Journal articles on the topic 'Physics, Low-Temperature, Quantum Simulations, Atomic Physics'
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1
Hinde, Robert J. "QSATS: MPI-driven quantum simulations of atomic solids at zero temperature." Computer Physics Communications 182, no. 11 (November 2011): 2339–49. http://dx.doi.org/10.1016/j.cpc.2011.04.024.
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Obhi, R. J. K., S. W. Schaefer, C. E. Valdivia, J. R. Liu, Z. G. Lu, P. J. Poole, and K. Hinzer. "Indium arsenide single quantum dash morphology and composition for wavelength tuning in quantum dash lasers." Applied Physics Letters 122, no. 5 (January 30, 2023): 051104. http://dx.doi.org/10.1063/5.0133657.
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InAs quantum dot and dash gain media demonstrate performance benefits, such as lower threshold current densities and reduced temperature sensitivity over quantum wells for lasers operating in the C-band telecommunications window. Quantum dashes are of much interest for their higher gain over quantum dots due to an increased density of states. We combine experimental results and simulations to understand how quantum dash morphology and composition can be used to tune the emission wavelengths of these nanoparticles. Atomic force microscopy (AFM) analysis is performed to determine the effect of growth temperature and sublayer type on InAs/InGaAsP/InP nanoparticle morphology and homogeneity. Uncapped InAs nanoparticles grown by CBE on a GaAs sublayer will have dash-like geometries with heights up to 2.36 nm for growth temperatures of 500–540 °C. GaP sublayers will induce taller quantum dots except for a growth temperature of 530 °C, where quantum dashes form. The dimensions extracted from AFM scans are used in conjunction with photoluminescence data to guide parabolic band simulations of an InAs quantum dash with a GaP or GaAs sublayer and InP cap buried within InGaAsP. The calculated emission energy of a buried 30 × 300 nm quantum dash decreases by ∼100 meV for increasing heights from 1.5 to 2.5 nm, or increases by ∼100 meV by addition of 20% phosphorus in the dash and wetting layers. Modifying the quantum dash height and leveraging the As/P intermixing that occurs between the InAs and InP layers are, thus, most effective for wavelength tuning.
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Halimeh, Jad C., Maarten Van Damme, Torsten V. Zache, Debasish Banerjee, and Philipp Hauke. "Achieving the quantum field theory limit in far-from-equilibrium quantum link models." Quantum 6 (December 19, 2022): 878. http://dx.doi.org/10.22331/q-2022-12-19-878.
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Realizations of gauge theories in setups of quantum synthetic matter open up the possibility of probing salient exotic phenomena in condensed matter and high-energy physics, along with potential applications in quantum information and science technologies. In light of the impressive ongoing efforts to achieve such realizations, a fundamental question regarding quantum link model regularizations of lattice gauge theories is how faithfully they capture the quantum field theory limit of gauge theories. Recent work \cite{zache2021achieving} has shown through analytic derivations, exact diagonalization, and infinite matrix product state calculations that the low-energy physics of 1+1D U(1) quantum link models approaches the quantum field theory limit already at small link spin length S. Here, we show that the approach to this limit also lends itself to the far-from-equilibrium quench dynamics of lattice gauge theories, as demonstrated by our numerical simulations of the Loschmidt return rate and the chiral condensate in infinite matrix product states, which work directly in the thermodynamic limit. Similar to our findings in equilibrium that show a distinct behavior between half-integer and integer link spin lengths, we find that criticality emerging in the Loschmidt return rate is fundamentally different between half-integer and integer spin quantum link models in the regime of strong electric-field coupling. Our results further affirm that state-of-the-art finite-size ultracold-atom and NISQ-device implementations of quantum link lattice gauge theories have the real potential to simulate their quantum field theory limit even in the far-from-equilibrium regime.
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Huang, Yang, and Michael Widom. "Vibrational Entropy of Crystalline Solids from Covariance of Atomic Displacements." Entropy 24, no. 5 (April 28, 2022): 618. http://dx.doi.org/10.3390/e24050618.
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The vibrational entropy of a solid at finite temperature is investigated from the perspective of information theory. Ab initio molecular dynamics (AIMD) simulations generate ensembles of atomic configurations at finite temperature from which we obtain the N-body distribution of atomic displacements, ρN. We calculate the information-theoretic entropy from the expectation value of lnρN. At a first level of approximation, treating individual atomic displacements independently, our method may be applied using Debye–Waller B-factors, allowing diffraction experiments to obtain an upper bound on the thermodynamic entropy. At the next level of approximation we correct the overestimation through inclusion of displacement covariances. We apply this approach to elemental body-centered cubic sodium and face-centered cubic aluminum, showing good agreement with experimental values above the Debye temperatures of the metals. Below the Debye temperatures, we extract an effective vibrational density of states from eigenvalues of the covariance matrix, and then evaluate the entropy quantum mechanically, again yielding good agreement with experiment down to low temperatures. Our method readily generalizes to complex solids, as we demonstrate for a high entropy alloy. Further, our method applies in cases where the quasiharmonic approximation fails, as we demonstrate by calculating the HCP/BCC transition in Ti.
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Han, Chuanbing, Huihui Sun, Fudong Liu, Xiangju Zhao, and Zheng Shan. "Computational Simulations of Fabrication of Aluminum-Based Josephson Junctions: Topological Aspects of the Barrier Structure." Entropy 25, no. 2 (January 17, 2023): 182. http://dx.doi.org/10.3390/e25020182.
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Although the performance of qubits has been improved in recent years, the differences in the microscopic atomic structure of the Josephson junctions, the core devices prepared under different preparation conditions, are still underexplored. In this paper, the effects of the oxygen temperature and upper aluminum deposition rate on the topology of the barrier layer in the aluminum-based Josephson junctions have been presented by classical molecular dynamics simulations. We apply a Voronoi tessellation method to characterize the topology of the interface and central regions of the barrier layers. We find that when the oxygen temperature is 573 K and the upper aluminum deposition rate is 4 Å/ps, the barrier has the fewest atomic voids and the most closely arranged atoms. However, if only the atomic arrangement of the central region is considered, the optimal rate of the aluminum deposition is 8 Å/ps. This work provides microscopic guidance for the experimental preparation of Josephson junctions, which helps to improve the performance of qubits and accelerate the practical application of quantum computers.
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Prevenslik, Thomas. "Validity of Molecular Dynamics Heat Transfer by Quantum Mechanics." Advanced Materials Research 829 (November 2013): 803–7. http://dx.doi.org/10.4028/www.scientific.net/amr.829.803.
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MD is commonly used in computational physics to determine the atomic response of nanostructures. MD stands for molecular dynamics. With theoretical basis in statistical mechanics, MD relates the thermal energy of the atom to its momentum by the equipartition theorem. Momenta of atoms are derived by solving Newtons equations with inter-atomic forces derived by Lennard-Jones or L-J potentials. MD implicitly assumes the atom always has heat capacity as otherwise the momenta of the atoms cannot be related to their temperature. In bulk materials, the continuum is simulated by imposing PBC on an ensemble of atoms, the atoms always having heat capacity. PBC stands for periodic boundary conditions. MD simulations of the bulk are therefore valid because atoms in the bulk do indeed have heat capacity. Nanostructures differ. Unlike the continuum, the atom confined in discrete submicron structures is precluded by QM from having the heat capacity necessary to conserve absorbed EM energy by an increase in temperature. QM stands for quantum mechanics and EM for electromagnetic. Quantum corrections of MD solutions that would show the heat capacity of nanostructures vanishes are not performed. What this means is the MD simulations of discrete nanostructures published in the literature not only have no physical meaning, but are knowingly invalid by QM. In the alternative, conservation of absorbed EM energy is proposed to proceed by the creation of QED induced non-thermal EM radiation at the TIR frequency of the nanostructure. QED stands for quantum electrodynamics and TIR for total internal reflection. QED radiation creates excitons (holon and electron pairs) that upon recombination produce EM radiation that charges the nanostructure or is lost to the surroundings a consequence only possible by QM as charge is not created in statistical mechanics. Valid and invalid MD simulations from the literature are illustrated with nanofluids and nanocars, respectively. Finally, valid and invalid MD solutions for the stiffening of NWs in tensile tests are presented to illustrate the unphysical findings if QM is ignored at the nanoscale. NW stands for nanowire.
