Artykuły w czasopismach: „Non-ergodicity in many body systems”

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De Roeck, Wojciech, i John Z. Imbrie. "Many-body localization: stability and instability". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, nr 2108 (30.10.2017): 20160422. http://dx.doi.org/10.1098/rsta.2016.0422.

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Rare regions with weak disorder (Griffiths regions) have the potential to spoil localization. We describe a non-perturbative construction of local integrals of motion (LIOMs) for a weakly interacting spin chain in one dimension, under a physically reasonable assumption on the statistics of eigenvalues. We discuss ideas about the situation in higher dimensions, where one can no longer ensure that interactions involving the Griffiths regions are much smaller than the typical energy-level spacing for such regions. We argue that ergodicity is restored in dimension d >1, although equilibration should be extremely slow, similar to the dynamics of glasses. This article is part of the themed issue ‘Breakdown of ergodicity in quantum systems: from solids to synthetic matter’.

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Blok, B., i X. G. Wen. "Many-body systems with non-abelian statistics". Nuclear Physics B 374, nr 3 (maj 1992): 615–46. http://dx.doi.org/10.1016/0550-3213(92)90402-w.

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Hess, P. W., P. Becker, H. B. Kaplan, A. Kyprianidis, A. C. Lee, B. Neyenhuis, G. Pagano i in. "Non-thermalization in trapped atomic ion spin chains". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, nr 2108 (30.10.2017): 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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Moore, Joel E. "A perspective on quantum integrability in many-body-localized and Yang–Baxter systems". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, nr 2108 (30.10.2017): 20160429. http://dx.doi.org/10.1098/rsta.2016.0429.

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Two of the most active areas in quantum many-particle dynamics involve systems with an unusually large number of conservation laws. Many-body-localized systems generalize ideas of Anderson localization by disorder to interacting systems. While localization still exists with interactions and inhibits thermalization, the interactions between conserved quantities lead to some dramatic differences from the Anderson case. Quantum integrable models such as the XXZ spin chain or Bose gas with delta-function interactions also have infinite sets of conservation laws, again leading to modifications of conventional thermalization. A practical way to treat the hydrodynamic evolution from local equilibrium to global equilibrium in such models is discussed. This paper expands upon a presentation at a discussion meeting of the Royal Society on 7 February 2017. The work described was carried out with a number of collaborators, including Jens Bardarson, Vir Bulchandani, Roni Ilan, Christoph Karrasch, Siddharth Parameswaran, Frank Pollmann and Romain Vasseur. This article is part of the themed issue ‘Breakdown of ergodicity in quantum systems: from solids to synthetic matter’.

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Ponte, Pedro, C. R. Laumann, David A. Huse i A. Chandran. "Thermal inclusions: how one spin can destroy a many-body localized phase". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, nr 2108 (30.10.2017): 20160428. http://dx.doi.org/10.1098/rsta.2016.0428.

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Many-body localized (MBL) systems lie outside the framework of statistical mechanics, as they fail to equilibrate under their own quantum dynamics. Even basic features of MBL systems, such as their stability to thermal inclusions and the nature of the dynamical transition to thermalizing behaviour, remain poorly understood. We study a simple central spin model to address these questions: a two-level system interacting with strength J with N ≫1 localized bits subject to random fields. On increasing J , the system transitions from an MBL to a delocalized phase on the vanishing scale J c ( N )∼1/ N , up to logarithmic corrections. In the transition region, the single-site eigenstate entanglement entropies exhibit bimodal distributions, so that localized bits are either ‘on’ (strongly entangled) or ‘off’ (weakly entangled) in eigenstates. The clusters of ‘on’ bits vary significantly between eigenstates of the same sample, which provides evidence for a heterogeneous discontinuous transition out of the localized phase in single-site observables. We obtain these results by perturbative mapping to bond percolation on the hypercube at small J and by numerical exact diagonalization of the full many-body system. Our results support the arguments that the MBL phase is unstable in systems with short-range interactions and quenched randomness in dimensions d that are high but finite. This article is part of the themed issue ‘Breakdown of ergodicity in quantum systems: from solids to synthetic matter’.

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Freese, Johannes, Boris Gutkin i Thomas Guhr. "Spreading in integrable and non-integrable many-body systems". Physica A: Statistical Mechanics and its Applications 461 (listopad 2016): 683–93. http://dx.doi.org/10.1016/j.physa.2016.06.008.

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Biehs, Svend-Age. "Thermal radiation in dipolar many-body systems". EPJ Web of Conferences 266 (2022): 07001. http://dx.doi.org/10.1051/epjconf/202226607001.

