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1
Gritsev, Vladimir, Peter Barmettler, and Eugene Demler. "Scaling approach to quantum non-equilibrium dynamics of many-body systems." New Journal of Physics 12, no. 11 (November 3, 2010): 113005. http://dx.doi.org/10.1088/1367-2630/12/11/113005.
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Cai, Zi. "Symmetries and effect of time dimension in non-equilibrium quantum matter." Acta Physica Sinica 70, no. 23 (2021): 230310. http://dx.doi.org/10.7498/aps.70.20211741.
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Non-equilibrium quantum many-body systems have attracted considerable attention in the past decades. The scope of the research of this kind of novel system involves interdisciplinary research of condensed matter, atomic and molecular physics, quantum optics, quantum information and quantum computation, as well as the non-equilibrium statistical physics. The non-equilibrium phenomena emerging from the aforementioned quantum systems can exhibit rich and universal behaviors, which have far from being well understood due to the novelties and complexities of these systems, and hence the quantum many-body physics becomes the research highlight. At the same time, with the rapid development of quantum techniques, the understanding of these complex systems is of important practical significance due to their potential applications in quantum computation and quantum manipulation. In this paper, we show our recent progress of non-equilibrium quantum many-body systems. We focus on the novel phenomena closely related to the temporary symmetry breaking, including the exotic quantum matter, quasi-particles as well as the dynamical universality classes in non-equilibrium quantum many-body systems.
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Goihl, Marcel, Mathis Friesdorf, Albert H. Werner, Winton Brown, and Jens Eisert. "Experimentally Accessible Witnesses of Many-Body Localization." Quantum Reports 1, no. 1 (June 17, 2019): 50–62. http://dx.doi.org/10.3390/quantum1010006.
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The phenomenon of many-body localized (MBL) systems has attracted significant interest in recent years, for its intriguing implications from a perspective of both condensed-matter and statistical physics: they are insulators even at non-zero temperature and fail to thermalize, violating expectations from quantum statistical mechanics. What is more, recent seminal experimental developments with ultra-cold atoms in optical lattices constituting analog quantum simulators have pushed many-body localized systems into the realm of physical systems that can be measured with high accuracy. In this work, we introduce experimentally accessible witnesses that directly probe distinct features of MBL, distinguishing it from its Anderson counterpart. We insist on building our toolbox from techniques available in the laboratory, including on-site addressing, super-lattices, and time-of-flight measurements, identifying witnesses based on fluctuations, density–density correlators, densities, and entanglement. We build upon the theory of out of equilibrium quantum systems, in conjunction with tensor network and exact simulations, showing the effectiveness of the tools for realistic models.
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SEIRINGER, ROBERT. "A CORRELATION ESTIMATE FOR QUANTUM MANY-BODY SYSTEMS AT POSITIVE TEMPERATURE." Reviews in Mathematical Physics 18, no. 03 (April 2006): 233–53. http://dx.doi.org/10.1142/s0129055x06002632.
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We present an inequality that gives a lower bound on the expectation value of certain two-body interaction potentials in a general state on Fock space in terms of the corresponding expectation value for thermal equilibrium states of non-interacting systems and the difference in the free energy. This bound can be viewed as a rigorous version of first-order perturbation theory for many-body systems at positive temperature. As an application, we give a proof of the first two terms in a high density (and high temperature) expansion of the free energy of jellium with Coulomb interactions, both in the fermionic and bosonic case. For bosons, our method works above the transition temperature (for the non-interacting gas) for Bose–Einstein condensation.
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Schmied, Christian-Marcel, Aleksandr N. Mikheev, and Thomas Gasenzer. "Non-thermal fixed points: Universal dynamics far from equilibrium." International Journal of Modern Physics A 34, no. 29 (October 20, 2019): 1941006. http://dx.doi.org/10.1142/s0217751x19410069.
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In this article we give an overview of the concept of universal dynamics near non-thermal fixed points in isolated quantum many-body systems. We outline a non-perturbative kinetic theory derived within a Schwinger–Keldysh closed-time path-integral approach, as well as a low-energy effective field theory which enable us to predict the universal scaling exponents characterizing the time evolution at the fixed point. We discuss the role of wave-turbulent transport in the context of such fixed points and discuss universal scaling evolution of systems bearing ensembles of (quasi) topological defects. This is rounded off by the recently introduced concept of prescaling as a generic feature of the evolution towards a non-thermal fixed point.
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Tarasov, Sergey, William Shannon, Vladimir Kocharovsky, and Vitaly Kocharovsky. "Multi-Qubit Bose–Einstein Condensate Trap for Atomic Boson Sampling." Entropy 24, no. 12 (December 3, 2022): 1771. http://dx.doi.org/10.3390/e24121771.
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We propose a multi-qubit Bose–Einstein-condensate (BEC) trap as a platform for studies of quantum statistical phenomena in many-body interacting systems. In particular, it could facilitate testing atomic boson sampling of the excited-state occupations and its quantum advantage over classical computing in a full, controllable and clear way. Contrary to a linear interferometer enabling Gaussian boson sampling of non-interacting non-equilibrium photons, the BEC trap platform pertains to an interacting equilibrium many-body system of atoms. We discuss a basic model and the main features of such a multi-qubit BEC trap.
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Hermanns, S., K. Balzer, and M. Bonitz. "The non-equilibrium Green function approach to inhomogeneous quantum many-body systems using the generalized Kadanoff–Baym ansatz." Physica Scripta T151 (November 1, 2012): 014036. http://dx.doi.org/10.1088/0031-8949/2012/t151/014036.
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Bonitz, M., N. H. Kwong, D. Semkat, and D. Kremp. "Generalized Kadanoff–Baym Theory for Non–Equilibrium Many–Body Systems in External Fields. An Effective Multi–Band Approach." Contributions to Plasma Physics 39, no. 1-2 (1999): 37–40. http://dx.doi.org/10.1002/ctpp.2150390109.
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Watanabe, Haruki, Yankang Liu, and Masaki Oshikawa. "On the General Properties of Non-linear Optical Conductivities." Journal of Statistical Physics 181, no. 6 (October 18, 2020): 2050–70. http://dx.doi.org/10.1007/s10955-020-02654-5.
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AbstractThe optical conductivity is the basic defining property of materials characterizing the current response toward time-dependent electric fields. In this work, following the approach of Kubo’s response theory, we study the general properties of the nonlinear optical conductivities of quantum many-body systems both in equilibrium and non-equilibrium. We obtain an expression of the second- and the third-order optical conductivity in terms of correlation functions and present a perturbative proof of the generalized Kohn formula proposed recently. We also discuss a generalization of the f-sum rule to a non-equilibrium setting by focusing on the instantaneous response.
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Mi, Xiao, Matteo Ippoliti, Chris Quintana, Ami Greene, Zijun Chen, Jonathan Gross, Frank Arute, et al. "Time-crystalline eigenstate order on a quantum processor." Nature 601, no. 7894 (November 30, 2021): 531–36. http://dx.doi.org/10.1038/s41586-021-04257-w.
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AbstractQuantum many-body systems display rich phase structure in their low-temperature equilibrium states1. However, much of nature is not in thermal equilibrium. Remarkably, it was recently predicted that out-of-equilibrium systems can exhibit novel dynamical phases2–8 that may otherwise be forbidden by equilibrium thermodynamics, a paradigmatic example being the discrete time crystal (DTC)7,9–15. Concretely, dynamical phases can be defined in periodically driven many-body-localized (MBL) systems via the concept of eigenstate order7,16,17. In eigenstate-ordered MBL phases, the entire many-body spectrum exhibits quantum correlations and long-range order, with characteristic signatures in late-time dynamics from all initial states. It is, however, challenging to experimentally distinguish such stable phases from transient phenomena, or from regimes in which the dynamics of a few select states can mask typical behaviour. Here we implement tunable controlled-phase (CPHASE) gates on an array of superconducting qubits to experimentally observe an MBL-DTC and demonstrate its characteristic spatiotemporal response for generic initial states7,9,10. Our work employs a time-reversal protocol to quantify the impact of external decoherence, and leverages quantum typicality to circumvent the exponential cost of densely sampling the eigenspectrum. Furthermore, we locate the phase transition out of the DTC with an experimental finite-size analysis. These results establish a scalable approach to studying non-equilibrium phases of matter on quantum processors.
