (United States); Joint Quantum Institute, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States); Wall, M. L. [Department of Physics, Colorado School of Mines, Golden, Colorado 80401 (United States); Brown, R. C.; Williams, J. E.; Clark, Charles W. [Joint Quantum Institute, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)

2010-01-15

237

Field-effect transistor self-electrooptic effect device: integrated photodiode, quantum well modulator and transistor  

Microsoft Academic Search

The authors propose and demonstrate the integration of a photodiode, a quantum-confined Stark-effect quantum-well optical modulator, and a metal-semiconductor field-effect transistor (MESFET) to make a field-effect transistor self-electrooptic effect device. This integration allows optical inputs and outputs on the surface of a GaAs-integrated circuit chip, compatible with standard MESFET processing. To provide an illustration of feasibility, the authors demonstrate signal

D. A. B. Miller; M. D. Feuer; T. Y. Chang; S. C. Shunk; J. E. Henry; D. J. Burrows; D. S. Chemla

1989-01-01

238

Effect of quantum therapy on pork quality  

PubMed Central

In this study the impact of quantum therapy on meat quality of slaughtered pigs was investigated. For this purpose the pigs were treated with different doses of magnet-infrared-laser (MIL) radiation. Animals were divided into four groups according to radiation doses (4096, 512, and 64 Hz, and control without application), which were applied in the lumbar area of musculus longissimus dorsi (loin) at various time intervals prior to the slaughter (14 d, 24 h, and 1 h). Animals were slaughtered and the meat quality was evaluated by determining of pH value (1, 3, and 24 h post slaughter), drip loss, colour, and lactic acid and phosphoric acid amounts. MIL therapy can be used in various fields of veterinary medicine as are surgery and orthopaedics, internal medicine, dentistry, pulmonology, gastroenterology, gynaecology, urology, nephrology, and dermatology. The results achieved showed that MIL radiation used in a short period before slaughter (1 h) can cause a change in the meat quality, as reflected by the non-standard development of pH values, increases in drip loss, and changes of meat colour.

Bodnar, Martin; Nagy, Jozef; Popelka, Peter; Korenekova, Beata; Macanga, Jan; Nagyova, Alena

2011-01-01

239

Evidence for the Josephson effect in quantum Hall bilayers  

NASA Astrophysics Data System (ADS)

This thesis presents tunneling measurements on bilayer two-dimensional (2D) electrons systems in GaAs/AlGaAs double quantum wells. 2D-2D tunneling is applied here as a probe of the inter-layer correlated quantum Hall state at total Landau level filling factor nuT = 1. This bilayer state is theoretically expected to be an excitonic superfluid with an associated dissipationless current and Josephson effect. In addition to the conventional signatures of the quantum Hall effect---a pronounced minimum in Rxx and associated quantization of Rxy---the strong interlayer correlations lead to a step-like discontinuity in the tunneling I--V. Although reminiscent of the DC Josephson effect, the tunneling discontinuity has a finite extent even at the lowest temperatures (the peak in conductance, dI/dV, is strongly temperature dependent even below 15 mK. The correlations develop when the inter- and intra-layer Coulomb interactions become comparable. The relative importance of which is determined by the ratio of layer separation to average electron spacing. Although this state is theoretically expected to be an excitonic superfluid, the degree to which intra-layer tunneling is Josephson-like is controversial. At a critical layer separation the zero-bias tunneling feature is lost, which we interpret as signaling the quantum phase transition to the uncorrelated state. We study the dependence of the phase transition on electron density and relative density imbalance. In the presence of a parallel magnetic field tunneling probes the response of the spectral function at finite wave vector. These tunneling spectra directly detect the expected linearly dispersing Goldstone mode; our measurement of this mode is in good agreement with theoretical expectations. There remains deep theoretical and experimental interest in this state, which represents a unprecedented convergence in the physics of quantum Hall effects and superconductivity.

Spielman, Ian Bairstow

240

Linear and nonlinear electrostatic modes in a strongly coupled quantum plasma  

SciTech Connect

The properties of linear and nonlinear electrostatic waves in a strongly coupled electron-ion quantum plasma are investigated. In this study, the inertialess electrons are degenerate, while non-degenerate inertial ions are strongly correlated. The ion dynamics is governed by the continuity and the generalized viscoelastic momentum equations. The quantum forces associated with the quantum statistical pressure and the quantum recoil effect act on the degenerate electron fluid, whereas strong ion correlation effects are embedded in generalized viscoelastic momentum equation through the viscoelastic relaxation of ion correlations and ion fluid shear viscosities. Hence, the spectra of linear electrostatic modes are significantly affected by the strong ion coupling effect. In the weakly nonlinear limit, due to ion-ion correlations, the quantum plasma supports a dispersive shock wave, the dynamics of which is governed by the Korteweg-de Vries Burgers' equation. For a particular value of the quantum recoil effect, only monotonic shock structure is observed. Possible applications of our investigation are briefly mentioned.

Ghosh, Samiran [Department of Applied Mathematics, University of Calcutta, 92, Acharya Prafulla Chandra Road, Kolkata 700 009 (India); Chakrabarti, Nikhil [Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata 700 064 (India); Shukla, P. K. [International Center for Advanced Studies in Physical Sciences and Institute for Theoretical Physics, Faculty of Physics and Astronomy, Ruhr University Bochum, D-44780 Bochum, Germany and Department of Mechanical and Aerospace Engineering and Centre for Energy Research, University of California San Diego, La Jolla, California 92093 (United States)

2012-07-15

241

Quantum transport of Dirac fermions in graphene field effect transistors  

Microsoft Academic Search

We present a quantum transport simulation of graphene field-effect transistors based on the self consistent solution of 2D-Poisson solver and Dirac equation within the non-equilibrium Green's function formalism. The device operation of double gate 2D-graphene field effect transistors is investigated. The study emphasizes the band-to-band and Klein tunneling processes of massless carriers and the resulting features of the electrostatic modulation

V. Hung Nguyen; A. Bournel; C. Chassat; P. Dollfus

2010-01-01

242

Quantum Hall effect in graphene decorated with disordered multilayer patches  

SciTech Connect

Quantum Hall effect (QHE) is observed in graphene grown by chemical vapour deposition using platinum catalyst. The QHE is even seen in samples which are irregularly decorated with disordered multilayer graphene patches and have very low mobility (<500 cm{sup 2}V{sup ?1}s{sup ?1}). The effect does not seem to depend on electronic mobility and uniformity of the resulting material, which indicates the robustness of QHE in graphene.

Nam, Youngwoo, E-mail: youngwoo.nam@chalmers.se [Department of Physics and Astronomy, Seoul National University, Seoul 151-747 (Korea, Republic of) [Department of Physics and Astronomy, Seoul National University, Seoul 151-747 (Korea, Republic of); Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-412 96 Gothenburg (Sweden); Sun, Jie, E-mail: jie.sun@chalmers.se; Lindvall, Niclas; Kireev, Dmitry; Yurgens, August [Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-412 96 Gothenburg (Sweden)] [Department of Microtechnology and Nanoscience, Chalmers University of Technology, SE-412 96 Gothenburg (Sweden); Jae Yang, Seung; Rae Park, Chong [Department of Materials Science and Engineering, Seoul National University, Seoul 151-747 (Korea, Republic of)] [Department of Materials Science and Engineering, Seoul National University, Seoul 151-747 (Korea, Republic of); Woo Park, Yung [Department of Physics and Astronomy, Seoul National University, Seoul 151-747 (Korea, Republic of)] [Department of Physics and Astronomy, Seoul National University, Seoul 151-747 (Korea, Republic of)

2013-12-02

243

Frequency and temporal effects in linear optical quantum computing  

SciTech Connect

Typically linear optical quantum computing (LOQC) models assume that all input photons are completely indistinguishable. In practice there will inevitably be nonidealities associated with the photons and the experimental setup which will introduce a degree of distinguishability between photons. We consider a nondeterministic optical controlled-NOT gate, a fundamental LOQC gate, and examine the effect of temporal and spectral distinguishability on its operation. We also consider the effect of utilizing nonideal photon counters, which have finite bandwidth and time response.

Rohde, Peter P.; Ralph, Timothy C. [Centre for Quantum Computer Technology, Department of Physics, University of Queensland, Queensland 4072 (Australia)

2005-03-01

244

Large size self-assembled quantum rings: quantum size effect and modulation on the surface diffusion.  

PubMed

We demonstrate experimentally the submicron size self-assembled (SA) GaAs quantum rings (QRs) by quantum size effect (QSE). An ultrathin In0.1?Ga0.9As layer with different thickness is deposited on the GaAs to modulate the surface nucleus diffusion barrier, and then the SA QRs are grown. It is found that the density of QRs is affected significantly by the thickness of inserted In0.1?Ga0.9As, and the diffusion barrier modulation reflects mainly on the first five monolayer . The physical mechanism behind is discussed. The further analysis shows that about 160 meV decrease in diffusion barrier can be achieved, which allows the SA QRs with density of as low as one QR per 6 ?m2. Finally, the QRs with diameters of 438 nm and outer diameters of 736 nm are fabricated using QSE. PMID:23006618

Tong, Cunzhu; Yoon, Soon Fatt; Wang, Lijun

2012-01-01

245

Mesoscopic effects in quantum phases of ultracold quantum gases in optical lattices  

NASA Astrophysics Data System (ADS)

We present a wide array of quantum measures on numerical solutions of one-dimensional Bose- and Fermi-Hubbard Hamiltonians for finite-size systems with open boundary conditions. Specifically, for the Bose-Hubbard Hamiltonian we calculate number, quantum depletion, local von Neumann entropy, generalized entanglement or Q measure, fidelity, and fidelity susceptibility; for the Fermi-Hubbard Hamiltonian we also calculate the pairing correlations, magnetization, charge-density correlations, and antiferromagnetic structure factor. Our numerical method is imaginary time propagation via time-evolving block decimation. As part of our study we provide a careful comparison of canonical versus grand canonical ensembles and Gutzwiller versus entangled simulations. The most striking effect of finite size occurs for bosons: we observe a strong blurring of the tips of the Mott lobes accompanied by higher depletion, and show how the location of the first Mott lobe tip approaches the thermodynamic value as a function of system size.

Carr, Lincoln D.; Wall, M. L.; Schirmer, D. G.; Brown, R. C.; Williams, J. E.; Clark, Charles W.

2010-03-01

246

Nonadiabatic effect on the quantum heat flux control  

NASA Astrophysics Data System (ADS)

We provide a general formula of quantum transfer that includes the nonadiabatic effect under periodic environmental modulation by using full counting statistics in Hilbert-Schmidt space. Applying the formula to an anharmonic junction model that interacts with two bosonic environments within the Markovian approximation, we find that the quantum transfer is divided into the adiabatic (dynamical and geometrical phases) and nonadiabatic contributions. This extension shows the dependence of quantum transfer on the initial condition of the anharmonic junction just before the modulation, as well as the characteristic environmental parameters such as interaction strength and cut-off frequency of spectral density. We show that the nonadiabatic contribution represents the reminiscent effect of past modulation including the transition from the initial condition of the anharmonic junction to a steady state determined by the very beginning of the modulation. This enables us to tune the frequency range of modulation, whereby we can obtain the quantum flux corresponding to the geometrical phase by setting the initial condition of the anharmonic junction.

Uchiyama, Chikako

2014-05-01

247

Is the Quantum Zeno Effect Evolution's Choice for the Avian Compass?  

Microsoft Academic Search

Magnetic-sensitive radical-ion-pair reactions are understood to underlie the biochemical magnetic compass used by avian species for navigation. Radical-ion-pair reactions were recently shown to manifest a host of quantum-information-science effects, like quantum jumps and the quantum Zeno effect. We here show that the quantum Zeno effect immunizes the magnetic and angular sensitivity of the avian compass mechanism against the deleterious and

I. K. Kominis

2009-01-01

248

Synchrotron-radiation experiments with recoil ions  

SciTech Connect

Studies of atoms, ions and molecules with synchrotron radiation have generally focused on measurements of properties of the electrons ejected during, or after, the photoionization process. Much can also be learned, however, about the atomic or molecular relaxation process by studies of the residual ions or molecular fragments following inner-shell photoionization. Measurements are reported of mean kinetic energies of highly charged argon, krypton, and xenon recoil ions produced by vacancy cascades following inner-shell photoionization using white and monochromatic synchrotron x radiation. Energies are much lower than for the same charge-state ions produced by charged-particle impact. The results may be applicable to design of future angle-resolved ion-atom collision experiments. Photoion charge distributions are presented and compared with other measurements and calculations. Related experiments with synchrotron-radiation produced recoil ion, including photoionization of stored ions and measurement of shakeoff in near-threshold excitation, are briefly discussed. 24 refs., 6 figs., 1 tab.

Levin, J.C.

1989-01-01

249

Plasma wave instability in a quantum field effect transistor with magnetic field effect  

SciTech Connect

The current-carrying state of a nanometer Field Effect Transistor (FET) may become unstable against the generation of high-frequency plasma waves and lead to generation of terahertz radiation. In this paper, the influences of magnetic field, quantum effects, electron exchange-correlation, and thermal motion of electrons on the instability of the plasma waves in a nanometer FET are reported. We find that, while the electron exchange-correlation suppresses the radiation power, the magnetic field, the quantum effects, and the thermal motion of electrons can enhance the radiation power. The radiation frequency increases with quantum effects and thermal motion of electrons, but decreases with electron exchange-correlation effect. Interestingly, we find that magnetic field can suppress the quantum effects and the thermal motion of electrons and the radiation frequency changes non-monotonely with the magnetic field. These properties could make the nanometer FET advantageous for realization of practical terahertz oscillations.

Zhang, Li-Ping; Xue, Ju-Kui [College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070 (China)] [College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou 730070 (China)

2013-08-15

250

Magnetic quantum ratchet effect in Si-MOSFETs  

NASA Astrophysics Data System (ADS)

We report on the observation of magnetic quantum ratchet effect in metal-oxide-semiconductor field-effect-transistors on silicon surface (Si-MOSFETs). We show that the excitation of an unbiased transistor by ac electric field of terahertz radiation at normal incidence leads to a direct electric current between the source and drain contacts if the transistor is subjected to an in-plane magnetic field. The current rises linearly with the magnetic field strength and quadratically with the ac electric field amplitude. It depends on the polarization state of the ac field and can be induced by both linearly and circularly polarized radiation. We present the quasi-classical and quantum theories of the observed effect and show that the current originates from the Lorentz force acting upon carriers in asymmetric inversion channels of the transistors.

Ganichev, S. D.; Tarasenko, S. A.; Karch, J.; Kamann, J.; Kvon, Z. D.

2014-06-01

251

Anti-Zeno effect for quantum transport in disordered systems  

SciTech Connect

We demonstrate that repeated measurements in disordered systems can induce a quantum anti-Zeno effect under certain conditions to enhance quantum transport. The enhancement of energy transfer is really exhibited in multisite models under repeated measurements. The optimal measurement interval for the anti-Zeno effect and the maximal efficiency of energy transfer are specified in terms of the relevant physical parameters. Since the environment acts as frequent measurements on the system, the decoherence-induced energy transfer, which has been discussed recently for photosynthetic complexes, may be interpreted in terms of the anti-Zeno effect. We further find an interesting phenomenon in a specific three-site case, where local decoherence or repeated measurements may even promote entanglement generation between the nonlocal sites.

Fujii, Keisuke; Yamamoto, Katsuji [Department of Nuclear Engineering, Kyoto University, Kyoto 606-8501 (Japan)

2010-10-15

252

Memory effects in attenuation and amplification quantum processes  

SciTech Connect

With increasing communication rates via quantum channels, memory effects become unavoidable whenever the use rate of the channel is comparable to the typical relaxation time of the channel environment. We introduce a model of a bosonic memory channel, describing correlated noise effects in quantum-optical processes via attenuating or amplifying media. To study such a channel model, we make use of a proper set of collective field variables, which allows us to unravel the memory effects, mapping the n-fold concatenation of the memory channel to a unitarily equivalent, direct product of n single-mode bosonic channels. We hence estimate the channel capacities by relying on known results for the memoryless setting. Our findings show that the model is characterized by two different regimes, in which the cross correlations induced by the noise among different channel uses are either exponentially enhanced or exponentially reduced.

Lupo, Cosmo [School of Science and Technology, University of Camerino, via Madonna delle Carceri 9, I-62032 Camerino (Italy); Giovannetti, Vittorio [NEST, Scuola Normale Superiore and Istituto Nanoscienze-CNR, Piazza dei Cavalieri 7, I-56126 Pisa (Italy); Mancini, Stefano [School of Science and Technology, University of Camerino, via Madonna delle Carceri 9, I-62032 Camerino (Italy); INFN-Sezione di Perugia, I-06123 Perugia (Italy)

2010-09-15

253

The quantum Zeno effect immunizes the avian compass against the deleterious effects of exchange and dipolar interactions.  

PubMed

Magnetic-sensitive radical-ion-pair reactions are understood to underlie the biochemical magnetic compass used by avian species for navigation. Recent experiments have provided growing evidence for the radical-ion-pair magnetoreception mechanism, while recent theoretical advances have unravelled the quantum nature of radical-ion-pair reactions, which were shown to manifest a host of quantum-information-science concepts and effects, like quantum measurement, quantum jumps and the quantum Zeno effect. We here show that the quantum Zeno effect provides for the robustness of the avian compass mechanism, and immunizes its magnetic and angular sensitivity against the deleterious and molecule-specific exchange and dipolar interactions. PMID:22142839

Dellis, A T; Kominis, I K

2012-03-01

254

Aharonov–Bohm effect in the tunnelling of a quantum rotor in a linear Paul trap  

NASA Astrophysics Data System (ADS)

Quantum tunnelling is a common fundamental quantum mechanical phenomenon that originates from the wave-like characteristics of quantum particles. Although the quantum tunnelling effect was first observed 85 years ago, some questions regarding the dynamics of quantum tunnelling remain unresolved. Here we realize a quantum tunnelling system using two-dimensional ionic structures in a linear Paul trap. We demonstrate that the charged particles in this quantum tunnelling system are coupled to the vector potential of a magnetic field throughout the entire process, even during quantum tunnelling, as indicated by the manifestation of the Aharonov–Bohm effect in this system. The tunnelling rate of the structures periodically depends on the strength of the magnetic field, whose period is the same as the magnetic flux quantum ?0 through the rotor [(0.99±0.07) × ?0].

Noguchi, Atsushi; Shikano, Yutaka; Toyoda, Kenji; Urabe, Shinji

2014-05-01

255

Aharonov-Bohm effect in the tunnelling of a quantum rotor in a linear Paul trap.  

PubMed

Quantum tunnelling is a common fundamental quantum mechanical phenomenon that originates from the wave-like characteristics of quantum particles. Although the quantum tunnelling effect was first observed 85 years ago, some questions regarding the dynamics of quantum tunnelling remain unresolved. Here we realize a quantum tunnelling system using two-dimensional ionic structures in a linear Paul trap. We demonstrate that the charged particles in this quantum tunnelling system are coupled to the vector potential of a magnetic field throughout the entire process, even during quantum tunnelling, as indicated by the manifestation of the Aharonov-Bohm effect in this system. The tunnelling rate of the structures periodically depends on the strength of the magnetic field, whose period is the same as the magnetic flux quantum ?0 through the rotor [(0.99±0.07) × ?0]. PMID:24820051

Noguchi, Atsushi; Shikano, Yutaka; Toyoda, Kenji; Urabe, Shinji

2014-01-01

256

Impurity effects on coupled quantum dot spin qubits in semiconductors  

NASA Astrophysics Data System (ADS)

Localized electron spins confined in semiconductor quantum dots are being studied by many groups as possible elementary qubits for solid-state quantum computation. We theoretically consider the effects of having unintentional charged impurities in laterally coupled two-dimensional double (GaAs) quantum dot systems, where each dot contains one or two electrons and a single charged impurity in the presence of an external magnetic field. We calculate the effect of the impurity on the 2-electron energy spectrum of each individual dot as well as on the spectrum of the coupled-double-dot 2-electron system. We find that the singlet-triplet exchange splitting between the two lowest energy states, both for the individual dots and the coupled dot system, depends sensitively on the location of the impurity and its coupling strength (i.e. the effective charge). We comment on the impurity effect in spin qubit operations in the double dot system based on our numerical results. This work is supported by LPS-CMTC and CNAM.

Nguyen, Nga; Das Sarma, Sankar

2011-03-01

257

Thermal effect in quantum-dot cellular automata  

NASA Astrophysics Data System (ADS)

We present a theoretical study of thermal effect in quantum-dot cellular automata (QCA). A quantum statistical model has been introduced to obtain the thermal average of polarization of a QCA cell. We have studied the thermal effect on an inverter, a majority gate and planar arrays of different sizes. The theoretical analysis has been approximated for a two-state model where the cells are in any one of the two possible eigenstates of the cell Hamiltonian. Hence, only the ±1 polarization values are taken into account for the statistical analysis. A numerical computational model has been developed to obtain all possible configurations of the cells in an array. In general, the average polarization of each cell decreases with temperature as well as with the distance from the driver cells. We have found the temperatures for thermal breakdown. The results demonstrate the critical nature of temperature dependence for the operation of QCA.

Sturzu, I.; Kanuchok, J. L.; Khatun, M.; Tougaw, P. D.

2005-03-01

258

Nonlocal Quantum Effects with Bose-Einstein Condensates  

SciTech Connect

We study theoretically the properties of two Bose-Einstein condensates in different spin states, represented by a double Fock state. Individual measurements of the spins of the particles are performed in transverse directions, giving access to the relative phase of the condensates. Initially, this phase is completely undefined, and the first measurements provide random results. But a fixed value of this phase rapidly emerges under the effect of the successive quantum measurements, giving rise to a quasiclassical situation where all spins have parallel transverse orientations. If the number of measurements reaches its maximum (the number of particles), quantum effects show up again, giving rise to violations of Bell type inequalities. The violation of Bell-Clauser-Horne-Shimony-Holt inequalities with an arbitrarily large number of spins may be comparable (or even equal) to that obtained with two spins.

Laloee, F. [Laboratoire Kastler Brossel, ENS, UPMC, CNRS, 24 rue Lhomond, 75005 Paris (France); Mullin, W. J. [Department of Physics, University of Massachusetts, Amherst, Massachusetts 01003 (United States)

2007-10-12

259

Nonlocal quantum effects with Bose-Einstein condensates.  

PubMed

We study theoretically the properties of two Bose-Einstein condensates in different spin states, represented by a double Fock state. Individual measurements of the spins of the particles are performed in transverse directions, giving access to the relative phase of the condensates. Initially, this phase is completely undefined, and the first measurements provide random results. But a fixed value of this phase rapidly emerges under the effect of the successive quantum measurements, giving rise to a quasiclassical situation where all spins have parallel transverse orientations. If the number of measurements reaches its maximum (the number of particles), quantum effects show up again, giving rise to violations of Bell type inequalities. The violation of Bell-Clauser-Horne-Shimony-Holt inequalities with an arbitrarily large number of spins may be comparable (or even equal) to that obtained with two spins. PMID:17995143

Laloë, F; Mullin, W J

2007-10-12

260

Parity effect and phase transitions in quantum Szilard engines.  

PubMed

Quantum Szilard engines with an arbitrary number of identical particles are studied in this paper. Analytical expressions for the total work in the low- and high-temperature limits are obtained. The total work depends on both the particle statistics, the odd-even parity, and the temperature of the system. The parity effect is drastic in fermion systems. An odd number of fermions perform work as if they were a single fermion, and an even number of fermions do not perform any work at all. For bosons, there exists a phase transition at a critical temperature under which work done by the engine is always negative. It is found that only above a certain temperature, bosonic quantum Szilard engine does more work than fermionic one. The possible experimental verification of these effects is discussed. PMID:22400530

Lu, Yao; Long, Gui Lu

2012-01-01

261

Parity effect and phase transitions in quantum Szilard engines  

NASA Astrophysics Data System (ADS)

Quantum Szilard engines with an arbitrary number of identical particles are studied in this paper. Analytical expressions for the total work in the low- and high-temperature limits are obtained. The total work depends on both the particle statistics, the odd-even parity, and the temperature of the system. The parity effect is drastic in fermion systems. An odd number of fermions perform work as if they were a single fermion, and an even number of fermions do not perform any work at all. For bosons, there exists a phase transition at a critical temperature under which work done by the engine is always negative. It is found that only above a certain temperature, bosonic quantum Szilard engine does more work than fermionic one. The possible experimental verification of these effects is discussed.