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The framework of fluctuational electrodynamics for dipolar many-body systems is one of the working horse for theoretical studies of thermal radiation at the nanoscale which includes dissipation and retardation in a naturally way. Based on this framework I will discuss near-field thermal radiation in non-reciprocal and topological many-body systems. The appearance of the Hall and non-reciprocal diode effect for thermal radiation illustrates nicely the interesting physics in such systems as well as the edge mode dominated heat transfer in topological Su-Schrieffer-Heeger chains and a honeycomb lattices of plasmonic nanoparticles. In the latter, the theory allows for quantifying the effciency of the edge-mode dominated heat transfer as function of the dissipation. Finally, I will present how the theoretical framework can be generalized to study far-field thermal emission of many-body systems close to an environment like a substrate, for instance. This theory might be particularly interesting for modelling thermal imaging microscopes.

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Lindgren, Ingvar, Sten Salomonson i Daniel Hedendahl. "New approach to many-body quantum-electrodynamics calculations:merging quantum electrodynamics with many-body perturbation". Canadian Journal of Physics 83, nr 4 (1.04.2005): 395–403. http://dx.doi.org/10.1139/p05-012.

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A new method for bound-state quantum electrodynamics (QED) calculations on many-electron systems is presented that is a combination of the non-QED many-body technique for quasi-degenerate systems and the newly developed covariant-evolution-operator technique for QED calculations. The latter technique has been successfully applied to the fine structure of excited states of medium-heavy heliumlike ions, and it is expected that the new method should be applicable also to light elements, hopefully down to neutral helium. PACS Nos.: 31.30.Jv, 31.15.Md, 31.25.Jf, 33.15.Pw

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Zhang, Xueyue, Eunjong Kim, Daniel K. Mark, Soonwon Choi i Oskar Painter. "A superconducting quantum simulator based on a photonic-bandgap metamaterial". Science 379, nr 6629 (20.01.2023): 278–83. http://dx.doi.org/10.1126/science.ade7651.

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Synthesizing many-body quantum systems with various ranges of interactions facilitates the study of quantum chaotic dynamics. Such extended interaction range can be enabled by using nonlocal degrees of freedom such as photonic modes in an otherwise locally connected structure. Here, we present a superconducting quantum simulator in which qubits are connected through an extensible photonic-bandgap metamaterial, thus realizing a one-dimensional Bose-Hubbard model with tunable hopping range and on-site interaction. Using individual site control and readout, we characterize the statistics of measurement outcomes from many-body quench dynamics, which enables in situ Hamiltonian learning. Further, the outcome statistics reveal the effect of increased hopping range, showing the predicted crossover from integrability to ergodicity. Our work enables the study of emergent randomness from chaotic many-body evolution and, more broadly, expands the accessible Hamiltonians for quantum simulation using superconducting circuits.

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Gritsev, Vladimir, Peter Barmettler i Eugene Demler. "Scaling approach to quantum non-equilibrium dynamics of many-body systems". New Journal of Physics 12, nr 11 (3.11.2010): 113005. http://dx.doi.org/10.1088/1367-2630/12/11/113005.

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Goihl, Marcel, Mathis Friesdorf, Albert H. Werner, Winton Brown i Jens Eisert. "Experimentally Accessible Witnesses of Many-Body Localization". Quantum Reports 1, nr 1 (17.06.2019): 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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Mossi, G., i A. Scardicchio. "Ergodic and localized regions in quantum spin glasses on the Bethe lattice". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, nr 2108 (30.10.2017): 20160424. http://dx.doi.org/10.1098/rsta.2016.0424.

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By considering the quantum dynamics of a transverse-field Ising spin glass on the Bethe lattice, we find the existence of a many-body localized (MBL) region at small transverse field and low temperature. The region is located within the thermodynamic spin glass phase. Accordingly, we conjecture that quantum dynamics inside the glassy region is split into a small MBL region and a large delocalized (but not necessarily ergodic) region. This has implications for the analysis of the performance of quantum adiabatic algorithms. This article is part of the themed issue ‘Breakdown of ergodicity in quantum systems: from solids to synthetic matter’.

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Dickhoff, W. H. "NONLINEAR ASPECTS OF NUCLEAR MANY-BODY THEORY". International Journal of Modern Physics C 05, nr 02 (kwiecień 1994): 285–87. http://dx.doi.org/10.1142/s0129183194000337.

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New developments in the self-consistent Green’s function (SCGF) method as applied to nuclear systems are discussed. Results for high-momentum components in the single-particle spectral function of 16O reveal that their observation is only feasible at a correspondingly high excitation energy in the (e, e′p) reaction. The consequences of the non-mean-field character of nucleons in the nuclear medium are further explored in the context of the nuclear matter saturation problem.

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Torres-Herrera, E. J., i Lea F. Santos. "Dynamical manifestations of quantum chaos: correlation hole and bulge". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, nr 2108 (30.10.2017): 20160434. http://dx.doi.org/10.1098/rsta.2016.0434.