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Chen, Lei, Zhidong Zhang, and Zhaoxin Liang. "Non-equilibrium dynamics of an ultracold Bose gas under multi-pulsed interaction quenches." Modern Physics Letters B 30, no. 30 (November 7, 2016): 1650367. http://dx.doi.org/10.1142/s021798491650367x.
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We investigate the non-equilibrium properties of a weakly interacting Bose gas subjected to a multi-pulsed quench at zero temperature, where the interaction parameter in the Hamiltonian system switches between values [Formula: see text] and [Formula: see text] for multiple times. The one-body and two-body correlation functions as well as Tan’s contact are calculated. The quench induced excitations are shown to increase with the number of quenches for both [Formula: see text] and [Formula: see text]. This implies the possibility to use multi-pulsed quantum quench as a more powerful way as compared to the “one-off” quench in controllable explorations of non-equilibrium quantum many-body systems. In addition, we study the ultra-short-range property of the two-body correlation function after multiple interaction quenches, which can serve as a probe of the “Tan’s contact” in the experiments. Our findings allow for an experimental probe using state of the art techniques with ultracold quantum gases.
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Zakharov, A. Yu, and M. A. Zakharov. "Microscopic dynamic mechanism of equilibration in crystals: one-dimensional model." Journal of Physics: Conference Series 2052, no. 1 (November 1, 2021): 012053. http://dx.doi.org/10.1088/1742-6596/2052/1/012053.
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Abstract The dynamics of free vibrations of a chain of atoms is investigated taking into account the retardation of interactions. It is shown that all oscillations of the circuit are damped. The dynamics of forced vibrations of this chain of atoms is investigated. It is shown that, regardless of the initial conditions, the system passes into a stationary state of dynamic equilibrium with an external field, which depends both on the properties of the system and on the parameters of the external field. A non-statistical dynamic mechanism of the process of irreversible establishment of the state of thermodynamic equilibrium in both many-body and few-body systems is proposed.
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Madeira, Lucas, and Vanderlei S. Bagnato. "Non-Thermal Fixed Points in Bose Gas Experiments." Symmetry 14, no. 4 (March 25, 2022): 678. http://dx.doi.org/10.3390/sym14040678.
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One of the most challenging tasks in physics has been understanding the route an out-of-equilibrium system takes to its thermalized state. This problem can be particularly overwhelming when one considers a many-body quantum system. However, several recent theoretical and experimental studies have indicated that some far-from-equilibrium systems display universal dynamics when close to a so-called non-thermal fixed point (NTFP), following a rescaling of both space and time. This opens up the possibility of a general framework for studying and categorizing out-of-equilibrium phenomena into well-defined universality classes. This paper reviews the recent advances in observing NTFPs in experiments involving Bose gases. We provide a brief introduction to the theory behind this universal scaling, focusing on experimental observations of NTFPs. We present the benefits of NTFP universality classes by analogy with renormalization group theory in equilibrium critical phenomena.
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Hess, P. W., P. Becker, H. B. Kaplan, A. Kyprianidis, A. C. Lee, B. Neyenhuis, G. Pagano, et al. "Non-thermalization in trapped atomic ion spin chains." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, no. 2108 (October 30, 2017): 20170107. http://dx.doi.org/10.1098/rsta.2017.0107.
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Linear arrays of trapped and laser-cooled atomic ions are a versatile platform for studying strongly interacting many-body quantum systems. Effective spins are encoded in long-lived electronic levels of each ion and made to interact through laser-mediated optical dipole forces. The advantages of experiments with cold trapped ions, including high spatio-temporal resolution, decoupling from the external environment and control over the system Hamiltonian, are used to measure quantum effects not always accessible in natural condensed matter samples. In this review, we highlight recent work using trapped ions to explore a variety of non-ergodic phenomena in long-range interacting spin models, effects that are heralded by the memory of out-of-equilibrium initial conditions. We observe long-lived memory in static magnetizations for quenched many-body localization and prethermalization, while memory is preserved in the periodic oscillations of a driven discrete time crystal state. This article is part of the themed issue ‘Breakdown of ergodicity in quantum systems: from solids to synthetic matter’.
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Zhang, Xu, Wenjie Jiang, Jinfeng Deng, Ke Wang, Jiachen Chen, Pengfei Zhang, Wenhui Ren, et al. "Digital quantum simulation of Floquet symmetry-protected topological phases." Nature 607, no. 7919 (July 20, 2022): 468–73. http://dx.doi.org/10.1038/s41586-022-04854-3.
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AbstractQuantum many-body systems away from equilibrium host a rich variety of exotic phenomena that are forbidden by equilibrium thermodynamics. A prominent example is that of discrete time crystals1–8, in which time-translational symmetry is spontaneously broken in periodically driven systems. Pioneering experiments have observed signatures of time crystalline phases with trapped ions9,10, solid-state spin systems11–15, ultracold atoms16,17 and superconducting qubits18–20. Here we report the observation of a distinct type of non-equilibrium state of matter, Floquet symmetry-protected topological phases, which are implemented through digital quantum simulation with an array of programmable superconducting qubits. We observe robust long-lived temporal correlations and subharmonic temporal response for the edge spins over up to 40 driving cycles using a circuit of depth exceeding 240 and acting on 26 qubits. We demonstrate that the subharmonic response is independent of the initial state, and experimentally map out a phase boundary between the Floquet symmetry-protected topological and thermal phases. Our results establish a versatile digital simulation approach to exploring exotic non-equilibrium phases of matter with current noisy intermediate-scale quantum processors21.
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Dyshlovenko, Pavel, Anastasia Batanova, Elena Gladkova, Alexey Nagatkin, and Azat Nizametdinov. "Elastic Properties of Charge Stabilized Colloidal Crystals with Simple Cubic Lattice." Materials Science Forum 845 (March 2016): 178–81. http://dx.doi.org/10.4028/www.scientific.net/msf.845.178.
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Elasticity of charge stabilized colloidal crystals is studied numerically within the approximation of static lattice. Description of the colloidal systems is based on the non-linear differential Poisson-Boltzmann equation. Corresponding boundary value problems are solved numerically by finite element method. The equilibrium pressure and elastic moduli are obtained for different values of the lattice parameter. The many-body effective interactions are briefly discussed.
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De Nardis, Jacopo, Benjamin Doyon, Marko Medenjak, and Miłosz Panfil. "Correlation functions and transport coefficients in generalised hydrodynamics." Journal of Statistical Mechanics: Theory and Experiment 2022, no. 1 (January 1, 2022): 014002. http://dx.doi.org/10.1088/1742-5468/ac3658.
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Abstract We review the recent advances on exact results for dynamical correlation functions at large scales and related transport coefficients in interacting integrable models. We discuss Drude weights, conductivity and diffusion constants, as well as linear and nonlinear response on top of equilibrium and non-equilibrium states. We consider the problems from the complementary perspectives of the general hydrodynamic theory of many-body systems, including hydrodynamic projections, and form-factor expansions in integrable models, and show how they provide a comprehensive and consistent set of exact methods to extract large scale behaviours. Finally, we overview various applications in integrable spin chains and field theories.
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HAFEZI, M. "SYNTHETIC GAUGE FIELDS WITH PHOTONS." International Journal of Modern Physics B 28, no. 02 (December 15, 2013): 1441002. http://dx.doi.org/10.1142/s0217979214410021.
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In this article, we review the recent progress in the implementation of synthetic gauge fields for photons and the investigation of new photonic phenomena, such as non-equilibrium quantum Hall physics. In the first part, we discuss the implementation of magnetic-like Hamiltonians in coupled resonator systems and provide a pedagogical connection between the transfer matrix approach and the couple mode theory to evaluate the system Hamiltonian. In the second part, we discuss the investigation of nonequilibrium fractional quantum Hall physics in photonic systems. In particular, we show that driven strongly interacting photons exhibit interesting many-body behaviors which can be probed using the conventional optical measurement techniques.
