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Advancing hybrid quantum-classical algorithms via mean operators

Physical Review A 2023年第1期108卷 L010401-L010401页

作者： Donggyu Kim Pureum Noh Hyun-Yong Lee Eun-Gook Moon Department of Physics Korea Advanced Institute of Science and Technology (KAIST) Daejeon 34141 Korea Department of Applied Physics Graduate School Korea University Sejong 30019 Korea Division of Display and Semiconductor Physics Korea University Sejong 30019 Korea Interdisciplinary Program in E·ICT-Culture-Sports Convergence Korea University Sejong 30019 Korea

Hybrid quantum-classical algorithms have been suggested to control the quantum entanglement of many-body systems in noisy intermediate-scale quantum technology, and yet their applicability is limited by the numbers of qubits and quantum operations. Here, we propose a mean-operator theory which overcomes limitations by combining the advantages of hybrid algorithms and standard mean-field theory. We demonstrate that an introduction of a mean operator prepares an entangled target many-body state with a significantly reduced number of quantum operations. We also show that a class of mean operators is expressed as time-evolution operators, which indicates that our theory is directly applicable to quantum simulations with Rydberg atoms and trapped ions.

关键词： Atom & ion trapping & guiding Quantum algorithms Quantum phase transitions Quantum simulation Strongly correlated systems Ultracold gases Symmetries in condensed matter Tensor network methods Variational wave functional methods

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Asymptotics of representation learning in finite Bayesian neural networks

arXiv

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arXiv 2021年

作者： Zavatone-Veth, Jacob A. Canatar, Abdulkadir Ruben, Benjamin S. Pehlevan, Cengiz Department of Physics Center for Brain Science Biophysics Graduate Program John A. Paulson School of Engineering and Applied Sciences Harvard University CambridgeMA02138 United States

Recent works have suggested that finite Bayesian neural networks may sometimes outperform their infinite cousins because finite networks can flexibly adapt their internal representations. However, our theoretical understanding of how the learned hidden layer representations of finite networks differ from the fixed representations of infinite networks remains incomplete. Perturbative finite-width corrections to the network prior and posterior have been studied, but the asymptotics of learned features have not been fully characterized. Here, we argue that the leading finite-width corrections to the average feature kernels for any Bayesian network with linear readout and Gaussian likelihood have a largely universal form. We illustrate this explicitly for three tractable network architectures: deep linear fully-connected and convolutional networks, and networks with a single nonlinear hidden layer. Our results begin to elucidate how task-relevant learning signals shape the hidden layer representations of wide Bayesian neural networks. © 2021, CC BY-NC-SA.

关键词： Network architecture

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Stochastic Treatment of Adsorbate Local-Potential Effects on Surface-Ion Neutralization

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Physical Review Letters 1993年第24期71卷 4075-4075页

作者： Zoran L. Mišković Sydney G. Davison Frank O. Goodman Department of Applied Mathematics University of Waterloo Waterloo Ont. N2L 3G1 Canada Institute of Nuclear Sciences-Vinča Belgrade Department of Physics University of Waterloo Guelph-Waterloo Program for Graduate Work in Physics

The influence of a laterally inhomogeneous electrostatic potential of an adsorbate-covered surface on the resonant charge transfer in ion-surface scattering is investigated by means of the time-dependent Anderson-Newns Hamiltonian. The adsorbate-induced random modulation of the projectile orbital energy level is treated as a stochastic process, and its role in the charge transfer is evaluated analytically, in the Gaussian-process approximation, for low projectile speeds and low surface coverage by alkali atoms.

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Characterization of Fossils by Gamma-Ray Spectrometry

SSRN

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SSRN 2023年

作者： Rodríguez, Duvan Gil Bastos, Rodrigo Oliveira Ikeoka, Renato Akio Graduate Program in Applied Chemistry Universidade Estadual do Centro Oeste do Paraná Brazil Department of Physics Universidade Estadual do Centro Oeste do Paraná Brazil

Non-destructive analytical techniques are essential tools for the study of objects with historical and cultural value. Restrictions and difficulties are imposed on the characterization, since the objects cannot be damaged in the sample preparation process. Gamma-ray spectrometry (GRS), without strict control of the measurement geometry, can serve as a complementary, low-cost and non-destructive technique in these research areas. Unlike most other nuclear analytical techniques, gamma spectrometry detects photons from all points in the sample volume, bringing results related to the total chemical and mineralogical composition of the piece. In the case of fossils, GRS data may be interpreted to provide information about some diagenesis processes (mineralization) and the redox conditions of the sedimentary environment in which they were formed. This article presents the GRS measurements of 32 fossil samples from the Guarapuava Museum of Natural Sciences. The results demonstrated the feasibility of characterizing fossil samples with irregular geometries and varied densities using gamma ray spectrometry. © 2023, The Authors. All rights reserved.