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A main feature of a chaotic quantum system is a rigid spectrum where the levels do not cross. We discuss how the presence of level repulsion in lattice many-body quantum systems can be detected from the analysis of their time evolution instead of their energy spectra. This approach is advantageous to experiments that deal with dynamics, but have limited or no direct access to spectroscopy. Dynamical manifestations of avoided crossings occur at long times. They correspond to a drop, referred to as correlation hole, below the asymptotic value of the survival probability and to a bulge above the saturation point of the von Neumann entanglement entropy and the Shannon information entropy. By contrast, the evolution of these quantities at shorter times reflects the level of delocalization of the initial state, but not necessarily a rigid spectrum. The correlation hole is a general indicator of the integrable–chaos transition in disordered and clean models and as such can be used to detect the transition to the many-body localized phase in disordered interacting systems. This article is part of the themed issue ‘Breakdown of ergodicity in quantum systems: from solids to synthetic matter’.

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SEIRINGER, ROBERT. "A CORRELATION ESTIMATE FOR QUANTUM MANY-BODY SYSTEMS AT POSITIVE TEMPERATURE". Reviews in Mathematical Physics 18, nr 03 (kwiecień 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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Vieira, Carlos H. S., Cristhiano Duarte, Raphael C. Drumond i Marcelo Terra Cunha. "Bell Non-Locality in Many-Body Quantum Systems with Exponential Decay of Correlations". Brazilian Journal of Physics 51, nr 6 (16.10.2021): 1603–16. http://dx.doi.org/10.1007/s13538-021-00998-1.

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Tuszyński, J. A., J. M. Dixon i A. M. Grundland. "Nonlinear Field Theories and Non-Gaussian Fluctuations for Near-Critical Many-Body Systems". Fortschritte der Physik/Progress of Physics 42, nr 4 (1994): 301–37. http://dx.doi.org/10.1002/prop.2190420402.

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DZYUBENKO, ALEXANDER. "MANY-BODY EFFECTS IN LANDAU LEVELS: NON-COMMUTATIVE GEOMETRY AND SQUEEZED CORRELATED STATES". International Journal of Modern Physics B 21, nr 08n09 (10.04.2007): 1476–80. http://dx.doi.org/10.1142/s021797920704304x.

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We discuss symmetry-driven squeezing and coherent states of few-particle systems in magnetic fields. An operator approach using canonical transformations and the SU(1, 1) algebras is developed for considering Coulomb correlations in the lowest Landau levels.

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Benet, L., M. Bienert i S. Yu Kun. "Thermalized non-equilibrated matter and high temperature superconducting state in quantum many-body systems". Radiation Effects and Defects in Solids 162, nr 7-8 (lipiec 2007): 605–12. http://dx.doi.org/10.1080/10420150701470894.

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Kriel, J. N., F. G. Scholtz i J. D. Thom. "Moyal implementation of flow equations—a non-perturbative approach to quantum many-body systems". Journal of Physics A: Mathematical and Theoretical 40, nr 31 (19.07.2007): 9483–505. http://dx.doi.org/10.1088/1751-8113/40/31/023.

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Iwata, Mami, i Shin-ichi Sasa. "Non-ergodic transitions in many-body Langevin systems: a method of dynamical system reduction". Journal of Statistical Mechanics: Theory and Experiment 2006, nr 10 (30.10.2006): L10003. http://dx.doi.org/10.1088/1742-5468/2006/10/l10003.

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Sanyal, Goutam, Seikh Hannan Mandal i Debashis Mukherjee. "Thermal averaging in quantum many-body systems: a non-perturbative thermal cluster cumulant approach". Chemical Physics Letters 192, nr 1 (kwiecień 1992): 55–61. http://dx.doi.org/10.1016/0009-2614(92)85427-c.

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Chevalier, Hadrien, Hyukjoon Kwon, Kiran E. Khosla, Igor Pikovski i M. S. Kim. "Many-body probes for quantum features of spacetime". AVS Quantum Science 4, nr 2 (czerwiec 2022): 021402. http://dx.doi.org/10.1116/5.0079675.

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Many theories of quantum gravity can be understood as imposing a minimum length scale the signatures of which can potentially be seen in precise table top experiments. In this work, we inspect the capacity for correlated many-body systems to probe non-classicalities of spacetime through modifications of the commutation relations. We find an analytic derivation of the dynamics for a single mode light field interacting with a single mechanical oscillator and with coupled oscillators to first order corrections to the commutation relations. Our solution is valid for any coupling function as we work out the full Magnus expansion. We numerically show that it is possible to have superquadratic scaling of a nonstandard phase term, arising from the modification to the commutation relations, with coupled mechanical oscillators.

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Cai, Zi. "Symmetries and effect of time dimension in non-equilibrium quantum matter". Acta Physica Sinica 70, nr 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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Liao, Yunxiang, i Victor Galitski. "Effective Field Theory of Random Quantum Circuits". Entropy 24, nr 6 (13.06.2022): 823. http://dx.doi.org/10.3390/e24060823.