Lu, Yao; Long, Gui Lu

2012-01-01

262

Charge Fractionalization in the Integer Quantum Hall Effect  

NASA Astrophysics Data System (ADS)

We report an observation, via sensitive shot noise measurements, of charge fractionalization of chiral edge electrons in the integer quantum Hall effect regime. Such fractionalization results solely from interchannel Coulomb interaction, leading electrons to decompose to excitations carrying fractional charges. The experiment was performed by guiding a partitioned current carrying edge channel in proximity to another unbiased edge channel, leading to shot noise in the unbiased edge channel without net current, which exhibited an unconventional dependence on the partitioning. The determination of the fractional excitations, as well as the relative velocities of the two original (prior to the interaction) channels, relied on a recent theory pertaining to this measurement. Our result exemplifies the correlated nature of multiple chiral edge channels in the integer quantum Hall effect regime.

Inoue, Hiroyuki; Grivnin, Anna; Ofek, Nissim; Neder, Izhar; Heiblum, Moty; Umansky, Vladimir; Mahalu, Diana

2014-04-01

263

Higher-Dimensional Quantum Hall Effect in String Theory  

SciTech Connect

We construct a string theory realization of the 4+1d quantum Hall effect recently discovered by Zhang and Hu. The string theory picture contains coincident D4-branes forming an S{sup 4} and having D0-branes (i.e. instantons) in their world-volume. The charged particles are modeled as string ends. Their configuration space approaches in the large n limit a CP{sup 3}, which is an S{sup 2} fibration over S{sup 4}, the extra S{sup 2} being made out of the Chan-Paton degrees of freedom. An alternative matrix theory description involves the fuzzy S{sup 4}. We also find that there is a hierarchy of quantum Hall effects in odd-dimensional spacetimes, generalizing the known cases in 2 + 1d and 4 + 1d.

Fabinger, Michal

2002-08-08

264

Self-generated cooperative light emission induced by atomic recoil  

NASA Astrophysics Data System (ADS)

The interaction of an atomic gas confined inside a cavity containing a strong electromagnetic field is numerically and theoretically investigated in a regime where recoil effects are not negligible. The spontaneous appearance of a density grating (atomic bunching) accompanied by the onset of a coherent, back-propagating electromagnetic wave is found to be ruled by a continuous phase transition. Numerical tests allow us to convincingly prove that the transition is steered by the appearence of a periodic atomic density modulation. Consideration of different experimental relaxation mechanisms induces us to analyze the problem in nearly analytic form, in the large detuning limit, using both a Vlasov approach and a Fokker-Planck description. The application of our predictions to recent experimental findings, reported by

Kruse et al. [Phys. Rev. Lett., 91 183601 (2003)
], yields a semiquantitative agreement with the observations.

Javaloyes, J.; Perrin, M.; Lippi, G. L.; Politi, A.

2004-08-01

265

Quantum statistics via perturbation effects of preparation procedures  

Microsoft Academic Search

We study the following problem: Is it possible to explain the quantum\\u000ainterference of probabilities in the purely corpuscular model for elementary\\u000aparticles? We demonstrate that (by taking into account perturbation effects of\\u000ameasurement and preparation procedures) we can obtain $\\\\cos\\\\theta$-perturbation\\u000a(interference term) in probabilistic rule connecting preparation procedures for\\u000apurely corpuscular objects. On one hand, our investigation demonstrated that

Andrei Khrennikov

2001-01-01

266

Large spin-orbit effects in small quantum dots  

Microsoft Academic Search

We consider small ballistic quantum dots weakly coupled to the leads in the\\u000achaotic regime and look for significant spin-orbit effects. We find that these\\u000aeffects can become quite prominent in the vicinity of degeneracies of many-body\\u000aenergies. We illustrate the idea by considering a case where the intrinsic\\u000aexchange term -JS^2 brings singlet and triplet many-body states near each

Ganpathy Murthy; R. Shankar

2006-01-01

267

Probing quantum-vacuum geometrical effects with cold atoms.  

PubMed

The lateral Casimir-Polder force between an atom and a corrugated surface should allow one to study experimentally nontrivial geometrical effects in the electromagnetic quantum vacuum. Here, we derive the theoretical expression of this force in the scattering approach. We show that large corrections to the "proximity force approximation" could be measured using present-day technology with a Bose-Einstein condensate used as a vacuum field sensor. PMID:18352246

Dalvit, Diego A R; Neto, Paulo A Maia; Lambrecht, Astrid; Reynaud, Serge

2008-02-01

268

Probing Quantum-Vacuum Geometrical Effects with Cold Atoms  

SciTech Connect

The lateral Casimir-Polder force between an atom and a corrugated surface should allow one to study experimentally nontrivial geometrical effects in the electromagnetic quantum vacuum. Here, we derive the theoretical expression of this force in the scattering approach. We show that large corrections to the 'proximity force approximation' could be measured using present-day technology with a Bose-Einstein condensate used as a vacuum field sensor.

Dalvit, Diego A. R. [Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Neto, Paulo A. Maia [Instituto de Fisica, UFRJ, CP 68528, Rio de Janeiro, RJ, 21941-972 (Brazil); Lambrecht, Astrid; Reynaud, Serge [Laboratoire Kastler Brossel, Case 74, CNRS, ENS, UPMC, Campus Jussieu, F-75252 Paris Cedex 05 (France)

2008-02-01

269

Dilution effects in classical and quantum orbital systems  

Microsoft Academic Search

We examine the dilution effects in an orbital model, termed the orbital compass model, which corresponds to the two-dimensional version of the eg-orbital model. An unconventional low-dimensional orbital alignment termed the directional order is confirmed to be realized by utilizing the quantum Monte-Carlo method. Impurity dependence of the ordering temperature of the directional order is numerically examined. We show that

T. Tanaka; M. Matsumoto; S. Ishihara

2007-01-01

270

Field theoretical quantities in the fractional quantum Hall effect  

Microsoft Academic Search

This thesis studies two models of the fractional quantum Hall effect (FQHE), the bosonic (Chern-Simons-Landau-Ginzburg) description and the fermionic (composite fermion gauge theory) description. The bosonic theory attempts to describe the FQHE states at filling fractions nu={1\\/ 2n+1} while the fermionic theory attempts to describe the states at nu={p\\/ 2np±1} and the metallic states in between. Within the bosonic theory,

Stephanie Hythe Curnoe

1997-01-01

271

Quantum effects in the hot electron microbolometer  

SciTech Connect

The theory of the hot electron microbolometer proposed by Nahum et al. assumed that the photon energy is thermalized in the electrons in the Cu absorber before relaxing to the lattice. Since the photons initially excite individual electrons to K{omega}>>k{sub B}T, however, direct relaxation of these hot electrons to phonons must also be considered. Theoretical estimates suggest that this extra relaxation channel increases the effective thermal conductance for K{omega}>>k{sub B}T and influences bolometer noise. Calculations of these effects are presented which predict very useful performance both for ground-based and spacebased astronomical photometry at millimeter and submillimeter wavelengths.

Tang, A.; Richards, P.L.

1994-10-01

272

Zel'Dovich Effect in Quantum Mechanics.  

National Technical Information Service (NTIS)

In systems bound by the Coulomb potential with a short-range distortion, the reconstruction of atomic spectrum (or Zel'dovich effect) can appear. Some peculiarities of this phenomenon for the state of nonzero angular momentum are discussed. Analytical pro...

B. M. Karnakov V. D. Mur A. E. Kudryavtsev V. S. Popov

1985-01-01

273

Spin-orbit effects in triple dot quantum shuttles  

NASA Astrophysics Data System (ADS)

Within the framework of a fully quantum mechanical approach we use a generalized density matrix formalism to study the spin-orbit coupling effects in a triple dot quantum shuttle. An interesting feature of this type of nanoelectromechanical systems is that the interplay between the electronic, spin, and mechanical degrees of freedom give rise to novel transport phenomena that has attracted a great deal of interest in both the applied and basic research. In this work, the effect of spin-orbit coupling is incorporated into the system by introducing non spin-conserving tunneling elements between the quantum dots. We explore the features of spin-polarized current by changing the Zeeman-split levels of the dots, and the frequency of the oscillating central dot. We show that the spin-orbit effect manifests itself as sidebands in the spin-polarized current, and that the tunneling channels can be controlled by adequately tuning the relative energies of the Zeeman-split levels, and by manipulating the current contribution from the vibrational modes.

Villavicencio, Jorge; Maldonado, Irene; Cota, Ernesto; Platero, Gloria

2012-02-01

274

Topological superconductivity, topological confinement, and the vortex quantum Hall effect  

SciTech Connect

Topological matter is characterized by the presence of a topological BF term in its long-distance effective action. Topological defects due to the compactness of the U(1) gauge fields induce quantum phase transitions between topological insulators, topological superconductors, and topological confinement. In conventional superconductivity, because of spontaneous symmetry breaking, the photon acquires a mass due to the Anderson-Higgs mechanism. In this paper we derive the corresponding effective actions for the electromagnetic field in topological superconductors and topological confinement phases. In topological superconductors magnetic flux is confined and the photon acquires a topological mass through the BF mechanism: no symmetry breaking is involved, the ground state has topological order, and the transition is induced by quantum fluctuations. In topological confinement, instead, electric charge is linearly confined and the photon becomes a massive antisymmetric tensor via the Stueckelberg mechanism. Oblique confinement phases arise when the string condensate carries both magnetic and electric flux (dyonic strings). Such phases are characterized by a vortex quantum Hall effect potentially relevant for the dissipationless transport of information stored on vortices.

Diamantini, M. Cristina; Trugenberger, Carlo A. [INFN and Dipartimento di Fisica, University of Perugia, via A. Pascoli, I-06100 Perugia (Italy); SwissScientific, chemin Diodati 10, CH-1223 Cologny (Switzerland)

2011-09-01

275

Semiclassical states, effective dynamics, and classical emergence in loop quantum cosmology  

SciTech Connect

We construct physical semiclassical states annihilated by the Hamiltonian constraint operator in the framework of loop quantum cosmology as a method of systematically determining the regime and validity of the semiclassical limit of the quantum theory. Our results indicate that the evolution can be effectively described using continuous classical equations of motion with nonperturbative corrections down to near the Planck scale below which the Universe can only be described by the discrete quantum constraint. These results, for the first time, provide concrete evidence of the emergence of classicality in loop quantum cosmology and also clearly demarcate the domain of validity of different effective theories. We prove the validity of modified Friedmann dynamics incorporating discrete quantum geometry effects which can lead to various new phenomenological applications. Furthermore the understanding of semiclassical states allows for a framework for interpreting the quantum wave functions and understanding questions of a semiclassical nature within the quantum theory of loop quantum cosmology.

Singh, Parampreet [Institute for Gravitational Physics and Geometry, Pennsylvania State University, 104 Davey Lab, University Park, Pennsylvania 16802 (United States); Vandersloot, Kevin [Institute for Gravitational Physics and Geometry, Pennsylvania State University, 104 Davey Lab, University Park, Pennsylvania 16802 (United States); Max-Planck-Institut fuer Gravitationsphysik, Albert-Einstein-Institut, Am Muehlenberg 1, D-14476 Golm (Germany)

2005-10-15

276

A proton recoil telescope for neutron spectroscopy  

NASA Astrophysics Data System (ADS)

A new proton recoil telescope (PRT) detector is presented: it is composed by an active multilayer of segmented plastic scintillators as neutron to proton converter, by two silicon strip detectors and by a final thick CsI(Tl) scintillator. The PRT can be used to measure neutron spectra in the range 2-160 MeV. The detector characteristics have been studied in detail with the help of Monte Carlo simulations. The overall energy resolution of the system ranges from about 20% at the lowest neutron energy to about 2% at 160 MeV. The global efficiency is about 3×10-5. Experimental tests have been performed by using the reaction 13C(d,n) at 40 MeV deuteron energy.

Donzella, A.; Barbui, M.; Bocci, F.; Bonomi, G.; Cinausero, M.; Fabris, D.; Fontana, A.; Giroletti, E.; Lunardon, M.; Moretto, S.; Nebbia, G.; Necchi, M. M.; Pesente, S.; Prete, G.; Rizzi, V.; Viesti, G.; Zenoni, A.

2010-01-01

277

A precision measurement of the photon recoil of an atom using atomic interferometry  

SciTech Connect

An experiment was performed to measure the recoil of an atom due to the absorption of up to 64 photons. Cesium atoms are magneto-optically trapped and laser-cooled, and then launched onto a fountian trajectory. Near their apogee, a series of Doppler-sensitive stimulated Raman pulses are applied. These give rise to two well-resolved sets of atomic interference fringes. The separation of the center frequencies of these sets of fringes is equal to an integral number of photon recoil shifts. The author has achieved a relative precision in the photon recoil measurement 0.1 ppm in two hours of data collection. This thesis describes this measurement and present a detailed theoretical and experimental study of systematic errors that can effect its accuracy. These results should be applicable to light pulse atomic interferometers in general. Measurement of the photon recoil allows us to determine [h bar]/m[sub cs], and hence the fine-structure constant. Straightforward changes in the apparatus should ultimately lead to a relative precision near 1 ppb.

Weiss, D.S.

1993-01-01

278

High-speed semiconductor light emitters based on quantum-confined field effect - Developed devices and inclusion of quantum microcavities  

Microsoft Academic Search

The paper describes the design principle and the structures of AlGaAs high-speed light emitters based on quantum-confined Stark effect (QCSE). The scheme of high-speed switching of spontaneous emissions in these devices does not rely on changes in carrier population, but depends instead on the effects of the electric fields on the oscillator strengths in quantum-well active layers of the devices

Masamichi Yamanishi

1992-01-01

279

Gravitational-wave probe of effective quantum gravity  

SciTech Connect

All modern routes leading to a quantum theory of gravity - i.e., perturbative quantum gravitational one-loop exact correction to the global chiral current in the standard model, string theory, and loop quantum gravity - require modification of the classical Einstein-Hilbert action for the spacetime metric by the addition of a parity-violating Chern-Simons term. The introduction of such a term leads to spacetimes that manifest an amplitude birefringence in the propagation of gravitational waves. While the degree of birefringence may be intrinsically small, its effects on a gravitational wave accumulate as the wave propagates. Observation of gravitational waves that have propagated over cosmological distances may allow the measurement of even a small birefringence, providing evidence of quantum gravitational effects. The proposed Laser Interferometer Space Antenna (LISA) will be sensitive enough to observe the gravitational waves from sources at cosmological distances great enough that interesting bounds on the Chern-Simons coupling may be found. Here we evaluate the effect of a Chern-Simons induced spacetime birefringence to the propagation of gravitational waves from such systems. Focusing attention on the gravitational waves from coalescing binary black holes systems, which LISA will be capable of observing at redshifts approaching 30, we find that the signature of Chern-Simons gravity is a time-dependent change in the apparent orientation of the binary's orbital angular momentum with respect to the observer line-of-sight, with the magnitude of change reflecting the integrated history of the Chern-Simons coupling over the worldline of the radiation wave front. While spin-orbit coupling in the binary system will also lead to an evolution of the system's orbital angular momentum, the time dependence and other details of this real effect are different than the apparent effect produced by Chern-Simons birefringence, allowing the two effects to be separately identified. In this way gravitational-wave observations with LISA may thus provide our first and only opportunity to probe the quantum structure of spacetime over cosmological distances.

Alexander, Stephon; Finn, Lee Samuel; Yunes, Nicolas [Pennsylvania State University, University Park, Pennsylvania 16802 (United States)

2008-09-15

280

Anharmonic effect of adiabatic quantum pumping  

NASA Astrophysics Data System (ADS)

Based on the scattering matrix approach, we systematically investigate the anharmonic effect of the pumped current in double-barrier structures with adiabatic time-modulation of two sinusoidal AC driven potential heights. The pumped current as a function of the phase difference between the two driven potentials looks like to be sinusoidal, but actually it contains sine functions of double and more phase difference. It is found that this kind of anharmonic effect of the pumped current is determined combinedly by the Berry curvature and parameter variation loop trajectory. Therefore small ratio of the driving amplitude and the static amplitude is not necessary for harmonic pattern in the pumped current to dominate for smooth Berry curvature on the surface within the parameter variation loop.

Deng, Wei-Yin; Zhong, Ke-Ju; Zhu, Rui; Deng, Wen-Ji

2014-04-01

281

Gravitational quantum effects in an isotropic universe  

NASA Astrophysics Data System (ADS)

The effects of polarization of a vacuum by an external gravitational field in a system of spinor, scalar, and vector mass-particles are analyzed within the framework of a model of a conformally planar space-time. Expressions for radiative corrections to the Einstein equations are derived, both of the second- and third-order. The role of these corrections in gravitational theory, in asymptotic regions of weak and strong gravitational fields are discussed.

Beilin, V. A.; Vereshkov, G. M.; Grishkan, Iu. S.; Ivanov, N. M.; Nesterenko, V. A.; Poltavtsev, A. N.

1980-06-01

282

Effect of carrier dynamics and temperature on two-state lasing in semiconductor quantum dot lasers  

SciTech Connect

It is analytically shown that the both the charge carrier dynamics in quantum dots and their capture into the quantum dots from the matrix material have a significant effect on two-state lasing phenomenon in quantum dot lasers. In particular, the consideration of desynchronization in electron and hole capture into quantum dots allows one to describe the quenching of ground-state lasing observed at high injection currents both qualitatevely and quantitatively. At the same time, an analysis of the charge carrier dynamics in a single quantum dot allowed us to describe the temperature dependences of the emission power via the ground- and excited-state optical transitions of quantum dots.

Korenev, V. V., E-mail: korenev@spbau.ru; Savelyev, A. V.; Zhukov, A. E.; Omelchenko, A. V.; Maximov, M. V. [Saint Petersburg Academic University-Nanotechnology Research and Education Center (Russian Federation)] [Saint Petersburg Academic University-Nanotechnology Research and Education Center (Russian Federation)

2013-10-15

283

Quantum gravitational optics: Effective Raychaudhuri equation  

SciTech Connect

Vacuum polarization in QED in a background gravitational field induces interactions which effectively modify the classical picture of light rays, as the null geodesics of spacetime. These interactions violate the strong equivalence principle and affect the propagation of light leading to superluminal photon velocities. Taking into account the QED vacuum polarization, we study the propagation of a bundle of rays in a background gravitational field. To do so we study the perturbative deformation of the Raychaudhuri equation through the influence of vacuum polarization on photon propagation. We analyze the contribution of the above interactions to the optical scalars, namely, shear, vorticity, and expansion using the Newman-Penrose formalism.

Ahmadi, N. [Department of Physics, University of Tehran, North Karegar Avenue, Tehran 14395-547 (Iran, Islamic Republic of); Nouri-Zonoz, M. [Department of Physics, University of Tehran, North Karegar Avenue, Tehran 14395-547 (Iran, Islamic Republic of); Institute for Studies in Theoretical Physics and Mathematics, P.O. Box 19395-5531 Tehran (Iran, Islamic Republic of)

2006-08-15

284

Quantum confined Stark effect in organic fluorophores.  

NASA Astrophysics Data System (ADS)

Fluorescent molecules have widely been used to detect and visualize structure and processes in biological samples due to its extraordinary sensitivity. However, the emission spectra of flurophores are usually broad and the accurate identification is difficult. Recently, experiments show that energy shifts by Stark effect can be used to aid the identification of organic molecules [1]. Stark effect originates from the shifting/splitting of energy levels when a molecule is under an external electric field, which shows a shift/splitting of a peak in absorption/emission spectra. The size of the shift depends on the magnitude of the external field and the molecular structure. In this talk we will show our theoretical study of the peak shifts on emission spectra for a series of organic fluorophores such as tyrosine, tryptophan, rhodamine123 and coumarin314 using density functional theory. We find that a particular peak shift is determined by the local dipole moments of molecular orbitals rather than the global dipole moment of the molecule. These molecular-specific shifts in emission spectra may enable to improve molecular identification in biosensors. Our results will be compared with experimental data. [1]Unpublished, S. Sarkar, B. Kanchibotla, S. Bandyopadhyay, G. Tepper, J. Edwards, J. Anderson, and R. Kessick.

Peng, Xihong; Anderson, John; Tepper, Gary; Bandyopadhyay, Supriyo; Nayak, Saroj

2008-03-01

285

Correlation effects in quasi-one-dimensional quantum wires  

NASA Astrophysics Data System (ADS)

We explore the role of electron correlation in quasi-one-dimensional quantum wires as the range of the interaction potential is changed and their thickness is varied by performing exact quantum Monte Carlo simulations at various electronic densities. In the case of unscreened interactions with a long-range 1/x tail there is a crossover from a liquid to a quasi-Wigner crystal state as the density decreases. When this interaction is screened, quasi-long-range order is prevented from forming, although a significant correlation with 4kF periodicity is still present at low densities. At even lower electron concentration, exchange is suppressed and the electrons behave like spinless fermions. Finally, we study the effect of electron correlations in the double quantum wire experiment [Steinberg , Phys. Rev. B 73, 113307 (2006)] by introducing an accurate model for the screening in the experiment and explicitly including the finite length of the system in our simulations. We find that decreasing the electron density continuously drives the system from a liquid to a state with quite strong 4kF correlations. This crossover takes place around 22?m-1 , near the density where the electron localization occurs in the experiment. The charge and spin velocities are also in good agreement with the experimental findings in the proximity of the crossover. We argue that correlation effects play an important role at the onset of the localization transition.

Shulenburger, Luke; Casula, Michele; Senatore, Gaetano; Martin, Richard M.

2008-10-01

286

Effects of GUP in quantum cosmological perfect fluid models  

NASA Astrophysics Data System (ADS)

Very recently Ali et al. (2009) [5] proposed a new Generalized Uncertainty Principle (or GUP) with a linear term in Plank length. In this Letter the effect of this GUP is studied in quantum cosmological models with dust and cosmic string as the perfect fluid. For the quantum mechanical description it is possible to find the wave packet which resulted from the superposition of the stationary wave functions of the Wheeler-deWitt equation. However the norm of the wave packets turned out to be time dependent and hence the model became non-unitary. The loss of unitarity is due to the fact that the presence of the linear term in Plank length in the Generalized Uncertainty Principle made the Hamiltonian non-Hermitian.

Majumder, Barun

2011-05-01

287

z = 3 antiferromagnetic quantum criticality driven by the Kondo effect.  

PubMed

We find that the Kondo effect results in a new universality class for an antiferromagnetic (AF) quantum critical point (QCP) in the heavy fermion quantum transition, described by deconfined bosonic spinons with the dynamical exponent z=3. We show that the thermodynamics and transport of the z=3 AF QCP are consistent with the well-known non-Fermi liquid physics such as the divergent Grüneisen ratio with an exponent 2/3 and temperature-linear resistivity. We propose that the hallmark of the Kondo-driven AF QCP is a uniform spin susceptibility that diverges with an exponent 2/3, remarkably consistent with the experimental observations for YbRh2Si2. PMID:20482002

Kim, Ki-Seok; Jia, Chenglong

2010-04-16

288

Dielectric function of spherical dome shells with quantum size effects.  

PubMed

Metallic spherical dome shells have received much attention in recent years because they have proven to possess highly impressive optical properties. The expected distinctive changes occurring owing to quantum confinement of conduction electrons in these nanoparticles as their thickness is reduced, have not been properly investigated. Here we carry out a detailed analytical derivation of the quantum contributions by introducing linearly shifted Associated Legendre Polynomials, which form an approximate orthonormal eigenbasis for the single-electron Hamiltonian of a spherical dome shell. Our analytical results clearly show the contribution of different elements of a spherical dome shell to the effective dielectric function. More specifically, our results provide an accurate, quantitative correction for the dielectric function of metallic spherical dome shells with thickness below 10 nm. PMID:24921317

Kumarasinghe, Chathurangi; Premaratne, Malin; Agrawal, Govind P

2014-05-19

289

Nuclear quantum effects and hydrogen bond fluctuations in water.  