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Apollaro, Tony J. G., and Salvatore Lorenzo. "Coexistence of Different Scaling Laws for the Entanglement Entropy in a Periodically Driven System." Proceedings 12, no. 1 (June 25, 2019): 6. http://dx.doi.org/10.3390/proceedings2019012006.
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The out-of-equilibrium dynamics of many body systems has recently received a burst of interest, also due to experimental implementations. The dynamics of observables, such as magnetization and susceptibilities, and quantum information related quantities, such as concurrence and entanglement entropy, have been investigated under different protocols bringing the system out of equilibrium. In this paper we focus on the entanglement entropy dynamics under a sinusoidal drive of the tranverse magnetic field in the 1D quantum Ising model. We find that the area and the volume law of the entanglement entropy coexist under periodic drive for an initial non-critical ground state. Furthermore, starting from a critical ground state, the entanglement entropy exhibits finite size scaling even under such a periodic drive. This critical-like behaviour of the out-of-equilibrium driven state can persist for arbitrarily long time, provided that the entanglement entropy is evaluated on increasingly subsytem sizes, whereas for smaller sizes a volume law holds. Finally, we give an interpretation of the simultaneous occurrence of critical and non-critical behaviour in terms of the propagation of Floquet quasi-particles.
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Yong, Xi, Man-Hong Yung, Xue-Ke Song, Xun Gao, and Angsheng Li. "Emergence of Network Bifurcation Triggered by Entanglement." Quantum 3 (June 3, 2019): 147. http://dx.doi.org/10.22331/q-2019-06-03-147.
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In many non-linear systems, such as plasma oscillation, boson condensation, chemical reaction, and even predatory-prey oscillation, the coarse-grained dynamics are governed by an equation containing anti-symmetric transitions, known as the anti-symmetric Lotka-Volterra (ALV) equations. In this work, we prove the existence of a novel bifurcation mechanism for the ALV equations, where the equilibrium state can be drastically changed by flipping the stability of a pair of fixed points. As an application, we focus on the implications of the bifurcation mechanism for evolutionary networks; we found that the bifurcation point can be determined quantitatively by the microscopic quantum entanglement. The equilibrium state can be critically changed from one type of global demographic condensation to another state that supports global cooperation for homogeneous networks. In other words, our results indicate that there exist a class of many-body systems where the macroscopic properties are invariant with a certain amount of microscopic entanglement, but they can be changed abruptly once the entanglement exceeds a critical value. Furthermore, we provide numerical evidence showing that the emergence of bifurcation is robust against the change of the network topologies, and the critical values are in good agreement with our theoretical prediction. These results show that the bifurcation mechanism could be ubiquitous in many physical systems, in addition to evolutionary networks.
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Sánchez, C. M., P. R. Levstein, L. Buljubasich, H. M. Pastawski, and A. K. Chattah. "Quantum dynamics of excitations and decoherence in many-spin systems detected with Loschmidt echoes: its relation to their spreading through the Hilbert space." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 374, no. 2069 (June 13, 2016): 20150155. http://dx.doi.org/10.1098/rsta.2015.0155.
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In this work, we overview time-reversal nuclear magnetic resonance (NMR) experiments in many-spin systems evolving under the dipolar Hamiltonian. The Loschmidt echo (LE) in NMR is the signal of excitations which, after evolving with a forward Hamiltonian, is recovered by means of a backward evolution. The presence of non-diagonal terms in the non-equilibrium density matrix of the many-body state is directly monitored experimentally by encoding the multiple quantum coherences. This enables a spin counting procedure, giving information on the spreading of an excitation through the Hilbert space and the formation of clusters of correlated spins. Two samples representing different spin systems with coupled networks were used in the experiments. Protons in polycrystalline ferrocene correspond to an ‘infinite’ network. By contrast, the liquid crystal N -(4-methoxybenzylidene)-4-butylaniline in the nematic mesophase represents a finite proton system with a hierarchical set of couplings. A close connection was established between the LE decay and the spin counting measurements, confirming the hypothesis that the complexity of the system is driven by the coherent dynamics.
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Meisinger, Peter N., and Michael C. Ogilvie. "PT symmetry in classical and quantum statistical mechanics." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 371, no. 1989 (April 28, 2013): 20120058. http://dx.doi.org/10.1098/rsta.2012.0058.
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-symmetric Hamiltonians and transfer matrices arise naturally in statistical mechanics. These classical and quantum models often require the use of complex or negative weights and thus fall outside the conventional equilibrium statistical mechanics of Hermitian systems. -symmetric models form a natural class where the partition function is necessarily real, but not necessarily positive. The correlation functions of these models display a much richer set of behaviours than Hermitian systems, displaying sinusoidally modulated exponential decay, as in a dense fluid, or even sinusoidal modulation without decay. Classical spin models with -symmetry include Z( N ) models with a complex magnetic field, the chiral Potts model and the anisotropic next-nearest-neighbour Ising model. Quantum many-body problems with a non-zero chemical potential have a natural -symmetric representation related to the sign problem. Two-dimensional quantum chromodynamics with heavy quarks at non-zero chemical potential can be solved by diagonalizing an appropriate -symmetric Hamiltonian.
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HOLLAND, M. J., J. COOPER, and R. WALSER. "QUANTUM KINETIC THEORY FOR A BOSE-EINSTEIN CONDENSED ALKALI GAS." International Journal of Modern Physics B 15, no. 10n11 (May 10, 2001): 1641–50. http://dx.doi.org/10.1142/s0217979201006148.
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The most salient features of the Bose-Einstein condensation of a magnetically confined alkali vapor is the diluteness of the gas and the extremely weak effective interactions. From a theoretical point of view, the interesting aspect is the potential formulation of the many-body quantum theory for a non-uniform and potentially non-equilibrium system founded entirely on microscopic physics. The crucial postulate is the rapid attenuation of many particle quantum correlations in the dilute system which can be motivated from universal considerations. In principle, it will be possible to provide direct comparison between theory and experiment over all temperature scales with no phenomenological parameters — a challenge facing the theoretical community in the near future. The dilute gas experiments provide an exciting stage on which to build bridges linking the theory of complex and collective phenomena in superconducting and superfluid systems, with the single particle microscopic physics described in quantum optics and laser physics.
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Tindall, Joseph, Frank Schlawin, Michael Sentef, and Dieter Jaksch. "Lieb's Theorem and Maximum Entropy Condensates." Quantum 5 (December 23, 2021): 610. http://dx.doi.org/10.22331/q-2021-12-23-610.
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Coherent driving has established itself as a powerful tool for guiding a many-body quantum system into a desirable, coherent non-equilibrium state. A thermodynamically large system will, however, almost always saturate to a featureless infinite temperature state under continuous driving and so the optical manipulation of many-body systems is considered feasible only if a transient, prethermal regime exists, where heating is suppressed. Here we show that, counterintuitively, in a broad class of lattices Floquet heating can actually be an advantageous effect. Specifically, we prove that the maximum entropy steady states which form upon driving the ground state of the Hubbard model on unbalanced bi-partite lattices possess uniform off-diagonal long-range order which remains finite even in the thermodynamic limit. This creation of a `hot' condensate can occur on any driven unbalanced lattice and provides an understanding of how heating can, at the macroscopic level, expose and alter the order in a quantum system. We discuss implications for recent experiments observing emergent superconductivity in photoexcited materials.
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Dunnett, Angus J., and Alex W. Chin. "Matrix Product State Simulations of Non-Equilibrium Steady States and Transient Heat Flows in the Two-Bath Spin-Boson Model at Finite Temperatures." Entropy 23, no. 1 (January 6, 2021): 77. http://dx.doi.org/10.3390/e23010077.