关键词： Nondestructive examination

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Polaronic quasiparticle picture for generation dynamics of coherent phonons in semiconductors: Transient and nonlinear Fano resonance

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Physical Review B 2017年第1期95卷 014301-014301页

作者： Yohei Watanabe Ken-ichi Hino Muneaki Hase Nobuya Maeshima Doctoral Program in Materials Science Graduate School of Pure and Applied Sciences University of Tsukuba Tsukuba Ibaraki 305-8573 Japan Division of Materials Science Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba 305-8573 Japan Center for Computational Sciences University of Tsukuba Tsukuba 305-8577 Japan Division of Applied Physics Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba 305-8573 Japan

We examine generation dynamics of coherent phonons in both polar and nonpolar semiconductors, such as GaAs and Si, based on a polaronic-quasiparticle (PQ) model. In this model, the PQ operator is composed of two kinds of operators: one is a quasiboson operator, defined as a linear combination of a set of pairs of electron operators, and the other is a longitudinal optical (LO) phonon operator. In particular, the problem of transient and nonlinear Fano resonance (FR) is tackled, where the vestige of this quantum interference effect was observed exclusively in lightly n-doped Si immediately after carriers were excited by an ultrashort pulse laser [M. Hase et al., Nature (London) 426, 51 (2003)], although not observed yet in GaAs. The PQ model enables us to show straightforwardly that the phonon energy state is embedded in continuum states formed by a set of adiabatic eigenstates of the quasiboson; this energy configuration is a necessary condition of the manifestation of the transient FR in the present optically nonlinear system. Numerical calculations are done for photoemission spectra relevant to the retarded longitudinal dielectric function of transient photoexcited states and for power spectra relevant to the LO-phonon displacement function of time. The photoemission spectra show that in undoped Si, an asymmetric spectral profile characteristic of FR comes into existence immediately after the instantaneous carrier excitation to fade out gradually, whereas in undoped GaAs, no asymmetry in spectra appears in the whole temporal region. The similar results are also obtained in the power spectra. These results are in harmony with the reported experimental results. It is found that the obtained difference in spectral profile between undoped Si and GaAs is attributed to a phase factor of an effective interaction between the LO phonon and the quasiboson. More detailed discussion of the FR dynamics is made in the text.

关键词： Optical phonons Polarons Ultrafast phenomena Elemental semiconductors Semiconductor compounds Semiconductors Linear response theory

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Bloch-Grüneisen temperature and universal scaling of normalized resistivity in doped graphene revisited

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Physical Review B 2021年第4期103卷 045425-045425页

作者： Khoe Van Nguyen Yia-Chung Chang Research Center for Applied Sciences Academia Sinica Taipei 115 Taiwan Molecular Science and Technology Taiwan International Graduate Program Academia Sinica Taipei 115 Taiwan Department of Physics National Central University Chungli 320 Taiwan Department of Physics National Cheng-Kung University Tainan 701 Taiwan

We resolved some controversial issues on the Bloch-Grüneisen (BG) temperature in doped graphene via analytical and numerical calculations based on full inelastic electron-acoustic-phonon (EAP) scattering rate and various approximation schemes. Analytic results for BG temperature obtained by semi-inelastic (SI) approximation (which gives scattering rates in excellent agreement with the full inelastic scattering rates) are compared with those obtained by quasielastic (QE) approximation and the commonly adopted value of ΘFLA=2ℏvLAkF/kB. It is found that the commonly adopted BG temperature in graphene (ΘFLA) is about 5 times larger than the value obtained by the QE approximation and about 2.5 times larger than that by the SI approximation, when using the crossing-point temperature where low-temperature and high-temperature limits of the resistivity (ρ) meet. The corrected analytic relation based on SI approximation agrees extremely well with the transition temperatures determined by fitting the low- and high-T behavior of available experimental data of graphene's resistivity. Using the analytic expression of ΘBG we can prove that the normalized resistivity defined as R=ρ(T)/ρ(ΘBG) plotted as a function of (T/ΘBG) is independent of the carrier density. We also introduced a way to determine the BG temperature including the full inelastic EAP scattering rate when the deviation of electron energy from the chemical potential is taken into account by finding the maximum of ∂ρ/∂T.

