Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session Y44: Thermalization and ChaosLive
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Sponsoring Units: DCMP Chair: Marko Znidaric, Univ of Ljubljana |
Friday, March 19, 2021 11:30AM - 11:42AM Live |
Y44.00001: Random matrix theory of quantum work in metallic grains Izabella Lovas, András Grabarits, Marton Kormos, Gergely Zarand We apply a random matrix approach to describe the statistics of work performed on generic disordered, noninteracting fermionic systems during quantum quenches [1]. We generalize and apply Anderson's orthogonality determinant formula to compute the full distribution of quantum work generated by deformations of the Hamiltonian. The energy absorbed increases linearly with time, while its variance exhibits a superdiffusive behavior, reflecting Pauli's exclusion principle. The probability of adiabaticity decays as a stretched exponential. In slowly driven systems work statistics exhibit universal features and can be understood in terms of fermion diffusion in energy space, generated by Landau-Zener transitions. This diffusion is very well captured by a Markovian symmetrical exclusion process, with the diffusion constant identified as the energy absorption rate. We test our theory in a 2D hopping model with random on-site energies, finding excellent agreement. Our predictions can be experimentally verified by calorimetric measurements performed on nanoscale circuits. |
Friday, March 19, 2021 11:42AM - 11:54AM Live |
Y44.00002: Many Body Scars as a Group Invariant Sector of Hilbert Space Kiryl Pakrouski, Preethi Pallegar, Fedor Popov, Igor R Klebanov We present a class of Hamiltonians H for which a sector of the Hilbert space invariant under a Lie group G, which is not a symmetry of H, possesses the essential properties of many-body scar states. |
Friday, March 19, 2021 11:54AM - 12:06PM Live |
Y44.00003: Quench dynamics of two unequal Luttinger liquids: "Large-scale" thermalization, prethermalization and impact of the temperature Paola Ruggiero, Laura Foini, Thierry Giamarchi We study the effect of a quantum quench between two tunnel coupled Tomonaga-Luttinger liquids (TLLs) with different speed of sound and interaction parameter. The quench dynamics is induced by switching off the tunnelling and letting the two systems evolve independently. Both the case of zero and finite temperature in the initial state are considered. We focus on correlation functions associated with the antisymmetric and symmetric combinations of the two TLLs (relevant for interference mea- surements), which turn out to be coupled due to the asymmetry in the two systems’ Hamiltonians. The rich phenomenology that emerges can play a crucial role for the correct description of currently running cold atoms experiments. |
Friday, March 19, 2021 12:06PM - 12:18PM Live |
Y44.00004: Linear and logarithmic entanglement production in an interacting chaotic quantum system Sanku Paul, Arnd Bäcker An isolated interacting quantum system whose internal dynamics make one subsystem act as an environment to the other is of great interest concerning entanglement spreading and decoherence. We investigate the entanglement dynamics of a pair of classically chaotic coupled kicked rotors. In this interacting system, one rotor acts as an environment to the other. As a consequence, it destroys the localization phenomenon, generally displayed by a single kicked rotor, and shows normal diffusion at long times. However, for weak coupling, the normal diffusion is preceded by an intermediate dynamical localization. We show that the localization-delocalization phenomenon directly corresponds to the system's distinct growth phases of the entanglement entropy. Surprisingly, the entanglement, characterized by the von Neumann entropy, shows a linear growth in the localized phase, followed by a logarithmic growth in the delocalized phase. We further provide an analytical expression for the time at which the entanglement entropy changes its profile from linear to logarithmic. |
Friday, March 19, 2021 12:18PM - 12:30PM Live |
Y44.00005: Probing eigenstate thermalization with the emergence of fluctuation-dissipation relations in quantum simulators Alexander Schuckert, Michael Knap We propose a theory-independent route to probe the full eigenstate thermalization hypothesis in quantum simulators by observing the emergence of fluctuation-dissipation relations (FDRs). We present protocols to independently measure fluctuations and dissipations as well as higher-order time ordered correlation functions. We first show how the emergence of FDRs from a nonequilibrium initial state can be observed for the 2D Bose-Hubbard model in superconducting qubits or quantum gas microscopes. In the long range transverse field Ising model implementable by trapped ions, we show that FDRs can be used to observe prethermalization to a Hamiltonian with an approximately conserved quantity at large transverse fields. Furthermore, our protocols make it possible to directly identify non-thermal excitations in experiment. The FDRs enable an experimental diagonalization of the Hamiltonian in integrable models. Our work paves the way to quantum simulate condensed matter pump-probe experiments. |