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Boudjemaa, Abdelaali, Karima Abbas, and Nadia Guebli. "Ultradilute Quantum Droplets in the Presence of Higher-Order Quantum Fluctuations." Atoms 10, no. 2 (June 17, 2022): 64. http://dx.doi.org/10.3390/atoms10020064.
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We investigate the effects of higher-order quantum fluctuations on the bulk properties of self-bound droplets in three-, two- and one-dimensional binary Bose mixtures using the Hartree–Fock–Bogoliubov theory. We calculate higher-order corrections to the equation of state of the droplet at both zero and finite temperatures. We show that our results for the ground-state energy are in a good agreement with recent quantum Monte Carlo simulations in any dimension. Our study extends to the finite temperature case where it is found that thermal fluctuations may destabilize the droplet state and eventually destroy it. In two dimensions, we reveal that the droplet occurs at temperatures well below the Berezinskii–Kosterlitz–Thouless transition temperature.
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Shchesnovich, Valery. "Distinguishing noisy boson sampling from classical simulations." Quantum 5 (March 29, 2021): 423. http://dx.doi.org/10.22331/q-2021-03-29-423.
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Giving a convincing experimental evidence of the quantum supremacy over classical simulations is a challenging goal. Noise is considered to be the main problem in such a demonstration, hence it is urgent to understand the effect of noise. Recently found classical algorithms can efficiently approximate, to any small error, the output of boson sampling with finite-amplitude noise. In this work it is shown analytically and confirmed by numerical simulations that one can efficiently distinguish the output distribution of such a noisy boson sampling from the approximations accounting for low-order quantum multiboson interferences, what includes the mentioned classical algorithms. The number of samples required to tell apart the quantum and classical output distributions is strongly affected by the previously unexplored parameter: density of bosons, i.e., the ratio of total number of interfering bosons to number of input ports of interferometer. Such critical dependence is strikingly reminiscent of the quantum-to-classical transition in systems of identical particles, which sets in when the system size scales up while density of particles vanishes.
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Siberchicot, Bruno, and Jean Clérouin. "An Equation of State of Amorphous β-Boron under High Pressure." Solid State Phenomena 172-174 (June 2011): 1220–21. http://dx.doi.org/10.4028/www.scientific.net/ssp.172-174.1220.
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Beyond 100 GPa at ambient temperature, β-boron exhibits an amorphization [1]. This paper presents Quantum Molecular Dynamics simulations of the equation of state (EoS) of amorphous boron under pressure.
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Gerodias, Kit M., Maria Victoria Carpio Bernido, and Christopher C. Bernido. "Resonant tunneling in natural photosynthetic systems." Physica Scripta 96, no. 12 (December 1, 2021): 125038. http://dx.doi.org/10.1088/1402-4896/ac3c58.
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Abstract The high internal quantum efficiency observed in higher plants remains an outstanding problem in understanding photosynthesis. Several approaches such as quantum entanglement and quantum coherence have been explored. However, none has yet drawn an analogy between superlattices and the geometrical structure of granal thylakoids in leaves. In this paper, we calculate the transmission coefficients and perform numerical simulations using the parameters relevant to a stack of thylakoid discs. We then show that quantum resonant tunneling can occur at low effective mass of particles for 680 nm and 700 nm incident wavelengths corresponding to energies at which photosynthesis occurs.
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Shu, Zhan, Junjie Qiao, Qi Yang, Yijia Song, Dazhi Wang, and Qing Xiong. "In situ probing of atmospheric-pressure warm air glow discharge for nitrogen fixation by multiple laser spectroscopies." Plasma Sources Science and Technology 32, no. 2 (February 1, 2023): 025009. http://dx.doi.org/10.1088/1361-6595/acb592.
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Abstract The fixation of atmospheric nitrogen into valuable compounds through reactive plasma processes has attracted intense interests due to its easy operation and compatibility with distributed renewable energy sources. However, practical implementation of plasma-assisted nitrogen fixation is hampered because of its relatively low throughput, which is dominantly limited by the unclear underlying mechanisms. In this study, effort was focused on the in situ production of key species in a DC-driven warm air glow discharge at atmospheric pressure with the help of advanced laser spectroscopic diagnostics. Laser Rayleigh scattering was applied to determine the gas temperature distribution in the discharge column. And mid-infrared quantum cascade laser absorption spectroscopy and one/two-photon absorption laser-induced fluorescence were performed on molecular nitric oxide (NO), atomic oxygen and nitrogen (O, N) for their absolute densities in the discharge. It is found that the spatial distributions of gas temperature, O and N atoms show peaks in the hot discharge center. In contrast, a hollow ‘doughnut’ shape characterized by the NO molecule was observed, particularly under conditions of high discharge current but low airflow rate. The steady-state simulation shows that the hollow pattern of NO is dominantly induced by the radial diffusion of species due to the steep spatial gradient of gas temperature in the discharge cross-section. Moreover, the reverse conversion by atomic N leads to a negative effect on the NO synthesis, especially at the discharge center where the N density and gas temperature are high. From the steady-state modeling, a similar hollow distribution of NO2 was depicted in the air glow discharge. These results demonstrate the strong dependence on atomic O for the major formation process of NO, and the importance of suppressing the reverse paths dominated by atomic N for higher NO production in the studied warm air plasma.
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Nomura, Junia, Tomohiko Momma, Yuki Kojima, Yusuke Hisai, Takumi Kobayashi, Daisuke Akamatsu, and Feng-Lei Hong. "Direct loading of Yb atoms into a 3D magneto-optical trap from a dispenser atomic source." AIP Advances 13, no. 2 (February 1, 2023): 025361. http://dx.doi.org/10.1063/5.0140774.
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The realization of cold atoms using a compact and low-power-consumption experimental setup is indispensable for cold atom experiments, including optical clocks and quantum simulations. We demonstrate the direct loading of Yb atoms into a 3D magneto-optical trap (MOT) from a dispenser atomic source without using a Zeeman slower. The power consumption of the dispenser was ∼3 W. Spectroscopy of the atomic beam from the dispenser on the 6s2 1S0–6s6p 1P1 Yb transition at 399 nm shows that the flux of the atomic beam reaches 1.4 × 1013 s−1 cm−2. We can load up to 4.1 × 107 atoms into the MOT with slowing and trapping laser powers of 20.3 and 35.0 mW, respectively. The realized cold atom system is reliable and can be adapted for experiments on alkaline earth and other alkaline earth-like atoms.
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Karpa, Leon. "Interactions of Ions and Ultracold Neutral Atom Ensembles in Composite Optical Dipole Traps: Developments and Perspectives." Atoms 9, no. 3 (July 4, 2021): 39. http://dx.doi.org/10.3390/atoms9030039.
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Ion–atom interactions are a comparatively recent field of research that has drawn considerable attention due to its applications in areas including quantum chemistry and quantum simulations. In first experiments, atomic ions and neutral atoms have been successfully overlapped by devising hybrid apparatuses combining established trapping methods, Paul traps for ions and optical or magneto-optical traps for neutral atoms, respectively. Since then, the field has seen considerable progress, but the inherent presence of radiofrequency (rf) fields in such hybrid traps was found to have a limiting impact on the achievable collision energies. Recently, it was shown that suitable combinations of optical dipole traps (ODTs) can be used for trapping both atoms and atomic ions alike, allowing to carry out experiments in absence of any rf fields. Here, we show that the expected cooling in such bichromatic traps is highly sensitive to relative position fluctuations between the two optical trapping beams, suggesting that this is the dominant mechanism limiting the currently observed cooling performance. We discuss strategies for mitigating these effects by using optimized setups featuring adapted ODT configurations. This includes proposed schemes that may mitigate three-body losses expected at very low temperatures, allowing to access the quantum dominated regime of interaction.