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Simulating the non-perturbative and non-Markovian dynamics of open quantum systems is a very challenging many body problem, due to the need to evolve both the system and its environments on an equal footing. Tensor network and matrix product states (MPS) have emerged as powerful tools for open system models, but the numerical resources required to treat finite-temperature environments grow extremely rapidly and limit their applications. In this study we use time-dependent variational evolution of MPS to explore the striking theory of Tamascelli et al. (Phys. Rev. Lett. 2019, 123, 090402.) that shows how finite-temperature open dynamics can be obtained from zero temperature, i.e., pure wave function, simulations. Using this approach, we produce a benchmark dataset for the dynamics of the Ohmic spin-boson model across a wide range of coupling strengths and temperatures, and also present a detailed analysis of the numerical costs of simulating non-equilibrium steady states, such as those emerging from the non-perturbative coupling of a qubit to baths at different temperatures. Despite ever-growing resource requirements, we find that converged non-perturbative results can be obtained, and we discuss a number of recent ideas and numerical techniques that should allow wide application of MPS to complex open quantum systems.
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Sierant, Piotr, Giuliano Chiriacò, Federica M. Surace, Shraddha Sharma, Xhek Turkeshi, Marcello Dalmonte, Rosario Fazio, and Guido Pagano. "Dissipative Floquet Dynamics: from Steady State to Measurement Induced Criticality in Trapped-ion Chains." Quantum 6 (February 2, 2022): 638. http://dx.doi.org/10.22331/q-2022-02-02-638.
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Quantum systems evolving unitarily and subject to quantum measurements exhibit various types of non-equilibrium phase transitions, arising from the competition between unitary evolution and measurements. Dissipative phase transitions in steady states of time-independent Liouvillians and measurement induced phase transitions at the level of quantum trajectories are two primary examples of such transitions. Investigating a many-body spin system subject to periodic resetting measurements, we argue that many-body dissipative Floquet dynamics provides a natural framework to analyze both types of transitions. We show that a dissipative phase transition between a ferromagnetic ordered phase and a paramagnetic disordered phase emerges for long-range systems as a function of measurement probabilities. A measurement induced transition of the entanglement entropy between volume law scaling and sub-volume law scaling is also present, and is distinct from the ordering transition. The two phases correspond to an error-correcting and a quantum-Zeno regimes, respectively. The ferromagnetic phase is lost for short range interactions, while the volume law phase of the entanglement is enhanced. An analysis of multifractal properties of wave function in Hilbert space provides a common perspective on both types of transitions in the system. Our findings are immediately relevant to trapped ion experiments, for which we detail a blueprint proposal based on currently available platforms.
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Hangleiter, Dominik, Ingo Roth, Daniel Nagaj, and Jens Eisert. "Easing the Monte Carlo sign problem." Science Advances 6, no. 33 (August 2020): eabb8341. http://dx.doi.org/10.1126/sciadv.abb8341.
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Quantum Monte Carlo (QMC) methods are the gold standard for studying equilibrium properties of quantum many-body systems. However, in many interesting situations, QMC methods are faced with a sign problem, causing the severe limitation of an exponential increase in the runtime of the QMC algorithm. In this work, we develop a systematic, generally applicable, and practically feasible methodology for easing the sign problem by efficiently computable basis changes and use it to rigorously assess the sign problem. Our framework introduces measures of non-stoquasticity that—as we demonstrate analytically and numerically—at the same time provide a practically relevant and efficiently computable figure of merit for the severity of the sign problem. Complementing this pragmatic mindset, we prove that easing the sign problem in terms of those measures is generally an NP-complete task for nearest-neighbor Hamiltonians and simple basis choices by a reduction to the MAXCUT-problem.
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Carrega, Matteo, Joonho Kim, and Dario Rosa. "Unveiling Operator Growth Using Spin Correlation Functions." Entropy 23, no. 5 (May 10, 2021): 587. http://dx.doi.org/10.3390/e23050587.
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In this paper, we study non-equilibrium dynamics induced by a sudden quench of strongly correlated Hamiltonians with all-to-all interactions. By relying on a Sachdev-Ye-Kitaev (SYK)-based quench protocol, we show that the time evolution of simple spin-spin correlation functions is highly sensitive to the degree of k-locality of the corresponding operators, once an appropriate set of fundamental fields is identified. By tracking the time-evolution of specific spin-spin correlation functions and their decay, we argue that it is possible to distinguish between operator-hopping and operator growth dynamics; the latter being a hallmark of quantum chaos in many-body quantum systems. Such an observation, in turn, could constitute a promising tool to probe the emergence of chaotic behavior, rather accessible in state-of-the-art quench setups.
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Esat, Ibrahim I., and Neviman Ozada. "Articular human joint modelling." Robotica 28, no. 2 (December 7, 2009): 321–39. http://dx.doi.org/10.1017/s0263574709990592.
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SUMMARYThe work reported in this paper encapsulates the theories and algorithms developed to drive the core analysis modules of the software which has been developed to model a musculoskeletal structure of anatomic joints. Due to local bone surface and contact geometry based joint kinematics, newly developed algorithms make the proposed modeller different from currently available modellers. There are many modellers that are capable of modelling gross human body motion. Nevertheless, none of the available modellers offer complete elements of joint modelling. It appears that joint modelling is an extension of their core analysis capability, which, in every case, appears to be musculoskeletal motion dynamics. It is felt that an analysis framework that is focused on human joints would have significant benefit and potential to be used in many orthopaedic applications. The local mobility of joints has a significant influence in human motion analysis, in understanding of joint loading, tissue behaviour and contact forces. However, in order to develop a bone surface based joint modeller, there are a number of major problems, from tissue idealizations to surface geometry discretization and non-linear motion analysis. This paper presents the following: (a) The physical deformation of biological tissues as linear or non-linear viscoelastic deformation, based on spring-dashpot elements. (b) The linear dynamic multibody modelling, where the linear formulation is established for small motions and is particularly useful for calculating the equilibrium position of the joint. This model can also be used for finding small motion behaviour or loading under static conditions. It also has the potential of quantifying the joint laxity. (c) The non-linear dynamic multibody modelling, where a non-matrix and algorithmic formulation is presented. The approach allows handling complex material and geometrical nonlinearity easily. (d) Shortest path algorithms for calculating soft tissue line of action geometries. The developed algorithms are based on calculating minimum ‘surface mass’ and ‘surface covariance’. An improved version of the ‘surface covariance’ algorithm is described as ‘residual covariance’. The resulting path is used to establish the direction of forces and moments acting on joints. This information is needed for linear or non-linear treatment of the joint motion. (e) The final contribution of the paper is the treatment of the collision. In the virtual world, the difficulty in analysing bodies in motion arises due to body interpenetrations. The collision algorithm proposed in the paper involves finding the shortest projected ray from one body to the other. The projection of the body is determined by the resultant forces acting on it due to soft tissue connections under tension. This enables the calculation of collision condition of non-convex objects accurately. After the initial collision detection, the analysis involves attaching special springs (stiffness only normal to the surfaces) at the ‘potentially colliding points’ and motion of bodies is recalculated. The collision algorithm incorporates the rotation as well as translation. The algorithm continues until the joint equilibrium is achieved. Finally, the results obtained based on the software are compared with experimental results obtained using cadaveric joints.
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Lee, Chiu Fan. "An infinite set of integral formulae for polar, nematic, and higher order structures at the interface of motility-induced phase separation." New Journal of Physics 24, no. 4 (April 1, 2022): 043010. http://dx.doi.org/10.1088/1367-2630/ac51aa.
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Abstract Motility-induced phase separation (MIPS) is a purely non-equilibrium phenomenon in which self-propelled particles phase separate without any attractive interactions. One surprising feature of MIPS is the emergence of polar, nematic, and higher order structures at the interfacial region, whose underlying physics remains poorly understood. Starting with a model of MIPS in which all many-body interactions are captured by an effective speed function and an effective pressure function that depend solely on the local particle density, I derive analytically an infinite set of integral formulae for the ordering structures at the interface. I then demonstrate that half of these IF are in fact exact for generic active Brownian particle systems. Finally, I test these integral formulae by applying them to numerical data from direct particle dynamics simulation and find that they remain valid to a great extent.