PubMed

The hydrogen bond (HB) is central to our understanding of the properties of water. However, despite intense theoretical and experimental study, it continues to hold some surprises. Here, we show from an analysis of ab initio simulations that take proper account of nuclear quantum effects that the hydrogen-bonded protons in liquid water experience significant excursions in the direction of the acceptor oxygen atoms. This generates a small but nonnegligible fraction of transient autoprotolysis events that are not seen in simulations with classical nuclei. These events are associated with major rearrangements of the electronic density, as revealed by an analysis of the computed Wannier centers and (1)H chemical shifts. We also show that the quantum fluctuations exhibit significant correlations across neighboring HBs, consistent with an ephemeral shuttling of protons along water wires. We end by suggesting possible implications for our understanding of how perturbations (solvated ions, interfaces, and confinement) might affect the HB network in water. PMID:24014589

Ceriotti, Michele; Cuny, Jérôme; Parrinello, Michele; Manolopoulos, David E

2013-09-24

290

Time-dependent optimized effective potential for quantum wells  

NASA Astrophysics Data System (ADS)

Most present applications in time-dependent density-functional theory employ adiabatic approximations for the exchange- correlation (XC) potential, ignoring all functional dependence on densities at previous times. In this talk, we describe the electron dynamics in quantum wells beyond the adiabatic approximation, using the time-dependent optimized effective potential (TDOEP) method. In TDOEP, the XC potential is a functional of the time-dependent orbitals, and follows from an integral equation over space and time. We solve the full TDOEP integral equation for quantum well intersubband dynamics in exact exchange as well as self-interaction corrected ALDA. Various properties of the resulting time-dependent XC potential, such as its asymptotics, memory dependence, and discontinuity upon population of a new subband level are discussed. This work is supported by NSF DMR-0553485 and Research Corporation.

Wijewardane, Harshani; Ullrich, Carsten A.

2007-03-01

291

Nuclear quantum effects and hydrogen bond fluctuations in water  

PubMed Central

The hydrogen bond (HB) is central to our understanding of the properties of water. However, despite intense theoretical and experimental study, it continues to hold some surprises. Here, we show from an analysis of ab initio simulations that take proper account of nuclear quantum effects that the hydrogen-bonded protons in liquid water experience significant excursions in the direction of the acceptor oxygen atoms. This generates a small but nonnegligible fraction of transient autoprotolysis events that are not seen in simulations with classical nuclei. These events are associated with major rearrangements of the electronic density, as revealed by an analysis of the computed Wannier centers and 1H chemical shifts. We also show that the quantum fluctuations exhibit significant correlations across neighboring HBs, consistent with an ephemeral shuttling of protons along water wires. We end by suggesting possible implications for our understanding of how perturbations (solvated ions, interfaces, and confinement) might affect the HB network in water.

Ceriotti, Michele; Cuny, Jerome; Parrinello, Michele; Manolopoulos, David E.

2013-01-01

292

A gun recoil system employing a magnetorheological fluid damper  

NASA Astrophysics Data System (ADS)

This research aims to design and control a full scale gun recoil buffering system which works under real firing impact loading conditions. A conventional gun recoil absorber is replaced with a controllable magnetorheological (MR) fluid damper. Through dynamic analysis of the gun recoil system, a theoretical model for optimal design and control of the MR fluid damper for impact loadings is derived. The optimal displacement, velocity and optimal design rules are obtained. By applying the optimal design theory to protect against impact loadings, an MR fluid damper for a full scale gun recoil system is designed and manufactured. An experimental study is carried out on a firing test rig which consists of a 30 mm caliber, multi-action automatic gun with an MR damper mounted to the fixed base through a sliding guide. Experimental buffering results under passive control and optimal control are obtained. By comparison, optimal control is better than passive control, because it produces smaller variation in the recoil force while achieving less displacement of the recoil body. The optimal control strategy presented in this paper is open-loop with no feedback system needed. This means that the control process is sensor-free. This is a great benefit for a buffering system under impact loading, especially for a gun recoil system which usually works in a harsh environment.

Li, Z. C.; Wang, J.

2012-10-01

293

Reply to ``Comment on `Computational approach to the quantum Zeno effect: Position measurements' ''  

NASA Astrophysics Data System (ADS)

This is a Reply to the preceding Comment by Home and Whitaker [Phys. Rev. A 48, 2502 (1993)]. Our aim is to indicate how we apply basic quantum mechanics to quantum measurement theory. We discuss the work of Misra and Sudarshan [J. Math. Phys. 18, 576 (1977)] and defend our own work on the quantum Zeno effect.

Fearn, H.; Lamb, W. E., Jr.

1993-09-01

294

Quantum confinement effects on the band structure and dielectric properties of nanostructured GaAs  

Microsoft Academic Search

The electronic band structure and dielectric properties of a GaAs quantum well have been investigated using the pseudopotential approach. The effect of quantum confinement on the electronic and dielectric properties of GaAs has been examined. It is found that significant variations in the studied properties occur at quantum well widths below 5 nm. The information may be useful in obtaining

Najah Hamed M. Al Wadiy; Nadir Bouarissa; M. Ajmal Khan

2011-01-01

295

Quantum-Enhanced Thermoelectric Effects in Polycyclic Molecular Junctions  

NASA Astrophysics Data System (ADS)

We calculate the thermoelectric response of a polycyclic molecular junction including electron-electron interactions. To do this, the molecular Green's function is determined via a Lanczos-based technique and ?-electron effective field theory is used to model the degrees of freedom most relevant to transport. In these junctions we find that the presence of multiple rings leads to higher order quantum interference features giving rise to dramatic enhancements of molecular thermoelectric effects, consistent with previous predictions based on Hueckel theory, which neglected electron correlations.

Barr, Joshua; Stafford, Charles

2012-02-01

296

Scintillation of liquid helium for low-energy nuclear recoils  

NASA Astrophysics Data System (ADS)

The scintillation properties of liquid helium upon the recoil of a low-energy helium atom are discussed in the context of the possible use of this medium as a detector of dark matter. It is found that the prompt scintillation yield in the range of recoil energies from a few keV to 100 keV is somewhat higher than that obtained by a linear extrapolation from the measured yield for a 5-MeV ? particle. A comparison is made of both the scintillation yield and the charge separation by an electric field for nuclear recoils and for electrons stopped in helium.

Ito, T. M.; Seidel, G. M.

2013-08-01

297

Unambiguous determination of quantum capture, carrier diffusion, and intrinsic effects in quantum-well laser dynamics using wavelength-selective optical modulation  

Microsoft Academic Search

A novel wavelength-dependent optical modulation technique capable of explicitly delineating the effects of quantum capture, carrier diffusion, and other intrinsic effects in quantum-well laser dynamics is described. Results for a compressively strained multiple-quantum-well laser are presented

D. Vassilovski; Ta-Chung Wu; S. Kan; K. Y. Lau; C. E. Zah

1995-01-01

298

Tunable interactions and the fractional quantum Hall effect  

NASA Astrophysics Data System (ADS)

We explore several realistic methods of tuning the interactions in two-dimensional electronic systems in high magnetic fields. We argue that these experimental probes can be useful in studying the interplay of topology, quantum geometry and symmetry breaking in the fractional quantum Hall effect (FQHE). In particular, we show that the mixing of subbands and Landau levels in GaAs wide quantum wells breaks the particle-hole symmetry between the Moore-Read Pfaffian state and its particle-hole conjugate, the anti-Pfaffian, in such a way that the latter is unambiguously favored and generically describes the ground state at 5/2 filling [1]. Furthermore, the tilting of the magnetic field, or more generally variation of the band mass tensor, probes the fluctuation of the intrinsic metric degree of freedom of the incompressible fluids, and ultimately induces the crossover to the broken-symmetry and nematic phases in higher Landau levels [2]. Some of these mechanisms also lead to an enhancement of the excitation gap of the non-Abelian states, as observed in recent experiments. Finally, we compare the tuning capabilities in conventional systems with that in multilayer graphene and related materials with Dirac-type carriers where tuning the band structure and dielectric environment provides a simple and direct method to engineer more robust FQHE states and to study quantum transitions between them [3]. [4pt] [1] Z. Papic, F. D. M. Haldane, and E. H. Rezayi, arXiv:1209.6606 (2012).[0pt] [2] Bo Yang, Z. Papic, E. H. Rezayi, R. N. Bhatt, F. D. M. Haldane, Phys. Rev. B 85, 165318 (2012).[0pt] [3] Z. Papic, R. Thomale, D. A. Abanin, Phys. Rev. Lett. 107, 176602 (2011); Z. Papic, D. A. Abanin, Y. Barlas, and R. N. Bhatt, Phys. Rev. B 84, 241306(R) (2011); D. A. Abanin, Z. Papic, Y. Barlas, and R. N. Bhatt, New J. Phys. 14, 025009 (2012).

Papic, Zlatko

2013-03-01

299

Edge states in graphene quantum dots: Fractional quantum Hall effect analogies and differences at zero magnetic field  

Microsoft Academic Search

We investigate the way that the degenerate manifold of midgap edge states in quasicircular graphene quantum dots with zigzag boundaries supports, under free-magnetic-field conditions, strongly correlated many-body behavior analogous to the fractional quantum Hall effect (FQHE), familiar from the case of semiconductor heterostructures in high-magnetic fields. Systematic exact-diagonalization (EXD) numerical studies are presented for 5<=N<=8 fully spin-polarized electrons and for

Igor Romanovsky; Constantine Yannouleas; Uzi Landman

2009-01-01

300

{theta} parameter in loop quantum gravity: Effects on quantum geometry and black hole entropy  

SciTech Connect

The precise analog of the {theta}-quantization ambiguity of Yang-Mills theory exists for the real SU(2) connection formulation of general relativity. As in the former case {theta} labels representations of large gauge transformations, which are superselection sectors in loop quantum gravity. We show that unless {theta}=0, the (kinematical) geometric operators such as area and volume are not well defined on spin network states. More precisely the intersection of their domain with the dense set Cyl in the kinematical Hilbert space H of loop quantum gravity is empty. The absence of a well-defined notion of area operator acting on spin network states seems at first in conflict with the expected finite black hole entropy. However, we show that the black hole (isolated) horizon area--which in contrast to kinematical area is a (Dirac) physical observable--is indeed well defined, and quantized so that the black hole entropy is proportional to the area. The effect of {theta} is negligible in the semiclassical limit where proportionality to area holds.

Rezende, Danilo Jimenez; Perez, Alejandro [Centre de Physique Theorique, Campus de Luminy, 13288 Marseille (France)

2008-10-15

301

Self-screening of the quantum confined Stark effect by the polarization induced bulk charges in the quantum barriers  

NASA Astrophysics Data System (ADS)

InGaN/GaN light-emitting diodes (LEDs) grown along the polar orientations significantly suffer from the quantum confined Stark effect (QCSE) caused by the strong polarization induced electric field in the quantum wells, which is a fundamental problem intrinsic to the III-nitrides. Here, we show that the QCSE is self-screened by the polarization induced bulk charges enabled by designing quantum barriers. The InN composition of the InGaN quantum barrier graded along the growth orientation opportunely generates the polarization induced bulk charges in the quantum barrier, which well compensate the polarization induced interface charges, thus avoiding the electric field in the quantum wells. Consequently, the optical output power and the external quantum efficiency are substantially improved for the LEDs. The ability to self-screen the QCSE using polarization induced bulk charges opens up new possibilities for device engineering of III-nitrides not only in LEDs but also in other optoelectronic devices.

Zhang, Zi-Hui; Liu, Wei; Ju, Zhengang; Tiam Tan, Swee; Ji, Yun; Kyaw, Zabu; Zhang, Xueliang; Wang, Liancheng; Wei Sun, Xiao; Volkan Demir, Hilmi

2014-06-01

302

Effect of quantum nuclear motion on hydrogen bonding  

NASA Astrophysics Data System (ADS)

This work considers how the properties of hydrogen bonded complexes, X-H⋯Y, are modified by the quantum motion of the shared proton. Using a simple two-diabatic state model Hamiltonian, the analysis of the symmetric case, where the donor (X) and acceptor (Y) have the same proton affinity, is carried out. For quantitative comparisons, a parametrization specific to the O-H⋯O complexes is used. The vibrational energy levels of the one-dimensional ground state adiabatic potential of the model are used to make quantitative comparisons with a vast body of condensed phase data, spanning a donor-acceptor separation (R) range of about 2.4 - 3.0 Å, i.e., from strong to weak hydrogen bonds. The position of the proton (which determines the X-H bond length) and its longitudinal vibrational frequency, along with the isotope effects in both are described quantitatively. An analysis of the secondary geometric isotope effect, using a simple extension of the two-state model, yields an improved agreement of the predicted variation with R of frequency isotope effects. The role of bending modes is also considered: their quantum effects compete with those of the stretching mode for weak to moderate H-bond strengths. In spite of the economy in the parametrization of the model used, it offers key insights into the defining features of H-bonds, and semi-quantitatively captures several trends.

McKenzie, Ross H.; Bekker, Christiaan; Athokpam, Bijyalaxmi; Ramesh, Sai G.

2014-05-01

303

Effect of quantum nuclear motion on hydrogen bonding.  

PubMed

This work considers how the properties of hydrogen bonded complexes, X-H?Y, are modified by the quantum motion of the shared proton. Using a simple two-diabatic state model Hamiltonian, the analysis of the symmetric case, where the donor (X) and acceptor (Y) have the same proton affinity, is carried out. For quantitative comparisons, a parametrization specific to the O-H?O complexes is used. The vibrational energy levels of the one-dimensional ground state adiabatic potential of the model are used to make quantitative comparisons with a vast body of condensed phase data, spanning a donor-acceptor separation (R) range of about 2.4 - 3.0 Å, i.e., from strong to weak hydrogen bonds. The position of the proton (which determines the X-H bond length) and its longitudinal vibrational frequency, along with the isotope effects in both are described quantitatively. An analysis of the secondary geometric isotope effect, using a simple extension of the two-state model, yields an improved agreement of the predicted variation with R of frequency isotope effects. The role of bending modes is also considered: their quantum effects compete with those of the stretching mode for weak to moderate H-bond strengths. In spite of the economy in the parametrization of the model used, it offers key insights into the defining features of H-bonds, and semi-quantitatively captures several trends. PMID:24811647

McKenzie, Ross H; Bekker, Christiaan; Athokpam, Bijyalaxmi; Ramesh, Sai G

2014-05-01

304

Quantum effects on the Rayleigh-Taylor instability of stratified fluid/plasma through porous media  

NASA Astrophysics Data System (ADS)

Quantum effect on Rayleigh-Taylor instability of stratified plasma layer through a porous medium are investigated. The linear growth rate is obtained analytically and is analyzed. In the presence of quantum effect, both the porosity of porous medium and the medium permeability has different influence on the coup point ( kcoup?) for stability, but they do not have influence on the critical point ( kc?) for stability. The quantum effect plays the principal role of the complete stability case for the system considered.

Hoshoudy, G. A.

2009-07-01

305

Role of Quantum Effects in the GlassTransition.  

SciTech Connect

It is shown that quantum effects lead to a significant decrease of the glass transition temperature Tg with respect to the melting temperature Tm, so that the ratio Tg=Tm can be much smaller than the typical value of 2=3 in materials where Tg is near or below 60 K. Furthermore, it is demonstrated that the viscosity or structural relaxation time in such low temperature glass formers should exhibit highly unusual temperature dependence, namely a decrease of the apparent activation energy upon approaching Tg (instead of traditional increase).

Novikov, Vladimir [ORNL; Sokolov, Alexei P [ORNL

2013-01-01

306

Computational Investigation of Quantum Size Effects in Gold Nanoparticles  

SciTech Connect

Electron density perturbation from carbon monoxide adsorption on a multi-hundred atom gold nanoparticle. The perturbation causes significant quantum size effects in CO catalysis on gold particles. Science: Jeff Greeley and Nick Romero, Argonne National Laboratory; Jesper Kleis, Karsten Jacobsen, Jens Nørskov, Technical University of Denmark? Visualization: Joseph Insley, Argonne National Laboratory This research used resources of the Argonne Leadership Computing Facility at Argonne National Laboratory, which is supported by the Office of Science of the U.S. Dept. of Energy under contract DE-AC02-06CH11357.

None

2010-01-01

307

Photoluminescence fine structures in the fractional quantum Hall effect regime  

NASA Astrophysics Data System (ADS)

We investigate polarization-resolved fine structure in the photoluminescence (PL) in the fractional quantum Hall effect regime at B =4-6 T, where small Zeeman energy allows spin-depolarized ground states. We observe up to five distinct peaks with characteristic polarization and temperature dependence in the vicinity of ? =1/3 and quenching of the PL from triplet charged quasiexcitons at around ? =1/4. Those findings appear to be consistent with results of exact diagonalization on a Haldane sphere including all spin configurations and are understood to be PL from fractionally charged quasiexcitons.

Nomura, S.; Yamaguchi, M.; Tamura, H.; Akazaki, T.; Hirayama, Y.; Korkusinski, M.; Hawrylak, P.

2014-03-01

308

Scalar spin chirality and quantum hall effect on triangular lattices  

SciTech Connect

We study the Kondo Lattice and Hubbard models on a triangular lattice for band filling factor 3/4. We show that a simple non-coplanar chiral spin ordering (scalar spin chirality) is naturally realized in both models due to perfect nesting of the fermi surface. The resulting triple-Q magnetic ordering is a natural counterpart of the collinear Neel ordering of the half-filled square lattice Hubbard model. We show that the obtained chiral phase exhibits a spontaneous quantum Hall-effect with {sigma}{sub xy} = e{sup 2}/h.

Martin, Ivar [Los Alamos National Laboratory; Batista, Cristian D [Los Alamos National Laboratory

2008-01-01

309

Theory of the quantum Hall effect in finite graphene devices  

NASA Astrophysics Data System (ADS)

We study the quantum Hall effect (QHE) in graphene based on the current injection model, which takes into account the finite rectangular geometry with source and drain electrodes. In our model, the presence of disorder, the edge-state picture, extended states, and localized states, which are believed to be indispensable ingredients in describing the QHE, do not play an important role. Instead the boundary conditions during the injection into the graphene sheet, which are enforced by the presence of the Ohmic contacts, determine the current-voltage characteristics.

Kramer, Tobias; Kreisbeck, Christoph; Krueckl, Viktor; Heller, Eric J.; Parrott, Robert E.; Liang, Chi-Te

2010-02-01

310

Computational Investigation of Quantum Size Effects in Gold Nanoparticles  

ScienceCinema

Electron density perturbation from carbon monoxide adsorption on a multi-hundred atom gold nanoparticle. The perturbation causes significant quantum size effects in CO catalysis on gold particles. Science: Jeff Greeley and Nick Romero, Argonne National Laboratory; Jesper Kleis, Karsten Jacobsen, Jens Nørskov, Technical University of Denmark? Visualization: Joseph Insley, Argonne National Laboratory This research used resources of the Argonne Leadership Computing Facility at Argonne National Laboratory, which is supported by the Office of Science of the U.S. Dept. of Energy under contract DE-AC02-06CH11357.

311

Comparison of recoil-induced resonances and the collective atomic recoil laser  

NASA Astrophysics Data System (ADS)

The theories of recoil-induced resonances (RIR) [J. Guo, P. R. Berman, B. Dubetsky, and G. Grynberg, Phys. Rev. A 46, 1426 (1992)] and the collective atomic recoil laser (CARL) [R. Bonifacio and L. De Salvo, Nucl. Instrum. Methods Phys. Res. A 341, 360 (1994)] are compared. Both theories can be used to derive expressions for the gain experienced by a probe field interacting with an ensemble of two-level atoms that are simultaneously driven by a pump field. It is shown that the underlying formalisms of the RIR and CARL are equivalent. Differences between the RIR and CARL arise because the theories are typically applied for different ranges of the parameters appearing in the theory. The RIR limit is one in which the time derivative of the probe field amplitude, dE2/dt, depends locally on E2(t) and the gain depends linearly on the atomic density, while the CARL limit is one in which dE2/dt=?t0f(t,t')E2(t')dt', where f is a kernel, and the gain has a nonlinear dependence on the atomic density. Validity conditions for the RIR or CARL limits are established in terms of the various parameters characterizing the atom-field interaction. The probe gain for a probe-pump detuning equal to zero is analyzed in some detail, in order to understand how gain arises in a system which, at first glance, appears to have a symmetry that would preclude the possibility for gain. Moreover, it is shown that these calculations, carried out in perturbation theory, have a range of applicability beyond the recoil problem. Experimental possibilities for observing CARL are discussed.

Berman, P. R.

1999-01-01

312

A Proton Recoil Telescope for Neutron Spectroscopy  

NASA Astrophysics Data System (ADS)

The N2P research program funded by the INFN committee for Experimental Nuclear Physics (CSNIII) has among his goals the construction of a Proton Recoil Telescope (PRT), a detector to measure neutron energy spectra. The interest in such a detector is primarily related to the SPES project for rare beams production at the Laboratori Nazionali di Legnaro. For the SPES project it is, in fact, of fundamental importance to have reliable information about energy spectra and yield for neutrons produced by d or p projectiles on thick light targets to model the ''conversion target'' in which the p or d are converted in neutrons. These neutrons, in a second stage, will induce the Uranium fission in the ''production target''. The fission products are subsequently extracted, selected and re-accelerated to produce the exotic beam. The neutron spectra and angular distribution are important parameters to define the final production of fission fragments. In addition, this detector can be used to measure neutron spectra in the field of cancer therapy (this topic is nowadays of particular interest to INFN, for the National Centre for Hadron therapy (CNAO) in Pavia) and space applications.

Cinausero, M.; Barbui, M.; Prete, G.; Rizzi, V.; Andrighetto, A.; Pesente, S.; Fabris, D.; Lunardon, M.; Nebbia, G.; Viesti, G.; Moretto, S.; Morando, M.; Zenoni, A.; Bocci, F.; Donzella, A.; Bonomi, G.; Fontana, A.

2006-05-01

313

Autler-Townes splitting and quantum confined Stark effect of sideband peak in asymmetric double quantum wells  

NASA Astrophysics Data System (ADS)

Optical absorption is investigated by self-consistent density matrix approach in asymmetric double quantum wells driven by an intense terahertz field and a direct current electric field polarized along the growth direction. Rich nonlinear dynamic behaviors of sideband absorption peaks are systematically studied in undoped asymmetric double quantum wells. When only in presence of a resonant terahertz field, the Autler-Townes splitting of the sideband peaks becomes pronounced with increasing the strength of the terahertz field. Quantum confined Stark effect of sideband peaks is discussed when an invariant terahertz field and a direct current electric field are simultaneously applied to the quantum well. It is shown that the sideband peaks of the 1s main absorption peak undergo a red-shift and the sideband peaks of the 2s main absorption peak undergo a blue-shift with increasing intensity of the direct current electric field. The presented results have potential applications in electro-optical devices.

Hong-wei, Wu; Xian-wu, Mi; Yong-gang, Huang; Ke-hui, Song

2013-01-01

314

Quantum gravity and spin-1/2 particle effective dynamics  

NASA Astrophysics Data System (ADS)

Quantum gravity phenomenology opens up the possibility of probing Planck scale physics. Thus, by exploiting the generic properties that a semiclassical state of the compound system fermions plus gravity should have, an effective dynamics of spin-1/2 particles is obtained within the framework of loop quantum gravity. Namely, at length scales much larger than Planck length lP˜10-33 cm and below the wavelength of the fermion, the spin-1/2 dynamics in flat spacetime includes Planck scale corrections. In particular we obtain modified dispersion relations in vacuo for fermions. These corrections yield a time of arrival delay of the spin-1/2 particles with respect to a light signal and, in the case of neutrinos, a novel flavor oscillation. To detect these effects the corresponding particles must be highly energetic and should travel long distances. Hence neutrino bursts accompanying gamma ray bursts or ultrahigh energy cosmic rays could be considered. Remarkably, future neutrino telescopes may be capable of testing such effects. This paper provides a detailed account of the calculations and elaborates on results previously reported in a Letter. These are further amended by introducing a real parameter ? aimed at encoding our lack of knowledge of scaling properties of the gravitational degrees of freedom.