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Zhang, Ya, Yuan-Hong Song, Yong-Tao Zhao, and You-Nian Wang. "Two-dimensional quantum hydrodynamic model for the heating of a solid target using a Gaussian cluster." Laser and Particle Beams 30, no. 4 (October 29, 2012): 671–77. http://dx.doi.org/10.1017/s0263034612000559.
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AbstractThis paper presents numerical simulations to study the heating of a two-dimensional (2D) solid target under an ion cluster interaction. 2D quantum hydrodynamic (QHD) model is employed for the heating of solid target to warm dense matter on a picosecond time scale. A Gaussian cluster is used to uniformly heat the solid target to a temperature of several eV. The density and temperature of the target are calculated by a full self-consistent treatment of the QHD formalisms and the Poisson's equation. The technique described in this paper provides a method for creating uniformly heated strongly coupled plasma states.
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Warshel, Arieh, and William W. Parson. "Dynamics of biochemical and biophysical reactions: insight from computer simulations." Quarterly Reviews of Biophysics 34, no. 4 (November 2001): 563–679. http://dx.doi.org/10.1017/s0033583501003730.
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1. Introduction 5632. Obtaining rate constants from molecular-dynamics simulations 5642.1 General relationships between quantum electronic structures and reaction rates 5642.2 The transition-state theory (TST) 5692.3 The transmission coefficient 5723. Simulating biological electron-transfer reactions 5753.1 Semi-classical surface-hopping and the Marcus equation 5753.2 Treating quantum mechanical nuclear tunneling by the dispersed-polaron/spin-boson method 5803.3 Density-matrix treatments 5833.4 Charge separation in photosynthetic bacterial reaction centers 5844. Light-induced photoisomerizations in rhodopsin and bacteriorhodopsin 5965. Energetics and dynamics of enzyme reactions 6145.1 The empirical-valence-bond treatment and free-energy perturbation methods 6145.2 Activation energies are decreased in enzymes relative to solution, often by electrostatic effects that stabilize the transition state 6205.3 Entropic effects in enzyme catalysis 6275.4 What is meant by dynamical contributions to catalysis? 6345.5 Transmission coefficients are similar for corresponding reactions in enzymes and water 6365.6 Non-equilibrium solvation effects contribute to catalysis mainly through Δg[Dagger], not the transmission coefficient 6415.7 Vibrationally assisted nuclear tunneling in enzyme catalysis 6485.8 Diffusive processes in enzyme reactions and transmembrane channels 6516. Concluding remarks 6587. Acknowledgements 6588. References 658Obtaining a detailed understanding of the dynamics of a biochemical reaction is a formidable challenge. Indeed, it might appear at first sight that reactions in proteins are too complex to analyze microscopically. At room temperature, even a relatively small protein can have as many as 1034 accessible conformational states (Dill, 1985). In many cases, however, we have detailed structural information about the active site of an enzyme, whereas such information is missing for corresponding chemical systems in solution. The atomic coordinates of the chromophore in bacteriorhodopsin, for example, are known to a resolution of 1–2 Å. In addition, experimental studies of biological processes such as photoisomerization and electron transfer have provided a wealth of detailed information that eventually may make some of these processes classical problems in chemical physics as well as biology.
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Wen, Boyu, and Dayan Ban. "Theoretical Study of Quasi One-Well Terahertz Quantum Cascade Laser." Photonics 9, no. 4 (April 9, 2022): 247. http://dx.doi.org/10.3390/photonics9040247.
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Developing a high-temperature terahertz (THz) quantum cascade laser (QCL) has been one of the major challenges in the THz QCL field over recent decades. The maximum lasing temperature of THz QCLs has gradually been increased, arguably by shortening the length of repeating periods of the quantum structure in the device’s active region from 7 wells/14 layers to 2 wells/4 layers per period. The current highest operating temperature of 250 K was achieved in a two-well direct-phonon design. In this paper, we propose a potential and promising novel quantum design scheme named the quasi one-well (Q1W) design, in which each quantum cascade period consists of only three semiconductor layers. This design is the narrowest of all existing THz QCL structures to date. We explore a series of the Q1W designs using the non-equilibrium green function (NEGF) and rate-equation (RE) models. Both models show that the Q1W designs exhibit the potential to achieve sufficient optical gain with low-temperature sensitivity. Our simulation results suggest that this novel Q1W scheme may potentially lead to relatively less temperature-sensitive THz QCLs. The thickness of the Q1W scheme is less than 20 nm per period, which is the narrowest of the reported THz QCL schemes.
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Tong, Yu, Victor V. Albert, Jarrod R. McClean, John Preskill, and Yuan Su. "Provably accurate simulation of gauge theories and bosonic systems." Quantum 6 (September 22, 2022): 816. http://dx.doi.org/10.22331/q-2022-09-22-816.
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Quantum many-body systems involving bosonic modes or gauge fields have infinite-dimensional local Hilbert spaces which must be truncated to perform simulations of real-time dynamics on classical or quantum computers. To analyze the truncation error, we develop methods for bounding the rate of growth of local quantum numbers such as the occupation number of a mode at a lattice site, or the electric field at a lattice link. Our approach applies to various models of bosons interacting with spins or fermions, and also to both abelian and non-abelian gauge theories. We show that if states in these models are truncated by imposing an upper limit Λ on each local quantum number, and if the initial state has low local quantum numbers, then an error at most ϵ can be achieved by choosing Λ to scale polylogarithmically with ϵ−1, an exponential improvement over previous bounds based on energy conservation. For the Hubbard-Holstein model, we numerically compute a bound on Λ that achieves accuracy ϵ, obtaining significantly improved estimates in various parameter regimes. We also establish a criterion for truncating the Hamiltonian with a provable guarantee on the accuracy of time evolution. Building on that result, we formulate quantum algorithms for dynamical simulation of lattice gauge theories and of models with bosonic modes; the gate complexity depends almost linearly on spacetime volume in the former case, and almost quadratically on time in the latter case. We establish a lower bound showing that there are systems involving bosons for which this quadratic scaling with time cannot be improved. By applying our result on the truncation error in time evolution, we also prove that spectrally isolated energy eigenstates can be approximated with accuracy ϵ by truncating local quantum numbers at Λ=polylog(ϵ−1).
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ZUBOV, V. I., J. F. SANCHEZ, N. P. TRETIAKOV, and A. E. YUSEF. "SELF-CONSISTENT THEORY OF ELASTIC PROPERTIES OF STRONGLY ANHARMONIC CRYSTALS I: GENERAL TREATMENT AND COMPARISON WITH COMPUTER SIMULATIONS AND EXPERIMENT FOR FCC CRYSTALS." International Journal of Modern Physics B 09, no. 07 (March 30, 1995): 803–17. http://dx.doi.org/10.1142/s0217979295000318.
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Based on the correlative method of an unsymmetrized self-consistent field,16–23 we have derived expressions for elastic constant tensors of strongly anharmonic crystals of cubic symmetry. Each isothermal elastic constant consists of four terms. The first one is the zeroth approximation containing the main anharmonicity (up to the fourth order). The second term is the quantum correction. It is important at temperatures below the De-bye characteristic temperature. Finally, the third and fourth terms are the perturbation theory corrections which take into account the influence of the correlations in atomic displacements from the lattice points and that of the high-order anharmonicity respectively. These corrections appear to be small up to the melting temperatures. It is sufficient for a personal computer to perform all our calculations with just a little computer time. A comparison with certain Monte Carlo simulations and with experimental data for Ar and Kr is made. For the most part, our results are between. The quasi-harmonic approximation fails at high temperatures, confirming once again the crucial role of strong anharmonicity.
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NARDI, ERAN, DIMITRI V. FISHER, MARKUS ROTH, ABEL BLAZEVIC, and DIETER H. H. HOFFMANN. "Charge state of Zn projectile ions in partially ionized plasma: Simulations." Laser and Particle Beams 24, no. 1 (March 2006): 131–41. http://dx.doi.org/10.1017/s0263034606060204.