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Kas, J. J., F. D. Vila, C. D. Pemmaraju, T. S. Tan, and J. J. Rehr. "Advanced calculations of X-ray spectroscopies with FEFF10 and Corvus." Journal of Synchrotron Radiation 28, no. 6 (October 5, 2021): 1801–10. http://dx.doi.org/10.1107/s1600577521008614.
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The real-space Green's function code FEFF has been extensively developed and used for calculations of X-ray and related spectra, including X-ray absorption (XAS), X-ray emission (XES), inelastic X-ray scattering, and electron energy-loss spectra. The code is particularly useful for the analysis and interpretation of the XAS fine-structure (EXAFS) and the near-edge structure (XANES) in materials throughout the periodic table. Nevertheless, many applications, such as non-equilibrium systems, and the analysis of ultra-fast pump–probe experiments, require extensions of the code including finite-temperature and auxiliary calculations of structure and vibrational properties. To enable these extensions, we have developed in tandem a new version FEFF10 and new FEFF-based workflows for the Corvus workflow manager, which allow users to easily augment the capabilities of FEFF10 via auxiliary codes. This coupling facilitates simplified input and automated calculations of spectra based on advanced theoretical techniques. The approach is illustrated with examples of high-temperature behavior, vibrational properties, many-body excitations in XAS, super-heavy materials, and fits of calculated spectra to experiment.
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Kas, J. J., F. D. Vila, C. D. Pemmaraju, T. S. Tan, and J. J. Rehr. "Advanced calculations of X-ray spectroscopies with FEFF10 and Corvus." Journal of Synchrotron Radiation 28, no. 6 (October 5, 2021): 1801–10. http://dx.doi.org/10.1107/s1600577521008614.
Full textAbstract:
The real-space Green's function code FEFF has been extensively developed and used for calculations of X-ray and related spectra, including X-ray absorption (XAS), X-ray emission (XES), inelastic X-ray scattering, and electron energy-loss spectra. The code is particularly useful for the analysis and interpretation of the XAS fine-structure (EXAFS) and the near-edge structure (XANES) in materials throughout the periodic table. Nevertheless, many applications, such as non-equilibrium systems, and the analysis of ultra-fast pump–probe experiments, require extensions of the code including finite-temperature and auxiliary calculations of structure and vibrational properties. To enable these extensions, we have developed in tandem a new version FEFF10 and new FEFF-based workflows for the Corvus workflow manager, which allow users to easily augment the capabilities of FEFF10 via auxiliary codes. This coupling facilitates simplified input and automated calculations of spectra based on advanced theoretical techniques. The approach is illustrated with examples of high-temperature behavior, vibrational properties, many-body excitations in XAS, super-heavy materials, and fits of calculated spectra to experiment.
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Aris Chatzidimitriou-Dreismann, C. "Quantumness of correlations in nanomaterials—experimental evidence and unconventional effects." AIMS Materials Science 9, no. 3 (2022): 382–405. http://dx.doi.org/10.3934/matersci.2022023.
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<abstract><p>Quantum correlations phenomena, such as entanglement, quantum discord and quantum coherence, are ubiquitous effects caused by interactions between physical systems—such as electrons and ions in a piece of metal, or H atoms/molecules adsorbed in nanoporous materials. Here, we address time-asymmetric quantumness of correlations (QoC), with particular emphasis on their energetic consequences for dynamics and non-equilibrium thermodynamics in condensed matter and/or many-body systems. Some known theoretical models—for example, the quantum Zeno effect and GKSL-type Markovian equations-of-motion, all of them being time-asymmetric—are shortly considered, with emphasis on the general character of one of their common and most intriguing result. Namely, that in clear contradistinction to conventional expectations, degradation (or destruction, decoherence, consumption, smearing out, coarse-graining) of quantum correlations can be a source of work (instead of heat production). The experimental relevance of the theoretical considerations is shown with the aid of a recent scattering experiment exploring the impulsively driven (by neutron collisions) translational dynamics of H$ _2 $ molecules in carbon nanotubes and other nanostructured materials—a topic of immediate relevance for material sciences and related technologies.</p></abstract>
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Roux, Benoît, Toby Allen, Simon Bernèche, and Wonpil Im. "Theoretical and computational models of biological ion channels." Quarterly Reviews of Biophysics 37, no. 1 (February 2004): 15–103. http://dx.doi.org/10.1017/s0033583504003968.
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1. Introduction 172. Dynamics of many-body systems 192.1 Effective dynamics of reduced systems 212.2 The constraint of thermodynamic equilibrium 242.3 Mean-field theories 253. Solvation free energy and electrostatics 273.1 Microscopic view of the Born model 273.2 Ion–Ion interactions in bulk solution 293.3 Continuum electrostatics and the PB equation 293.4 Limitations of continuum dielectric models 323.5 The dielectric barrier 333.6 The transmembrane potential and the PB-V equation 354. Statistical mechanical equilibrium theory 404.1 Multi-ion PMF 404.2 Equilibrium probabilities of occupancy 434.3 Coupling to the membrane potential 444.4 Ionic selectivity 484.5 Reduction to a one-dimensional (1D) free-energy profile 495. From MD toI–V: a practical guide 505.1 Extracting the essential ingredients from MD 515.1.1 Channel conductance from equilibrium and non-equilibrium MD 515.1.2 PMF techniques 525.1.3 Friction and diffusion coefficient techniques 535.1.4 About computational times 555.2 Ion permeation models 565.2.1 The 1D-NP electrodiffusion theory 565.2.2 Discrete-state Markov chains 575.2.3 The GCMC/BD algorithm 585.2.4 PNP electrodiffusion theory 626. Computational studies of ion channels 636.1 Computational studies of gA 656.1.1 Free-energy surface for K+ permeation 666.1.2 Mean-force decomposition 696.1.3 Cation-binding sites 696.1.4 Channel conductance 706.1.5 Selectivity 726.2 Computational studies of KcsA 726.2.1 Multi-ion free-energy surface and cation-binding sites 736.2.2 Channel conductance 746.2.3 Mechanism of ion conduction 776.2.4 Selectivity 786.3 Computational studies of OmpF 796.3.1 The need to compare the different level of approximations 796.3.2 Equilibrium protein fluctuations and ion distribution 806.3.3 Non-equilibrium ion fluxes 806.3.4 Reversal potential and selectivity 846.4 Successes and limitations 876.4.1 Channel structure 876.4.2 Ion-binding sites 876.4.3 Ion conduction 886.4.4 Ion selectivity 897. Conclusion 908. Acknowledgments 939. References 93The goal of this review is to establish a broad and rigorous theoretical framework to describe ion permeation through biological channels. This framework is developed in the context of atomic models on the basis of the statistical mechanical projection-operator formalism of Mori and Zwanzig. The review is divided into two main parts. The first part introduces the fundamental concepts needed to construct a hierarchy of dynamical models at different level of approximation. In particular, the potential of mean force (PMF) as a configuration-dependent free energy is introduced, and its significance concerning equilibrium and non-equilibrium phenomena is discussed. In addition, fundamental aspects of membrane electrostatics, with a particular emphasis on the influence of the transmembrane potential, as well as important computational techniques for extracting essential information from all-atom molecular dynamics (MD) simulations are described and discussed. The first part of the review provides a theoretical formalism to ‘translate’ the information from the atomic structure into the familiar language of phenomenological models of ion permeation. The second part is aimed at reviewing and contrasting results obtained in recent computational studies of three very different channels; the gramicidin A (gA) channel, which is a narrow one-ion pore (at moderate concentration), the KcsA channel from Streptomyces lividans, which is a narrow multi-ion pore, and the outer membrane matrix porin F (OmpF) from Escherichia coli, which is a trimer of three β-barrel subunits each forming wide aqueous multi-ion pores. Comparison with experiments demonstrates that current computational models are approaching semi-quantitative accuracy and are able to provide significant insight into the microscopic mechanisms of ion conduction and selectivity. We conclude that all-atom MD with explicit water molecules can represent important structural features of complex biological channels accurately, including such features as the location of ion-binding sites along the permeation pathway. We finally discuss the broader issue of the validity of ion permeation models and an outlook to the future.