Friday, March 19, 2021 12:30PM - 12:42PM Live |
Y44.00006: Spectral statistics in many-body quantum chaotic systems with symmetries Sanjay Moudgalya, Abhinav Prem, David A Huse, Amos Chan
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Friday, March 19, 2021 12:42PM - 12:54PM Live |
Y44.00007: Quasi-symmetry groups and many-body scar dynamics Jie Ren, Chenguang Liang, Chen Fang In quantum systems, a subspace spanned by degenerate eigenvectors of the Hamiltonian may have higher symmetries than those of the Hamiltonian itself. When this enhanced-symmetry group can be generated from local operators, we call it a quasi-symmetry group. When the group is a Lie group, an external field coupled to certain generators of the quasi-symmetry group lifts the degeneracy, and results in exactly periodic dynamics within the degenerate subspace, namely the many-body-scar dynamics (given that Hamiltonian is non-integrable). We provide two related schemes for constructing one-dimensional spin models having on-demand quasi-symmetry groups, with exact periodic evolution of a pre-chosen product or matrix-product state under certain external fields. |
Friday, March 19, 2021 12:54PM - 1:06PM Live |
Y44.00008: Quantum scars of bosons with correlated hopping Ana Hudomal, Ivana Vasic, Nicolas Regnault, Zlatko Papic Recent experiments on Rydberg atom arrays have found evidence of anomalously slow thermalization and persistent density oscillations, which have been interpreted as a many-body analog of the phenomenon of quantum scars. Periodic dynamics and atypical scarred eigenstates originate from a "hard" kinetic constraint: the neighboring Rydberg atoms cannot be simultaneously excited. Here we propose a realization of quantum many-body scars in a 1D bosonic lattice model with a "soft" constraint in the form of density-assisted hopping. We discuss the relation of this model to the standard Bose-Hubbard model and possible experimental realizations using ultracold atoms. We find that this model exhibits similar phenomenology to the Rydberg atom chain, including weakly entangled eigenstates at high energy densities and the presence of a large number of exact zero energy states, with distinct algebraic structure. |
Friday, March 19, 2021 1:06PM - 1:18PM Live |
Y44.00009: Hilbert-space fragmentation from strict confinement Zhicheng Yang, Fangli Liu, Alexey V Gorshkov, Thomas Iadecola We study one-dimensional spin-1/2 models in which strict confinement of Ising domain walls leads to the fragmentation of Hilbert space into exponentially many disconnected subspaces. Whereas most previous works emphasize dipole moment conservation as an essential ingredient for such fragmentation, we instead require two commuting U(1) conserved quantities associated with the total domain-wall number and the total magnetization. The latter arises naturally from the confinement of domain walls. Remarkably, while some connected components of the Hilbert space thermalize, others are integrable by Bethe ansatz. We further demonstrate how this Hilbert-space fragmentation pattern arises perturbatively in the confining limit of Z2 gauge theory coupled to fermionic matter, leading to a hierarchy of timescales for motion of the fermions. This model can be realized experimentally in two complementary settings. |
Friday, March 19, 2021 1:18PM - 1:30PM Live |
Y44.00010: The random quantum comb: from compact localized states to many-body scars Giuseppe De Tomasi, Claudio Castelnovo, Ollie Hart In this work we investigate the effects of configurational disorder on the eigenstates and dynamical properties of a tight-binding model on a quasi-one-dimensional comb lattice, consisting of a backbone decorated with linear offshoots of randomly distributed lengths. We show that all eigenstates are exponentially localized along the backbone of the comb. Moreover, we demonstrate the presence of an extensive number of compact localized states with precisely zero localization length. We provide an analytical understanding of these states and show that they survive in the presence of density-density interactions along the backbone of the system where, for sufficiently low but finite particle densities, they form many-body scar states. Finally, we discuss the implications of these compact localized states on the dynamical properties of systems with configurational disorder, and the corresponding appearance of long-lived transient behaviour in the time evolution of physically relevant product states. |
