09:00 - 12:00
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informal discussions (on-site & in gather.town)
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12:30 - 13:20
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Lunch
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Chair: Maksym Serbyn
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13:30 - 14:10
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Konstantin Tikhonov
(Skoltech)
Many-body localization in quantum dot models and Anderson localization on random graphs (virtual)
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14:10 - 14:35
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Ivan Khaymovich
(MPIPKS Dresden)
Random-matrix approach to slow dynamics in quantum systems
In this talk, we will discuss a random-matrix approach to the description of disordered many-body systems and their Hilbert-space structure, mostly focusing on the slow dynamics in such models.
As a generic example of this approach, we consider the static and the dynamical phases in a Rosenzweig-Porter random matrix ensemble with a distribution of off-diagonal matrix elements of the form of the large-deviation ansatz.
We present a general theory of survival probability in such a random-matrix model and show that the averaged survival probability may decay with time as a simple exponent, as a stretch-exponent and as a power-law or slower. Correspondingly, we identify the exponential, the stretch-exponential and the frozen-dynamics phases.
We consider the mapping of the Anderson localization model on Random Regular Graph, the known proxy of MBL, onto the RP model and find exact values of the stretch-exponent kappa in the thermodynamic limit.
Our theory allows to describe analytically the finite-size multifractality and to compute the critical length with the exponent 1 associated with it.
Corresponding publication:
I. M. Khaymovich and V. E. Kravtsov "Dynamical phases in a "multifractal" Rosenzweig-Porter model" [arxiv:2106.01965]
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14:35 - 15:00
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Henning Schomerus
(Lancaster University)
Fock space and random matrix perspective on ergodicity-breaking many-body states
I combine a geometric perspective on Fock space with considerations from random-matrix theory to provide insights into quantum systems that obey an area law on entanglement induced by disorder or measurements.
For instance, individual many-body-localized eigenstates are well approximated by a Slater determinant of single-particle orbitals, but the orbitals of different eigenstates in a given system display an imperfect degree of compatibility, close to that of completely random states. Such considerations also illuminate the strongly dressed nature of any emergent local conserved quantities, as well as the universal properties of such systems.
Universality of Entanglement Transitions from Stroboscopic to Continuous Measurements
M. Szyniszewski, A. Romito, and H. Schomerus, Phys. Rev. Lett. 125, 210602 (2020).
Fock-space geometry and strong correlations in many-body localized systems
Christian P. Chen and Henning Schomerus,
arXiv:2107.05502 [cond-mat.dis-nn]. (2021)
Random-matrix perspective on many-body entanglement with a finite localization length
Marcin Szyniszewski and Henning Schomerus,
Phys. Rev. Research 2, 032010(R) (2020).
Entanglement transition from variable-strength weak measurements
M. Szyniszewski, A. Romito, and H. Schomerus,
Phys. Rev. B 100, 064204 (2019).
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15:00 - 15:25
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Ken-Ichiro Imura
(Hiroshima University)
Unusual diffusion and entanglement dynamics in disordered non-Hermitian systems (virtual)
Taking the Hatano-Nelson model as a concrete example, we first consider how diffusion occurs in a non-Hermitian disordered system,
and show that it is very different from the Hermitian case. Interestingly, a cascade like diffusion process of an initial wave packet as in the Hermitian case is suppressed in the clean limit and at weak disorder, while it revives in the vicinity the localization-delocalization transition. Based on this observation, we then analyze how the entanglement entropy of the system evolves in time in the interacting non-Hermitian model, revealing its non-monotonic evolution in time. We clarify the different roles of dephasing in the time evolution of entanglement entropy.