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This study deals with the simulation of the experimental study of Roth et al. (2000) on the interaction of energetic Zn projectiles in partially ionized laser produced carbon targets, and with similar type experiments. Particular attention is paid to the specific contributions of the K and L shell target electrons to electron recombination in the energetic Zn ionic projectile. The classical Bohr–Lindhard model was used for describing recombination, while quantum mechanical models were also introduced for scaling the L to K cross-section ratios. It was found that even for a hydrogen-like carbon target, the effect of the missing five bound electrons brings about an increase of only 0.6 charge units in the equilibrium charge state as compared to the cold target value of 23. A collisional radiative calculation was employed for analyzing the type of plasma produced in the experimental study. It was found that for the plasma conditions characteristic of this experiment, some fully ionized target plasma atoms should be present. However in order to explain the experimentally observed large increase in the projectile charge state a very dominant component of the fully ionized plasma must comprise the target plasma. A procedure for calculating the dynamic evolvement of the projectile charge state within partially ionized plasma is also presented and applied to the type of plasma encountered in the experiment of Roth et al. (2000). The low temperature and density tail on the back of the target brings about a decrease in the exiting charge state, while the value of the average charge state within the target is dependent on the absolute value of the cross-sections.
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Lander Gower, Nathalie, Silvia Piperno, and Asaf Albo. "Comparison of THz-QCL Designs Supporting Clean N-Level Systems." Photonics 8, no. 7 (June 30, 2021): 248. http://dx.doi.org/10.3390/photonics8070248.
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Three different Terahertz quantum-cascade-laser designs supporting clean n-level systems were analyzed using nonequilibrium Green’s functions. In clean n-level systems, most of the electrons occupy the active laser levels, with thermally activated leakage channels being suppressed almost entirely up to room temperature. Simulations of the three designs, namely a resonant phonon design, a two-well design, and a split-well direct-phonon design were investigated. The results from the simulations indicated that the two-well design would perform best overall, in terms of variations in current density, interface roughness, and ionized impurity scattering. We conclude that future research aiming to improve the temperature performance of such laser designs should be based on a two-well design.
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Grospellier, Antoine, Lucien Grouès, Anirudh Krishna, and Anthony Leverrier. "Combining hard and soft decoders for hypergraph product codes." Quantum 5 (April 15, 2021): 432. http://dx.doi.org/10.22331/q-2021-04-15-432.
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Hypergraph product codes are a class of constant-rate quantum low-density parity-check (LDPC) codes equipped with a linear-time decoder called small-set-flip (SSF). This decoder displays sub-optimal performance in practice and requires very large error correcting codes to be effective. In this work, we present new hybrid decoders that combine the belief propagation (BP) algorithm with the SSF decoder. We present the results of numerical simulations when codes are subject to independent bit-flip and phase-flip errors. We provide evidence that the threshold of these codes is roughly 7.5% assuming an ideal syndrome extraction, and remains close to 3% in the presence of syndrome noise. This result subsumes and significantly improves upon an earlier work by Grospellier and Krishna (arXiv:1810.03681). The low-complexity high-performance of these heuristic decoders suggests that decoding should not be a substantial difficulty when moving from zero-rate surface codes to constant-rate LDPC codes and gives a further hint that such codes are well-worth investigating in the context of building large universal quantum computers.
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Alihosseini, Faramarz, Aref Rasoulzadeh Zali, Tavakol Pakizeh, and Hesam Zandi. "Plasmonic internal-photoemission-based Si photodetector design suitable for optical communication." Applied Optics 61, no. 23 (August 8, 2022): 6939. http://dx.doi.org/10.1364/ao.462171.
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We propose a high-performance plasmonic photodetector based on the internal photoemission (IPE) process for the C-band communication wavelength. This photodetector takes advantage of an embedded nanohole array in Schottky metal. Owing to localized surface plasmon resonance, the absorption of the active metal layer increases, which results in the generation of more hot carriers and subsequently compensates for the low efficiency of IPE-based photodetectors. Simulations show that for the proposed photodetector with 2-nm-thick Au, Cu, and Ag Schottky contacts, the absorptance dramatically enhances to 95.1%, 93.2%, and 98.2%, respectively, at the wavelength of 1.55 µm. For the detector based on Au, the highest external quantum efficiency of 25.3% and responsivity of 0.32 A/W are achieved at a reverse bias voltage of 1 V. Furthermore, the 3 dB bandwidth can exceed 369 GHz owing to the low capacitance of the structure and the fast transit time of carriers from the thin p-Si layer. Finally, by studying the current–voltage characteristics of the photodetector, it is shown that under the reverse bias voltage of 1 V, the dark current is 665 nA at room temperature, and by reducing the temperature to 200 K, it improves three orders of magnitude and decreases to 810 pA.
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Zhu, Lei, and Liang Dong. "Electromagnetically induced transparency metamaterials: theories, designs and applications." Journal of Physics D: Applied Physics 55, no. 26 (April 6, 2022): 263003. http://dx.doi.org/10.1088/1361-6463/ac60cc.
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Abstract Electromagnetically induced transparency (EIT) stems from a quantum system, where an opaque atomic medium appears the narrow transparent state within a wide absorption area. This phenomenon can be achieved by quantum interference of pumping light and detecting light at different energy levels of transitions. In the generation process of EIT effect, in addition to transparent state, the atomic medium is usually accompanied with a strong dispersion effect, which will bright about a significant reduction of light velocity, thus realizing many important applications, such as slow light propagations. Although the EIT effect has many important applications, its application scenarios are greatly limited due to the fact that EIT realization usually requires specific and complicated conditions, such as refrigeration temperature, high intensity laser, etc. Recently, the analogue of EIT effect in metamaterial has attracted increasing attentions due to its advantages such as controllable room temperature and large operating bandwidth. Metamaterial analogue of EIT effect has become a new research focus. In this article, we review current research progresses on EIT metamaterials. Firstly, we describe the theoretical models for analyzing EIT metamaterials, including the mechanical oscillator model and the equivalent circuit model. Then, we describe the simulations, designs and experiments of passive EIT metamaterials with fixed structures and active EIT metamaterials with tunable elements. Furthermore, the applications of EIT metamaterials in the areas of slow lights, sensings, absorptions and other fields are also reviewed. Finally, the possible directions and key issues of future EIT metamaterial researches are prospected.
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Zahran, Saeed, Mahdi Mahmoudzadeh, Fabrice Wallois, Nacim Betrouni, Philippe Derambure, Matthieu Le Prado, Agustin Palacios-Laloy, and Etienne Labyt. "Performance Analysis of Optically Pumped 4He Magnetometers vs. Conventional SQUIDs: From Adult to Infant Head Models." Sensors 22, no. 8 (April 18, 2022): 3093. http://dx.doi.org/10.3390/s22083093.
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Optically pumped magnetometers (OPMs) are new, room-temperature alternatives to superconducting quantum interference devices (SQUIDs) for measuring the brain’s magnetic fields. The most used OPM in MagnetoEncephaloGraphy (MEG) are based on alkali atoms operating in the spin-exchange relaxation-free (SERF) regime. These sensors do not require cooling but have to be heated. Another kind of OPM, based on the parametric resonance of 4He atoms are operated at room temperature, suppressing the heat dissipation issue. They also have an advantageous bandwidth and dynamic range more suitable for MEG recordings. We quantitatively assessed the improvement (relative to a SQUID magnetometers array) in recording the magnetic field with a wearable 4He OPM-MEG system through data simulations. The OPM array and magnetoencephalography forward models were based on anatomical MRI data from an adult, a nine-year-old child, and 10 infants aged between one month and two years. Our simulations showed that a 4He OPMs array offers markedly better spatial specificity than a SQUID magnetometers array in various key performance areas (e.g., signal power, information content, and spatial resolution). Our results are also discussed regarding previous simulation results obtained for alkali OPM.
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Zakharov, Vasily Sergeevich, Mikhail Evgenievich Zhukovskiy, Sergey Vasilievich Zakharov, and Mikhail Borisovich Markov. "Electron scattering cross-sections for particle transport modeling in a weakly ionized air plasma." Mathematica Montisnigri 51 (August 2021): 96–111. http://dx.doi.org/10.20948/mathmontis-2021-51-7.