Alfaro, Jorge; Morales-Técotl, Hugo A.; Urrutia, Luis F.

2002-12-01

315

Experimental demonstration of the quantum Zeno effect in NMR with entanglement-based measurements  

NASA Astrophysics Data System (ADS)

We experimentally demonstrate a dynamic fashion of quantum Zeno effect in nuclear magnetic resonance systems. The frequent measurements are implemented through quantum entanglement between the target qubit(s) and the measuring qubit, which dynamically results from the unitary evolution of duration ?m due to dispersive coupling. Experimental results testify to the presence of “the critical measurement time effect,” that is, the quantum Zeno effect does not occur when ?m takes some critical values, even if the measurements are frequent enough. Moreover, we provide an experimental demonstration of an entanglement preservation mechanism based on such a dynamic quantum Zeno effect.

Zheng, Wenqiang; Xu, D. Z.; Peng, Xinhua; Zhou, Xianyi; Du, Jiangfeng; Sun, C. P.

2013-03-01

316

Quantum confinement in Si and Ge nanostructures: effect of crystallinity  

NASA Astrophysics Data System (ADS)

We look at the relationship between the preparation method of Si and Ge nanostructures (NSs) and the structural, electronic, and optical properties in terms of quantum confinement (QC). QC in NSs causes a blue shift of the gap energy with decreasing NS dimension. Directly measuring the effect of QC is complicated by additional parameters, such as stress, interface and defect states. In addition, differences in NS preparation lead to differences in the relevant parameter set. A relatively simple model of QC, using a `particle-in-a-box'-type perturbation to the effective mass theory, was applied to Si and Ge quantum wells, wires and dots across a variety of preparation methods. The choice of the model was made in order to distinguish contributions that are solely due to the effects of QC, where the only varied experimental parameter was the crystallinity. It was found that the hole becomes de-localized in the case of amorphous materials, which leads to stronger confinement effects. The origin of this result was partly attributed to differences in the effective mass between the amorphous and crystalline NS as well as between the electron and hole. Corrections to our QC model take into account a position dependent effective mass. This term includes an inverse length scale dependent on the displacement from the origin. Thus, when the deBroglie wavelength or the Bohr radius of the carriers is on the order of the dimension of the NS the carriers `feel' the confinement potential altering their effective mass. Furthermore, it was found that certain interface states (Si-O-Si) act to pin the hole state, thus reducing the oscillator strength.

Barbagiovanni, Eric G.; Lockwood, David J.; Costa Filho, Raimundo N.; Goncharova, Lyudmila V.; Simpson, Peter J.

2013-10-01

317

Dust ion-acoustic waves in magnetized quantum dusty plasmas with polarity effect  

SciTech Connect

The obliquely propagating two-dimensional quantum dust ion-acoustic solitary waves in a magnetized quantum dusty plasma are studied by using the quantum hydrodynamic model. A linear dispersion relation is obtained using the Fourier analysis, and a nonlinear quantum Zakharov-Kuznetsov equation is derived for small-amplitude perturbations. A stationary solution of this equation is obtained to investigate the effects of quantum corrections, concentration of dust particles, and the angle of propagation on the amplitude, width, and energy of the soliton. The relevance of the present investigation to the astrophysical dusty plasmas is discussed.

Khan, S. A.; Mushtaq, A.; Masood, W. [Department of Physics, COMSATS Institute of Information Technology, Islamabad (Pakistan) and Department of Physics, Government College, Bagh AJK (Pakistan); Theoretical Plasma Physics Division, PINSTECH, P. O. Nilore, Islamabad (Pakistan)

2008-01-15

318

The Josephson Effect as a Probe of Macroscopic Quantum Phenomena  

NASA Astrophysics Data System (ADS)

The aim of this lecture is to give a short survey of the Josephson effect, confining the attention to main recent achievements and some stimulating perspectives.To render the lecture self contained a brief introduction will be given to remind of much aspects of the subject.Although it is always quite difficult to make any claim of novelty for a field which is under the limelight of the scientific community since almost 40 years, the Josephson effect remains a very fashionable subject for both the underlying physics and device applications. Attention will be also payed to its unique role in the investigations of physical phenomena whose interest goes beyond the specific issue of superconductivity. Examples of the Josephson effect as a powerful tool for the investigation of quantum mechanics at a macroscopic level wil be discussed.

Barone, Antonio

2000-09-01

319

Efficient Multi-Dimensional Simulation of Quantum Confinement Effects in Advanced MOS Devices  

NASA Technical Reports Server (NTRS)

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.

Biegel, Bryan A.; Ancona, Mario G.; Rafferty, Conor S.; Yu, Zhiping

2000-01-01

320

In-beam spectroscopy using the JYFL gas-filled magnetic recoil separator RITU  

Microsoft Academic Search

The techniques of recoil-gating and recoil-decay tagging have been employed at Jyväskylä to perform in-beam ?-ray and electron spectroscopy studies of heavy nuclei. The JUROSPHERE ?-ray array and the SACRED electron spectrometer have been placed at the target position of the JYFL gas-filled recoil separator recoil ion transport unit (RITU). The RITU separator has been used to collect the recoils

J. Uusitalo; P. Jones; P. Greenlees; P. Rahkila; M. Leino; A. N. Andreyev; P. A. Butler; T. Enqvist; K. Eskola; T. Grahn; R.-D. Herzberg; F. Hessberger; R. Julin; S. Juutinen; A. Keenan; H. Kettunen; P. Kuusiniemi; A. P. Leppänen; P. Nieminen; R. Page; J. Pakarinen; C. Scholey

2003-01-01

321

Phase transitions and quantum effects in pore condensates: A path integral Monte Carlo study  

Microsoft Academic Search

Lennard-Jones condensates in cylindrical pores are studied by path integral Monte Carlo simulations with particular emphasis on phase transitions and quantum effects. The pore diameter effect and the influence of the interaction strength between the cylinder wall and the adsorbate particles on the structures and the location of the phase boundaries is studied and the quantum effect on the phase

J. Hoffmann; P. Nielaba

2003-01-01

322

Exponential speed-up with a single bit of quantum information: Testing the quantum butterfly effect  

Microsoft Academic Search

We present an efficient quantum algorithm to measure the average fidelity\\u000adecay of a quantum map under perturbation using a single bit of quantum\\u000ainformation. Our algorithm scales only as the complexity of the map under\\u000ainvestigation, so for those maps admitting an efficient gate decomposition, it\\u000aprovides an exponential speed up over known classical procedures. Fidelity\\u000adecay is important

David Poulin; Robin Blume-Kohout; Raymond Laflamme; Harold Ollivier

2003-01-01

323

39Ar and 37Ar recoil loss during neutron irradiation of sanidine and plagioclase  

Microsoft Academic Search

The 40Ar\\/39Ar dating technique requires the activation of 39Ar via neutron irradiation. The energy produced by the reaction is transferred to the daughter atom as kinetic energy and triggers its displacement, known as the recoil effect. Significant amounts of 39Ar and 37Ar can be lost from minerals leading to spurious ages and biased age spectra. Through two experiments, we present

Fred Jourdan; Jennifer P. Matzel; Paul R. Renne

2007-01-01

324

Effects of quasiparticle dissipation on quantum fluctuations in granular superconductors  

SciTech Connect

Quasiparticle dissipation in a granular superconductor is modeled by an effective nearest-neighbor capacitance {Delta}{ital C} between the grains of a superconducting array. Using an expansion in 1/{ital z}, where {ital z} is the number of nearest neighbors in the array, I study the effects of quasiparticle dissipation on the transition temperature and short-range order of a granular superconductor. In agreement with experimental results, quasiparticle dissipation suppresses the quantum fluctuations in a superconducting array. If the self-capacitance of a grain is {ital C}{sub 0}, then both the long-range and the short-range order of the array are enhanced as the ratio {lambda}={ital C}{sub 0}/{ital z}{Delta}{ital C} decreases. In disagreement with other work, the transition temperature is not reentrant for any value of {lambda}. The results of this formalism, which consistently treats quantum fluctuations to first order in 1/{ital z}, should be valid in three-dimensional materials.

Fishman, R.S. (Department of Physics, North Dakota State University, Fargo, ND (USA))

1990-08-01

325

Quantum resonance effects in exchange, photodissociation, and recombination reactions  

SciTech Connect

This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). This project studied quantum resonance effects on chemical reactions. The authors accurate reactive scattering calculations showed that quantum resonance phenomena dominate most chemical reactions and are essential to any real understanding of reactivity. It was found that, as long-lived metastable states of the colliding system, resonances can decay to reactants, products, or a mixture of both. Only the latter contribute to reaction. Conditions under which resonances can be neglected or treated statistically were studied. Important implications about the mechanism of recombination reactions were discovered, and some remarkable effects of geometric phases on the symmetries and energies of resonances were also discovered. Calculations were completed for the reaction H + O{sub 2} {yields} OH + O, which is the rate limiting step in the combustion of all hydrocarbons and the single most important reaction in all of combustion chemistry.

Pack, R.; Kendrick, B.; Kress, J.; Walker, R. [Los Alamos National Lab., NM (United States); Hayes, E. [Ohio State Univ., Columbus, OH (United States); Lagana, A. [Univ. of Perugia (Italy); Parker, G. [Univ. of Oklahoma, Norman, OK (United States); Butcher, E. [Auburn Univ., AL (United States)

1996-04-01

326

The effect of gravitational tidal forces on renormalized quantum fields  

NASA Astrophysics Data System (ADS)

The effect of gravitational tidal forces on renormalized quantum fields propagating in curved spacetime is investigated and a generalisation of the optical theorem to curved spacetime is proved. In the case of QED, the interaction of tidal forces with the vacuum polarization cloud of virtual e + e - pairs dressing the renormalized photon has been shown to produce several novel phenomena. In particular, the photon field amplitude can locally increase as well as decrease, corresponding to a negative imaginary part of the refractive index, in apparent violation of unitarity and the optical theorem. Below threshold decays into e + e - pairs may also occur. In this paper, these issues are studied from the point of view of a non-equilibrium initial-value problem, with the field evolution from an initial null surface being calculated for physically distinct initial conditions and for both scalar field theories and QED. It is shown how a generalised version of the optical theorem, valid in curved spacetime, allows a local increase in amplitude while maintaining consistency with unitarity. The picture emerges of the field being dressed and undressed as it propagates through curved spacetime, with the local gravitational tidal forces determining the degree of dressing and hence the amplitude of the renormalized quantum field. These effects are illustrated with many examples, including a description of the undressing of a photon in the vicinity of a black hole singularity.

Hollowood, Timothy J.; Shore, Graham M.

2012-02-01

327

Effective computation of complex-shaped quantum-dot structures  

NASA Astrophysics Data System (ADS)

The possibility of growing complex-shaped nanodot structures of various material composition allows optimization of certain physical parameters. In the present work, we present effective analytical methods for computing conduction-band eigenstates in quantum-dot structures of complex shape. Comparison with detailed finite-element computations is made. The electronic bandstructure model used is a one-band k\\cdot?c {p} model assuming infinite barriers. Results based on two semi-analytical models are presented. The first model employs geometrical perturbation theory to obtain the quantitative effect of quantum-dot surface perturbations on electron energy levels. Furthermore, the method output includes the level of degeneracy and variations with geometry to be assessed. The second model allows both energy levels and eigenstates to be easily determined for three-dimensional axisymmetrical GaAs structures of varying radius embedded in an AlGaAs matrix by extending a method originally due to Stevenson on electromagnetic waveguide structures (Stevenson in J. Appl. Phys. 22:1447, 1951) to account for electron states. The latter model simplifies the description of a three-dimensional partial-differential equation problem into a small set of ordinary differential equations. For structures with a large aspect ratio, the small set reduces to a single ordinary differential equation yet maintaining high accuracy. A case study is presented to exemplify the models shown.

Lassen, B.; Willatzen, M.

2009-08-01

328

Disorder effects in the quantum Hall effect of graphene p-n junctions  

NASA Astrophysics Data System (ADS)

The quantum Hall effect in graphene p-n junctions is studied numerically with emphasis on the effect of disorder at the interface of two adjacent regions. Conductance plateaus are found to be attached to the intensity of the disorder and are accompanied by universal conductance fluctuations in the bipolar regime, which is in good agreement with theoretical predictions of the random matrix theory on quantum chaotic cavities. The calculated Fano factors can be used in an experimental identification of the underlying transport character.

Li, Jian; Shen, Shun-Qing

2008-11-01

329

Effective interactions and elementary excitations in quantum liquids  

SciTech Connect

The effective interactions which provide a wavevector and frequency dependent restoring force for collective modes in quantum liquids are derived for the helium liquids by means of physical arguments and sum rule and continuity considerations. A simple model is used to take into account mode-mode coupling between collective and multiparticle excitations, and the results for the zero-temperature liquid /sup 4/He phonon-maxon-roton spectrum are shown to compare favorably with experiment and with microscopic calculation. The role played by spin-dependent backflow in liquid /sup 3/He is analyzed, and a physical interpretation of its variation with density and spin-polarization is presented. A progress report is given on recent work on effective interactions and elementary excitations in nuclear matter, with particular attention to features encountered in the latter system which have no counterparts in the helium liquids.

Pines, D.

1986-01-01

330

Electrostatically Shielded Quantum Confined Stark Effect Inside Polar Nanostructures  

PubMed Central

The effect of electrostatic shielding of the polarization fields in nanostructures at high carrier densities is studied. A simplified analytical model, employing screened, exponentially decaying polarization potentials, localized at the edges of a QW, is introduced for the ES-shielded quantum confined Stark effect (QCSE). Wave function trapping within the Debye-length edge-potential causes blue shifting of energy levels and gradual elimination of the QCSE red-shifting with increasing carrier density. The increase in the e?h wave function overlap and the decrease of the radiative emission time are, however, delayed until the “edge-localization” energy exceeds the peak-voltage of the charged layer. Then the wave function center shifts to the middle of the QW, and behavior becomes similar to that of an unbiased square QW. Our theoretical estimates of the radiative emission time show a complete elimination of the QCSE at doping densities ?1020 cm?3, in quantitative agreement with experimental measurements.

2009-01-01

331

Quantum size effects in ?-plutonium (020) surface layers  

NASA Astrophysics Data System (ADS)

We present a systematic first principles density functional theory (DFT) based study of the (020) surface of ?-plutonium using the projector-augmented-wave formalism as implemented in the Vienna Ab Initio Simulation Package (VASP). The surface was modeled by a periodic slab geometry comprised of anti-ferromagnetic atomic layers, with a thickness of up to ten atomic layers. The total and cohesive energies indicate a monotonically decreasing and increasing slope to the bulk values, respectively. The surface energies, in contrast to the work functions, exhibit a significant oscillatory pattern indicating persistent quantum size effects and possible magnetic frustration as well as other effects. The 5f electron density of states indicates progressive delocalization with increasing slab thickness.

Hernandez, S. C.; Ray, A. K.; Taylor, C. D.

2013-10-01

332

Spin effects in coupled quantum dots under ac electric fields  

NASA Astrophysics Data System (ADS)

Spin control has recently attracted attention for applications in spin-based devices. Different effects and applied fields have been suggested to accomplish the goal. We explore the time evolution of electronic spin in coupled quantum dots under harmonic electric fields. Using the Floquet formalism, we obtain the time dependent wave function in terms of the Floquet states and the quasi-energy spectrum for a single electron in double InSb dots. The spatial part of the wave function includes the SIA and BIA spin-orbit effects. The spectral force is analyzed at anti-crossings of the quasi-energy bands as a function of the field strength. The resulting dynamical symmetries and the way they reflect in the time evolution of the spin clouds will be discussed.

Meza-Montes, Lilia; Hernandez, Arezky H.; Ulloa, Sergio E.

2007-03-01

333

Sagnac effect in a chain of mesoscopic quantum rings  

SciTech Connect

The ability to interferometrically detect inertial rotations via the Sagnac effect has been a strong stimulus for the development of atom interferometry because of the potential 10{sup 10} enhancement of the rotational phase shift in comparison to optical Sagnac gyroscopes. Here we analyze ballistic transport of matter waves in a one-dimensional chain of N coherently coupled quantum rings in the presence of a rotation of angular frequency {omega}. We show that the transmission probability, T, exhibits zero transmission stop gaps as a function of the rotation rate interspersed with regions of rapidly oscillating finite transmission. With increasing N, the transition from zero transmission to the oscillatory regime becomes an increasingly sharp function of {omega} with a slope {partial_derivative}T/{partial_derivative}{omega}{approx}N{sup 2}. The steepness of this slope dramatically enhances the response to rotations in comparison to conventional single ring interferometers such as the Mach-Zehnder interferometer and leads to a phase sensitivity well below the quantum shot-noise limit typical of atom interferometers.

Search, Christopher P.; Toland, John R. E.; Zivkovic, Marko [Department of Physics and Engineering Physics, Stevens Institute of Technology, Hoboken, New Jersey 07030 (United States)

2009-05-15

334

Quantum gravity effects at a black hole horizon  

NASA Astrophysics Data System (ADS)

Quantum fluctuations in the background geometry of a black hole are shown to affect the propagation of matter states falling into the black hole in a foliation that corresponds to observations purely outside the horizon. A state that starts as a Minkowski vacuum at past null infinity gets entangled with the gravity sector, so that close to the horizon it can be represented by a statistical ensemble of orthogonal states. We construct an operator connecting the different states and comment on the possible physical meaning of the above construction. The induced energy-momentum tensor of these states is computed in the neighbourhood of the horizon, and it is found that energy-momentum fluctuations become large in the region where the bulk of the Hawking radiation is produced. The background spacetime as seen by an outside observer may be drastically altered in this region, and an outside observer should see significant interactions between the infalling matter and the outgoing Hawking radiation. The boundary of the region of strong quantum gravitational effects is given by a time-like hypersurface of constant Schwarzschild radius $r$ one Planck unit away from the horizon. This boundary hypersurface is an example of a stretched horizon.

Lifschytz, Gilad; Ortiz, Miguel

1995-02-01

335

Quantum effects in a half-polarized pyrochlore antiferromagnet.  

PubMed

We study quantum effects in a spin-3/2 antiferromagnet on the pyrochlore lattice in an external magnetic field, focusing on the vicinity of a plateau in the magnetization at half the saturation value, observed in CdCr2O4 and HgCr2O4. Our theory, based on quantum fluctuations, predicts the existence of a symmetry-broken state on the plateau, even with only nearest-neighbor microscopic exchange. This symmetry-broken state consists of a particular arrangement of spins polarized parallel and antiparallel to the field in a 3:1 ratio on each tetrahedron. It quadruples the lattice unit cell, and reduces the space group from Fd3m to P4(3)32. We also predict that for fields just above the plateau, the low-temperature phase has transverse spin order, describable as a Bose-Einstein condensate of magnons. Other comparisons to and suggestions for experiments are discussed. PMID:16606312

Bergman, Doron L; Shindou, Ryuichi; Fiete, Gregory A; Balents, Leon

2006-03-10

336

Electronic transport and quantum localization effects in organic semiconductors  

NASA Astrophysics Data System (ADS)

We explore the charge transport mechanism in organic semiconductors based on a model that accounts for the thermal intermolecular disorder at work in pure crystalline compounds, as well as extrinsic sources of disorder that are present in current experimental devices. Starting from the Kubo formula, we describe a theoretical framework that relates the time-dependent quantum dynamics of electrons to the frequency-dependent conductivity. The electron mobility is then calculated through a relaxation time approximation that accounts for quantum localization corrections beyond Boltzmann theory, and allows us to efficiently address the interplay between highly conducting states in the band range and localized states induced by disorder in the band tails. The emergence of a “transient localization” phenomenon is shown to be a general feature of organic semiconductors that is compatible with the bandlike temperature dependence of the mobility observed in pure compounds. Carrier trapping by extrinsic disorder causes a crossover to a thermally activated behavior at low temperature, which is progressively suppressed upon increasing the carrier concentration, as is commonly observed in organic field-effect transistors. Our results establish a direct connection between the localization of the electronic states and their conductive properties, formalizing phenomenological considerations that are commonly used in the literature.

Ciuchi, S.; Fratini, S.

2012-12-01

337

Quantum Hall Effect near the charge neutrality point in graphene  

NASA Astrophysics Data System (ADS)

The Quantum Hall effect (QHE) of a two-dimensional (2D) electron gas in a strong magnetic field is one of the most fascinating quantum phenomena discovered in condensed matter physics. In this work we propose to study the transport properties of the single layer and bilayer of graphene at the charge neutrality point (CNP) and compare it with random magnetic model developed in theoretical papers in which we argue that at CNP graphene layer is still inhomogeneous, very likely due to random potential of impurities. The random potential fluctuations induce smooth fluctuations in the local filling factor around ?=0. In this case the transport is determined by special class of trajectories, ``the snake states'', propagating along contour ?=0. The situation is very similar to the transport of a two-dimensional particles moving in a spatially modulated random magnetic field with zero mean value. We especially emphasize that our results may be equally relevant to the composite fermions description of the half-filled Landau level.

Leon, Jorge A.; Gusev, Guennadii M.; Plentz, Flavio O.

2013-03-01

338

Quantum Effects in the Diffusion of Hydrogen on Ru(0001)  

PubMed Central

An understanding of hydrogen diffusion on metal surfaces is important not only for its role in heterogeneous catalysis and hydrogen fuel cell technology but also because it provides model systems where tunneling can be studied under well-defined conditions. Here we report helium spin–echo measurements of the atomic-scale motion of hydrogen on the Ru(0001) surface between 75 and 250 K. Quantum effects are evident at temperatures as high as 200 K, while below 120 K we observe a tunneling-dominated temperature-independent jump rate of 1.9 × 109 s–1, many orders of magnitude faster than previously seen. Quantum transition-state theory calculations based on ab initio path-integral simulations reproduce the temperature dependence of the rate at higher temperatures and predict a crossover to tunneling-dominated diffusion at low temperatures. However, the tunneling rate is underestimated, highlighting the need for future experimental and theoretical studies of hydrogen diffusion on this and other well-defined surfaces.

2013-01-01

339

The quantum transverse-field Ising chain in circuit quantum electrodynamics: effects of disorder on the nonequilibrium dynamics  

NASA Astrophysics Data System (ADS)

We study several dynamical properties of a recently proposed implementation of the quantum transverse-field Ising chain in the framework of circuit quantum electrodynamics (QED). Particular emphasis is placed on the effects of disorder on the nonequilibrium behavior of the system. We show that small amounts of fabrication-induced disorder in the system parameters do not jeopardize the observation of previously predicted phenomena. Based on a numerical extraction of the mean free path of a wave packet in the system, we also provide a simple quantitative estimate for certain disorder effects on the nonequilibrium dynamics of the circuit QED quantum simulator. We discuss the transition from weak to strong disorder, characterized by the onset of Anderson localization of the system's wave functions, and the qualitatively different dynamics it leads to.

Viehmann, Oliver; von Delft, Jan; Marquardt, Florian

2013-03-01

340

Valley-polarized quantum anomalous Hall effect in silicene.  