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Quantum circuits have been widely used as a platform to simulate generic quantum many-body systems. In particular, random quantum circuits provide a means to probe universal features of many-body quantum chaos and ergodicity. Some such features have already been experimentally demonstrated in noisy intermediate-scale quantum (NISQ) devices. On the theory side, properties of random quantum circuits have been studied on a case-by-case basis and for certain specific systems, and a hallmark of quantum chaos—universal Wigner–Dyson level statistics—has been derived. This work develops an effective field theory for a large class of random quantum circuits. The theory has the form of a replica sigma model and is similar to the low-energy approach to diffusion in disordered systems. The method is used to explicitly derive the universal random matrix behavior of a large family of random circuits. In particular, we rederive the Wigner–Dyson spectral statistics of the brickwork circuit model by Chan, De Luca, and Chalker [Phys. Rev. X 8, 041019 (2018)] and show within the same calculation that its various permutations and higher-dimensional generalizations preserve the universal level statistics. Finally, we use the replica sigma model framework to rederive the Weingarten calculus, which is a method of evaluating integrals of polynomials of matrix elements with respect to the Haar measure over compact groups and has many applications in the study of quantum circuits. The effective field theory derived here provides both a method to quantitatively characterize the quantum dynamics of random Floquet systems (e.g., calculating operator and entanglement spreading) and a path to understanding the general fundamental mechanism behind quantum chaos and thermalization in these systems.

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Devakul, Trithep, Vedika Khemani, Frank Pollmann, David A. Huse i S. L. Sondhi. "Obtaining highly excited eigenstates of the localized XX chain via DMRG-X". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, nr 2108 (30.10.2017): 20160431. http://dx.doi.org/10.1098/rsta.2016.0431.

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We benchmark a variant of the recently introduced density matrix renormalization group (DMRG)-X algorithm against exact results for the localized random field XX chain. We find that the eigenstates obtained via DMRG-X exhibit a highly accurate l-bit description for system sizes much bigger than the direct, many-body, exact diagonalization in the spin variables is able to access. We take advantage of the underlying free fermion description of the XX model to accurately test the strengths and limitations of this algorithm for large system sizes. We discuss the theoretical constraints on the performance of the algorithm from the entanglement properties of the eigenstates, and its actual performance at different values of disorder. A small but significant improvement to the algorithm is also presented, which helps significantly with convergence. We find that, at high entanglement, DMRG-X shows a bias towards eigenstates with low entanglement, but can be improved with increased bond dimension. This result suggests that one must be careful when applying the algorithm for interacting many-body localized spin models near a transition. This article is part of the themed issue ‘Breakdown of ergodicity in quantum systems: from solids to synthetic matter’.

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Erdős, László, Benjamin Schlein i Horng-Tzer Yau. "Derivation of the cubic non-linear Schrödinger equation from quantum dynamics of many-body systems". Inventiones mathematicae 167, nr 3 (20.12.2006): 515–614. http://dx.doi.org/10.1007/s00222-006-0022-1.

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Moldoveanu, Manolescu i Gudmundsson. "Generalized Master Equation Approach to Time-Dependent Many-Body Transport". Entropy 21, nr 8 (25.07.2019): 731. http://dx.doi.org/10.3390/e21080731.

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We recall theoretical studies on transient transport through interacting mesoscopic systems.It is shown that a generalized master equation (GME) written and solved in terms of many-body statesprovides the suitable formal framework to capture both the effects of the Coulomb interaction andelectron–photon coupling due to a surrounding single-mode cavity. We outline the derivation of thisequation within the Nakajima–Zwanzig formalism and point out technical problems related to itsnumerical implementation for more realistic systems which can neither be described by non-interactingtwo-level models nor by a steady-stateMarkov–Lindblad equation. We first solve the GME for a latticemodel and discuss the dynamics of many-body states in a two-dimensional nanowire, the dynamicalonset of the current-current correlations in electrostatically coupled parallel quantum dots and transientthermoelectric properties. Secondly, we rely on a continuous model to get the Rabi oscillations ofthe photocurrent through a double-dot etched in a nanowire and embedded in a quantum cavity.A many-bodyMarkovian version of the GME for cavity-coupled systems is also presented.

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Ding, Peize, i Wei Yi. "Two-body exceptional points in open dissipative systems". Chinese Physics B 31, nr 1 (1.01.2022): 010309. http://dx.doi.org/10.1088/1674-1056/ac3396.

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We study two-body non-Hermitian physics in the context of an open dissipative system depicted by the Lindblad master equation. Adopting a minimal lattice model of a handful of interacting fermions with single-particle dissipation, we show that the non-Hermitian effective Hamiltonian of the master equation gives rise to two-body scattering states with state- and interaction-dependent parity–time transition. The resulting two-body exceptional points can be extracted from the trace-preserving density-matrix dynamics of the same dissipative system with three atoms. Our results not only demonstrate the interplay of parity-time symmetry and interaction on the exact few-body level, but also serve as a minimal illustration on how key features of non-Hermitian few-body physics can be probed in an open dissipative many-body system.