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Data on processes of electron scattering on ions and neutral atoms are required in fundamental studies and in applied research in such fields as astro- and laser physics, low density plasma simulations, kinetic modeling etc. Experimental and computational data on elastic and inelastic electron scattering in a wide range of electron energies is available mostly for the electron interaction with neutral atoms, but are very limited for the scattering on ions, notably for elastic processes. In present work the calculational approaches for the cross-section computation of electron elastic and inelastic scattering on neutral atoms and ions are considered. The atomic and ion properties obtained in quantum-statistical Hartree-Fock-Slater model are used in the direct computation of electron elastic scattering and ionization cross-sections by a partial waves method, semiclassical and distorted-wave approximations. Calculated cross-sections for elastic scattering on nitrogen and oxygen atoms and ions, and electron ionisation cross-sections are compared with the available experimental data and widely used approximations and propose consistent results. Considering applicability of Hartree-Fock-Slater model in wide scope of temperatures and densities, such approach to the cross-section calculation can be used in a broad range of energies and ion charges.
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Zhang, Yaolong, Junfan Xia, and Bin Jiang. "REANN: A PyTorch-based end-to-end multi-functional deep neural network package for molecular, reactive, and periodic systems." Journal of Chemical Physics 156, no. 11 (March 21, 2022): 114801. http://dx.doi.org/10.1063/5.0080766.
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In this work, we present a general purpose deep neural network package for representing energies, forces, dipole moments, and polarizabilities of atomistic systems. This so-called recursively embedded atom neural network model takes advantages of both the physically inspired atomic descriptor based neural networks and the message-passing based neural networks. Implemented in the PyTorch framework, the training process is parallelized on both the central processing unit and the graphics processing unit with high efficiency and low memory in which all hyperparameters can be optimized automatically. We demonstrate the state-of-the-art accuracy, high efficiency, scalability, and universality of this package by learning not only energies (with or without forces) but also dipole moment vectors and polarizability tensors in various molecular, reactive, and periodic systems. An interface between a trained model and LAMMPs is provided for large scale molecular dynamics simulations. We hope that this open-source toolbox will allow for future method development and applications of machine learned potential energy surfaces and quantum-chemical properties of molecules, reactions, and materials.
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Green, P. J., M. J. Grant, J. W. Nevin, P. M. Walmsley, and A. I. Golov. "Quantized Vortex Rings and Loop Solitons." Journal of Low Temperature Physics 201, no. 1-2 (August 29, 2020): 11–17. http://dx.doi.org/10.1007/s10909-020-02516-0.
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Abstract The vortex filament model is used to investigate the interaction of a quantized vortex ring with a straight vortex line and also the interaction of two solitons traveling in opposite directions along a vortex. When a ring reconnects with a line, we find that a likely outcome is the formation of a loop soliton. When they collide, loop solitons reconnect as they overlap each other producing either one or two vortex rings. These simulations are relevant for experiments on quantum turbulence in the zero temperature limit where small vortex rings are expected to be numerous. It seems that loop solitons might also commonly occur on vortex lines as they act as transient states between the absorption of a vortex ring before another ring is emitted when the soliton is involved in a reconnection.
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Nagpal, Swati. "CdS quantum dots in a novel glass with a very low activation energy and its variation of diffusivity with temperature." Journal of Nanoparticle Research 13, no. 7 (May 29, 2011): 2733–41. http://dx.doi.org/10.1007/s11051-010-0083-3.
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Bezerra, Anibal Thiago. "The application of a modified Levine model to quantum-well infrared photodetectors in the low-temperature regime." Journal of Computational Electronics 19, no. 4 (July 18, 2020): 1645–50. http://dx.doi.org/10.1007/s10825-020-01547-w.
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Jiao, J., B. Zhang, J. Yu, Z. Zhang, Y. Yan, S. He, Z. Deng, J. Teng, W. Hong, and Y. Gu. "Generating high-yield positrons and relativistic collisionless shocks by 10 PW laser." Laser and Particle Beams 35, no. 2 (March 6, 2017): 234–40. http://dx.doi.org/10.1017/s0263034617000106.
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AbstractRelativistic collisionless shock charged particle acceleration is considered as a possible origin of high-energy cosmic rays. However, it is hard to explore the nature of relativistic collisionless shock due to its low occurring frequency and remote detecting distance. Recently, there are some works attempt to solve this problem by generating relativistic collisionless shock in laboratory conditions. In laboratory, the scheme of generation of relativistic collisionless shock is that two electron–positron pair plasmas knock each other. However, in laboratory, the appropriate pair plasmas have been not generated. The 10 PW laser pulse maybe generates the pair plasmas that satisfy the formation condition of relativistic collisionless shock due to its ultrahigh intensity and energy. In this paper, we study the positron production by ultraintense laser high Z target interaction using numerical simulations, which consider quantum electrodynamics effect. The simulation results show that the forward positron beam up to 1013/kJ can be generated by 10 PW laser pulse interacting with lead target. The estimation of relativistic collisionless shock formation shows that the positron yield satisfies formation condition and the positron divergence needs to be controlled. Our results indicate that the generation of relativistic collisionless shock by 10 PW laser facilities in laboratory is possible.
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Ngo, Gia Long, Jean-Pierre Hermier, and Ngoc Diep Lai. "Single-photon splitting by polymeric submicropillars structures." AVS Quantum Science 5, no. 1 (March 2023): 011403. http://dx.doi.org/10.1116/5.0135915.
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Optical splitters are one of the most important interconnects in the optical chips of future optical quantum computers. Here, we introduce novel quantum photonic splitters based on polymeric submicropillars that split the single-photon signal generated by a colloidal quantum dot (QD) into multiple outputs, which can be easily accessed through a conventional confocal scanning optical system. Using a single continuous-wave laser with a low absorption wavelength for both polymer material and QDs, we were able to first deterministically place a single-photon emitter (SPE) within one of the submicropillars and then characterize the single-photon guiding effect of the fabricated structures. The submicropillars, with their size and position which are comprehensively optimized by numerical simulations, act as single-mode directional coupler guiding both the laser excitation and the single-photon emission thanks to the evanescent wave coupling effect. With one-step fabrication, we can create a well-distributed array of “imaginary” SPEs from an original SPE. Our method opens various applications in integrated devices based on solid-state quantum emitters.
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Прасолов, Н. Д., А. А. Гуткин, and П. Н. Брунков. "Исследование с помощью молекулярной динамики образования димеров на поверхности (001) GaAs при низких температурах." Физика и техника полупроводников 55, no. 2 (2021): 134. http://dx.doi.org/10.21883/ftp.2021.02.50498.9516.
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The simulation of dimers formation during the low-temperature reconstruction of GaAs (001) surface terminated with Ga or As atoms was performed by the molecular dynamics method using the analytical Bond-Order Potential based on quantum mechanical theory incorporating both σ- and π- bonds between atoms. A decrease in values of potential energy of the atoms during formation of isolated surface dimer have been determined. It has been found that potential energy of an atom in As-dimer is several tenths of an eV lower than in Ga-dimer. Kinetics of the initial stages of Ga-dimers formation in the temperature range of 25 - 40 K was studied. It was found that the characteristic thermal activation energy of single isolated Ga-dimers formation is ~ 29 meV, which is lower than the same value for As-dimers (~ 38 meV). Time constants characterizing the average rate of transformation of one dimer into a chain of two dimers at temperature range of 28 - 37 K were estimated. Inverse values of these parameters for paired Ga- and As-dimers are in the ranges of 10^11 – 10^12 s^-1 and 10^9 – 10^10 s^-1, respectively, while corresponding parameters for the formation of single dimers are in the ranges of 4·10^6 – 10^8 s^-1 and 1.4·10^6 – 7.4·10^7 s^-1.
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Ghasemian, E., and M. K. Tavassoly. "Population imbalance, macroscopic tunneling and intermodal entanglement of two-mode Bose–Einstein condensate under the influence of dissipation process." International Journal of Modern Physics B 33, no. 17 (July 10, 2019): 1950181. http://dx.doi.org/10.1142/s0217979219501819.