PubMed

We find theoretically a new quantum state of matter-the valley-polarized quantum anomalous Hall state in silicene. In the presence of Rashba spin-orbit coupling and an exchange field, silicene hosts a quantum anomalous Hall state with Chern number C=2. We show that through tuning the Rashba spin-orbit coupling, a topological phase transition results in a valley-polarized quantum anomalous Hall state, i.e., a quantum state that exhibits the electronic properties of both the quantum valley Hall state (valley Chern number Cv=3) and quantum anomalous Hall state with C=-1. This finding provides a platform for designing dissipationless valleytronics in a more robust manner. PMID:24679320

Pan, Hui; Li, Zhenshan; Liu, Cheng-Cheng; Zhu, Guobao; Qiao, Zhenhua; Yao, Yugui

2014-03-14

341

A path integral Monte Carlo study of liquid neon and the quantum effective pair potential  

Microsoft Academic Search

The path integral Monte Carlo (PIMC) method is used to simulate liquid neon at T=40 K. It is shown that quantum effects are not negligible and that when the quantum effective pair potential is used in a classical molecular dynamics simulation the results obtained for the radial distribution function agrees with that predicted by a full path integral Monte Carlo

D. Thirumalai; Randall W. Hall; B. J. Berne

1984-01-01

342

Unconventional quantum Hall effect and Berry's phase of 2pi in bilayer graphene  

Microsoft Academic Search

There are two known distinct types of the integer quantum Hall effect. One is the conventional quantum Hall effect, characteristic of two-dimensional semiconductor systems, and the other is its relativistic counterpart observed in graphene, where charge carriers mimic Dirac fermions characterized by Berry's phase pi, which results in shifted positions of the Hall plateaus. Here we report a third type

K. S. Novoselov; E. McCann; S. V. Morozov; V. I. Fal'Ko; M. I. Katsnelson; U. Zeitler; D. Jiang; F. Schedin; A. K. Geim

2006-01-01

343

Contacts and edge-state equilibration in the fractional quantum Hall effect  

Microsoft Academic Search

We develop a simple kinetic equation description of edge-state dynamics in the fractional quantum Hall effect (FQHE), which allows us to examine in detail equilibration processes between multiple edge modes. As in the integer quantum Hall effect, intermode equilibration is a prerequisite for quantization of the Hall conductance. Two sources for such equilibration are considered: edge-impurity scattering and equilibration by

C. L. Kane; Matthew P. A. Fisher

1995-01-01

344

Effective Potentials of the Spherical Quantum Dots Modeled by the Spin Density Functional Theory  

Microsoft Academic Search

The novel properties of quantum dots revealed the evolution of the bulk electronic structure with increasing size, which has been calculated using spin density functional theory (SDFT). Both the theoretical and experimental information on spherical quantum dots, that is, physical and chemical properties like effective potential, specific shell structure and the structural relationship are sparse. The interaction effects of the

Manickam Mahendran

2006-01-01

345

Spin effects on the instability and propagation modes of electrostatic plasma waves in quantum plasmas  

SciTech Connect

The effects of the electron spin interaction on the pure instability and propagation modes of the quantum electrostatic waves are investigated in cold quantum electron plasmas. It is found that the influence of the electron spin interaction increases the group velocity of the propagation mode of the quantum electrostatic wave. In addition, it is shown that the electron spin interaction enhances the growth rate of the instability mode of the quantum electrostatic wave. It is also found that the effects of the electron spin interaction would be more important in the domain of small Fermi wave numbers.

Ki, Dae-Han; Jung, Young-Dae [Department of Applied Physics, Hanyang University, Ansan, Kyunggi-Do 426-791 (Korea, Republic of)

2011-09-19

346

Controllable effects of quantum fluctuations on spin free-induction decay at room temperature.  

PubMed

Fluctuations of local fields cause decoherence of quantum objects. Usually at high temperatures, thermal noises are much stronger than quantum fluctuations unless the thermal effects are suppressed by certain techniques such as spin echo. Here we report the discovery of strong quantum-fluctuation effects of nuclear spin baths on free-induction decay of single electron spins in solids at room temperature. We find that the competition between the quantum and thermal fluctuations is controllable by an external magnetic field. These findings are based on Ramsey interference measurement of single nitrogen-vacancy center spins in diamond and numerical simulation of the decoherence, which are in excellent agreement. PMID:22666535

Liu, Gang-Qin; Pan, Xin-Yu; Jiang, Zhan-Feng; Zhao, Nan; Liu, Ren-Bao

2012-01-01

347

Controllable effects of quantum fluctuations on spin free-induction decay at room temperature  

PubMed Central

Fluctuations of local fields cause decoherence of quantum objects. Usually at high temperatures, thermal noises are much stronger than quantum fluctuations unless the thermal effects are suppressed by certain techniques such as spin echo. Here we report the discovery of strong quantum-fluctuation effects of nuclear spin baths on free-induction decay of single electron spins in solids at room temperature. We find that the competition between the quantum and thermal fluctuations is controllable by an external magnetic field. These findings are based on Ramsey interference measurement of single nitrogen-vacancy center spins in diamond and numerical simulation of the decoherence, which are in excellent agreement.

Liu, Gang-Qin; Pan, Xin-Yu; Jiang, Zhan-Feng; Zhao, Nan; Liu, Ren-Bao

2012-01-01

348

The effect of dust size distribution on quantum dust acoustic wave  

SciTech Connect

Based on the quantum hydrodynamics theory, a proposed model for quantum dust acoustic waves (QDAWs) is presented including the dust size distribution (DSD) effect. A quantum version of Zakharov-Kuznetsov equation is derived adequate for describing QDAWs. Two different DSD functions are applied. The relevance of the wave velocity, amplitude, and width to the DSD is investigated numerically. The quantum effect changes only the soliton width. A brief conclusion is presented to the current findings and their relevance to astrophysics data is also discussed.

El-Labany, S. K.; El-Taibany, W. F.; Behery, E. E. [Department of Physics, Faculty of Science, Mansoura University, Damietta Branch, Damietta El-Gedida, P.O. 34517 (Egypt); El-Siragy, N. M. [Department of Physics, Faculty of Science, Tanta University, Tanta, P.O. 31527 (Egypt)

2009-09-15

349

Group velocity of extraordinary waves in superdense magnetized quantum plasma with spin-1/2 effects  

SciTech Connect

Based on the one component plasma model, a new dispersion relation and group velocity of elliptically polarized extraordinary electromagnetic waves in a superdense quantum magnetoplasma are derived. The group velocity of the extraordinary wave is modified due to the quantum forces and magnetization effects within a certain range of wave numbers. It means that the quantum spin-1/2 effects can reduce the transport of energy in such quantum plasma systems. Our work should be of relevance for the dense astrophysical environments and the condensed matter physics.

Li Chunhua; Ren Haijun; Yang Weihong [Department of Modern Physics, University of Science and Technology of China, 230026 Hefei (China); Wu Zhengwei [Department of Modern Physics, University of Science and Technology of China, 230026 Hefei (China); Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon (Hong Kong); Chu, Paul K. [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon (Hong Kong)

2012-12-15

350

Efficient Multi-Dimensional Simulation of Quantum Confinement Effects in Advanced MOS Devices  

NASA Technical Reports Server (NTRS)

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.

Biegel, Bryan A.; Rafferty, Conor S.; Ancona, Mario G.; Yu, Zhi-Ping

2000-01-01

351

Submillisecond Elastic Recoil Reveals Molecular Origins of Fibrin Fiber Mechanics  

PubMed Central

Fibrin fibers form the structural scaffold of blood clots. Thus, their mechanical properties are of central importance to understanding hemostasis and thrombotic disease. Recent studies have revealed that fibrin fibers are elastomeric despite their high degree of molecular ordering. These results have inspired a variety of molecular models for fibrin’s elasticity, ranging from reversible protein unfolding to rubber-like elasticity. An important property that has not been explored is the timescale of elastic recoil, a parameter that is critical for fibrin’s mechanical function and places a temporal constraint on molecular models of fiber elasticity. Using high-frame-rate imaging and atomic force microscopy-based nanomanipulation, we measured the recoil dynamics of individual fibrin fibers and found that the recoil was orders of magnitude faster than anticipated from models involving protein refolding. We also performed steered discrete molecular-dynamics simulations to investigate the molecular origins of the observed recoil. Our results point to the unstructured ?C regions of the otherwise structured fibrin molecule as being responsible for the elastic recoil of the fibers.

Hudson, Nathan E.; Ding, Feng; Bucay, Igal; O'Brien, E. Timothy; Gorkun, Oleg V.; Superfine, Richard; Lord, Susan T.; Dokholyan, Nikolay V.; Falvo, Michael R.

2013-01-01

352

A Black Hole Recoil Candidate in a Nearby Dwarf Galaxy  

NASA Astrophysics Data System (ADS)

We have discovered a potential black hole recoil candidate offset from a nearby dwarf galaxy by 0.8 kpc. The object, is a point source that shows broad Balmer lines and was originally classified as a supernova because of its non-detection in 2005. We however, detect it in recent observations indicating it is still luminous and shows variability over 63 years from DSS, SDSS, and Pan-Starrs data obtained since 1950. The object shows broad Balmer, Fe II, Ca II, and He I lines consistent with classical AGN optical spectra, but offset by 300 km/s from the galaxy redshift. The observed narrow line emission is consistent with originating from host galaxy contamination. Our adaptive optics observations constrain the source size to be smaller than 10 pc, suggesting that all of the emission is coming from an extremely small region. Overall these properties are consistent with theoretical predictions of a runaway black hole caused by general relativistic effects predicted in black hole mergers.

Koss, Michael; Blecha, L.; Mushotzky, R.; Veilleux, S.; Hung, C.; Man, A.; Li, Y.

2014-01-01

353

Quantum confinement and surface-state effects in bismuth nanowires  

NASA Astrophysics Data System (ADS)

Bulk bismuth is an efficient thermoelectric material. Assuming intrinsic conditions, the theory of quantum confinement of bismuth nanowires by Hicks and Dresselhaus predicts a semimetal-to-semiconductor transformation for critical diameters of around 50 nm. For nanowires of diameters below the critical diameter, electronic states can be considered to be one dimensional and therefore the thermopower can be very large. However, angle-resolved photoemission spectroscopy (ARPES) studies of Bi planar surfaces present direct evidence of heavy mass surface states that can inhibit the semimetal-to-semiconductor transformation. We present a study of the Fermi surface of Bi nanowires of diameters ranging between 200 and 30 nm employing the Shubnikov-de Haas method. Our results can be understood in terms of the model of surface states. For 30 nm nanowires we find that the Fermi surface is spherical, that the carriers have high effective mass, and that the number of carriers corresponds to that inferred from ARPES measurements.

Huber, T. E.; Nikolaeva, A.; Gitsu, D.; Konopko, L.; Graf, M. J.

2007-03-01

354

Thermoelectric effects in molecular quantum dots with contacts  

NASA Astrophysics Data System (ADS)

We consider the steady-state thermoelectric transport through a vibrating molecular quantum dot that is contacted to macroscopic leads. For moderate electron-phonon interaction strength and comparable electronic and phononic timescales, we investigate the impact of the formation of a local polaron on the thermoelectric properties of the junction. We apply a variational Lang-Firsov transformation and solve the equations of motion in the Kadanoff-Baym formalism up to second order in the dot-lead coupling parameter. We calculate the thermoelectric current and voltage for finite temperature differences in the resonant and inelastic tunneling regimes. For a near resonant dot level, the formation of a local polaron can boost the thermoelectric effect because of the Franck-Condon blockade. The line shape of the thermoelectric voltage signal becomes asymmetrical due to the varying polaronic character of the dot state and in the nonlinear transport regime, vibrational signatures arise.

Koch, T.; Loos, J.; Fehske, H.

2014-04-01

355

Quantum Anomalous Hall Effect in 2D Organic Topological Insulators  

NASA Astrophysics Data System (ADS)

Quantum anomalous Hall effect (QAHE) is a fundamental transport phenomenon in the field of condensed-matter physics. Without external magnetic field, spontaneous magnetization combined with spin-orbit coupling give rise to a quantized Hall conductivity. So far, a number of theoretical proposals have been made to realize the QAHE, but all based on inorganic materials. Here, using first-principles calculations, we predict a family of 2D organic topological insulators (OTIs) for realizing the QAHE. Designed by assembling molecular building blocks of triphenyl-transition-metal compounds into a hexagonal lattice, this new classes of organic materials are shown to have a nonzero Chern number and exhibit a gapless chiral edge state within the Dirac gap.

Wang, Zhengfei; Liu, Zheng; Liu, Feng

2013-03-01

356

Quantum Anomalous Hall Effect in 2D Organic Topological Insulators  

NASA Astrophysics Data System (ADS)

The quantum anomalous Hall effect (QAHE) is a fundamental transport phenomenon in the field of condensed-matter physics. Without an external magnetic field, spontaneous magnetization combined with spin-orbit coupling gives rise to a quantized Hall conductivity. So far, a number of theoretical proposals have been made to realize the QAHE, but all based on inorganic materials. Here, using first-principles calculations, we predict a family of 2D organic topological insulators for realizing the QAHE. Designed by assembling molecular building blocks of triphenyl-transition-metal compounds into a hexagonal lattice, this new class of organic materials is shown to have a nonzero Chern number and exhibits a gapless chiral edge state within the Dirac gap.

Wang, Z. F.; Liu, Zheng; Liu, Feng

2013-05-01

357

Anatomy of competing quantum effects in liquid water.  

NASA Astrophysics Data System (ADS)

ct- Molecules like water have vibrational modes with zero point energy well above room temperature. As a consequence, classical molecular dynamics simulations of liquid water largely underestimate the kinetic energy of the ions, which translates into an underestimation of covalent interatomic distances. In this work, we show that it is possible to apply generalized Langevin equation with suppressed noise in combination with Nose-Hoover thermostats to achieve an efficient zero-point temperature of independent modes of liquid water. Using this method we deconstruct the competing quantum effects in liquid water. We demonstrate how the structure and dynamical modes of liquid water respond to non-equilibrium distribution of zero point temperatures on the normal modes.

Ramirez, Rafa; Ganeshan, Sriram; Fernandez-Serra, M. V.

2013-03-01

358

Ferromagnetic Kondo effect in a triple quantum dot system.  

PubMed

A simple device of three laterally coupled quantum dots, the central one contacted by metal leads, provides a realization of the ferromagnetic Kondo model, which is characterized by interesting properties like a nonanalytic inverted zero-bias anomaly and an extreme sensitivity to a magnetic field. Tuning the gate voltages of the lateral dots allows us to study the transition from a ferromagnetic to antiferromagnetic Kondo effect, a simple case of a Berezinskii-Kosterlitz-Thouless transition. We model the device by three coupled Anderson impurities that we study by numerical renormalization group. We calculate the single-particle spectral function of the central dot, which at zero frequency is proportional to the zero-bias conductance, across the transition, both in the absence and in the presence of a magnetic field. PMID:23931401

Baruselli, P P; Requist, R; Fabrizio, M; Tosatti, E

2013-07-26

359

The origins of cosmic rays and quantum effects on gravity  

NASA Astrophysics Data System (ADS)

The energy spectrum of primary cosmic rays is explained by particles emitted during a thermal expansion of explosive objects inside and near the galaxy, remnants of which may be supernova and/or active talaxies, or even stars or galaxies that disappeared from our sight after the explosion. A power law energy spectrum for cosmic rays, E to the (-alpha -1, is obtained from an expansion rate T is proportional to R to the alpha. Using the solution of the Einstein equation, we obtain a spectrum which agrees very well with experimental data. The implication of an inflationary early universe on the cosmic ray spectrum is also discussed. It is also suggested that the conflict between this model and the singularity theorem in classical general relativity may be eliminated by quantum effects.

Tomozawa, Y.

1985-08-01

360

Influence of quantum size effects on island coarsening.  

PubMed

Surface x-ray scattering and scanning-tunneling microscopy experiments reveal novel coarsening behavior of Pb nanocrystals grown on Si(111)-(7 x 7). It is found that quantum size effects lead to the breakdown of the classical Gibbs-Thomson analysis. This is manifested by the lack of scaling of the island densities. In addition, island decay times tau are orders of magnitude faster than expected from the classical analysis and have an unusual dependence on the growth flux F (i.e., tau is approximately 1/F). As a result, a highly monodispersed 7-layer island height distribution is found after coarsening if the islands are grown at high rather than low flux rates. These results have important implications, especially at low temperatures, for the controlled growth and self-organization of nanostructures. PMID:16605766

Jeffrey, C A; Conrad, E H; Feng, R; Hupalo, M; Kim, C; Ryan, P J; Miceli, P F; Tringides, M C

2006-03-17

361

Magnetic quantum coherence effect in Ni4 molecular transistors.  

PubMed

We present a theoretical study of electron transport in Ni4 molecular transistors in the presence of Zeeman spin splitting and magnetic quantum coherence (MQC). The Zeeman interaction is extended along the leads which produces gaps in the energy spectrum which allow electron transport with spin polarized along a certain direction. We show that the coherent states in resonance with the spin up or down states in the leads induces an effective coupling between localized spin states and continuum spin states in the single molecule magnet and leads, respectively. We investigate the conductance at zero temperature as a function of the applied bias and magnetic field by means of the Landauer formula, and show that the MQC is responsible for the appearence of resonances. Accordingly, we name them MQC resonances. PMID:24918902

González, Gabriel; Leuenberger, Michael N

2014-07-01

362

Magnetic quantum coherence effect in Ni4 molecular transistors  

NASA Astrophysics Data System (ADS)

We present a theoretical study of electron transport in Ni4 molecular transistors in the presence of Zeeman spin splitting and magnetic quantum coherence (MQC). The Zeeman interaction is extended along the leads which produces gaps in the energy spectrum which allow electron transport with spin polarized along a certain direction. We show that the coherent states in resonance with the spin up or down states in the leads induces an effective coupling between localized spin states and continuum spin states in the single molecule magnet and leads, respectively. We investigate the conductance at zero temperature as a function of the applied bias and magnetic field by means of the Landauer formula, and show that the MQC is responsible for the appearence of resonances. Accordingly, we name them MQC resonances.

González, Gabriel; Leuenberger, Michael N.

2014-07-01

363

Quantum anomalous Hall effect in 2D organic topological insulators.  

PubMed

The quantum anomalous Hall effect (QAHE) is a fundamental transport phenomenon in the field of condensed-matter physics. Without an external magnetic field, spontaneous magnetization combined with spin-orbit coupling gives rise to a quantized Hall conductivity. So far, a number of theoretical proposals have been made to realize the QAHE, but all based on inorganic materials. Here, using first-principles calculations, we predict a family of 2D organic topological insulators for realizing the QAHE. Designed by assembling molecular building blocks of triphenyl-transition-metal compounds into a hexagonal lattice, this new class of organic materials is shown to have a nonzero Chern number and exhibits a gapless chiral edge state within the Dirac gap. PMID:23705732

Wang, Z F; Liu, Zheng; Liu, Feng

2013-05-10

364

Searching for the fractional quantum Hall effect in graphite.  

PubMed

Measurements of basal plane longitudinal rho(b)(B) and Hall rho(H)(B) resistivities were performed on highly oriented pyrolytic graphite samples in a pulsed magnetic field up to B=50 T applied perpendicular to graphene planes, and temperatures 1.5 K30 T and for all studied samples, we observed a sign change in rho(H)(B) from electron- to holelike. For our best quality sample, the measurements revealed the enhancement in rho(b)(B) for B>34 T (T=1.8 K), presumably associated with the field-driven charge density wave or Wigner crystallization transition. In addition, well-defined plateaus in rho(H)(B) were detected in the ultraquantum limit revealing possible signatures of the fractional quantum Hall effect in graphite. PMID:19792390

Kopelevich, Y; Raquet, B; Goiran, M; Escoffier, W; da Silva, R R; Pantoja, J C Medina; Luk'yanchuk, I A; Sinchenko, A; Monceau, P

2009-09-11

365

Spin quantum Hall effects in featureless nonfractionalized spin-1 magnets  

NASA Astrophysics Data System (ADS)

The Affleck-Kennedy-Lieb-Tasaki state (or Haldane phase) in a spin-1 chain represents a large class of gapped topological paramagnets that host symmetry-protected gapless excitations on the boundary. In this work, we show how to realize this type of featureless spin-1 state on a generic two-dimensional lattice. These states have a gapped spectrum in the bulk, but they support gapless edge states protected by spin rotational symmetry along a certain direction, and they exhibit the spin quantum Hall effect. Using a fermion representation of integer spins, we show a concrete example of such spin-1 topological paramagnets on a kagome lattice, and we suggest a microscopic spin-1 Hamiltonian that may realize it.

Lu, Yuan-Ming; Lee, Dung-Hai

2014-05-01

366

Experimental observation of the quantum Hall effect and Berry's phase in graphene  

Microsoft Academic Search

When electrons are confined in two-dimensional materials, quantum-mechanically enhanced transport phenomena such as the quantum Hall effect can be observed. Graphene, consisting of an isolated single atomic layer of graphite, is an ideal realization of such a two-dimensional system. However, its behaviour is expected to differ markedly from the well-studied case of quantum wells in conventional semiconductor interfaces. This difference

Yuanbo Zhang; Yan-Wen Tan; Horst L. Stormer; Philip Kim

2005-01-01

367

Temperature and Magnetic Field Effects on the Transport Controlled Charge State of a Single Quantum Dot  

PubMed Central

Individual InAs/GaAs quantum dots are studied by micro-photoluminescence. By varying the strength of an applied external magnetic field and/or the temperature, it is demonstrated that the charge state of a single quantum dot can be tuned. This tuning effect is shown to be related to the in-plane electron and hole transport, prior to capture into the quantum dot, since the photo-excited carriers are primarily generated in the barrier.

2010-01-01

368

Synthesis of CdSe quantum dots: Effect of surfactant on the photoluminescence property  

Microsoft Academic Search

This paper reports the synthesis of highly lumimescence CdSe quantum dots via wet-chemical process and the study of the surfactant concentration effect on the improvement of the photoluminescence characteristic. Here, we also discussed in detail the quantum dots synthesis procedure and the mechanism for the improvement of the luminescence characteristic of CdSe quantum dots under a different surfactant concentration.

N. A. Bakar; A. A. Umar; T. H. T. Aziz; S. H. Abdullah; M. M. Salleh; M. Yahaya; B. Y. Majlis

2008-01-01

369

Quantum Anomalous Hall Effects and Topological Phase Transitions in Silicene  

NASA Astrophysics Data System (ADS)

Silicene is a monolayer of silicon atoms forming a two-dimensional honeycomb lattice, which is experimentally manufactured this year. The low energy theory is described by Dirac electrons, but they are massive due to a relatively large spin-orbit interaction. I will explain the following properties of silicene: 1) The band structure is controllable by applying an electric field [1]. Silicene undergoes a phase transition from a topological insulator to a band insulator by applying external electric field [1]. 2) The topological phase transition can be detected experimentally by way of diamagnetism [7]. 3) There is a novel circular dichroism and spinvalley selection rules by way of photon absorption [6]. 4) Silicene shows a quantum anomalous Hall effects when ferromagnet is attached onto silicone [3]. 5) Silicene shows a photo-induced quantum Hall effects when we apply strong laser onto silicene [8]. 6) Single Dirac cone state emerges when we apply photo-irradiation and electric field, where the gap is open at the K point and closed at the K' point [8].[4pt] [1] M. Ezawa, New J. Phys. 14, 033003 (2012).[0pt] [2] M. Ezawa, J. Phys. Jpn. 81, 064705 (2012). [0pt] [3] M. Ezawa, Phys. Rev. Lett. 109, 055502 (2012)[0pt] [4] M. Ezawa, Europhysics Letters 98, 67001 (2012).[0pt] [5] M. Ezawa, J. Phys. Soc. Jpn. 81, 104713 (2012).[0pt] [6] M. Ezawa, Phys. Rev. B 86, 161407(R) (2012).[0pt] [7] M. Ezawa, cond-mat/arXiv:1205.6541 (to be published in EPJB).[0pt] [8] M. Ezawa, cond-mat/arXiv:1207.6694.[0pt] [9] M. Ezawa, cond-mat/arXiv: 1209.2580.