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CHIERCHIA, LUIGI, i FABIO PUSATERI. "Analytic Lagrangian tori for the planetary many-body problem". Ergodic Theory and Dynamical Systems 29, nr 3 (czerwiec 2009): 849–73. http://dx.doi.org/10.1017/s0143385708000503.

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AbstractIn 2004, Féjoz [Démonstration du ‘théoréme d’Arnold’ sur la stabilité du système planétaire (d’après M. Herman). Ergod. Th. & Dynam. Sys.24(5) (2004), 1521–1582], completing investigations of Herman’s [Démonstration d’un théoréme de V.I. Arnold. Séminaire de Systémes Dynamiques et manuscripts, 1998], gave a complete proof of ‘Arnold’s Theorem’ [V. I. Arnol’d. Small denominators and problems of stability of motion in classical and celestial mechanics. Uspekhi Mat. Nauk. 18(6(114)) (1963), 91–192] on the planetary many-body problem, establishing, in particular, the existence of a positive measure set of smooth (C∞) Lagrangian invariant tori for the planetary many-body problem. Here, using Rüßmann’s 2001 KAM theory [H. Rüßmann. Invariant tori in non-degenerate nearly integrable Hamiltonian systems. R. & C. Dynamics2(6) (2001), 119–203], we prove the above result in the real-analytic class.

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Wang, Qi, Sergey Yu Kun, Wendong Tian, Songlin Li, Zhonghe Jiang, Yuchuan Dong, Zhichang Li i in. "Experimental Test of Spontaneous Correlation and Anomalous Sensitivity in Finite Highly Excited Many-Body Systems". International Journal of Modern Physics E 12, nr 03 (czerwiec 2003): 377–93. http://dx.doi.org/10.1142/s0218301303001314.

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We have tested recent suggestion of anomalous sensitivity in highly excited quantum many-body systems. Two independent measurements of cross sections for the 19 F + 93 Nb strongly dissipative heavy-ion collisions have been performed at incident energies from 102 to 108 MeV in steps of 250 keV. In the two measurements we used different, independently prepared, 93Nb target foils with nominally the same thickness. The data indicate statistically significant non-reproducibility of the energy oscillating yields in the two measurements. The observed non-reproducibility is consistent with recent theoretical arguments on spontaneous correlation, slow phase randomization and chaos in highly excited complex quantum systems.

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Khetselius, O. Yu, V. B. Ternovsky, A. A. Svinarenko, Yu V. Dubrovskaya i I. N. Serga. "Parity non-conservation effect in heavy atomic systems within relativistic many-body perturbation theory: Advanced data". Journal of Physics: Conference Series 1289 (lipiec 2019): 012025. http://dx.doi.org/10.1088/1742-6596/1289/1/012025.

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Tkatchenko, Alexandre, Dario Alfè i Kwang S. Kim. "First-Principles Modeling of Non-Covalent Interactions in Supramolecular Systems: The Role of Many-Body Effects". Journal of Chemical Theory and Computation 8, nr 11 (18.10.2012): 4317–22. http://dx.doi.org/10.1021/ct300711r.

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Finsterhölzl, Regina, Manuel Katzer, Andreas Knorr i Alexander Carmele. "Using Matrix-Product States for Open Quantum Many-Body Systems: Efficient Algorithms for Markovian and Non-Markovian Time-Evolution". Entropy 22, nr 9 (4.09.2020): 984. http://dx.doi.org/10.3390/e22090984.

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This paper presents an efficient algorithm for the time evolution of open quantum many-body systems using matrix-product states (MPS) proposing a convenient structure of the MPS-architecture, which exploits the initial state of system and reservoir. By doing so, numerically expensive re-ordering protocols are circumvented. It is applicable to systems with a Markovian type of interaction, where only the present state of the reservoir needs to be taken into account. Its adaption to a non-Markovian type of interaction between the many-body system and the reservoir is demonstrated, where the information backflow from the reservoir needs to be included in the computation. Also, the derivation of the basis in the quantum stochastic Schrödinger picture is shown. As a paradigmatic model, the Heisenberg spin chain with nearest-neighbor interaction is used. It is demonstrated that the algorithm allows for the access of large systems sizes. As an example for a non-Markovian type of interaction, the generation of highly unusual steady states in the many-body system with coherent feedback control is demonstrated for a chain length of N=30.

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35

Tomaselli, M., D. Ursescu, S. Fritzsche i T. Kühl. "Correlations in many electron systems: theory and applications". Canadian Journal of Physics 85, nr 5 (1.05.2007): 573–84. http://dx.doi.org/10.1139/p07-029.