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15:25 - 16:15
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Coffee break
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Chair: Vedika Khemani
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16:15 - 16:55
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Dragana Popovic
(The National High Magnetic Field Laboratory)
Screening the Coulomb interaction leads to a prethermal regime in two-dimensional bad conductors (virtual)
The absence of thermalization in certain isolated many-body systems is of great fundamental interest and potential technological importance. However, it is not well understood how the interplay of disorder and interactions affects thermalization, especially in two dimensions (2D), and experiments on solid-state materials remain scarce. We report on the study of nonequilibrium dynamics exhibited after a rapid change of electron density $n_\mathrm{s}$, in two sets of disordered 2D electron systems in Si, poorly coupled to a thermal bath. In the low conductivity regime at low $n_\mathrm{s}$, we find that, while the dynamics is glassy in devices with the long-range Coulomb interaction, in the case of screened Coulomb interaction the thermalization is anomalously slow, consistent with the proximity to a many-body-localized (MBL) phase, i.e. the MBL-like, prethermal regime. Our results demonstrate that the MBL phase in a 2D electron system can be approached by tuning the interaction range, thus paving the way to further studies of the breakdown of thermalization and MBL in real materials.
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16:55 - 17:35
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Jens H. Bardarson
(KTH Royal Institute of Technology)
Time-evolution of local information: thermalization dynamics of local observables (virtual)
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17:35 - 18:15
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William Morong
(University of Maryland, College Park)
Quantum simulations of non-thermal phenomena with trapped ions
Recent years have seen the development of isolated quantum simulator platforms capable of exploring interesting questions at the frontiers of many-body physics. We describe our platform, based on a chain of Ytterbium ions in a linear trap, and describe its capabilities, which include long-range spin-spin interactions and single-site manipulation and readout. We then describe some recent studies undertaken with this machine, focusing on two. The first is the observation of domain-wall confinement, in which the long-range interactions cause individual domain walls to become bound into meson-like quasiparticles. The second, observation of Stark many-body localization, in which a linearly increasing gradient halts thermalization in favor of a state similar to disorder-induced many-body localization. These results show some of the richness possible in non-thermalizing behavior, and we discuss possible relations between them and recently studied mechanisms for breaking ergodicity such as Hilbert space fragmentation.
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18:15 - 19:30
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Dinner
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Chair: Romain Vasseur
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19:30 - 20:10
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Ehud Altman
(University of California, Berkeley)
Critical behavior near the many-body localization transition in driven open systems (virtual)
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20:10 - 20:35
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Andrea De Luca
(CNRS)
Spectral form factor in extended translational invariant systems (virtual)
We introduce a class of unitary circuits which are invariant under translations. In the limit of large local Hilbert space dimensions, we compute explicitly the spectral form factor, characterizing the spectral correlation of the model. We show that at time larger than the Thouless time, the random matrix behavior is recovered. Additionally, we identify a scaling function which characterize an extended transient regime towards the random matrix prediction. Compared with the inhomogeneous system, we identify logarithmic corrections which are the direct consequence of translation invariance. We discuss the generalization of these results to arbitrary chaotic model which have a translation symmetry.
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20:35 - 21:00
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Sergey Syzranov
(University of California, Santa Cruz)
Equivalence of interacting semimetals and low-density many-body systems to single-particle systems with quenched disorder (virtual)
We demonstrate that a broad class of interacting disorder-free systems, such as nodal semimetals (e.g. graphene, Weyl, nodal-line semimetals) and dilute interacting gases, can be mapped to non-interacting systems with quenched disorder. The interacting systems that allow for such a mapping include systems with a small single-particle density of states at the chemical potential (e.g. near a nodal point or a nodal line in a topological semimetal), which leads to a suppressed screening of the interactions. The established duality suggests a new approach for analytical and numerical studies of many-body phenomena in a class of interacting disorder-free systems by reducing them to single-particle problems. It allows one to predict, describe and classify many-body phenomena by mapping them to the effects known for disordered non-interacting systems. We illustrate the mapping by showing that clean semimetals with attractive interactions exhibit interaction-driven transitions at low temperatures in the same universality classes as the non-Anderson disorder-driven transitions predicted in high-dimensional non-interacting semimetals. Furthermore, we find a new non-Anderson disorder-driven transition dual to a previously known interaction-driven transition in clean bosonic gases. The established principle may also be used to classify and describe phase transitions in dissipative systems described by non-Hermitian Hamiltonians.
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21:00 - 21:15
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Closing
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