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MACDONALD, ALLAN. "SPIN AND PSEUDOSPIN TRANSFER." International Journal of Modern Physics B 22, no. 01n02 (January 20, 2008): 121. http://dx.doi.org/10.1142/s0217979208046220.
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Electrons in a Fermi liquid can be regarded as non-interacting particles (quasiparticles) in an effective potential that is a consequence of interactions between electrons. In many-body theory the effective potential is known as the electronic self-energy. When the electronic system has a broken symmetry, the effective potential can have different symmetries than the potential term that appears in the single particle Hamiltonian. For example, the effective potential of a superconductor includes terms that change the electron particle number and the effective potential of a ferromagnet includes terms that change the electron spin. When the electron system is not in equilibrium, the effective potential is altered. I will present a view of spin-transfer phenomena in ferromagnetic metals in which current-induced spin torques arise from changes in the ferromagnet's spin-dependent effective potential when the quasiparticle system is held out of equilibrium by applying a bias potential. In this view spin-transfer is an example of a more general set of phenomena and is not fundamentally associated with an approximate conservation law, for example the approximate conservation of total spin angular momentum. I will illustrate this point of view by discussing other examples of spin-transfer like phenomena, including transport anomalies that have been observed in bilayer quantum Hall systems, current-driven magnetization changes in antiferromagnetic metals, and current-drive bond-weakening in molecular electronics. Note from Publisher: This article contains the abstract only.
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Wang, Haina, Frank H. Stillinger, and Salvatore Torquato. "Realizability of iso-g2 processes via effective pair interactions." Journal of Chemical Physics 157, no. 22 (December 14, 2022): 224106. http://dx.doi.org/10.1063/5.0130679.
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An outstanding problem in statistical mechanics is the determination of whether prescribed functional forms of the pair correlation function g2( r) [or equivalently, structure factor S( k)] at some number density ρ can be achieved by many-body systems in d-dimensional Euclidean space. The Zhang–Torquato conjecture states that any realizable set of pair statistics, whether from a nonequilibrium or equilibrium system, can be achieved by equilibrium systems involving up to two-body interactions. To further test this conjecture, we study the realizability problem of the nonequilibrium iso- g2 process, i.e., the determination of density-dependent effective potentials that yield equilibrium states in which g2 remains invariant for a positive range of densities. Using a precise inverse algorithm that determines effective potentials that match hypothesized functional forms of g2( r) for all r and S( k) for all k, we show that the unit-step function g2, which is the zero-density limit of the hard-sphere potential, is remarkably realizable up to the packing fraction ϕ = 0.49 for d = 1. For d = 2 and 3, it is realizable up to the maximum “terminal” packing fraction ϕ c = 1/2 d, at which the systems are hyperuniform, implying that the explicitly known necessary conditions for realizability are sufficient up through ϕ c. For ϕ near but below ϕ c, the large- r behaviors of the effective potentials are given exactly by the functional forms exp[ − κ( ϕ) r] for d = 1, r−1/2 exp[ − κ( ϕ) r] for d = 2, and r−1 exp[ − κ( ϕ) r] (Yukawa form) for d = 3, where κ−1( ϕ) is a screening length, and for ϕ = ϕ c, the potentials at large r are given by the pure Coulomb forms in the respective dimensions as predicted by Torquato and Stillinger [Phys. Rev. E 68, 041113 (2003)]. We also find that the effective potential for the pair statistics of the 3D “ghost” random sequential addition at the maximum packing fraction ϕ c = 1/8 is much shorter ranged than that for the 3D unit-step function g2 at ϕ c; thus, it does not constrain the realizability of the unit-step function g2. Our inverse methodology yields effective potentials for realizable targets, and, as expected, it does not reach convergence for a target that is known to be non-realizable, despite the fact that it satisfies all known explicit necessary conditions. Our findings demonstrate that exploring the iso- g2 process via our inverse methodology is an effective and robust means to tackle the realizability problem and is expected to facilitate the design of novel nanoparticle systems with density-dependent effective potentials, including exotic hyperuniform states of matter.
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Malov, Yuri S., and Igor M. Borisov. "Norm and human health." Bulletin of the Russian Military Medical Academy 23, no. 2 (July 12, 2021): 229–36. http://dx.doi.org/10.17816/brmma70958.
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The concept of norms is common to biology and medicine. It represents the essence of any phenomenon. In medicine, human health is expressed through the category of norm. The basis of the construction of the norm (normology) should be based on the principle of correspondence of morphofunctional properties of the organism to the environment, and not their nature. And then indicators that reflect the stability of a living non-equilibrium system or the state of an adapted organism will characterize (normal) human health. The norm is always stable, otherwise it will not be the norm. The science of human health developed through analysis the decomposition of a complex whole into simple parts. In this case, the object disappeared as a whole, as a system with all its inherent features. The norm was derived from the fitness, balance of the body with the environment. Recently, it has become possible to consider a person as a system that is determined by the relationship of the whole and its parts (the golden ratio). In biology, the golden ratio manifests itself in many ways, from the structure of polypeptides to the human body. The study of a living organism as a system allowed us to establish the harmonic essence of its structure. The idea of the harmony of the world of systems is connected with the relations of "opposites" within the object. The "golden opposites" of healthy people are a kind of norm reference. What brings "opposites" to unity is harmony. Harmony is closely related to the golden ratio. Golden harmony is the basis of human health. Mathematical expression of harmony, symmetry a method of assessing (norm) human health. Deviations from the "golden" relations can be used in medicine as indicators (criteria) for the diagnosis of pathological disorders.
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DAVIDSON, P. A. "An energy criterion for the linear stability of conservative flows." Journal of Fluid Mechanics 402 (January 10, 2000): 329–48. http://dx.doi.org/10.1017/s002211209900693x.
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We investigate the linear stability of inviscid flows which are subject to a conservative body force. This includes a broad range of familiar conservative systems, such as ideal MHD, natural convection, flows driven by electrostatic forces and axisymmetric, swirling, recirculating flow. We provide a simple, unified, linear stability criterion valid for any conservative system. In particular, we establish a principle of maximum action of the formformula herewhere η is the Lagrangian displacement,e is a measure of the disturbance energy, T and V are the kinetic and potential energies, and L is the Lagrangian. Here d represents a variation of the type normally associated with Hamilton's principle, in which the particle trajectories are perturbed in such a way that the time of flight for each particle remains the same. (In practice this may be achieved by advecting the streamlines of the base flow in a frozen-in manner.) A simple test for stability is that e is positive definite and this is achieved if L(η) is a maximum at equilibrium. This captures many familiar criteria, such as Rayleigh's circulation criterion, the Rayleigh–Taylor criterion for stratified fluids, Bernstein's principle for magnetostatics, Frieman & Rotenberg's stability test for ideal MHD equilibria, and Arnold's variational principle applied to Euler flows and to ideal MHD. There are three advantages to our test: (i) d2T(η) has a particularly simple quadratic form so the test is easy to apply; (ii) the test is universal and applies to any conservative system; and (iii) unlike other energy principles, such as the energy-Casimir method or the Kelvin–Arnold variational principle, there is no need to identify all of the integral invariants of the flow as a precursor to performing the stability analysis. We end by looking at the particular case of MHD equilibria. Here we note that when u and B are co-linear there exists a broad range of stable steady flows. Moreover, their stability may be assessed by examining the stability of an equivalent magnetostatic equilibrium. When u and B are non-parallel, however, the flow invariably violates the energy criterion and so could, but need not, be unstable. In such cases we identify one mode in which the Lagrangian displacement grows linearly in time. This is reminiscent of the short-wavelength instability of non-Beltrami Euler flows.
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Špička, Václav, Bedřich Velický, and Anděla Kalvová. "Electron systems out of equilibrium: Nonequilibrium Green's function approach." International Journal of Modern Physics B 28, no. 23 (July 13, 2014): 1430013. http://dx.doi.org/10.1142/s0217979214300138.