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In this paper, we study the dissipative dynamics of a system which is composed of two atomic Bose–Einstein condensates (BECs) interacting through the Josephson-like coupling. To model a more realistic physical system, the inevitable dissipation effect is considered via the interaction between the system and its environment, in particular, a thermal reservoir. In this respect, after introducing a proper Hamiltonian for the model, we analytically solve the corresponding quantum Heisenberg–Langevin equations and then obtain explicit analytical expressions for population imbalance, macroscopic tunneling current and intermodal entanglement. Generally, the dynamics of the system is very sensitive to the chosen values of tunneling coupling strength, initial population as well as the characteristics of interaction between the system and its reservoirs. Also, the time evolution of the above-mentioned physical quantities shows oscillatory decaying behavior where the frequency of oscillations depends on the strength of tunneling interaction between the two subsystems. The oscillatory pattern of population imbalance and tunneling current is more regular in comparison with the intermodal entanglement. Although the system is always separable for low initial population, we show that it tends to an entangled state as its initial population is increased. In particular, the amount and the time interval of the entanglement can be effectively controlled via the dissipation parameter. Also, to get an insight into the effect of nonlinear interaction on the behavior of dynamical evolution of the considered system, we numerically investigate the population imbalance in the absence and presence of such interactions. A qualitative comparison shows that the previous theoretical works and numerical simulations confirm our obtained results.
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Xu, Jixi, Weichang Li, Xin Wang, Jingping Tang, Wei Chen, Shubin Chen, and Lili Hu. "Numerical Simulations of the Influence on the Temperature Fields of Large-Sized Nd-Glass Slab with Designed Edge-Cladding Materials, Methods, and Structures." Photonics 9, no. 12 (December 2, 2022): 931. http://dx.doi.org/10.3390/photonics9120931.
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The good cladding of a large-sized Nd-doped phosphate glass slab as a laser amplifier requires not only the amplified spontaneous emission and parasitic oscillation to be fully absorbed, to hold up the small signal gain coefficient of the Nd ions, but also the absorbed heat energy to be appropriately dissipated to extend a uniform temperature field for the larger laser beam aperture of the edge-cladded Nd–glass slab. In the present work, numerical simulations were performed based on the developed feasible edge-cladding designs for a 786 × 436 × 40 mm3 Nd–glass slab, including the following alterations: optical absorptivity, quantum-dot absorption centers, ceramics with higher thermal diffusivity, glasses with lower and higher specific heat values, 3D printing edge-cladding methods, double-deck edge-cladding structure with transparent strips as a buffer layer, and thickening of the edge-cladding. All of these designed edge-cladding materials, methods, and structures satisfy both requirements of sufficiently absorbing and precisely matching with the refractive index, as emphasized by the edge-cladding for the Nd–glass. Some of the designed edge-claddings resulted in a much more uniform temperature field than the composite polymer–glass edge-cladding as the standard for comparison, which could be utilized to extend the effective laser aperture of the Nd–glass slab, thus being beneficial to the laser beam size and laser energy in the optics recycle loop strategy.
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Gusakov, Vasilii E. "Coefficient of Diffusion in Crystals of Si1-xGex: Role of Preexponential Factor." Solid State Phenomena 178-179 (August 2011): 94–99. http://dx.doi.org/10.4028/www.scientific.net/ssp.178-179.94.
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In the present work the results of theoretical analysis of the process of diffusion of covalently bonded atoms (interstitial oxygen atoms) in Si1-xGex alloys are presented. The diffusion coefficient (activation energy and pre-exponential factor) was calculated by means of quantum-chemical simulations (Hartree–Fock, NDDO, PM5) and the dependences of the activation energy and pre-exponential factor on Ge atoms concentration (x) were analyzed with the use of the percolation theory. The study has revealed that the diffusivity of impurities (defects) in alloys can decrease considerably at low concentration (x<0.05) of a minor alloy component and this variation results from the fact that the pre-exponential factor depends on the concentration of component elements of the alloy. The alloy-induced decrease in the pre-exponential factor is associated with removal of the degeneracy of the number of equivalent diffusion paths. It is found that a sharp decrease in the pre-exponential factor causes experimentally observed decreases in the coefficient of diffusion of interstitial oxygen atoms and in the rate of formation of oxygen thermal donors in Si1‑xGex crystals at x~0.01.
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Maksymov, Ivan S., Bui Quoc Huy Nguyen, Andrey Pototsky, and Sergey Suslov. "Acoustic, Phononic, Brillouin Light Scattering and Faraday Wave-Based Frequency Combs: Physical Foundations and Applications." Sensors 22, no. 10 (May 22, 2022): 3921. http://dx.doi.org/10.3390/s22103921.
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Frequency combs (FCs)—spectra containing equidistant coherent peaks—have enabled researchers and engineers to measure the frequencies of complex signals with high precision, thereby revolutionising the areas of sensing, metrology and communications and also benefiting the fundamental science. Although mostly optical FCs have found widespread applications thus far, in general FCs can be generated using waves other than light. Here, we review and summarise recent achievements in the emergent field of acoustic frequency combs (AFCs), including phononic FCs and relevant acousto-optical, Brillouin light scattering and Faraday wave-based techniques that have enabled the development of phonon lasers, quantum computers and advanced vibration sensors. In particular, our discussion is centred around potential applications of AFCs in precision measurements in various physical, chemical and biological systems in conditions where using light, and hence optical FCs, faces technical and fundamental limitations, which is, for example, the case in underwater distance measurements and biomedical imaging applications. This review article will also be of interest to readers seeking a discussion of specific theoretical aspects of different classes of AFCs. To that end, we support the mainstream discussion by the results of our original analysis and numerical simulations that can be used to design the spectra of AFCs generated using oscillations of gas bubbles in liquids, vibrations of liquid drops and plasmonic enhancement of Brillouin light scattering in metal nanostructures. We also discuss the application of non-toxic room-temperature liquid–metal alloys in the field of AFC generation.
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MEI, ZHONG-HAO, and XIANG-QIAN LUO. "EXOTIC MESONS FROM QUANTUM CHROMODYNAMICS WITH IMPROVED GLUON AND QUARK ACTIONS ON THE ANISOTROPIC LATTICE." International Journal of Modern Physics A 18, no. 31 (December 20, 2003): 5713–24. http://dx.doi.org/10.1142/s0217751x03017038.
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Hybrid (exotic) mesons, which are important predictions of quantum chromodynamics (QCD), are states of quarks and antiquarks bound by excited gluons. First principle lattice study of such states would help us understand the role of "dynamical" color in low energy QCD and provide valuable information for experimental search for these new particles. In this paper, we apply both improved gluon and quark actions to the hybrid mesons, which might be much more efficient than the previous works in reducing lattice spacing error and finite volume effect. Quenched simulations were done at β=2.6 and on a ξ=3 anisotropic 123×36 lattice using our PC cluster. We obtain 2013±26±71 MeV for the mass of the 1-+ hybrid meson [Formula: see text] in the light quark sector, and 4369±37±99 MeV in the charm quark sector; the mass splitting between the 1-+ hybrid meson [Formula: see text] in the charm quark sector and the spin averaged S-wave charmonium mass is estimated to be 1302±37±99 MeV. As a byproduct, we obtain 1438±32±57 MeV for the mass of a P-wave 1++[Formula: see text] or [Formula: see text] meson and 1499±28±65 MeV for the mass of a P-wave 1++[Formula: see text] meson, which are comparable to their experimental value 1426 MeV for the f1(1420) meson. The first error is statistical, and the second one is systematical. The mixing of the hybrid meson with a four quark state is also discussed.
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Dong, Boqun, Andrei Afanasev, Rolland Johnson, and Mona Zaghloul. "Enhancement of Photoemission on p-Type GaAs Using Surface Acoustic Waves." Sensors 20, no. 8 (April 24, 2020): 2419. http://dx.doi.org/10.3390/s20082419.