Ezawa, Motohiko

2013-03-01

370

CHANDRA HIGH-RESOLUTION OBSERVATIONS OF CID-42, A CANDIDATE RECOILING SUPERMASSIVE BLACK HOLE  

SciTech Connect

We present Chandra High Resolution Camera observations of CID-42, a candidate recoiling supermassive black hole (SMBH) at z = 0.359 in the COSMOS survey. CID-42 shows two optical compact sources resolved in the HST/ACS image embedded in the same galaxy structure and a velocity offset of {approx}1300 km s{sup -1} between the H{beta} broad and narrow emission line, as presented by Civano et al. Two scenarios have been proposed to explain the properties of CID-42: a gravitational wave (GW) recoiling SMBH and a double Type 1/Type 2 active galactic nucleus (AGN) system, where one of the two is recoiling because of slingshot effect. In both scenarios, one of the optical nuclei hosts an unobscured AGN, while the other one, either an obscured AGN or a star-forming compact region. The X-ray Chandra data allow us to unambiguously resolve the X-ray emission and unveil the nature of the two optical sources in CID-42. We find that only one of the optical nuclei is responsible for the whole X-ray unobscured emission observed and a 3{sigma} upper limit on the flux of the second optical nucleus is measured. The upper limit on the X-ray luminosity plus the analysis of the multiwavelength spectral energy distribution indicate the presence of a star-forming region in the second source rather than an obscured SMBH, thus favoring the GW recoil scenario. However, the presence of a very obscured SMBH cannot be fully ruled out. A new X-ray feature, in a SW direction with respect to the main source, is discovered and discussed.

Civano, F.; Elvis, M.; Lanzuisi, G.; Aldcroft, T.; Trichas, M.; Fruscione, A. [Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138 (United States); Bongiorno, A.; Brusa, M. [Max-Planck-Institut fuer extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching (Germany); Blecha, L.; Loeb, A. [Department of Astronomy, Harvard University, 60 Garden Street, Cambridge, MA 02138 (United States); Comastri, A.; Gilli, R. [INAF-Osservatorio Astronomico di Bologna, Via Ranzani 1, Bologna 40127 (Italy); Salvato, M.; Komossa, S. [Max-Planck-Institute for Plasma Physics, Excellence Cluster, Boltzmannstrass 2, 85748 Garching (Germany); Koekemoer, A. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Mainieri, V. [ESO, Karl-Schwarzschild-Strasse 2, 85748 Garching (Germany); Piconcelli, E. [INAF-Osservatorio Astronomico di Roma, Via Frascati 33, Monteporzio-Catone 00040 (Italy); Vignali, C. [Dipartimento di Astronomia, Universita di Bologna, Via Ranzani 1, Bologna 40127 (Italy)

2012-06-10

371

Recoil velocity at second post-Newtonian order for spinning black hole binaries  

SciTech Connect

We compute the flux of linear momentum carried by gravitational waves emitted from spinning binary black holes at second post-Newtonian (2PN) order for generic orbits. In particular we provide explicit expressions of three new types of terms, namely, next-to-leading order spin-orbit terms at 1.5 post-Newtonian (1.5PN) order, spin-orbit tail terms at 2PN order, and spin-spin terms at 2PN order. Restricting ourselves to quasicircular orbits, we integrate the linear-momentum flux over time to obtain the recoil velocity as function of orbital frequency. We find that in the so-called superkick configuration the higher-order spin corrections can increase the recoil velocity up to a factor {approx}3 with respect to the leading-order PN prediction. Whereas the recoil velocity computed in PN theory within the adiabatic approximation can accurately describe the early inspiral phase, we find that its fast increase during the late inspiral and plunge, and the arbitrariness in determining until when it should be trusted, makes the PN predictions for the total recoil not very accurate and robust. Nevertheless, the linear-momentum flux at higher PN orders can be employed to build more reliable resummed expressions aimed at capturing the nonperturbative effects until merger. Furthermore, we provide expressions valid for generic orbits, and accurate at 2PN order, for the energy and angular momentum carried by gravitational waves emitted from spinning binary black holes. Specializing to quasicircular orbits we compute the spin-spin terms at 2PN order in the expression for the evolution of the orbital frequency and found agreement with Mikoczi, Vasuth, and Gergely. We also verified that in the limit of extreme mass ratio our expressions for the energy and angular momentum fluxes match the ones of Tagoshi, Shibata, Tanaka, and Sasaki obtained in the context of black hole perturbation theory.

Racine, Etienne; Buonanno, Alessandra [Maryland Center for Fundamental Physics, Department of Physics, University of Maryland, College Park, Maryland 20742 (United States); Kidder, Larry [Center for Radiophysics and Space Research, Cornell University, Ithaca, New York 14853 (United States)

2009-08-15

372

SIMULATIONS OF RECOILING MASSIVE BLACK HOLES IN THE VIA LACTEA HALO  

SciTech Connect

The coalescence of a massive black hole (MBH) binary leads to the gravitational-wave recoil of the system and its ejection from the galaxy core. We have carried out N-body simulations of the motion of a M{sub BH} = 3.7 x 10{sup 6} M{sub sun} MBH remnant in the 'Via Lactea I' simulation, a Milky Way-sized dark matter halo. The black hole receives a recoil velocity of V{sub kick} = 80, 120, 200, 300, and 400 km s{sup -1} at redshift 1.5, and its orbit is followed for over 1 Gyr within a 'live' host halo, subject only to gravity and dynamical friction against the dark matter background. We show that, owing to asphericities in the dark matter potential, the orbit of the MBH is highly nonradial, resulting in a significantly increased decay timescale compared to a spherical halo. The simulations are used to construct a semi-analytic model of the motion of the MBH in a time-varying triaxial Navarro-Frenk-White dark matter halo plus a spherical stellar bulge, where the dynamical friction force is calculated directly from the velocity dispersion tensor. Such a model should offer a realistic picture of the dynamics of kicked MBHs in situations where gas drag, friction by disk stars, and the flattening of the central cusp by the returning black hole are all negligible effects. We find that MBHs ejected with initial recoil velocities V{sub kick} {approx}> 500 km s{sup -1} do not return to the host center within a Hubble time. In a Milky Way-sized galaxy, a recoiling hole carrying a gaseous disk of initial mass {approx}M{sub BH} may shine as a quasar for a substantial fraction of its 'wandering' phase. The long decay timescales of kicked MBHs predicted by this study may thus be favorable to the detection of off-nuclear quasar activity.

Guedes, J.; Madau, P.; Diemand, J. [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Kuhlen, M. [Institute for Advanced Study, Einstein Drive, Princeton, NJ 08540 (United States); Zemp, M. [Astronomy Department, University of Michigan, Ann Arbor, MI 48109 (United States)

2009-09-10

373

Strong quantum-confined Stark effect from light hole related direct-gap transitions in Ge quantum wells  

NASA Astrophysics Data System (ADS)

A strong quantum-confined Stark effect (QCSE) from light hole related transitions at the ? point (LH1-c?1) in Ge/Si0.15Ge0.85 multiple quantum wells is demonstrated from both photocurrent and optical transmission measurements. Our experimental results show a large and sharp optical absorption peak due to LH1-c?1 transitions, and its associated strong absorption change based on the QCSE. By exploiting LH1-c?1 transitions, optical modulators with improved compactness and competitive extinction ratio and optical loss can be envisioned for low energy chip-scale optical interconnect applications.

Chaisakul, P.; Marris-Morini, D.; Rouifed, M. S.; Frigerio, J.; Isella, G.; Chrastina, D.; Coudevylle, J.-R.; Le Roux, X.; Edmond, S.; Bouville, D.; Vivien, L.

2013-05-01

374

Radiation Effects in Nanostructures: Comparison of Proton Irradiation Induced Changes on Quantum Dots and Quantum Wells  

NASA Technical Reports Server (NTRS)

Successful implementation of technology using self-forming semiconductor Quantum Dots (QDs) has already demonstrated that temperature independent Dirac-delta density of states can be exploited in low current threshold QD lasers and QD infrared photodetectors.

Leon, R.; Swift, G.; Magness, B.; Taylor, W.; Tang, Y.; Wang, K.; Dowd, P.; Zhang, Y.

2000-01-01

375

Quantum effects in non-maximally symmetric spaces  

SciTech Connect

Non-Maximally symmetric spaces provide a more general background to explore the relation between the geometry of the manifold and the quantum fields defined in the manifold than those with maximally symmetric spaces. A static Taub universe is used to study the effect of curvature anisotropy on the spontaneous symmetry breaking of a self-interacting scalar field. The one-loop effective potential on a lambdaphi/sup 4/ field with arbitrary coupling xi is computed by zeta function regularization. For massless minimal coupled scalar fields, first order phase transitions can occur. Keeping the shape invariant but decreasing the curvature radius of the universe induces symmetry breaking. If the curvature radius is held constant, increasing deformation can restore the symmetry. Studies on the higher-dimensional Kaluza-Klein theories are also focused on the deformation effect. Using the dimensional regularization, the effective potential of the free scalar fields in M/sup 4/ x T/sup N/ and M/sup 4/ x (Taub)/sup 3/ spaces are obtained. The stability criterions for the static solutions of the self-consistent Einstein equations are derived. Stable solutions of the M/sup 4/ x S/sup N/ topology do not exist. With the Taub space as the internal space, the gauge coupling constants of SU(2), and U(1) can be determined geometrically. The weak angle is therefore predicted by geometry in this model.

Shen, T.C.

1985-01-01

376

Quantum effects in non-maximally symmetric spaces  

NASA Astrophysics Data System (ADS)

Non-maximally symmetric spaces provide a more general background to explore the relation between the geometry of the manifold and the quantum fields defined in the manifold than those with maximally symmetric spaces. A static Taub universe is used to study the effect of curvature anisotropy on the spontaneous symmetry breaking of a self-interacting scalar field. The one-loop effective potential of lambda phi to the 4th power field with arbitrary coupling Xi is computed by zeta function regularization. We find that for massless minimal coupled scalar field, first order phase transition can occur. Keeping the shape invariant but decreasing the curvature radius of the universe induces symmetry breaking. If the curvature radius is held constant, increasing deformation can restore the symmetry. Studies on the higher-dimensional Kaluza-Klein theories are also focused on the deformation effect. Using the dimensional regularization, the effective potential of the free scalar fields in M4 x Tn and M4 x (taub) to the 3rd power spaces are obtained. The stability criterions for the static solutions of the self-consistent Einstein equations are derived. We find the stable solutions of the M4 x SN topology do not exist. With the Taub space as the internal space, the gauge coupling constants of SU(2), and U(1) can be determined geometrically. The weak angle is therefore predicted by geometry in this model.

Shen, T. C.

1985-12-01

377

Laser-cooled Li for Recoil Ion Momentum Spectroscopy  

NASA Astrophysics Data System (ADS)

The detailed understanding of the dynamics of ionization processes remains a fundamental issue in atomic physics. Recently, a powerful new spectroscopic technique, cold target recoil ion momentum spectroscopy (COLTRIMS), which retains high momentum resolution while achieving almost complete solid angle coverage has been developed. Most studies have used supersonically-cooled inert gas targets to achieve high momentum resolution. We use laser-cooling techniques to introduce new targets. A magneto-optic trap of Li atoms for precision studies of ionization processes using recoil ion momentum spectroscopy has been realized. A simplified loading scheme was used to achieve the Li MOT, resulting in modest densities of order 10^9 atoms/cm^3. Simple methods to increase the trap density, commensurate with the requirement of the stabilizing the trap in the uniform electric field required for ion extraction, are being pursued. Design of the combined MOT-recoil ion spectrometer and initial tests will be described.

Hasegawa, S.; Lu, Z.-T.; Young, L.; Lindsay, M.; Sibener, S. J.

1998-05-01

378

Numerical simulations of a loop quantum cosmos: robustness of the quantum bounce and the validity of effective dynamics  

NASA Astrophysics Data System (ADS)

A key result of isotropic loop quantum cosmology is the existence of a quantum bounce which occurs when the energy density of the matter field approaches a universal maximum close to the Planck density. Though the bounce has been exhibited in various matter models, due to severe computational challenges, some important questions have so far remained unaddressed. These include the demonstration of the bounce for widely spread states, its detailed properties for the states when matter field probes regions close to the Planck volume and the reliability of the continuum effective spacetime description in general. In this manuscript we rigorously answer these questions using the Chimera numerical scheme for the isotropic spatially flat model sourced with a massless scalar field. We show that, as expected from an exactly solvable model, the quantum bounce is a generic feature of states even with a very wide spread, and for those which bounce much closer to the Planck volume. We perform a detailed analysis of the departures from the effective description and find some expected, and some surprising results. At a coarse level of description, the effective dynamics can be regarded as a good approximation to the underlying quantum dynamics unless the states correspond to small scalar field momenta, in which case they bounce closer to the Planck volume or are very widely spread. Quantifying the amount of discrepancy between the quantum and the effective dynamics, we find that the departure between them depends in a subtle and non-monotonic way on the field momentum and different fluctuations. Interestingly, the departures are generically found to be such that the effective dynamics overestimates the spacetime curvature, and underestimates the volume at the bounce.

Diener, Peter; Gupt, Brajesh; Singh, Parampreet

2014-05-01

379

Landau damping and the onset of particle trapping in quantum plasmas  

NASA Astrophysics Data System (ADS)

Using analytical theory and simulations, we assess the impact of quantum effects on non-linear wave-particle interactions in quantum plasmas. We more specifically focus on the resonant interaction between Langmuir waves and electrons, which, in classical plasmas, lead to particle trapping. Two regimes are identified depending on the difference between the time scale of oscillation tB(k)=?m /eEk of a trapped electron and the quantum time scale tq(k)=2m /?k2 related to recoil effect, where E and k are the wave amplitude and wave vector. In the classical-like regime, tB(k) < tq(k), resonant electrons are trapped in the wave troughs and greatly affect the evolution of the system long before the wave has had time to Landau damp by a large amount according to linear theory. In the quantum regime, tB(k) > tq(k), particle trapping is hampered by the finite recoil imparted to resonant electrons in their interactions with plasmons.

Daligault, Jérôme

2014-04-01

380

Quantum-dot gain without inversion: Effects of dark plasmon-exciton hybridization  

NASA Astrophysics Data System (ADS)

We propose an initial-state-dependent quantum-dot gain without population inversion in the vicinity of a resonant metallic nanoparticle. The gain originates from the hybridization of a dark plasmon-exciton and is accompanied by efficient energy transfer from the nanoparticle to the quantum dot. This hybridization of the dark plasmon-exciton, attached to the hybridization of the bright plasmon-exciton, strengthens nonlinear light-quantum emitter interactions at the nanoscale, thus the spectral overlap between the dark and the bright plasmons enhances the gain effect. This hybrid system has potential applications in ultracompact tunable quantum devices.

Zhao, Dongxing; Gu, Ying; Wu, Jiarui; Zhang, Junxiang; Zhang, Tiancai; Gerardot, Brian D.; Gong, Qihuang

2014-06-01

381

Hamiltonian flows, short-time propagators and the quantum Zeno effect  

NASA Astrophysics Data System (ADS)

In a recent paper we have examined the short-time propagator for the Schrödinger equation of a point source. An accurate expression modulo ?t2 for the propagator showed that it was independent of the quantum potential implying that the quantum motion is classical for very short times. In this paper we apply these results to the experiment of Itano, Heinzen, Bollinger and Wineland which demonstrates the quantum Zeno effect in beryllium. We show that the transition is inhibited because the applied continuous wave radiation suppresses the quantum potential necessary for the transition to occur. This shows there is no need to appeal to wave function collapse.

de Gosson, Maurice A.; Hiley, Basil J.

2014-04-01

382

Piezoelectric effect in InAs/InP quantum rod nanowires grown on silicon substrate  

NASA Astrophysics Data System (ADS)

We report on the evidence of a strain-induced piezoelectric field in wurtzite InAs/InP quantum rod nanowires. This electric field, caused by the lattice mismatch between InAs and InP, results in the quantum confined Stark effect and, as a consequence, affects the optical properties of the nanowire heterostructure. It is shown that the piezoelectric field can be screened by photogenerated carriers or removed by increasing temperature. Moreover, a dependence of the piezoelectric field on the quantum rod diameter is observed in agreement with simulations of wurtzite InAs/InP quantum rod nanowire heterostructures.

Anufriev, Roman; Chauvin, Nicolas; Khmissi, Hammadi; Naji, Khalid; Patriarche, Gilles; Gendry, Michel; Bru-Chevallier, Catherine

2014-05-01

383

Elastic Recoil Detection Analysis of FeN thin films.  

PubMed

Thin films of transition metal nitrides are interesting materials due to their special features such as high hardness and chemical inertness. In our present work, we are reporting Elastic Recoil Detection Analysis of FeN/Si system using 100 MeV Au beam. Recoils ions were detected using ?E-E detector telescope. Diffraction pattern of pristine FeN thin films indicates amorphous nature of iron nitride thin film. MOKE results show irradiation can be used for controlling the magnetic properties such as coercivity. PMID:22871447

Dhunna, Renu; Jain, I P; Sahajwalla, Veena

2012-10-01

384

Effective action approach for quantum phase transitions in bosonic lattices  

NASA Astrophysics Data System (ADS)

Based on standard field-theoretic considerations, we develop an effective action approach for investigating quantum phase transitions in lattice Bose systems at arbitrary temperature. We begin by adding to the Hamiltonian of interest a symmetry breaking source term. Using time-dependent perturbation theory, we then expand the grand-canonical free energy as a double power series in both the tunneling and the source term. From here, an order parameter field is introduced in the standard way and the underlying effective action is derived via a Legendre transformation. Determining the Ginzburg-Landau expansion to first order in the tunneling term, expressions for the Mott insulator-superfluid phase boundary, condensate density, average particle number, and compressibility are derived and analyzed in detail. Additionally, excitation spectra in the ordered phase are found by considering both longitudinal and transverse variations of the order parameter. Finally, these results are applied to the concrete case of the Bose-Hubbard Hamiltonian on a three-dimensional cubic lattice, and compared with the corresponding results from mean-field theory. Although both approaches yield the same Mott insulator-superfluid phase boundary to first order in the tunneling, the predictions of our effective action theory turn out to be superior to the mean-field results deeper into the superfluid phase.

Bradlyn, Barry; Dos Santos, Francisco Ednilson A.; Pelster, Axel

2009-01-01

385

Photonic realization of nonlocal memory effects and non-Markovian quantum probes  

NASA Astrophysics Data System (ADS)

The study of open quantum systems is important for fundamental issues of quantum physics as well as for technological applications such as quantum information processing. Recent developments in this field have increased our basic understanding on how non-Markovian effects influence the dynamics of an open quantum system, paving the way to exploit memory effects for various quantum control tasks. Most often, the environment of an open system is thought to act as a sink for the system information. However, here we demonstrate experimentally that a photonic open system can exploit the information initially held by its environment. Correlations in the environmental degrees of freedom induce nonlocal memory effects where the bipartite open system displays, counterintuitively, local Markovian and global non-Markovian character. Our results also provide novel methods to protect and distribute entanglement, and to experimentally quantify correlations in photonic environments.

Liu, Bi-Heng; Cao, Dong-Yang; Huang, Yun-Feng; Li, Chuan-Feng; Guo, Guang-Can; Laine, Elsi-Mari; Breuer, Heinz-Peter; Piilo, Jyrki

2013-05-01

386

Photonic realization of nonlocal memory effects and non-Markovian quantum probes  

PubMed Central

The study of open quantum systems is important for fundamental issues of quantum physics as well as for technological applications such as quantum information processing. Recent developments in this field have increased our basic understanding on how non-Markovian effects influence the dynamics of an open quantum system, paving the way to exploit memory effects for various quantum control tasks. Most often, the environment of an open system is thought to act as a sink for the system information. However, here we demonstrate experimentally that a photonic open system can exploit the information initially held by its environment. Correlations in the environmental degrees of freedom induce nonlocal memory effects where the bipartite open system displays, counterintuitively, local Markovian and global non-Markovian character. Our results also provide novel methods to protect and distribute entanglement, and to experimentally quantify correlations in photonic environments.

Liu, Bi-Heng; Cao, Dong-Yang; Huang, Yun-Feng; Li, Chuan-Feng; Guo, Guang-Can; Laine, Elsi-Mari; Breuer, Heinz-Peter; Piilo, Jyrki

2013-01-01

387

Classical limit of the quantum Zeno effect by environmental decoherence  

NASA Astrophysics Data System (ADS)

We consider a point particle in one dimension initially confined to a finite spatial region whose state is frequently monitored by projection operators onto that region. In the limit of infinitely frequent monitoring, the state never escapes from the region—this is the Zeno effect. In the corresponding classical problem, by contrast, the state diffuses out of the region with the frequent monitoring simply removing probability. The aim of this paper is to show how the Zeno effect disappears in the classical limit in this and similar examples. We give a general argument showing that the Zeno effect is suppressed in the presence of a decoherence mechanism which suppresses interference between histories. We show how this works explicitly in two examples involving projections onto a one-dimensional subspace and identify the key time scales for the process. We extend this understanding to our main problem of interest, the case of a particle in a spatial region, by coupling it to a decohering environment. Smoothed projectors are required to give the problem proper definition and this implies the existence of a momentum cutoff and minimum length scale. We show that the escape rate from the region approaches the classically expected result, and hence the Zeno effect is suppressed, as long as the environmentally induced fluctuations in momentum are sufficiently large. We establish the time scale on which an arbitrary initial state develops sufficiently large fluctuations to satisfy this condition. We link our results to earlier work on the ? ?0 limit of the Zeno effect. We illustrate our results by plotting the probability flux lines for the density matrix (which are equivalent to Bohm trajectories in the pure-state case). These illustrate both the Zeno and anti-Zeno effects very clearly, and their suppression. Our results are closely related to our earlier paper [Phys. Rev. A 88, 022128 (2013), 10.1103/PhysRevA.88.022128], demonstrating the suppression of quantum-mechanical reflection by decoherence.

Bedingham, D.; Halliwell, J. J.

2014-04-01

388

Quantum-mechanical effects on the threshold voltage of ultrathin-SOI nMOSFETs  

Microsoft Academic Search

A theoretical description is given of the dependence of the threshold voltage, VTH, of SOI MOSFETs on a wide range to top silicon layer thickness, ts, using both classical and quantum-mechanical methods. The quantum-mechanical effects become remarkable below the critical thickness and raise VTH with decreasing ts. The classical method cannot be applied in such a thin ts region, since

Yasuhisa Omura; Seiji Horiguchi; Michiharu Tabe; Kenji Kishi

1993-01-01

389

Acceleration of positrons by a relativistic electron beam in the presence of quantum effects  

SciTech Connect

Using the quantum magnetohydrodynamic model and obtaining the dispersion relation of the Cherenkov and cyclotron waves, the acceleration of positrons by a relativistic electron beam is investigated. The Cherenkov and cyclotron acceleration mechanisms of positrons are compared together. It is shown that growth rate and, therefore, the acceleration of positrons can be increased in the presence of quantum effects.

Niknam, A. R. [Laser and Plasma Research Institute, Shahid Beheshti University, G.C., Tehran (Iran, Islamic Republic of)] [Laser and Plasma Research Institute, Shahid Beheshti University, G.C., Tehran (Iran, Islamic Republic of); Aki, H.; Khorashadizadeh, S. M. [Physics Department, Birjand University, Birjand (Iran, Islamic Republic of)] [Physics Department, Birjand University, Birjand (Iran, Islamic Republic of)

2013-09-15

390

Absolute absorption cross sections from photon recoil in a matter-wave interferometer.  

PubMed

We measure the absolute absorption cross section of molecules using a matter-wave interferometer. A nanostructured density distribution is imprinted onto a dilute molecular beam through quantum interference. As the beam crosses the light field of a probe laser some molecules will absorb a single photon. These absorption events impart a momentum recoil which shifts the position of the molecule relative to the unperturbed beam. Averaging over the shifted and unshifted components within the beam leads to a reduction of the fringe visibility, enabling the absolute absorption cross section to be extracted with high accuracy. This technique is independent of the molecular density, it is minimally invasive and successfully eliminates many problems related to photon cycling, state mixing, photobleaching, photoinduced heating, fragmentation, and ionization. It can therefore be extended to a wide variety of neutral molecules, clusters, and nanoparticles. PMID:25014795

Eibenberger, Sandra; Cheng, Xiaxi; Cotter, J P; Arndt, Markus

2014-06-27

391

Quantum Chaotic Environments, the Butterfly Effect, and Decoherence  

NASA Astrophysics Data System (ADS)

We investigate the sensitivity of quantum systems that are chaotic in a classical limit to small perturbations of their equations of motion. This sensitivity, originally studied in the context of defining quantum chaos, is relevant to decoherence when the environment has a chaotic classical counterpart.