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This review deals with the state of the art and perspectives of description of nonequilibrium many-body systems using the nonequilibrium Green's function (NGF) method. The basic aim is to describe time evolution of the many-body system from its initial state over its transient dynamics to its long time asymptotic evolution. First, we discuss basic aims of transport theories to motivate the introduction of the NGF techniques. Second, this article summarizes the present view on construction of the electron transport equations formulated within the NGF approach to nonequilibrium. We discuss incorporation of complex initial conditions to the NGF formalism, and the NGF reconstruction theorem, which serves as a tool to derive simplified kinetic equations. Three stages of evolution of the nonequilibrium, the first described by the full NGF description, the second by a non-Markovian generalized master equation and the third by a Markovian master equation will be related to each other.
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Ansari, Lida, Paul Hurley, and Farzan Gity. "Two-Dimensional Gallium Selenide (GaSe) Material for Nanoelectronics Application." ECS Meeting Abstracts MA2022-01, no. 12 (July 7, 2022): 868. http://dx.doi.org/10.1149/ma2022-0112868mtgabs.
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As silicon-based transistors have approached their physical limits, it is urgent to explore alternative materials with a suitable bandgap and high mobility for next generation electronic logic devices. Two‐dimensional (2D) materials have attracted significant attention in the last few years due to their potential exotic transport physics and technological applications in various fields, such as a significant device downscaling for high intensity integration. Recently, a variety of 2D materials have been explored, including graphene [1] and transition metal dichalcogenides (TMDs), e.g., MoS2 [2,3], WS2 [4], and PtSe2 [5-7]. Although most research has focused on TMDs, recently 2D layered metal monochalcogenides, e.g., GaSe, have attracted increasing interest as a result of their unique electronic properties, making this class of materials different from TMDs. GaSe crystal structure comprises vertically stacked Ga-Se-Se-Ga layers with relatively weak van der Waals interactions. There are two main GaSe polytypes which differ in the stacking sequence of the basis layer units. Side- and top-view schematics of β‐GaSe and ε‐GaSe are shown in Fig. 1a. In this study, the electronic structure of both GaSe layered material polytypes is investigated using density functional theory (DFT) as implemented in QuantumATK [8]. Brillouin-zone integrations were performed according to the Monkhorst-Pack scheme [9] with a density of approximately 10 k-points per angstrom. Geometry optimizations were performed with the convergence criterion of 0.02 eV/Å [10]. Van der Waals (vdW) interactions improve the structural and electronic properties description obtained by DFT calculations and is included in our calculations through D3 version of Grimme’s dispersion corrections [11]. To provide an improved determination of the bandgap energies, the GW (G: Green's function and W: screened Coulomb interaction) method in conjunction with a many body perturbation theory (MBPT) correction could be used. However, GW technique is computationally very expensive and could be implemented for systems with very limited number of atoms [12,13]. Hence, for this study, methods such as Heyd-Scuseria-Ernzerhof (HSE) hybrid functional [14,15] and GGA-1/2 [16] methods were included in our model to achieve more accurate bandgap compared to the experimental values. The β‐GaSe exhibits a DFT-obtained direct bandgap of ~1 eV while the corrected value is 2 eV. ε‐GaSe, however, shows slight indirect bandgap of 0.8 eV (DFT) and 1.7 eV (corrected), with just 25 meV difference between the indirect gap and indirect gap. A double-gate Schottky barrier field-effect transistor (FET) consisting of Ti source and drain contacts and ultrathin GaSe channel is also investigated. Schematic of the FET is shown in Fig. 1b. The device performance analysis such as current-voltage characteristics, subthreshold slope, and on/off ratio are carried out by means of non-equilibrium Green’s function together with DFT Hamiltonian [17]. The output characteristic of the proposed device exhibits an ON/OFF current ratio of more than 7 orders of magnitude. The presence of point defects in ultrathin 2D films is largely inevitable [18], even under optimized synthesis conditions, which can be either engineered and considered as a useful feature, or undesirable. In either case, understanding the impacts of point defects on the electronic structure of 2D materials are required to allow application-based optimization. In this talk, to provide insight into the defect-induced modifications to the GaSe electronic properties, in particular the properties of the states associated with the defects, we will compare the band-structure of the pristine GaSe with the band-structure of the GaSe with Ge and Se vacancies, for both GaSe polytypes. We have also fabricated back-gated devices by mechanically exfoliating ultrathin GaSe flakes from bulk crystal onto oxide-on-Si substrate. Fig. 1c shows an SEM image of the device. Our experimental results demonstrate the basic transport characteristics of thin-film transistor, which may offer more opportunities for potential applications such as photodetectors, gas sensors, and optoelectronic devices, in addition to nanoelectronics FETs, due to GaSe large bandgap. References: [1] Nature Materials, 6, 183, 2007. [2] 2D Materials, 8, 025008, 2020. [3] 2D Materials, 7, 025040, 2020. [4] ACS Materials Letters, 2, 511, 2020. [5] ACS Omega, 4, pp. 17487-17493, 2019. [6] Advanced Functional Materials, 2103936, 2021. [7] Advanced Functional Materials, 2105722, 2021. [8] J. Phys.: Condens. Matter, 32 015901, 2020 [9] Phys. Rev. B, 13, 5188, 1976. [10] J. Applied Physics, 129, 015701, 2021. [11] J. Chem. Phys., 132, 154104, 2010. [12] J. Phys.: Condens. Matter, 29 065301, 2017. [13] Appl. Phys. Lett., 110, 093111, 2017. [14] J. Chem. Phys. 118, 8207, 2003. [15] Applied Materials Today, 25, 101163, 2021. [16] AIP Advances, 1, 032119, 2011. [17] J. Phys.: Condens. Matter., 30, 414003, 2018. [18] Npj 2D Materials and Applications, 5, 14, 2021. . Figure 1
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Fauseweh, Benedikt, and Jian-Xin Zhu. "Digital quantum simulation of non-equilibrium quantum many-body systems." Quantum Information Processing 20, no. 4 (April 2021). http://dx.doi.org/10.1007/s11128-021-03079-z.
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Yoshida, Tsuneya, Robert Peters, Norio Kawakami, and Yasuhiro Hatsugai. "Exceptional band touching for strongly correlated systems in equilibrium." Progress of Theoretical and Experimental Physics 2020, no. 12 (July 24, 2020). http://dx.doi.org/10.1093/ptep/ptaa059.
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Abstract Quasi-particles described by Green‘s functions of equilibrium systems exhibit non-Hermitian topological phenomena because of their finite lifetime. This non-Hermitian perspective on equilibrium systems provides new insights into correlated systems and attracts much interest because of its potential to solve open questions in correlated compounds. We provide a concise review of the non-Hermitian topological band structures for quantum many-body systems in equilibrium, as well as their classification.
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Ridley, Michael, N. Walter Talarico, Daniel Karlsson, Nicola Lo Gullo, and Riku Tuovinen. "A many-body approach to transport in quantum systems: From the transient regime to the stationary state." Journal of Physics A: Mathematical and Theoretical, May 18, 2022. http://dx.doi.org/10.1088/1751-8121/ac7119.
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Abstract We review one of the most versatile theoretical approaches to the study of time-dependent correlated quantum transport in nano-systems: the non-equilibrium Green's function (NEGF) formalism. Within this formalism, one can treat, on the same footing, inter-particle interactions, external drives and/or perturbations, and coupling to baths with a (piece-wise) continuum set of degrees of freedom. After a historical overview on the theory of transport in quantum systems, we present a modern introduction of the NEGF approach to quantum transport. We discuss the inclusion of inter-particle interactions using diagrammatic techniques, and the use of the so-called embedding and inbedding techniques which take the bath couplings into account non-perturbatively. In various limits, such as the non-interacting limit and the steady-state limit, we then show how the NEGF formalism elegantly reduces to well-known formulae in quantum transport as special cases. We then discuss non-equilibrium transport in general, for both particle and energy currents. Under the presence of a time-dependent drive -- encompassing pump--probe scenarios as well as driven quantum systems -- we discuss the transient as well as asymptotic behavior, and also how to use NEGF to infer information on the out-of-equilibrium system. As illustrative examples, we consider model systems general enough to pave the way to realistic systems. These examples encompass one- and two-dimensional electronic systems, systems with electron--phonon couplings, topological superconductors, and optically responsive molecular junctions where electron--photon couplings are relevant.