关键词： Electrical conductivity Graphene Scaling methods

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Cementing the grain boundary defects in the strain relaxed mixed Sn-Pb perovskite solar cells

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Chemical Engineering Journal 2025年

作者： Abhishek Kumar Zeeshan Alam Ansari Chintam Hanmandlu Soumallya Banerjee Yu-Te Chen Po-Yu Yang Ahmed Fouad Musa Yun-Wen Yu Chun-Wei Pao Tzu-Chien Wei Jing-Jong Shyue Yu-Jung Lu Chih-Wei Chu Department of Physics National Taiwan University Sec. 4 Roosevelt Road Taipei 106 Taiwan ROC Research Center for Applied Sciences Academia Sinica 128 Academia Road Section 2 Nangang Taipei 11529 Taiwan ROC Nano-Science and Technology Program Taiwan International Graduate Program Academia Sinica Taipei 106 Taiwan ROC Department of Materials Science and Engineering National Yang Ming Chiao Tung University Hsinchu 300 Taiwan ROC Department of Chemical Engineering National Tsing Hua University 101 Section 2 Kuang-Fu Road Hsinchu City 300044 Taiwan ROC College of Engineering Center for Green Technology Chang Gung University Taoyuan City 333002 Taiwan ROC Department of Photonics National Yang Ming Chiao Tung University Hsinchu City 30010 Taiwan ROC Institute of Applied Mechanics National Taiwan University Sec. 4 Roosevelt Road Taipei 106 Taiwan ROC

Mixed Tin-lead (Sn-Pb) perovskite solar cells (PSCs) offer a promising avenue for achieving high power conversion efficiencies (PCEs) due to their narrow bandgaps and substantial optical absorption in the visible–near-infrared region. However, the disparated reaction kinetics of PbI 2 and SnI 2 with organic salts, resulting in an uneven spatial distribution of Sn 2+ and Pb 2+ within the perovskite lattice, inducing micro-strain in the film and a Sn-rich surface vulnerable to oxidation-Sn 2+ to Sn 4+ , thereby elevating nonradiative recombination. Here, we report the incorporation of 2,5-Dibromo-3,4-pyridinediamine (DBPDA) as an additive in the mixed Sn-Pb perovskite precursor solution, designed to mitigate micro-strain formation, reduce defect density by suppressing Sn 4+ formation, and enhance the passivation of undercoordinated Sn/Pb species through synergistic bonding interaction. The best performing PSCs achieved an impressive PCE of 21.24 % with a high open circuit voltage ( V oc ) of 0.85 V, alongside significantly improved long-term stability, retaining near 80 % of their initial PCE after 1,008 h in a nitrogen-filled glovebox without encapsulation. In contrast, the control devices retained only 18 % of their initial efficiency under identical conditions. Additionally, an enhanced field effect hole mobility, increasing from 0.18 cm 2 /V-s in the control film to 1.43 cm 2 /V-s in the target film, was achieved in mixed Sn-Pb perovskite thin film transistors (TFTs) using these films as active layers. These findings present a viable strategy for strain-relieved perovskite films, enabling stable and high-performance mixed Sn-Pb PSCs and TFTs.

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Mixed-order topology of Benalcazar-Bernevig-Hughes models

arXiv

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arXiv 2022年

作者： Sur, Shouvik Tyner, Alexander C. Goswami, Pallab Department of Physics and Astronomy Northwestern University EvanstonIL60208 United States Department of Physics and Astronomy Rice University HoustonTX77005 United States Graduate Program in Applied Physics Northwestern University EvanstonIL60208 United States

Benalcazar-Bernevig-Hughes (BBH) models, defined on D-dimensional simple cubic lattice, are paradigmatic toy models for studying D-th order topology and corner-localized, mid-gap states. Under periodic boundary conditions, the Wilson loops of non-Abelian Berry connection of BBH models along all high-symmetry axes have been argued to exhibit gapped spectra, which predict gapped surface-states under open boundary conditions. In this work, we identify 1D, 2D, and 3D topological invariants for characterizing higher order topological insulators. Further, we demonstrate the existence of cubic-symmetry-protected, gapless spectra of Wilson loops and surface-states along the body diagonal directions of the Brillouin zone of BBH models. We show the gapless surface-states are described by 2D−1-component, massless Dirac fermions. Thus, BBH models can exhibit the signatures of first and D-th order topological insulators, depending on the details of externally imposed boundary conditions. © 2022, CC BY-NC-SA.