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In this contribution, we present calculations performed for interacting electron systems within a nonperturbative formulation of the cluster theory. Extrapolation of the model to describe the time dependence of the interacting systems is feasible and planned. The theory is based on the unitary operator eiS (S is the correlation operator) formalism which, in this paper, is treated non perturbatively within many-particle correlations. The application of the derived equations to few-body systems is realized in terms of generalized linearization approximations and via the cluster factorization theory. To check the reliability of the model, we present two different applications. In the first, we evaluate the transitions energies in helium-, lithium-, beryllium-, and boron-like oxygen. The calculation aims for a precise determination of the satellite transitions that play an important role in plasma diagnostics. In the second application we investigate a nonperturbative method to evaluate the charge radii of the helium and lithium isotopes by using the isotopic shift theory. We found that our model leads naturally to components of e––e+ pair in the two-electron wave functions of the helium isotopes and three-electron wave functions of the lithium isotopes. The possible connection of these terms to the quantum electrodynamics leading diagrams is postulated.PACS Nos.: 31.10.+z, 31.30.Gs, 32.30.–r

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36

Tuszyński, J. A., i J. M. Dixon. "Non-linearity and the emergence of coherence in strongly interacting many-body systems near a critical point". Physics Letters A 140, nr 4 (wrzesień 1989): 179–84. http://dx.doi.org/10.1016/0375-9601(89)90889-x.

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Doyon, Benjamin. "Hydrodynamic Projections and the Emergence of Linearised Euler Equations in One-Dimensional Isolated Systems". Communications in Mathematical Physics 391, nr 1 (27.01.2022): 293–356. http://dx.doi.org/10.1007/s00220-022-04310-3.

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AbstractOne of the most profound questions of mathematical physics is that of establishing from first principles the hydrodynamic equations in large, isolated, strongly interacting many-body systems. This involves understanding relaxation at long times under reversible dynamics, determining the space of emergent collective degrees of freedom (the ballistic waves), showing that projection occurs onto them, and establishing their dynamics (the hydrodynamic equations). We make progress in these directions, focussing for simplicity on one-dimensional systems. Under a model-independent definition of the complete space of extensive conserved charges, we show that hydrodynamic projection occurs in Euler-scale two-point correlation functions. A fundamental ingredient is a property of relaxation: we establish ergodicity of correlation functions along almost every direction in space and time. We further show that to every extensive conserved charge with a local density is associated a local current and a continuity equation; and that Euler-scale two-point correlation functions of local conserved densities satisfy a hydrodynamic equation. The results are established rigorously within a general framework based on Hilbert spaces of observables. These spaces occur naturally in the $$C^*$$ C ∗ algebra description of statistical mechanics by the Gelfand–Naimark–Segal construction. Using Araki’s exponential clustering and the Lieb–Robinson bound, we show that the results hold, for instance, in every nonzero-temperature Gibbs state of short-range quantum spin chains. Many techniques we introduce are generalisable to higher dimensions. This provides a precise and universal theory for the emergence of ballistic waves at the Euler scale and how they propagate within homogeneous, stationary states.

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38

Hermanns, S., K. Balzer i M. Bonitz. "The non-equilibrium Green function approach to inhomogeneous quantum many-body systems using the generalized Kadanoff–Baym ansatz". Physica Scripta T151 (1.11.2012): 014036. http://dx.doi.org/10.1088/0031-8949/2012/t151/014036.

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Bonitz, M., N. H. Kwong, D. Semkat i 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, nr 1-2 (1999): 37–40. http://dx.doi.org/10.1002/ctpp.2150390109.

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Engl, Thomas, Juan Diego Urbina i Klaus Richter. "The semiclassical propagator in Fock space: dynamical echo and many-body interference". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 374, nr 2069 (13.06.2016): 20150159. http://dx.doi.org/10.1098/rsta.2015.0159.

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We present a semiclassical approach to many-body quantum propagation in terms of coherent sums over quantum amplitudes associated with the solutions of corresponding classical nonlinear wave equations. This approach adequately describes interference effects in the many-body space of interacting bosonic systems. The main quantity of interest, the transition amplitude between Fock states when the dynamics is driven by both single-particle contributions and many-body interactions of similar magnitude, is non-perturbatively constructed in the spirit of Gutzwiller’s derivation of the van Vleck propagator from the path integral representation of the time evolution operator, but lifted to the space of symmetrized many-body states. Effects beyond mean-field, here representing the classical limit of the theory, are semiclassically described by means of interfering amplitudes where the action and stability of the classical solutions enter. In this way, a genuinely many-body echo phenomenon, coherent backscattering in Fock space, is presented arising due to coherent quantum interference between classical solutions related by time reversal.

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41

Arakawa, Naoya. "Many-body effects on the resistivity of a multi-orbital system beyond Landau's Fermi-liquid theory". Modern Physics Letters B 29, nr 15 (10.06.2015): 1530005. http://dx.doi.org/10.1142/s0217984915300057.