Friday, March 19, 2021 1:30PM - 1:42PM Live |
Y44.00011: Pure state equilibration and dynamical correlation functions Jonathon Riddell, Álvaro Alhambra, Luis Garcia-Pintos In this talk we aim to shed light on the process of pure state equilibration in a large class of quantum many body systems. First this topic is approached by studying two point correlation functions, which model time evolution for systems after weak pertubations away from equilibrium. This reveals that under general assumptions, these correlation functions factorize in late time proving dissiptation emerges from unitary dynamics. An upper bound on the timescale for equilibration in autocorrelations is derived, and numerically investigated. Then, revisting the work from Srednicki (J. Phys. A 32 (1999) 1163) we link this work to the problem of pure state equilibration. We provide arguments that constrain the initial behavior of the equilibration after generic quantum quenches. These constraints are verified through extensive numerical simulations. |
Friday, March 19, 2021 1:42PM - 1:54PM Live |
Y44.00012: Entanglement negativity spectrum of random mixed states: A diagrammatic approach Hassan Shapourian, Shang Liu, Jonah L Kudler-Flam, Ashvin Vishwanath The entanglement properties of random pure states are relevant to a variety of problems ranging from chaotic quantum dynamics to black hole physics. The averaged bipartite entanglement entropy of such states follows the celebrated Page curve. In this talk, we discuss how to generalize this setup to random mixed states by coupling the system to a bath and use the partial transpose to study their entanglement properties. We develop a diagrammatic method to incorporate partial transpose within random matrix theory and formulate a perturbation theory in the inverse of the Hilbert space dimension. As long as the bath is smaller than the system, we find that upon sweeping the subregion size, the logarithmic negativity shows an initial increase and a final decrease similar to the Page curve, while it admits a plateau in the intermediate regime where the logarithmic negativity only depends on the size of the system and of the bath but not on how the system is partitioned. This intermediate phase has no analog in random pure states and is separated from the two other regimes by a critical point. We further show that when the bath is larger than the system by at least two extra qubits the logarithmic negativity is identically zero which implies that there is no distillable entanglement. |
Friday, March 19, 2021 1:54PM - 2:06PM Live |
Y44.00013: Quantum scars as embeddings of weakly "broken" Lie algebra representations Kieran Bull, Jean-Yves Desaules, Zlatko Papic We present an interpretation of scar states and quantum revivals as weakly "broken" representations of Lie algebras spanned by a subset of eigenstates of a many-body quantum system. We show that the PXP model, describing strongly-interacting Rydberg atoms, supports a "loose" embedding of multiple su(2) Lie algebras corresponding to distinct families of scarred eigenstates. Moreover, we demonstrate that these embeddings can be made progressively more accurate via an iterative process which results in optimal perturbations that stabilize revivals from arbitrary charge density wave product states, |Zn>, including ones that show no revivals in the unperturbed PXP model. We discuss the relation between the loose embeddings of Lie algebras present in the PXP model and recent exact constructions of scarred states in related models. |
Friday, March 19, 2021 2:06PM - 2:18PM Live |
Y44.00014: Entanglement of Local Operators and the Butterfly Effect Mao Tian Tan, Jonah L Kudler-Flam, Masahiro Nozaki, Shinsei Ryu The scrambling properties of local operators are analyzed by studying the local operator entanglement and related measures of multi-partite entanglement. The amount of information delocalization is measured by the tri-partite operator mutual information. It is shown that chaotic systems like holographic CFTs and Haar random unitary circuits scramble the maximal amount of information possible, which is proportional to the volume of the input Hilbert space, while integrable systems such as the free Fermion and Clifford circuits scramble only an O(1) amount. |
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