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We demonstrate that photoemission properties of p-type GaAs can be altered by surface acoustic waves (SAWs) generated on the GaAs surface due to dynamical piezoelectric fields of SAWs. Multiphysics simulations indicate that charge-carrier recombination is greatly reduced, and electron effective lifetime in p-doped GaAs may increase by a factor of 10× to 20×. It implies a significant increase, by a factor of 2× to 3×, of quantum efficiency (QE) for GaAs photoemission applications, like GaAs photocathodes. Conditions of different SAW wavelengths, swept SAW intensities, and varied incident photon energies were investigated. Essential steps in SAW device fabrication on a GaAs substrate are demonstrated, including deposition of an additional layer of ZnO for piezoelectric effect enhancement, measurements of current–voltage (I–V) characteristics of the SAW device, and ability to survive high-temperature annealing. Results obtained and reported in this study provide the potential and basis for future studies on building SAW-enhanced photocathodes, as well as other GaAs photoelectric applications.
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Dehzangi, Arash, Farhad Larki, Sawal Hamid Md Ali, Sabar Derita Hutagalung, Md Shabiul Islam, Mohd Nizar Hamidon, Susthitha Menon, Azman Jalar, Jumiah Hassan, and Burhanuddin Yeop Majlis. "Study of the side gate junctionless transistor in accumulation region." Microelectronics International 33, no. 2 (May 3, 2016): 61–67. http://dx.doi.org/10.1108/mi-03-2015-0027.
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Purpose The purpose of this paper is to analyse the operation of p-type side gate junctionless silicon transistor (SGJLT) in accumulation region through experimental measurements and 3-D TCAD simulation results. The variation of electric field components, carrier’s concentration and valence band edge energy towards the accumulation region is explored with the aim of finding the origin of SGJLT performance in the accumulation operational condition. Design/methodology/approach The device is fabricated by atomic force microscopy nanolithography on silicon-on-insulator wafer. The output and transfer characteristics of the device are obtained using 3-D Technology Computer Aided Design (TCAD) Sentaurus software and compared with experimental measurement results. The advantages of AFM nanolithography in contact mode and Silicon on Insulator (SOI) technology were implemented to fabricate a simple structure which exhibits the behaviour of field effect transistors. The device has 200-nm channel length, 100-nm gate gap and 4 μm for the distance between the source and drain contacts. The characteristics of the fabricated device were measured using an Agilent HP4156C semiconductor parameter analyzer (SPA). A 3-D TCAD Sentaurus tool is used as the simulation platform. The Boltzmann statistics is adopted because of the low doping concentration of the channel. Hydrodynamic model is taken to be as the main transport model for all simulations, and the quantum mechanical effects are ignored. A doping dependent Masetti mobility model was also included as well as an electric field dependent model with Shockley–Read–Hall (SRH) carrier recombination/generation. Findings We have obtained that the device is a normally on state device mainly because of the lack of work functional difference between the gate and the channel. Analysis of electric field components’ variation, carrier’s concentration and valence band edge energy reveals that increasing the negative gate voltage drives the device into accumulation region; however, it is unable to increase the drain current significantly. The positive slope of the hole quasi-Fermi level in the accumulation region presents mechanism of carriers’ movement from source to drain. The influence of electric field because of drain and gate voltage on charge distribution explains a low increasing of the drain current when the device operates in accumulation regime. Originality/value The proposed side gate junctionless transistors simplify the fabrication process, because of the lack of gate oxide and physical junctions, and implement the atomic force microscopy nanolithography for fabrication process. The optimized structure with lower gap between gate and channel and narrower channel would present the output characteristics near the ideal transistors for next generation of scaled-down devices in both accumulation and depletion region. The presented findings are verified through experimental measurements and simulation results.
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Zhang, Hewei, Yang Tian, Qian Li, Wenqiang Ding, Xuzhen Yu, Zebiao Lin, Xuyang Feng, and Yanli Zhao. "Photon-Trapping Microstructure for InGaAs/Si Avalanche Photodiodes Operating at 1.31 μm." Sensors 22, no. 20 (October 12, 2022): 7724. http://dx.doi.org/10.3390/s22207724.
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With the rapid development of photo-communication technologies, avalanche photodiode (APD) will play an increasingly important role in the future due to its high quantum efficiency, low power consumption, and small size. The monolithic integration of optical components and signal processing electronics on silicon substrate chips is crucial to driving cost reduction and performance improvement; thus, the technical research on InGaAs/Si APD is of great significance. This work is the first to demonstrate the use of a photon-trapping (PT) structure to improve the performance of the InGaAs/Si APD based on an SOI substrate, which exhibits very high absorption efficiency at 1310 nm wavelength while the thickness of the absorption layer is kept at 800 nm. Based on the optical and electrical simulations, an optimized InGaAs/Si PT-APD is proposed, which exhibits a better performance and a higher responsivity compared to the original InGaAs/Si APD.
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Zhu, Xunmin, Nan Li, Jianyu Yang, Xingfan Chen, and Huizhu Hu. "Displacement Detection Decoupling in Counter-Propagating Dual-Beams Optical Tweezers with Large-Sized Particle." Sensors 20, no. 17 (August 31, 2020): 4916. http://dx.doi.org/10.3390/s20174916.
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As a kind of ultra-sensitive acceleration sensing platform, optical tweezers show a minimum measurable value inversely proportional to the square of the diameter of the levitated spherical particle. However, with increasing diameter, the coupling of the displacement measurement between the axes becomes noticeable. This paper analyzes the source of coupling in a forward-scattering far-field detection regime and proposes a novel method of suppression. We theoretically and experimentally demonstrated that when three variable irises are added into the detection optics without changing other parts of optical structures, the decoupling of triaxial displacement signals mixed with each other show significant improvement. A coupling detection ratio reduction of 49.1 dB and 22.9 dB was realized in radial and axial directions, respectively, which is principally in accord with the simulations. This low-cost and robust approach makes it possible to accurately measure three-dimensional mechanical quantities simultaneously and may be helpful to actively cool the particle motion in optical tweezers even to the quantum ground state in the future.
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Silvério, Henrique, Sebastián Grijalva, Constantin Dalyac, Lucas Leclerc, Peter J. Karalekas, Nathan Shammah, Mourad Beji, Louis-Paul Henry, and Loïc Henriet. "Pulser: An open-source package for the design of pulse sequences in programmable neutral-atom arrays." Quantum 6 (January 24, 2022): 629. http://dx.doi.org/10.22331/q-2022-01-24-629.
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Programmable arrays of hundreds of Rydberg atoms have recently enabled the exploration of remarkable phenomena in many-body quantum physics. In addition, the development of high-fidelity quantum gates are making them promising architectures for the implementation of quantum circuits.We present here Pulser, an open-source Python library for programming neutral-atom devices at the pulse level. The low-level nature of Pulser makes it a versatile framework for quantum control both in the digital and analog settings. The library also contains simulation routines for studying and exploring the outcome of pulse sequences for small systems.
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ZHAO, CHANG, M. ZHAO, Y. WANG, A. J. LV, G. M. WU, and G. J. XING. "MONTE CARLO SIMULATION OF THE KINETICS IN THE GROWTH OF SEMICONDUCTOR QUANTUM DOTS." Modern Physics Letters B 25, no. 07 (March 20, 2011): 465–71. http://dx.doi.org/10.1142/s0217984911025869.
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By means of kinetic Monte Carlo simulation, which is based on the random selection of the surface hops of single adatom, we investigate the atoms' kinetics during the growth of the semiconductor quantum dots in a molecular beam epitaxy system, the deposition, diffusion and nucleation are considered as the main relevant processes during the growth of the quantum dots, taking into account the contribution of the dangling bond of the adatoms in the simulation. The dependence of the quantum dot size on the temperature and flux as well as the atomic kinetic effects are discussed in detail. The simulation results are in good qualitative agreement with those of the experiment.
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Young, Kevin C., Mohan Sarovar, Jon Aytac, C. M. Herdman, and K. Birgitta Whaley. "Finite temperature quantum simulation of stabilizer Hamiltonians." Journal of Physics B: Atomic, Molecular and Optical Physics 45, no. 15 (July 30, 2012): 154012. http://dx.doi.org/10.1088/0953-4075/45/15/154012.