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I review many-body effects on the resistivity of a multi-orbital system beyond Landau's Fermi-liquid (FL) theory. Landau's FL theory succeeds in describing electronic properties of some correlated electron systems at low temperatures. However, the behaviors deviating from the temperature dependence in the FL, non-FL-like behaviors, emerge near a magnetic quantum-critical point (QCP). These indicate the importance of many-body effects beyond Landau's FL theory. Those effects in multi-orbital systems have been little understood, although their understanding is important to deduce ubiquitous properties of correlated electron systems and characteristic properties of multi-orbital systems. To improve this situation, I formulate the resistivity of a multi-orbital Hubbard model using the extended Éliashberg theory and adopt this method to the inplane resistivity of quasi-two-dimensional paramagnetic ruthenates in combination with the fluctuation-exchange approximation including the current vertex corrections arising from the self-energy and Maki–Thompson term. The results away from and near the antiferromagnetic QCP reproduce the temperature dependence observed in Sr 2 RuO 4 and Sr 2 Ru 0.075 Ti 0.025 O 4, respectively. I highlight the importance of not only the momentum and the temperature dependence of the damping of a quasiparticle but also its orbital dependence in discussing the resistivity of correlated electron systems.

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Mohajeri, Mohammad Javad, Mehdi Shafieefar i Soheil Radfar. "NUMERICAL MODELING OF NON-COHESIVE CONTACT IN MULTI-BODY HYDRODYNAMIC SYSTEMS WITH SPH". Coastal Engineering Proceedings, nr 35 (23.06.2017): 49. http://dx.doi.org/10.9753/icce.v35.structures.49.

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Enforcing solid boundary conditions is one of the most challenging parts of the Smoothed Particle Hydrodynamics (SPH) method and many different approaches have been recently developed. Better understanding of interaction forces between solid bodies is of great importance in the investigation of structural stability and armor layer displacement in breakwaters. In this study, performance of repulsive force and dynamic boundary conditions have been investigated and showed that non-physical results are presented in non-cohesive contact. In this paper, a non-cohesive contact model in multi-body hydrodynamic systems has been developed and validated against other common boundary conditions. Using the developed contact model, the effect of regular and irregular placement of cubic concrete armors has been investigated. Also, comparison has been made with Van Buchem (2009) experimental results and concluded that in the irregular case it is more possible that a unit moves toward instability.

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Zakharov, Anatoly Yu. "Field Form of the Dynamics of Classical Many- and Few-Body Systems: From Microscopic Dynamics to Kinetics, Thermodynamics and Synergetics". Quantum Reports 4, nr 4 (20.11.2022): 533–43. http://dx.doi.org/10.3390/quantum4040038.

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A method is proposed for describing the dynamics of systems of interacting particles in terms of an auxiliary field, which in the static mode is equivalent to given interatomic potentials, and in the dynamic mode is a classical relativistic composite field. It is established that for interatomic potentials, the Fourier transform of which is a rational algebraic function of the wave vector, the auxiliary field is a composition of elementary fields that satisfy the Klein-Gordon equation with complex masses. The interaction between particles carried by the auxiliary field is nonlocal both in space variables and in time. The temporal non-locality is due to the dynamic nature of the auxiliary field and can be described in terms of functional-differential equations of retarded type. Due to the finiteness mass of the auxiliary field, the delay in interactions between particles can be arbitrarily large. A qualitative analysis of the dynamics of few-body and many-body systems with retarded interactions has been carried out, and a non-statistical mechanisms for both the thermodynamic behavior of systems and synergistic effects has been established.

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Naón, C. M., M. C. von Reichenbach i M. L. Trobo. "Path-integral bosonization of a non-local interaction and its application to the study of 1d many-body systems". Nuclear Physics B 435, nr 3 (luty 1995): 567–84. http://dx.doi.org/10.1016/0550-3213(94)00534-l.

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Ott, H. R. "OPEN PROBLEMS IN HEAVY-ELECTRON SYSTEMS". International Journal of Modern Physics B 06, nr 05n06 (marzec 1992): 473–96. http://dx.doi.org/10.1142/s021797929200027x.

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Some of the outstanding and newly discovered features of heavy-electron systems are reviewed. Unconventional superconductivity, small-moment ordering, and possible non-Fermi-liquid behaviour are the most intriguing properties that deserve further experimental and theoretical studies because they touch upon important questions related with strong many-body effects in general. Possible ground states of these systems are strongly influenced by small variations of chemical composition or by mere lattice defects.

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46

Palos, Etienne, Saswata Dasgupta, Eleftherios Lambros i Francesco Paesani. "Data-driven many-body potentials from density functional theory for aqueous phase chemistry". Chemical Physics Reviews 4, nr 1 (marzec 2023): 011301. http://dx.doi.org/10.1063/5.0129613.