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Tang, Jiachen, Su-Peng Kou, and Gaoyong Sun. "Dynamical scaling of Loschmidt echo in non-Hermitian systems." Europhysics Letters, February 10, 2022. http://dx.doi.org/10.1209/0295-5075/ac53c4.
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Abstract We show that non-Hermitian biorthogonal many-body phase transitions can be characterized by the enhanced decay of Loschmidt echo. The quantum criticality is numerically investigated in a non-Hermitian transverse field Ising model by performing the finite-size dynamical scaling of Loschmidt echo. We determine the equilibrium correlation length critical exponents that are consistent with previous results from the exact diagonalization. More importantly, we introduce a simple method to detect quantum phase transitions with the short-time average of rate function motivated by the critically enhanced decay behavior of Loschmidt echo. Our studies show how to detect equilibrium many-body phase transitions with biorthogonal Loschmidt echo that can be observed in future experiments via quantum dynamics after a quench.
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Zhang Xi-Zheng, Wang Peng, Zhang Kun-Liang, Yang Xue-Min, and Song Zhi. "Non-Hermitian critical dynamics and its application to quantum many-body systems." Acta Physica Sinica, 2022, 0. http://dx.doi.org/10.7498/aps.71.20220914.
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In recent years, two independent research fields, non-Hermitian and strongly correlated systems, began to merge and form an important research field in physics. The progress of relevant theories and experiments has reshaped our understanding of matter. In this field, the research object is not limited to the influence of non-Hermiticity on the energy spectrum and eigenstate properties of many-body systems. Researchers pay more attention to the manipulation of quantum states. As the most significant feature of non-Hermitian quantum mechanics distinct from Hermitian quantum mechanics, exceptional points have attracted extensive attention. In addition to the recent advances in nonHermitian topological band theory and quantum sensing around the exceptional points, this paper concentrate on the non-Hermitian critical dynamical phenomenon and its application to the quantum many-body system. When the system has an exceptional point, an arbitrary initial state belonged to the coalescent subspace will be projected on the coalescent state. Based on the directionality of the evolved quantum state, this paper reviews several representative works of our research group in recent years, including local-field-induced dynamical magnetization, quantum phase transition in transverse field Ising model at non-zero temperature, quantum mold casting in the center-environment system, as well as superconducting state preparation in the non-Hermitian strongly correlated system. We focus on the new preparation methods and detection schemes of non-equilibrium quantum states related to exception points.
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Hyrkäs, Markku, Daniel Karlsson, and Robert van Leeuwen. "Cutting rules and positivity in finite temperature many-body theory." Journal of Physics A: Mathematical and Theoretical, July 11, 2022. http://dx.doi.org/10.1088/1751-8121/ac802d.
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Abstract For a given diagrammatic approximation in many-body perturbation theory it is not guaranteed that positive observables, such as the density or the spectral function, retain their positivity. For zero-temperature systems we developed a method [Phys.Rev.B{\bf 90},115134 (2014)] based on so-called cutting rules for Feynman diagrams that enforces these properties diagrammatically, thus solving the problem of negative spectral densities observed for various vertex approximations. In this work we extend this method to systems at finite temperature by formulating the cutting rules in terms of retarded $N$-point functions, thereby simplifying earlier approaches and simultaneously solving the issue of non-vanishing vacuum diagrams that has plagued finite temperature expansions. Our approach is moreover valid for nonequilibrium systems in initial equilibrium and allows us to show that important commonly used approximations, namely the $GW$, second Born and $T$-matrix approximation, retain positive spectral functions at finite temperature. Finally we derive an analytic continuation relation between the spectral forms of retarded $N$-point functions and their Matsubara counterparts and a set of Feynman rules to evaluate them.
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Perfetto, Gabriele, and Benjamin Doyon. "Euler-scale dynamical fluctuations in non-equilibrium interacting integrable systems." SciPost Physics 10, no. 5 (May 27, 2021). http://dx.doi.org/10.21468/scipostphys.10.5.116.
Full textAbstract:
We derive an exact formula for the scaled cumulant generating function of the time-integrated current associated to an arbitrary ballistically transported conserved charge. Our results rely on the Euler-scale description of interacting, many-body, integrable models out of equilibrium given by the generalized hydrodynamics, and on the large deviation theory. Crucially, our findings extend previous studies by accounting for inhomogeneous and dynamical initial states in interacting systems. We present exact expressions for the first three cumulants of the time-integrated current. Considering the non-interacting limit of our general expression for the scaled cumulant generating function, we further show that for the partitioning protocol initial state our result coincides with previous results of the literature. Given the universality of the generalized hydrodynamics, the expression obtained for the scaled cumulant generating function is applicable to any interacting integrable model obeying the hydrodynamic equations, both classical and quantum.
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Huber, Julian, Peter Kirton, and Peter Rabl. "Phase-space methods for simulating the dissipative many-body dynamics of collective spin systems." SciPost Physics 10, no. 2 (February 22, 2021). http://dx.doi.org/10.21468/scipostphys.10.2.045.
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We describe an efficient numerical method for simulating the dynamics and steady states of collective spin systems in the presence of dephasing and decay. The method is based on the Schwinger boson representation of spin operators and uses an extension of the truncated Wigner approximation to map the exact open system dynamics onto stochastic differential equations for the corresponding phase space distribution. This approach is most effective in the limit of very large spin quantum numbers, where exact numerical simulations and other approximation methods are no longer applicable. We benchmark this numerical technique for known superradiant decay and spin-squeezing processes and illustrate its application for the simulation of non-equilibrium phase transitions in dissipative spin lattice models.
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Gnesotto, Federico S., Grzegorz Gradziuk, Pierre Ronceray, and Chase P. Broedersz. "Learning the non-equilibrium dynamics of Brownian movies." Nature Communications 11, no. 1 (October 23, 2020). http://dx.doi.org/10.1038/s41467-020-18796-9.
Full textAbstract:
Abstract Time-lapse microscopy imaging provides direct access to the dynamics of soft and living systems. At mesoscopic scales, such microscopy experiments reveal intrinsic thermal and non-equilibrium fluctuations. These fluctuations, together with measurement noise, pose a challenge for the dynamical analysis of these Brownian movies. Traditionally, methods to analyze such experimental data rely on tracking embedded or endogenous probes. However, it is in general unclear, especially in complex many-body systems, which degrees of freedom are the most informative about their non-equilibrium nature. Here, we introduce an alternative, tracking-free approach that overcomes these difficulties via an unsupervised analysis of the Brownian movie. We develop a dimensional reduction scheme selecting a basis of modes based on dissipation. Subsequently, we learn the non-equilibrium dynamics, thereby estimating the entropy production rate and time-resolved force maps. After benchmarking our method against a minimal model, we illustrate its broader applicability with an example inspired by active biopolymer gels.
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Benary, Jens, Christian Baals, Erik Bernhard, Jian Jiang, Marvin Röhrle, and Herwig Ott. "Experimental observation of a dissipative phase transition in a multi-mode many-body quantum system." New Journal of Physics, October 5, 2022. http://dx.doi.org/10.1088/1367-2630/ac97b6.
Full textAbstract:
Abstract Dissipative phase transitions are a characteristic feature of open systems. One of the paradigmatic examples for a first order dissipative phase transition is the driven nonlinear single mode optical resonator. In this work, we study a realization with an ultracold bosonic quantum gas, which generalizes the single mode system to many modes and stronger interactions. We measure the effective Liouvillian gap of the system and find evidence for a first order dissipative phase transition. Due to the multi-mode nature of the system, the microscopic dynamics is much richer and allows us to identify a non-equilibrium condensation process.