Karkuszewski, Zbyszek P.; Jarzynski, Christopher; Zurek, Wojciech H.

2002-10-01

392

Quantum chaotic environments, the butterfly effect, and decoherence.  

PubMed

We investigate the sensitivity of quantum systems that are chaotic in a classical limit to small perturbations of their equations of motion. This sensitivity, originally studied in the context of defining quantum chaos, is relevant to decoherence when the environment has a chaotic classical counterpart. PMID:12398653

Karkusz ewski, Zbys ek P; Jar ynski, Christopher; Zurek, Wojciech H

2002-10-21

393

Quantum Chaotic Environments, the Butterfly Effect, and Decoherence  

Microsoft Academic Search

We investigate the sensitivity of quantum systems that are chaotic in a classical limit to small perturbations of their equations of motion. This sensitivity, originally studied in the context of defining quantum chaos, is relevant to decoherence when the environment has a chaotic classical counterpart.

Zbyszek P. Karkuszewski; Christopher Jarzynski; Wojciech H. Zurek

2002-01-01

394

Quantum Chaotic Environments, the Butterfly Effect, and Decoherence  

Microsoft Academic Search

We investigate the sensitivity of quantum systems that are chaotic in a\\u000aclassical limit, to small perturbations of their equations of motion. This\\u000asensitivity, originally studied in the context of defining quantum chaos, is\\u000arelevant to decoherence in situations when the environment has a chaotic\\u000aclassical counterpart.

Zbyszek P. Karkuszewski; Christopher Jarzynski; Wojciech H. Zurek

2002-01-01

395

Quantum effects in the dynamics of biological systems  

Microsoft Academic Search

The performance of biological sensory systems is shown to reach the quantum limits to measurement, this being true in spite of the high levels of thermal noise associated with operation at phisiological temperatures. Theoretical issues associated with quantum-limited measurement at high temperatures are addressed and strategies for such measurements which make use of active filtering are formulated. Experimental and theoretical

Bialek

1983-01-01

396

Effectiveness of Quantum Operations for Eavesdropping on Sealed Messages.  

National Technical Information Service (NTIS)

A quantum protocol is described which enables a user to send sealed messages and that allows for the detection of active eavesdroppers. We examine a class of eavesdropping strategies, those that make use of quantum operations, and we determine the informa...

P. A. Lopata T. B. Bahder

2007-01-01

397

Magnetic field and symmetry effects in small quantum dots  

NASA Astrophysics Data System (ADS)

Shell phenomena in small quantum dots with a few electrons under a perpendicular magnetic field are discussed within a simple model. It is shown that various kinds of shell structures, which occur at specific values for the magnetic field lead to a disappearance of the orbital magnetization for particular magic numbers for noninteracting electrons in small quantum dots. Including the Coulomb interaction between two electrons, we found that the magnetic field gives rise to dynamical symmetries of a three-dimensional axially symmetric two-electron quantum dot with a parabolic confinement. These symmetries manifest themselves as near-degeneracy in the quantum spectrum at specific values of the magnetic field and are robust at any strength of the electron-electron interaction. A remarkable agreement between experimental data and calculations exhibits the important role of the thickness for the two-electron quantum dot for analysis of ground state transitions in a perpendicular magnetic field.

Nazmitdinov, R. G.

2009-01-01

398

The surface termination effect on the quantum confinement and electron affinities of 3C-SiC quantum dots: a first-principles study  

NASA Astrophysics Data System (ADS)

In light of the established differences between the quantum confinement effect and the electron affinities between hydrogen-passivated C and Si quantum dots, we carried out theoretical investigations on SiC quantum dots, with surfaces uniformly terminated by C-H or Si-H bonds, to explore the role of surface terminations on these two aspects. Surprisingly, it was found that the quantum confinement effect is present (or absent) in the highest occupied (or lowest unoccupied) molecular orbital of the SiC quantum dots regardless of their surface terminations. Thus, the quantum confinement effect related to the energy gap observed experimentally (Phys. Rev. Lett., 2005, 94, 026102) is contributed to by the size-dependence of the highest occupied states; the absence of quantum confinement in the lowest unoccupied states is in contrary to the usual belief based on hydrogen-passivated C quantum dots. However, the cause of the absence of the quantum confinement in C nanodots is not transferable to SiC. We propose a model that provides a clear explanation for all findings on the basis of the nearest-neighbor and next-nearest-neighbor interactions between the valence atomic p-orbital in the frontier occupied/unoccupied states. We also found that the electron affinities of the SiC quantum dots, which closely depend on the surface environments, are negative for the C-H termination and positive for the Si-H termination. The prediction of negative electron affinities in SiC quantum dots by simple C-H termination indicates a promising application for these materials in electron-emitter devices. Our model predicts that GeC quantum dots with hydrogen passivation exhibit similar features to SiC quantum dots and our study confirms the crucial role that the surface environment plays in these nanoscale systems.In light of the established differences between the quantum confinement effect and the electron affinities between hydrogen-passivated C and Si quantum dots, we carried out theoretical investigations on SiC quantum dots, with surfaces uniformly terminated by C-H or Si-H bonds, to explore the role of surface terminations on these two aspects. Surprisingly, it was found that the quantum confinement effect is present (or absent) in the highest occupied (or lowest unoccupied) molecular orbital of the SiC quantum dots regardless of their surface terminations. Thus, the quantum confinement effect related to the energy gap observed experimentally (Phys. Rev. Lett., 2005, 94, 026102) is contributed to by the size-dependence of the highest occupied states; the absence of quantum confinement in the lowest unoccupied states is in contrary to the usual belief based on hydrogen-passivated C quantum dots. However, the cause of the absence of the quantum confinement in C nanodots is not transferable to SiC. We propose a model that provides a clear explanation for all findings on the basis of the nearest-neighbor and next-nearest-neighbor interactions between the valence atomic p-orbital in the frontier occupied/unoccupied states. We also found that the electron affinities of the SiC quantum dots, which closely depend on the surface environments, are negative for the C-H termination and positive for the Si-H termination. The prediction of negative electron affinities in SiC quantum dots by simple C-H termination indicates a promising application for these materials in electron-emitter devices. Our model predicts that GeC quantum dots with hydrogen passivation exhibit similar features to SiC quantum dots and our study confirms the crucial role that the surface environment plays in these nanoscale systems. Electronic supplementary information (ESI) available. See DOI: 10.1039/c2nr12099b

Zhang, Zhenkui; Dai, Ying; Yu, Lin; Guo, Meng; Huang, Baibiao; Whangbo, Myung-Hwan

2012-02-01

399

The effect of quantum confinement on tunneling field-effect transistors with high-? gate dielectric  

NASA Astrophysics Data System (ADS)

In this letter, we study the impact of quantum confinement in double gate tunneling field-effect transistors with different body thicknesses in the presence of high-? gate dielectrics. Although better ON currents have been reported for these devices coming out from semiclassical simulations, the inclusion of quantum effects makes the formerly continuous conduction and valence bands become a discrete set of energy subbands, thus, increasing the effective bandgap, and consequently, reducing the current levels. If the high-? dielectric layer covers both the source and the drain, the band energy structure at the tunneling junction is modified (tunneling widths are increased), hence resulting in performance degradation. An optimal configuration seeking to improve ON currents would require low permittivity dielectrics over S/D regions along with high-? materials under the gates.

Padilla, J. L.; Gámiz, F.; Godoy, A.

2013-09-01

400

Induced spin-accumulation and spin-polarization in a quantum-dot ring by using magnetic quantum dots and Rashba spin-orbit effect  

NASA Astrophysics Data System (ADS)

The effect of magnetic contacts on spin-dependent electron transport and spin-accumulation in a quantum ring, which is threaded by a magnetic flux, is studied. The quantum ring is made up of four quantum dots, where two of them possess magnetic structure and other ones are subjected to the Rashba spin-orbit coupling. The magnetic quantum dots, referred to as magnetic quantum contacts, are connected to two external leads. Two different configurations of magnetic moments of the quantum contacts are considered; the parallel and the anti-parallel ones. When the magnetic moments are parallel, the degeneracy between the transmission coefficients of spin-up and spin-down electrons is lifted and the system can be adjusted to operate as a spin-filter. In addition, the accumulation of spin-up and spin-down electrons in non-magnetic quantum dots are different in the case of parallel magnetic moments. When the intra-dot Coulomb interaction is taken into account, we find that the electron interactions participate in separation between the accumulations of electrons with different spin directions in non-magnetic quantum dots. Furthermore, the spin-accumulation in non-magnetic quantum dots can be tuned in the both parallel and anti-parallel magnetic moments by adjusting the Rashba spin-orbit strength and the magnetic flux. Thus, the quantum ring with magnetic quantum contacts could be utilized to create tunable local magnetic moments which can be used in designing optimized nanodevices.

Eslami, L.; Faizabadi, E.

2014-05-01

401

Effective Gain Measurement in Quantum Cascade Lasers: A new method to measure gain in Quantum Cascade Lasers  

NSDL National Science Digital Library

Gain and Loss are the fundamental factors contributing to laser effectiveness. Simply put, the gain is the light produced by stimulated emission and loss is then the light lost. This can happen if a photon hits an electron in a low energy level state and the electron absorbs the energy and moves to a higher energy level state. It can also happen when light escapes the laser cavity. Lasing is the condition when the gain exceeds the loss. It is very important to know the gain to see how effective your laser really is. The traditional Hakki-Paoli Method was found to be ineffective for measuring gain in quantum cascade lasers. A new, more effective method of measuring gain in quantum cascade lasers was developed and tested.

Haslam, Bryan

2005-08-05

402

Comment on ``Computational approach to the quantum Zeno effect: Position measurements''  

NASA Astrophysics Data System (ADS)

We examine results presented by Fearn and Lamb [Phys. Rev. A 46, 1199 (1992)], who search for, but fail to find, the quantum Zeno effect in measurements of the position of a particle in a double potential well, and criticize the basic statement of the effect given by Misra and Sudarshan [J. Math. Phys. 18, 756 (1977)]. We suggest that position measurements are an inappropriate area to look for the effect; nevertheless, we show that some of the results of Fearn and Lamb should, and do, exhibit a form of weak effect. Though the collapse postulate, as used by Misra and Sudarshan, is not required to discuss quantum measurement and the quantum Zeno effect, its application describes adequately the results of measurement, and we reject the idea that the basic statement of the quantum Zeno effect is flawed.

Home, D.; Whitaker, M. A. B.

1993-09-01

403

Tuning The Properties of Quantum Dots Via The Effective Mass  

NASA Astrophysics Data System (ADS)

In the present work we revisit effective mass theory (EMT) for a semiconductor quantum dot (QD) and employ the BenDaniel-Duke (BDD) boundary condition. In effective mass theory mass mi inside the dot of radius R is different from the mass mo outside the dot. That gives us a crucial factor in determining the electronic spectrum namely ? = mi/m0. We show both by numerical calculations and asymptotic analysis that the ground state energy and the surface charge density, ?(r) can be large. We also show that the dependence of the ground state energy on the radius of the well is infraquadratic. We demonstrate that the significance of BDD condition is pronounced at large R. We also study the dependence of excited state on the radius as well as the difference between energy states. Both exhibit an infra quadratic behavior with radius. The energy difference is important in study of absorption and emission spectra. We find that the BDD condition substantially alters the energy difference. Hence the interpretation of experimental result may need to be reexamined.

Singh, R. A.; Sinha, Abhinav; Pathak, Praveen

2011-07-01

404

Memory Effects in CdSe Nanocrystal Quantum Dots  

NASA Astrophysics Data System (ADS)

Memory effects in the charge transport in arrays of CdSe nanocrystals have been observed and characterized. These semiconducting colloidal quantum dots have previously been shown to demonstrate a non-steady state current transient response to the application of a constant negative source-drain voltage bias. In this study we have shown that CdSe nanocrystals display memory of the voltage pulses applied to them. In particular, for a sequence of two negative voltage pulses, the nanocrystals' response to the second pulse will be dependent on the value and duration of the first pulse. We define the first voltage pulse as the ``write'' step and the second voltage pulse as the ``read'' step. To probe the programmability of the nanocrystals, a range of different write steps were performed and the current transients generated by the read steps were characterized. We have demonstrated the ability to undo the effect of the write steps by either shining band gap light on the nanocrystals or by applying a positive voltage bias; such events are naturally defined as ``erase'' steps. The full write-read-erase cycle demonstrates the potential for the application of CdSe nanocrystals to memory technology and offers new information on the charge transport. * This work is supported by the ONR Young Investigator Award # N000140410489, the American Chemical Society PRF award, and the startup funds at Penn. MF acknowledges funding from the NSF IGERT Program.

Fischbein, Michael

2005-03-01

405

Many-Body Effects in Quantum-Well Intersubband Transitions  

NASA Technical Reports Server (NTRS)

Intersubband polarization couples to collective excitations of the interacting electron gas confined in a semiconductor quantum well (Qw) structure. Such excitations include correlated pair excitations (repellons) and intersubband plasmons (ISPs). The oscillator strength of intersubband transitions (ISBTs) strongly varies with QW parameters and electron density because of this coupling. We have developed a set of kinetic equations, termed the intersubband semiconductor Bloch equations (ISBEs), from density matrix theory with the Hartree-Fock approximation, that enables a consistent description of these many-body effects. Using the ISBEs for a two-conduction-subband model, various many-body effects in intersubband transitions are studied in this work. We find interesting spectral changes of intersubband absorption coefficient due to interplay of the Fermi-edge singularity, subband renormalization, intersubband plasmon oscillation, and nonparabolicity of bandstructure. Our results uncover a new perspective for ISBTs and indicate the necessity of proper many-body theoretical treatment in order for modeling and prediction of ISBT line shape.

Li, Jian-Zhong; Ning, Cun-Zheng

2003-01-01

406

Tuning The Properties of Quantum Dots Via The Effective Mass  

SciTech Connect

In the present work we revisit effective mass theory (EMT) for a semiconductor quantum dot (QD) and employ the BenDaniel-Duke (BDD) boundary condition. In effective mass theory mass m{sub i} inside the dot of radius R is different from the mass m{sub o} outside the dot. That gives us a crucial factor in determining the electronic spectrum namely {beta} = m{sub i}/m{sub 0}. We show both by numerical calculations and asymptotic analysis that the ground state energy and the surface charge density, {rho}(r) can be large. We also show that the dependence of the ground state energy on the radius of the well is infraquadratic. We demonstrate that the significance of BDD condition is pronounced at large R. We also study the dependence of excited state on the radius as well as the difference between energy states. Both exhibit an infra quadratic behavior with radius. The energy difference is important in study of absorption and emission spectra. We find that the BDD condition substantially alters the energy difference. Hence the interpretation of experimental result may need to be reexamined.

Singh, R. A. [Dr. H. S. Gour University, Sagar (M.P.), India 470 002 (India); Sinha, Abhinav [Electrical Engineering Department, IIT Bombay, Mumbai, India 400076 (India); Pathak, Praveen [Homi Bhabha Centre for Science Education (TIFR), V.N. Purav Marg, Mankhurd, Mumbai, India 400088 (India)

2011-07-15

407

Quantum rod-sensitized solar cell: nanocrystal shape effect on the photovoltaic properties.  

PubMed

The effect of the shape of nanocrystal sensitizers in photoelectrochemical cells is reported. CdSe quantum rods of different dimensions were effectively deposited rapidly by electrophoresis onto mesoporous TiO(2) electrodes and compared with quantum dots. Photovoltaic efficiency values of up to 2.7% were measured for the QRSSC, notably high values for TiO(2) solar cells with ex situ synthesized nanoparticle sensitizers. The quantum rod-based solar cells exhibit a red shift of the electron injection onset and charge recombination is significantly suppressed compared to dot sensitizers. The improved photoelectrochemical characteristics of the quantum rods over the dots as sensitizers is assigned to the elongated shape, allowing the build-up of a dipole moment along the rod that leads to a downward shift of the TiO(2) energy bands relative to the quantum rods, leading to improved charge injection. PMID:22452287

Salant, Asaf; Shalom, Menny; Tachan, Zion; Buhbut, Sophia; Zaban, Arie; Banin, Uri

2012-04-11

408

Scintillation response of liquid xenon to low energy nuclear recoils  

SciTech Connect

Liquid Xenon (LXe) is expected to be an excellent target and detection medium to search for dark matter in the form of Weakly Interacting Massive Particles (WIMPs). We have measured the scintillation efficiency of nuclear recoils with kinetic energy between 10.4 and 56.5 keV relative to that of 122 keV gamma rays from {sup 57}Co. The scintillation yield of 56.5 keV recoils was also measured as a function of applied electric field, and compared to that of gamma rays and alpha particles. The Xe recoils were produced by elastic scattering of 2.4 MeV neutrons in liquid xenon at a variety of scattering angles. The relative scintillation efficiency is 0.130{+-}0.024 and 0.227{+-}0.016 for the lowest and highest energy recoils, respectively. This is about 15% less than the value predicted by Lindhard, based on nuclear quenching. Our results are in good agreement with more recent theoretical predictions that consider the additional reduction of scintillation yield due to biexcitonic collisions in LXe.

Aprile, E.; Giboni, K.L.; Majewski, P.; Ni, K.; Yamashita, M.; Hasty, R.; Manzur, A.; McKinsey, D.N. [Physics Department and Astrophysics Laboratory, Columbia University, New York, New York 10027 (United States); Department of Physics, Yale University, P.O. Box 208120, New Haven, Connecticut 06520 (United States)

2005-10-01

409

THE BEHAVIOUR OF RECOIL ATOMS IN IONIC SOLIDS  

Microsoft Academic Search

The rate of escape of Rn²²° from solids containing radiothorium ; depends upon both recoil and diffusion and is steady at any temperature if the ; distribution of radioactive material remains unchanged. At very high ; temperatures the emanating power of ThOâ (and other oxides) increases with ; time at constant temperature; the emanating powertemperature characteristics ; eventually resemble those

J. S. Anderson; D. J. M. Bevan; J. P. Burden

1963-01-01

410

Detection system for the St. George recoil mass separator  

NASA Astrophysics Data System (ADS)

The St. George recoil mass separator is designed for the study of low energy (?,?) reactions of astrophysical interest in inverse kinematics. The energy range of recoils will be 0.07 to 0.9 MeV/nucleon. A detection system is being developed for separating the recoils from the residual scattered beam at the focal plane. The detection system will consist of two position sensitive microchannel plate (MCPs) timing detectors separated by 50cm followed by a single sided silicon strip detector. Simulations were performed using the codes SIMION and GEANT4. Different designs for guiding the secondary electrons emitted from a thin carbon foil to the MCP were studied in the simulations. Good timing and position resolution and minimization of transmission loss due to grids were key factors in selecting the final design. Time of flight will be recorded between the two MCPs. The delay line technique will be used for extracting the position information from the MCPs. The energy of the recoils will be recorded by the Si detector. A dedicated vacuum chamber and the modular design of the detection system will facilitate future improvements and customization for particular experiments.

Kalkal, S.; Hinnefeld, J.; Morales, L.; Robertson, D.; Stech, E.; Berg, G. P. A.; Gorres, J.; Couder, M.; Wiescher, M.

2012-10-01

411

Laser-cooled Li for Recoil Ion Momentum Spectroscopy  

Microsoft Academic Search

The detailed understanding of the dynamics of ionization processes remains a fundamental issue in atomic physics. Recently, a powerful new spectroscopic technique, cold target recoil ion momentum spectroscopy (COLTRIMS), which retains high momentum resolution while achieving almost complete solid angle coverage has been developed. Most studies have used supersonically-cooled inert gas targets to achieve high momentum resolution. We use laser-cooling

S. Hasegawa; Z.-T. Lu; L. Young; M. Lindsay; S. J. Sibener

1998-01-01

412

Effects of a nanoscale silica matrix on the fluorescence quantum yield of encapsulated dye molecules.  

PubMed

The effects that nanometer-sized matrices have on the properties of molecules encapsulated within the nanomatrix are not fully understood. In this work, dye-doped silica nanoparticles were employed as a model for studying the effects of a nanomatrix on the fluorescence quantum yield of encapsulated dye molecules. Two types of dye molecules were selected based on their different responses to the surrounding media. Several factors that affect fluorescence quantum yields were investigated, including aggregation of dye molecules, diffusion of atmospheric oxygen, concentration of dye molecules, and size of the nanomatrix. The results showed that the silica nanomatrix has a varied effect on the fluorescence quantum yield of encapsulated dye molecules, including enhancement, quenching and insignificant changes. Both the properties of dye molecules and the conditions of the nanomatrix played important roles in these effects. Finally, a physical model was proposed to explain the varied nanomatrix effects on the fluorescence quantum yield of encapsulated dye molecules. PMID:23958712

Liang, Song; Shephard, Kali; Pierce, David T; Zhao, Julia Xiaojun

2013-10-01

413

Dimensional hierarchy in quantum Hall effects on fuzzy spheres  

NASA Astrophysics Data System (ADS)

We construct higher-dimensional quantum Hall systems based on fuzzy spheres. It is shown that fuzzy spheres are realized as spheres in colored monopole backgrounds. The space noncommutativity is related to higher spins which is originated from the internal structure of fuzzy spheres. In 2 k-dimensional quantum Hall systems, Laughlin-like wave function supports fractionally charged excitations, q=m ( m is odd). Topological objects are ( 2k-2)-branes whose statistics are determined by the linking number related to the general Hopf map. Higher-dimensional quantum Hall systems exhibit a dimensional hierarchy, where lower-dimensional branes condense to make higher-dimensional incompressible liquid.

Hasebe, Kazuki; Kimura, Yusuke

2004-11-01

414

Design of Magneto Rhenological Recoil Dampers for Fire Out of Battery Control.  

National Technical Information Service (NTIS)

The application of magneto rheological dampers for controlling recoil dynamics is examined, using a recoil demonstrator that includes a 0.50 caliber gun and a MR damper (referred to as 'recoil demonstrator'). Upon providing a brief background on MR damper...

M. Ahmadian

2001-01-01

415

Quantum wavepacket ab initio molecular dynamics: Simulating quantum nuclear effects in complex systems  

NASA Astrophysics Data System (ADS)

A methodology, Quantum Wavepacket Ab Initio Molecular Dynamics (QWAIMD), for the efficient, simultaneous dynamics of electrons and nuclei is presented. This approach allows for the quantum-dynamical treatment of a subset of nuclei in complex, molecular systems while treating the remaining nuclei and electrons within in the ab initio molecular dynamics (AIMD) paradigm. Developments of QWAIMD discussed within include: (a) a novel sampling algorithm dubbed Time-Dependent Deterministic Sampling (TDDS), which increases the computational efficiency by several orders of magnitude; (b) generalizations to hybrid QM/QM and QM/MM electronic structure methods via a combination of the ONIOM and empirical valence bond approaches, which may allow for the accurate simulation of large molecules; and (c) a novel velocity-flux autocorrelation function to calculate the vibrational density-of-states of quantum-classical systems. These techniques are benchmarked on calculations of small, hydrogen-bound clusters. Furthermore, since many chemical processes occur over time-scales inaccessible to computation, a scheme is discussed and benchmarked here which can bias both QWAIMD and classical-AIMD dynamics to sample these long time-scale events, like proton transfer in enzyme catalysis. Finally, hydrogen tunneling in an enzyme, soybean lipoxygenase-1 (SLO-1) is examined by calculating the orbitals (eigenstates) of the transferring proton along the reaction coordinate. This orbital analysis is then supplemented by using quantum measurement theory to reexamine the transfer.