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Density functional theory (DFT) has been applied to modeling molecular interactions in water for over three decades. The ubiquity of water in chemical and biological processes demands a unified understanding of its physics, from the single molecule to the thermodynamic limit and everything in between. Recent advances in the development of data-driven and machine-learning potentials have accelerated simulation of water and aqueous systems with DFT accuracy. However, anomalous properties of water in the condensed phase, where a rigorous treatment of both local and non-local many-body (MB) interactions is in order, are often unsatisfactory or partially missing in DFT models of water. In this review, we discuss the modeling of water and aqueous systems based on DFT and provide a comprehensive description of a general theoretical/computational framework for the development of data-driven many-body potentials from DFT reference data. This framework, coined MB-DFT, readily enables efficient many-body molecular dynamics (MD) simulations of small molecules, in both gas and condensed phases, while preserving the accuracy of the underlying DFT model. Theoretical considerations are emphasized, including the role that the delocalization error plays in MB-DFT potentials of water and the possibility to elevate DFT and MB-DFT to near-chemical-accuracy through a density-corrected formalism. The development of the MB-DFT framework is described in detail, along with its application in MB-MD simulations and recent extension to the modeling of reactive processes in solution within a quantum mechanics/MB molecular mechanics (QM/MB-MM) scheme, using water as a prototypical solvent. Finally, we identify open challenges and discuss future directions for MB-DFT and QM/MB-MM simulations in condensed phases.

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Chen, Qianqian, Shuai A. Chen i Zheng Zhu. "Weak ergodicity breaking in non-Hermitian many-body systems". SciPost Physics 15, nr 2 (7.08.2023). http://dx.doi.org/10.21468/scipostphys.15.2.052.

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The recent discovery of persistent revivals in the Rydberg-atom quantum simulator has revealed a weakly ergodicity-breaking mechanism dubbed quantum many-body scars, which are a set of nonthermal states embedded in otherwise thermal spectra. Until now, such a mechanism has been mainly studied in Hermitian systems. Here, we establish the non-Hermitian quantum many-body scars and systematically characterize their nature from dynamic revivals, entanglement entropy, physical observables, and energy level statistics. Notably, we find the non-Hermitian quantum many-body scars exhibit significantly enhanced coherent revival dynamics when approaching the exceptional point. The signatures of non-Hermitian scars switch from the real-energy axis to the imaginary-energy axis after a real-to-complex spectrum transition driven by increasing non-Hermiticity, where an exceptional point and a quantum tricritical point emerge simultaneously. We further examine the stability of non-Hermitian quantum many-body scars against external fields, reveal the non-Hermitian quantum criticality and eventually set up the whole phase diagram. The possible connection to the open quantum many-body systems is also explored. Our findings offer insights for realizing long-lived coherent states in non-Hermitian many-body systems.

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Regnault, Nicolas, Sanjay Moudgalya i B. Andrei Bernevig. "Quantum Many-Body Scars and Hilbert Space Fragmentation: A Review of Exact Results". Reports on Progress in Physics, 26.05.2022. http://dx.doi.org/10.1088/1361-6633/ac73a0.

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Abstract The discovery of Quantum Many-Body Scars (QMBS) both in Rydberg atom simulators and in the Aﬄeck-Kennedy-Lieb-Tasaki (AKLT) spin-1 chain model, have shown that a weak violation of ergodicity can still lead to rich experimental and theoretical physics. In this review, we provide a pedagogical introduction to and an overview of the exact results on weak ergodicity breaking via QMBS in isolated quantum systems with the help of simple examples such as the fermionic Hubbard model. We also discuss various mechanisms and unifying formalisms that have been proposed to encompass the plethora of systems exhibiting QMBS. We cover examples of equally-spaced towers that lead to exact revivals for particular initial states, as well as isolated examples of QMBS. Finally, we review Hilbert Space Fragmentation, a related phenomenon where systems exhibit a richer variety of ergodic and non-ergodic behaviors, and discuss its connections to QMBS.

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Žnidarič, Marko, Tomaž Prosen, Giuliano Benenti, Giulio Casati i Davide Rossini. "Thermalization and ergodicity in one-dimensional many-body open quantum systems". Physical Review E 81, nr 5 (27.05.2010). http://dx.doi.org/10.1103/physreve.81.051135.

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Scherg, Sebastian, Thomas Kohlert, Pablo Sala, Frank Pollmann, Bharath Hebbe Madhusudhana, Immanuel Bloch i Monika Aidelsburger. "Observing non-ergodicity due to kinetic constraints in tilted Fermi-Hubbard chains". Nature Communications 12, nr 1 (23.07.2021). http://dx.doi.org/10.1038/s41467-021-24726-0.

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AbstractThe thermalization of isolated quantum many-body systems is deeply related to fundamental questions of quantum information theory. While integrable or many-body localized systems display non-ergodic behavior due to extensively many conserved quantities, recent theoretical studies have identified a rich variety of more exotic phenomena in between these two extreme limits. The tilted one-dimensional Fermi-Hubbard model, which is readily accessible in experiments with ultracold atoms, emerged as an intriguing playground to study non-ergodic behavior in a clean disorder-free system. While non-ergodic behavior was established theoretically in certain limiting cases, there is no complete understanding of the complex thermalization properties of this model. In this work, we experimentally study the relaxation of an initial charge-density wave and find a remarkably long-lived initial-state memory over a wide range of parameters. Our observations are well reproduced by numerical simulations of a clean system. Using analytical calculations we further provide a detailed microscopic understanding of this behavior, which can be attributed to emergent kinetic constraints.

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