关键词： Surface states

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Ultrafast asymmetric Rosen-Zener-like coherent phonon responses observed in silicon

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Physical Review B 2019年第17期99卷 174304-174304页

作者： Yohei Watanabe Ken-ichi Hino Nobuya Maeshima Hrvoje Petek Muneaki Hase Doctoral Program in Materials Science Graduate School of Pure and Applied Sciences University of Tsukuba Tsukuba Ibaraki 305-8573 Japan Division of Materials Science Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba 305-8573 Japan Center for Computational Sciences University of Tsukuba Tsukuba 305-8577 Japan Department of Physics and Astronomy and Pittsburgh Quantum Institute University of Pittsburgh Pittsburgh Pennsylvania 15260 USA Division of Applied Physics Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba 305-8573 Japan

We investigate the spectral profiles of time signals attributed to coherent phonon generation in an undoped Si crystal. Here, the retarded longitudinal-optical- (LO-) phonon Green function relevant to the temporal variance of induced charge density of ionic cores is calculated by employing the polaronic quasiparticle model developed by the authors [Y. Watanabe et al., Phys. Rev. B 95, 014301 (2017); Phys. Rev. B 96, 125204 (2017)]. A spectral asymmetry is revealed in the frequency domain of the signals under the condition that an LO-phonon mode stays almost energetically resonant with a plasmon mode in the early time region; this lasts for approximately 100 fs immediately after the irradiation of an ultrashort pump-laser pulse. It is understood that based on the adiabatic picture in time, this asymmetry is caused by the Rosen-Zener coupling between both modes. The associated experimental results are obtained by measuring time-dependent electro-optic reflectivity signals, and it is proved that these are in harmony with the calculated ones. The spectra become more symmetric, as the photoexcited carrier density further changes from that meeting the above condition to higher and lower sides of carrier densities. Moreover, the effect of optical nutation of carrier density on the coherent phonon signals is addressed, and the present results are compared with the asymmetry caused by transient Fano resonance and the spectral profiles observed in a GaAs crystal.

关键词： Irradiation effects Optical phonons Photoinduced effect Elemental semiconductors Femtosecond laser irradiation Reflectivity

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Fractonic quantum quench in dipole-constrained bosons

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Physical Review Research 2024年第2期6卷 023269-023269页

作者： Yun-Tak Oh Jung Hoon Han Hyun-Yong Lee Division of Display and Semiconductor Physics Korea University Sejong 30019 South Korea Department of Physics Department of Applied Physics Graduate School Korea University Sejong 30019 South Korea Interdisciplinary Program in E·ICT-Culture-Sports Convergence Korea University Sejong 30019 South Korea

We investigate the quench dynamics in the dipolar Bose-Hubbard model (DBHM) in one dimension. The boson hopping is constrained by dipole conservation and shows fractonic dynamics. The ground states at large Hubbard interaction U are Mott insulators at integer filling and a period-2 charge density wave (CDW) at half-integer filling. We focus on Mott-to-Mott and CDW-to-CDW quenches and find that dipole correlation spreading shows the light-cone behavior with the Lieb-Robinson (LR) velocity proportional to the dipole kinetic energy J and the square of the density in the case of Mott quench at integer filling. An effective model for postquench dynamics is constructed under the dilute-dipole approximation and fits the numerical results well. For the CDW quench, we observe a much reduced LR velocity of order J2/U and additional periodic features in the time direction. The emergence of a CDW ground state and the reduced LR velocity at half-integer filling can both be understood by careful application of the second-order perturbation theory. The oscillatory behavior arises from quantum scars in the quadrupole sector of the spectrum and is captured by a PXP-like model that we derive by projecting the DBHM to the quadrupolar sector of the Hilbert space.

关键词： Atomic & molecular processes in external fields Dynamical phase transitions Fractons Quantum quench 1-dimensional systems Bose gases Mott insulators Trapped atoms Approximation methods for many-body systems Bose-Hubbard model Density matrix renormalization group Matrix product states

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