Sumner, Isaiah

416

Quantum-electrodynamics corrections in pionic hydrogen  

SciTech Connect

We investigate all pure quantum-electrodynamics corrections to the np{yields}1s, n=2-4 transition energies of pionic hydrogen larger than 1 meV, which requires an accurate evaluation of all relevant contributions up to order {alpha}{sup 5}. These values are needed to extract an accurate strong interaction shift from experiment. Many small effects, such as second-order and double vacuum polarization contribution, proton and pion self-energies, finite size and recoil effects are included with exact mass dependence. Our final value differs from previous calculations by up to {approx_equal}11 ppm for the 1s state, while a recent experiment aims at a 4 ppm accuracy.

Schlesser, S.; Le Bigot, E.-O.; Indelicato, P. [Laboratoire Kastler Brossel, Ecole Normale Superieure, CNRS, Universite Pierre et Marie Curie-Paris 6, Case 74, 4 place Jussieu, F-75005 Paris (France); Pachucki, K. [Faculty of Physics, University of Warsaw, Hoza 69, PL-00-681 Warsaw (Poland)

2011-07-15

417

The quantum Hall effect at 5/2 filling factor  

NASA Astrophysics Data System (ADS)

Experimental discovery of a quantized Hall state at 5/2 filling factor presented an enigmatic finding in an established field of study that has remained an open issue for more than twenty years. In this review we first examine the experimental requirements for observing this state and outline the initial theoretical implications and predictions. We will then follow the chronology of experimental studies over the years and present the theoretical developments as they pertain to experiments, directed at sets of issues. These topics will include theoretical and experimental examination of the spin properties at 5/2; is the state spin polarized? What properties of the higher Landau levels promote development of the 5/2 state, what other correlation effects are observed there, and what are their interactions with the 5/2 state? The 5/2 state is not a robust example of the fractional quantum Hall effect: what experimental and material developments have allowed enhancement of the effect? Theoretical developments from initial pictures have promoted the possibility that 5/2 excitations are exceptional; do they obey non-abelian statistics? The proposed experiments to determine this and their executions in various forms will be presented: this is the heart of this review. Experimental examination of the 5/2 excitations through interference measurements will be reviewed in some detail, focusing on recent results that demonstrate consistency with the picture of non-abelian charges. The implications of this in the more general physics picture is that the 5/2 excitations, shown to be non-abelian, should exhibit the properties of Majorana operators. This will be the topic of the last review section.

Willett, R. L.

2013-07-01

418

Effective-field-theory model for the fractional quantum Hall effect  

NASA Technical Reports Server (NTRS)

Starting directly from the microscopic Hamiltonian, a field-theory model is derived for the fractional quantum Hall effect. By considering an approximate coarse-grained version of the same model, a Landau-Ginzburg theory similar to that of Girvin (1986) is constructed. The partition function of the model exhibits cusps as a function of density. It is shown that the collective density fluctuations are massive.

Zhang, S. C.; Hansson, T. H.; Kivelson, S.

1989-01-01

419

Interaction effects and quantum phase transitions in topological insulators  

SciTech Connect

We study strong correlation effects in topological insulators via the Lanczos algorithm, which we utilize to calculate the exact many-particle ground-state wave function and its topological properties. We analyze the simple, noninteracting Haldane model on a honeycomb lattice with known topological properties and demonstrate that these properties are already evident in small clusters. Next, we consider interacting fermions by introducing repulsive nearest-neighbor interactions. A first-order quantum phase transition was discovered at finite interaction strength between the topological band insulator and a topologically trivial Mott insulating phase by use of the fidelity metric and the charge-density-wave structure factor. We construct the phase diagram at T=0 as a function of the interaction strength and the complex phase for the next-nearest-neighbor hoppings. Finally, we consider the Haldane model with interacting hard-core bosons, where no evidence for a topological phase is observed. An important general conclusion of our work is that despite the intrinsic nonlocality of topological phases their key topological properties manifest themselves already in small systems and therefore can be studied numerically via exact diagonalization and observed experimentally, e.g., with trapped ions and cold atoms in optical lattices.

Varney, Christopher N. [Department of Physics, Georgetown University, Washington, DC 20057 (United States); Joint Quantum Institute and Department of Physics, University of Maryland, College Park, Maryland 20742 (United States); Sun Kai; Galitski, Victor [Joint Quantum Institute and Department of Physics, University of Maryland, College Park, Maryland 20742 (United States); Condensed Matter Theory Center, Department of Physics, University of Maryland, College Park, Maryland 20742 (United States); Rigol, Marcos [Department of Physics, Georgetown University, Washington, DC 20057 (United States)

2010-09-15

420

Quantum Zeno effect and the impact of flavour in leptogenesis  

NASA Astrophysics Data System (ADS)

In thermal leptogenesis, the cosmic matter antimatter asymmetry is produced by CP violation in the decays N\\to \\ell+\\Phi of heavy right-handed Majorana neutrinos N into ordinary leptons \\ell and Higgs particles ?. If some charged-lepton Yukawa couplings are in equilibrium during the leptogenesis epoch, the \\ell interactions with the background medium are flavour-sensitive and the coherence of their flavour content defined by N\\to \\ell+\\Phi is destroyed, modifying the efficiency of the inverse decays. We point out, however, that it is not enough that the flavour-sensitive processes are fast on the cosmic expansion timescale, they must be fast relative to the N\\leftrightarrow \\ell+\\Phi reactions lest the flavour amplitudes of \\ell remain frozen by the repeated N\\leftrightarrow \\ell+\\Phi 'measurements'. Our more restrictive requirement is significant in the most interesting 'strong wash-out case' where N\\leftrightarrow \\ell+\\Phi is fast relative to the cosmic expansion rate. We derive conditions for the unflavoured treatment to be adequate and for flavour effects to be maximal. In this 'fully flavoured regime' a neutrino mass bound survives. To decide if this bound can be circumvented in the intermediate case, a full quantum kinetic treatment is required.

Blanchet, S.; Di Bari, P.; Raffelt, G. G.

2007-03-01

421

Energy spectrum and quantum Hall effect in twisted bilayer graphene  

NASA Astrophysics Data System (ADS)

We investigate the electronic structure and the quantum Hall effect in twisted bilayer graphenes with various rotation angles in the presence of magnetic field. Using a low-energy approximation, which incorporates the rigorous interlayer interaction, we computed the energy spectrum and the quantized Hall conductivity in a wide range of magnetic field from the semiclassical regime to the fractal spectrum regime. In weak magnetic fields, the low-energy conduction band is quantized into electronlike and holelike Landau levels at energies below and above the van Hove singularity, respectively, and the Hall conductivity sharply drops from positive to negative when the Fermi energy goes through the transition point. In increasing magnetic field, the spectrum gradually evolves into a fractal band structure called Hofstadter's butterfly, where the Hall conductivity exhibits a nonmonotonic behavior as a function of Fermi energy. The typical electron density and magnetic field amplitude characterizing the spectrum monotonically decrease as the rotation angle is reduced, indicating that the rich electronic structure may be observed in a moderate condition.

Moon, Pilkyung; Koshino, Mikito

2012-05-01

422

Effect of laser polarization on quantum electrodynamical cascading  

NASA Astrophysics Data System (ADS)

Development of quantum electrodynamical (QED) cascades in a standing electromagnetic wave for circular and linear polarizations is simulated numerically with a 3D PIC-MC code. It is demonstrated that for the same laser energy the number of particles produced in a circularly polarized field is greater than in a linearly polarized field, though the acquiring mean energy per particle is larger in the latter case. The qualitative model of laser-assisted QED cascades is extended by including the effect of polarization of the field. It turns out that cascade dynamics is notably more complicated in the case of linearly polarized field, where separation into the qualitatively different "electric" and "magnetic" regions (where the electric field is stronger than the magnetic field and vice versa) becomes essential. In the "magnetic" regions, acceleration is suppressed, and moreover the high-energy electrons are even getting cooled by photon emission. The volumes of the "electric" and "magnetic" regions evolve periodically in time and so does the cascade growth rate. In contrast to the linear polarization, the charged particles can be accelerated by circularly polarized wave even in "magnetic region." The "electric" and "magnetic" regions do not evolve in time, and cascade growth rate almost does not depend on time for circular polarization.

Bashmakov, V. F.; Nerush, E. N.; Kostyukov, I. Yu.; Fedotov, A. M.; Narozhny, N. B.

2014-01-01

423

Theory of integer quantum Hall effect in insulating bilayer graphene  

NASA Astrophysics Data System (ADS)

A variational ground state for insulating bilayer graphene (BLG), subject to quantizing magnetic fields, is proposed. Due to the Zeeman coupling, the layer antiferromagnet (LAF) order parameter in fully gapped BLG gets projected onto the spin easy plane, and simultaneously a ferromagnet order, which can further be enhanced by exchange interaction, develops in the direction of the magnetic field. The activation gap for the ? =0 Hall state then displays a crossover from quadratic to linear scaling with the magnetic field, as it gets stronger, and I obtain excellent agreement with a number of recent experiments with realistic strengths for the ferromagnetic interaction. A component of the LAF order, parallel to the external magnetic field, gives birth to additional incompressible Hall states at filling ? =±2, whereas the remote hopping in BLG yields ? =±1 Hall states. Evolution of the LAF order in tilted magnetic fields, scaling of the gap at ? =2, the effect of external electric fields on various Hall plateaus, and different possible hierarchies of fractional quantum Hall states are highlighted.

Roy, Bitan

2014-05-01

424

Effect of disorder on modulated quantum Hall systems  

NASA Astrophysics Data System (ADS)

We present a numerical study of the quantum Hall effect in modulated two-dimensional (2D) electron systems in presence of disorder. Theoretically, it is known that a 2D periodic potential in a strong magnetic field gives rise to a recursive subband structure in Landau levels, which is called the Hofstadter butterfly[1]. Recently, the nonmonotonic behavior of the Hall conductivity peculiar to this system was observed in lateral superlattices patterned on GaAs/AlGaAs heterostructures [2,3]. To study how the Hall plateau emerges in those split Landau levels, we numerically calculate the Hall conductivity in a disordered 2D electron system with weak modulations under various magnetic fields. We investigate the scaling property of the Hall conductivity as well as the localization length, to identify the critical energies where the extended states exist. The dependence on the field amplitudes and the Landau levels is also discussed. [1] D. R. Hofstadter, Phys. Rev. B 14, 2239 (1976). [2] C. Albrecht, et al. Phys. Rev. Lett. 86, 147 (2001) [3] M. C. Geisler, et al., Phys. Rev. Lett. 92, 256801 (2004).

Koshino, Mikito; Ando, Tsuneya

2005-03-01

425

New Precise Method for Accurate Modeling of Thermal Recoil Forces  

NASA Astrophysics Data System (ADS)

The exact modeling of external and internal perturbations acting on spacecraft becomes increasingly important as the scientific requirements become more demanding. Disturbance models included in orbit determination and propagation tools need to be improved to account for the needed accuracy. The simulation of perturbations which are caused by thermal effects are particularly challenging because the optical properties of spacecraft surfaces can change during the mission due to exposure to the space environment. At ZARM (Center of Applied Space Technology and Microgravity) algorithms for the simulation and analysis of thermal perturbations have been developed. These codes include the simulation of the thermal recoil force (waste heat dissipation), Earth Albedo influence as well as Solar radiation pressure. The applied methods are based on the inclusion of the actual spacecraft geometry by means of Finite Element (FE) models in the calculation of the disturbance forces. Thus the modeling accuracy is increased considerably and also housekeeping and sensor data can be included in the calculations. As an application for the developed method a test case model of the Pioneer 11 radio isotopic thermal generators is presented. For accurate thermal modeling the knowledge of optical surface properties and their change during the mission of a spacecraft is crucial. Looking at material behaviour in space, in-situ experiments are indispensable because in ground tests space environment can be simulated only partially. At ZARM a dedicated nano satellite concept has been developed which enables the low cost and repeatable observation of material behaviour in space. The concept consists of a bus cube in the center of the satellite and two experiment cubes attached at the sides which include thermal sensors for the direct measurement of the thermo-optical properties of different materials. The design and the mission will be presented and the impact on thermal modeling will be discussed.

Rievers, Benny; Lämmerzahl, C.

2009-05-01

426

The effect of finite Larmor radius corrections on Jeans instability of quantum plasma  

SciTech Connect

The influence of finite Larmor radius (FLR) effects on the Jeans instability of infinitely conducting homogeneous quantum plasma is investigated. The quantum magnetohydrodynamic (QMHD) model is used to formulate the problem. The contribution of FLR is incorporated to the QMHD set of equations in the present analysis. The general dispersion relation is obtained analytically using the normal mode analysis technique which is modified due to the contribution of FLR corrections. From general dispersion relation, the condition of instability is obtained and it is found that Jeans condition is modified due to quantum effect. The general dispersion relation is reduced for both transverse and longitudinal mode of propagations. The condition of gravitational instability is modified due to the presence of both FLR and quantum corrections in the transverse mode of propagation. In longitudinal case, it is found to be unaffected by the FLR effects but modified due to the quantum corrections. The growth rate of Jeans instability is discussed numerically for various values of quantum and FLR corrections of the medium. It is found that the quantum parameter and FLR effects have stabilizing influence on the growth rate of instability of the system.

Sharma, Prerana [Physics Department, Ujjain Engineering College, Ujjain, Madhya Pradesh 465010 (India)] [Physics Department, Ujjain Engineering College, Ujjain, Madhya Pradesh 465010 (India); Chhajlani, R. K. [School of Studies in Physics, Vikram University Ujjain, Madhya Pradesh 465010 (India)] [School of Studies in Physics, Vikram University Ujjain, Madhya Pradesh 465010 (India)

2013-09-15

427

Young Double Slit Interference Effects at Quantum Level  

NASA Astrophysics Data System (ADS)

The currently accepted model for quantum interference resulting from the emission of electron waves from two scattering centers induced by either light or charged particle impact is analogous to Young's emission of two light waves from two slits. In this work we show that this simple classical wave model is incomplete and that there is a more complicated quantum interference pattern for low energy ionization caused by electron impact.

Ozer, Z. N.; Chaluvadi, H.; Ulu, M.; Dogan, M.; Aktas, B.; Madison, D.

2014-04-01

428

The Effect of Boundaries in One-Loop Quantum Cosmology  

Microsoft Academic Search

The problem of boundary conditions in a supersymmetric theory of quantum cosmology is studied, with application to the one-loop prefactor in the quantum amplitude. Our background cosmological model is flat Euclidean space bounded by a three-sphere, and our calculations are based on the generalized Riemann zeta-function. One possible set of supersymmetric local boundary conditions involves field strengths for spins 1,

Peter D. D'Eath; Giampiero Esposito

1995-01-01

429

Stable switch action based on quantum interference effect  

NASA Astrophysics Data System (ADS)

Although devices working on quantum principles can revolutionize the electronic industry, they have not been achieved yet as it is difficult to control their stability. We show that one can use evanescent modes to build stable quantum switches. The physical principles that make this possible is explained in detail. Demonstrations are given using a multichannel Aharonov-Bohm interferometer. We propose a new S matrix for multichannel junctions to solve the scattering problem.

Mukherjee, Sreemoyee; Yadav, Ashutosh; Singha Deo, P.

2013-01-01

430

Effects of quantum space time foam in the neutrino sector  

Microsoft Academic Search

We discuss violations of CPT and quantum mechanics due to interactions of neutrinos with space-time quantum foam. Neutrinoless\\u000a double beta decay and oscillations of neutrinos from astrophysical sources (supernovae, active galactic nuclei) are analysed.\\u000a It is found that the propagation distance is the crucial quantity entering any bounds on EHNS parameters. Thus, while the\\u000a bounds from neutrinoless double beta decay

H. V. Klapdor-Kleingrothaus; H. Päs; U. Sarkar

2000-01-01

431

Magnetic field and symmetry effects in small quantum dots  

Microsoft Academic Search

Shell phenomena in small quantum dots with a few electrons under a perpendicular magnetic field are discussed within a simple\\u000a model. It is shown that various kinds of shell structures, which occur at specific values for the magnetic field lead to a\\u000a disappearance of the orbital magnetization for particular magic numbers for noninteracting electrons in small quantum dots.\\u000a Including the

R. G. Nazmitdinov

2009-01-01

432

Optimizing hierarchical equations of motion for quantum dissipation and quantifying quantum bath effects on quantum transfer mechanisms.  

PubMed

We present an optimized hierarchical equations of motion theory for quantum dissipation in multiple Brownian oscillators bath environment, followed by a mechanistic study on a model donor-bridge-acceptor system. We show that the optimal hierarchy construction, via the memory-frequency decomposition for any specified Brownian oscillators bath, is generally achievable through a universal pre-screening search. The algorithm goes by identifying the candidates for the best be just some selected Padé spectrum decomposition based schemes, together with a priori accuracy control criterions on the sole approximation, the white-noise residue ansatz, involved in the hierarchical construction. Beside the universal screening search, we also analytically identify the best for the case of Drude dissipation and that for the Brownian oscillators environment without strongly underdamped bath vibrations. For the mechanistic study, we quantify the quantum nature of bath influence and further address the issue of localization versus delocalization. Proposed are a reduced system entropy measure and a state-resolved constructive versus destructive interference measure. Their performances on quantifying the correlated system-environment coherence are exemplified in conjunction with the optimized hierarchical equations of motion evaluation of the model system dynamics, at some representing bath parameters and temperatures. Analysis also reveals the localization to delocalization transition as temperature decreases. PMID:22713032

Ding, Jin-Jin; Xu, Rui-Xue; Yan, YiJing

2012-06-14

433

Optimizing hierarchical equations of motion for quantum dissipation and quantifying quantum bath effects on quantum transfer mechanisms  

NASA Astrophysics Data System (ADS)

We present an optimized hierarchical equations of motion theory for quantum dissipation in multiple Brownian oscillators bath environment, followed by a mechanistic study on a model donor-bridge-acceptor system. We show that the optimal hierarchy construction, via the memory-frequency decomposition for any specified Brownian oscillators bath, is generally achievable through a universal pre-screening search. The algorithm goes by identifying the candidates for the best be just some selected Padé spectrum decomposition based schemes, together with a priori accuracy control criterions on the sole approximation, the white-noise residue ansatz, involved in the hierarchical construction. Beside the universal screening search, we also analytically identify the best for the case of Drude dissipation and that for the Brownian oscillators environment without strongly underdamped bath vibrations. For the mechanistic study, we quantify the quantum nature of bath influence and further address the issue of localization versus delocalization. Proposed are a reduced system entropy measure and a state-resolved constructive versus destructive interference measure. Their performances on quantifying the correlated system-environment coherence are exemplified in conjunction with the optimized hierarchical equations of motion evaluation of the model system dynamics, at some representing bath parameters and temperatures. Analysis also reveals the localization to delocalization transition as temperature decreases.

Ding, Jin-Jin; Xu, Rui-Xue; Yan, YiJing

2012-06-01

434

Role of Localization within the Vortex Picture of the Fractional Quantum Hall Effect.  

National Technical Information Service (NTIS)

Plateau formation in the fractional quantum Hall effect is shown to arise because, by pinning of vortices in the incompressible electron liquid, the canonical filling factor can be stationarily maintained in the interconnected region between the vortices....

H. Bruus O. P. Hansen E. B. Hansen

1988-01-01

435

Quantum ion-acoustic solitary waves: The effect of exchange correlation  

NASA Astrophysics Data System (ADS)

Quantum ion-acoustic solitary waves are studied by considering the effects of exchange and correlation for the electrons. Starting from one-dimensional quantum hydrodynamic equations, including the term of exchange correlation for electrons, we obtain a model in which two dimensionless parameters appear (in addition to the parameter measuring the quantum diffraction) measuring the exchange and the correlation. A new deformed Korteweg-de Vries equation is derived. The effect of exchange and correlation is reflected in the phase speed as well as in the nonlinear and dispersion terms. Its solution shows that the exchange-correlation effects modify the amplitude as well as the width of the weak solitary waves. In the arbitrary amplitude regime, and as may be expected, a pseudopotential analysis shows that the exchange-correlation effects may change the nature (compressive or rarefactive) of the quantum ion-acoustic solitary waves. Our results complement and give new insight into the previously published work on this problem.

Ourabah, Kamel; Tribeche, Mouloud

2013-10-01

436

Electric Field Effect on Optical Absorption of Quantum Confined CdSe Nanoplatelets  

NASA Astrophysics Data System (ADS)

We studied electro-optical effects in 2D quantum confined CdSe nanoplatelets synthesized by colloidal chemistry. They were incorporated into transparent polymeric film sandwiched between two ITO electrodes to which the electric potential has been applied. The electro-optical response in the nanoplatelets has a Stark-like character similar to observed elsewhere for CdSe quantum dots and nanorods. However, the magnitude of the Stark effect in the platelets is of the order of magnitude higher than that in quantum dots or nanorods of an equivalent diameter. The electro-optical response from the nanoplatelets is partially polarized.

Artemyev, M. V.; Prudnikau, A. V.; Ermolenko, M. V.; Gurinovich, L. I.; Gaponenko, S. V.

2013-05-01

437

Is the Quantum Zeno Effect Evolution's Choice for the Avian Compass?  

Microsoft Academic Search

Magnetic-sensitive radical-ion-pair reactions are understood to underlie the\\u000abiochemical magnetic compass used by avian species for navigation.\\u000aRadical-ion-pair reactions were recently shown to manifest a host of\\u000aquantum-information-science effects, like quantum jumps and the quantum Zeno\\u000aeffect. We here show that the quantum Zeno effect immunizes the magnetic and\\u000aangular sensitivity of the avian compass mechanism against the deleterious and

I. K. Kominis

2009-01-01

438

Effect of organic materials used in the synthesis on the emission from CdSe quantum dots  

NASA Astrophysics Data System (ADS)

Quantum-dot nanocrystals have particular optical properties due to the quantum confinement effect and the surface effect. This study focuses on the effect of surface conditions on the emission from quantum dots. The quantum dots prepared with 1-hexadecylamine (HDA) in the synthesis show strong emission while the quantum dots prepared without HDA show weak emission, as well as emission from surface energy traps. The comparison of the X-ray patterns of these two sets of quantum dots reveals that HDA forms a layer on the surface of quantum dot during the synthesis. This surface passivation with a layer of HDA reduces surface energy traps, therefore the emission from surface trap levels is suppressed in the quantum dots synthesized with HDA.

Lee, Jae-Won; Yang, Ho-Soon; Hong, K. S.; Kim, S. M.

2013-12-01

439

Purcell effect on CdSe/ZnSe quantum dots em bedded in pillar microcavities  

NASA Astrophysics Data System (ADS)

We present results on two approaches for placing II-VI quantum dots in resonance with a pillar microcavity. The first approach consists in growing a fully epitaxial structure: a ZnTe 3/2 cavity containing CdTe quantum dots sandwiched between two CdMgTe/CdZnMgTe distributed Bragg reflectors. We observed a strong enhancement of the emission intensity for a dot well located into a 0.9 ?m diameter pillars. More striking results were obtained using CdSe QDs in a /2 ZnSe cavity sandwiched between SiO2/TiO2 Bragg reflectors. We probed the Purcell effect by time-resolved photoluminescence and intensity saturation measurements performed on single quantum dots located in a 1.1 ?m diameter hybrid pillar. A four-fold enhancement of quantum dot spontaneous emission rate is observed for quantum dots in resonance with excited degenerated modes of the pillar.

Robin, I. C.; André, R.; Balocchi, A.; Carayon, S.; Gérard, J. M.; Kheng, K.; Dang, Le Si; Mariette, H.; Moehl, Sebastien; Tinjod, Frank

2005-11-01

440

Quantum Zeno and anti-Zeno effect of a nanomechanical resonator measured by a point contact  

Microsoft Academic Search

The occurrence of either the quantum Zeno effect (QZE) or anti-Zeno effect (AZE) resulting from the short-time behavior of the environment-induced decoherence for quantum Brownian motion (QBM) model has been discussed [S. Maniscalco, J. Piilo, and K. A. Suominen, Phys. Rev. Lett. 97, 130402 (2006)]. We discuss here while the shuttering time period (length) of the frequent observations is changed,

Po-Wen Chen; Dong-Bang Tsai; Philip Bennett

2010-01-01