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Dec, Bartłomiej, Robert Bogdanowicz, and Krzysztof Pyrchla. "Ab-initio study of electrical and optical properties of allylamine." Photonics Letters of Poland 10, no. 3 (October 1, 2018): 94. http://dx.doi.org/10.4302/plp.v10i3.847.
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The Density functional theory is one of most promising methodology in fast and accurate calculations of electrical and optical properties from the atomic basis. In this paper, we calculate electrical and optical properties of allylamine (2-propen 1- amine) in terms of accuracy and speed of calculations obtained by selection of DFT-1/2 method with ultrasoft Vanderbilt pseudopotentials. Comparison of density of states between molecule and bulk configuration shows great agreement between them, therefore we calculated refractive index which showed even better agreement with experimental data. Full Text: PDF ReferencesW. Kohn and L. J. Sham, 'Self-Consistent Equations Including Exchange and Correlation Effects', Phys. Rev., vol. 140, no. 4A, pp. A1133–A1138, Nov. 1965. CrossRef J. P. Perdew, K. Burke, and M. Ernzerhof, 'Generalized Gradient Approximation Made Simple', Phys. Rev. Lett., vol. 77, no. 18, pp. 3865–3868, Oct. 1996. CrossRef L. G. Ferreira, M. Marques, and L. K. Teles, 'Approximation to density functional theory for the calculation of band gaps of semiconductors', Physical Review B, vol. 78, no. 12, Sep. 2008. CrossRef L. G. Ferreira, M. Marques, and L. K. Teles, 'Slater half-occupation technique revisited: the LDA-1/2 and GGA-1/2 approaches for atomic ionization energies and band gaps in semiconductors', AIP Advances, vol. 1, no. 3, p. 032119, Aug. 2011. CrossRef M. Schlipf and F. Gygi, 'Optimization algorithm for the generation of ONCV pseudopotentials', Computer Physics Communications, vol. 196, pp. 36–44, Nov. 2015. CrossRef P. Prayongpan and C. Michael Greenlief, 'Density functional study of ethylamine and allylamine on Si(100)-2×1 and Ge(100)-2×1 surfaces', Surface Science, vol. 603, no. 7, pp. 1055–1069, Apr. 2009. CrossRef M. T. van Os, B. Menges, R. Foerch, G. J. Vancso, and W. Knoll, 'Characterization of Plasma-Polymerized Allylamine Using Waveguide Mode Spectroscopy', Chemistry of Materials, vol. 11, no. 11, pp. 3252–3257, Nov. 1999. CrossRef J. Zeng, R.-Q. Zhang, and H. Treutlein, Quantum Simulations of Materials and Biological Systems. Springer Science & Business Media, 2012. CrossRef I. Del Villar, I. R. Matias, and F. J. Arregui, 'Enhancement of sensitivity in long-period fiber gratings with deposition of low-refractive-index materials', Optics Letters, vol. 30, no. 18, p. 2363, Sep. 2005. CrossRef D. Nidzworski et al., 'A rapid-response ultrasensitive biosensor for influenza virus detection using antibody modified boron-doped diamond', Sci Rep, vol. 7, Nov. 2017. CrossRef Synopsys QuantumWise, Atomistix Toolkit version 2018.06 .D. C. Liu and J. Nocedal, 'On the limited memory BFGS method for large scale optimization', Mathematical Programming, vol. 45, no. 1–3, pp. 503–528, Aug. 1989. CrossRef K. F. Garrity, J. W. Bennett, K. M. Rabe, and D. Vanderbilt, 'Pseudopotentials for high-throughput DFT calculations', Computational Materials Science, vol. 81, pp. 446–452, Jan. 2014. CrossRef Yu Cai, T. Zhang, A. B. Anderson, J. C. Angus, L. N. Kostadinov, and T. V. Albu, 'The origin of shallow n-type conductivity in boron-doped diamond with H or S co-doping: Density functional theory study', Diamond and Related Materials, vol. 15, no. 11, pp. 1868–1877, Nov. 2006. CrossRef
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Zhao, Chang, M. Zhao, Y. Wang, A. J. Lv, G. J. Xing, and Y. C. Ma. "Atomic kinetic research of ordered quantum dot growth induced by dislocation on the substrate." Modern Physics Letters B 28, no. 05 (February 18, 2014): 1450033. http://dx.doi.org/10.1142/s021798491450033x.
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In this study, the modified effects of stress originating from the dislocation on the substrate to the semiconductor quantum dot growth are investigated by performing an event-based continuous kinetic Monte Carlo simulation, in which the contribution of the dangling bond of the atom is considered. The research results indicate that the change of binding energy initiated by the stress between the deposit atom and the substrate's atoms may significantly influence the atoms' kinetic behaviors, and on the pattern surface the atoms' kinetic effects are very sensitive to the initial condition of the substrate. In addition, the dependence of the atomic kinetics on the growth flux and temperature are also studied. The simulation results are in good qualitative agreement with those of our experiment.
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GERNOTH, K. A., MANFRED L. RISTIG, and THOMAS LINDENAU. "QUANTUM BOLTZMANN LIQUIDS." International Journal of Modern Physics B 21, no. 13n14 (May 30, 2007): 2157–68. http://dx.doi.org/10.1142/s0217979207043555.
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We study homogeneous normal systems of bosons under the influence of interparticle forces with a strongly repulsive component at short relative particle-particle distances. The repulsion prevents short-ranged exchange between the bosonic constituents in the quantum fluid. Consequently, the bosons remain distinguishable at temperatures far below the classical high-temperature regime. At these low temperatures such fluids and liquids display nevertheless distinct quantum effects due to quantum-mechanical phase-phase correlations. Typical examples are liquid para-hydrogen and fluid 4 He under certain thermodynamic conditions. The study employs Correlated Density-Matrix theory and Path-Integral Monte-Carlo simulations.
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Schran, Christoph, and Dominik Marx. "Quantum nature of the hydrogen bond from ambient conditions down to ultra-low temperatures." Physical Chemistry Chemical Physics 21, no. 45 (2019): 24967–75. http://dx.doi.org/10.1039/c9cp04795f.
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Li, Zi-Xiang, and Hong Yao. "Sign-Problem-Free Fermionic Quantum Monte Carlo: Developments and Applications." Annual Review of Condensed Matter Physics 10, no. 1 (March 10, 2019): 337–56. http://dx.doi.org/10.1146/annurev-conmatphys-033117-054307.
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Reliable simulations of correlated quantum systems, including high-temperature superconductors and frustrated magnets, are increasingly desired nowadays to further our understanding of essential features in such systems. Quantum Monte Carlo (QMC) is a unique numerically exact and intrinsically unbiased method to simulate interacting quantum many-body systems. More importantly, when QMC simulations are free from the notorious fermion sign problem, they can reliably simulate interacting quantum models with large system size and low temperature to reveal low-energy physics such as spontaneously broken symmetries and universal quantum critical behaviors. Here, we concisely review recent progress made in developing new sign-problem-free QMC algorithms, including those employing Majorana representation and those utilizing hot-spot physics. We also discuss applications of these novel sign-problem-free QMC algorithms in simulations of various interesting quantum many-body models. Finally, we discuss possible future directions of designing sign-problem-free QMC methods.
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Leng, Yang, and Li Yang. "Protecting the quantum state from a finite temperature decoherence source by parity-time symmetric operation." Laser Physics 32, no. 2 (December 24, 2021): 025201. http://dx.doi.org/10.1088/1555-6611/ac42d3.
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Abstract We examine the validity of the parity-time ( P T )-symmetric operation in protecting quantum state and entanglement in the non-zero temperature environment. Special attention is paid to the dependence of quantum fidelity and entanglement on the temperature. In particular, by solving the master equation, we get the exact analytical or numerical simulation expressions of the explicit formulas of protection, showing explicitly that P T -symmetric operation does indeed help in protecting quantum state from finite temperature decoherence.