Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session A33: Disorder and Localization in AMO SystemsFocus Recordings Available
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Sponsoring Units: DAMOP DCMP Chair: Mohammad-Ali Miri, Queen's College Room: McCormick Place W-192C |
Monday, March 14, 2022 8:00AM - 8:12AM |
A33.00001: Random Projections with Transverse Disorder in Optical Waveguide Arrays Mohammad-Ali Miri Random projection is an efficient method for dimensionality reduction when dealing with very high-dimensional data. In this technique, data are mapped linearly from a high-dimensional space to a low-dimensional subspace, while nearly preserving their Euclidean distances during this transformation. Here, we show that random projection can be performed optically, by propagating spatially modulated light in photonic lattices with transverse disorder and by random sampling at the waveguide outputs. This realization allows for the integrated photonic implementation of random projection. We show that proper implementation of random projection requires transverse diagonal disorder of a critical strength that ensures diffusive transport of light rather than ballistic or localized transport. |
Monday, March 14, 2022 8:12AM - 8:24AM |
A33.00002: Universal features of dynamics of localized electronic states Anatoly Obzhirov, Eric J Heller In a number of systems, electronic transport can be viewed as dynamics of localized electronic states. However, there is no universal theory that describes time evolution of localized states. In this work, we present universal features of such motion. They originate from the concept of adiabatic change of character near an avoided crossing. It is shown that localized electronic states move by interchanging positions with adjacent localized states that form an avoided crossing. Avoided crossings formed by two adjacent electronic states would be adiabatic, whereas avoided crossing formed by two distant electronic states would be diabatic. To illustrate this idea, we develop a numerical model based on Anderson localized states. Based on our observations, we discuss universal features of relaxation time. The presented perspective could give new insights on Metal-Insulator transitions and electron transport in nanostructures, superlattices, and disordered semiconductors. |
Monday, March 14, 2022 8:24AM - 8:36AM |
A33.00003: Experimental signatures of an extended multifractal phase in a kicked Aubry-André-Harper Hamiltonian Hasan E Kondakci, Toshihiko Shimasaki, Max Prichard, Jared E Pagett, Yifei Bai, Peter Dotti, Alec J Cao, Tsung-Cheng Lu, Tarun Grover, David M Weld The fractal dimension of quantum matter, defined as a scaling exponent, can acquire multiple values in numerous physical contexts. Such multifractality is commonly observed at a critical point rather than as an extended phase. Here, we experimentally demonstrate that kicked Aubry-André-Harper (kAAH) quasicrystals exhibit a multifractal quantum phase across an extended range in parameter space. These experiments use Bose-Einstein condensates of strontium atoms loaded into an optical lattice and kicked with a secondary lattice of an incommensurate wavelength. To eliminate interband heating and preserve the tight-binding character of the Hamiltonian, we engineer the kick waveforms based on a multiband time-domain model, a technique analogous to apodization in optics or RF engineering. This enables access to a phase diagram spanning a parameter space 5 orders of magnitude larger than that accessible with simple kicking schemes. Transport measurements show signatures of the extended multifractal phase and anomalous disorder-driven re-entrant delocalization. |
Monday, March 14, 2022 8:36AM - 8:48AM |
A33.00004: Observation of the quantum boomerang effect Roshan Sajjad, Jeremy Tanlimco, Hector Mas, Alec J Cao, Eber Nolasco-Martinez, Ethan Q Simmons, Flavio Santos, Patrizia Vignolo, Tommaso Macr`ı, David M Weld A particle in an Anderson-localized system, if launched in any direction, should on average return to its starting point and stay there. Despite the central role played by Anderson localization in the modern understanding of condensed matter, this "quantum boomerang" effect, an essential feature of the localized state, was only recently theoretically predicted and has not previously been observed. We report the experimental observation of the quantum boomerang effect. Using a degenerate gas and a phase-shifted pair of optical lattices, we probe the role of time reversal symmetry breaking, Floquet gauge, and initial state symmetry in supporting or disrupting the boomerang effect. Highlighting the key role of localization, we observe that as stochastic kicking destroys dynamical localization, the quantum boomerang effect also disappears. Measured dynamics are in agreement with analytical and numerical predictions. These results showcase a unique experimental probe of the underlying quantum nature of Anderson localized matter. |
Monday, March 14, 2022 8:48AM - 9:00AM |
A33.00005: Exact mobility edges in the non-Hermitian t1-t2 model Xiao Li, Xu Xia, Ke Huang, Shubo Wang Quantum localization in 1D non-Hermitian systems, especially the search for exact single-particle mobility edges, has attracted considerable interest recently. While much progress has been made, the available methods to determine the ME in such models are still limited. In this work we use a new method to find a new class of exact mobility edges in 1D non-Hermitian quasiperiodic models with parity-time ($\PT$) symmetry. We illustrate our method by studying a specific model. We first use our method to determine the energy-dependent mobility edge as well as the spectrum for localized eigenstates in this model. We then demonstrate that the metal-insulator transition must occur simultaneously with the spontaneous $\PT$-symmetry breaking transition in this model. Finally, we propose an experimental protocol based on a 1D photonic lattice to distinguish the extended and localized single-particle states in our model. The results in our work can be applied to studying other non-Hermitian quasiperiodic models. |
Monday, March 14, 2022 9:00AM - 9:12AM |
A33.00006: Characterization 1-D Hubbard systems with long-range Coulomb interaction using machine learning: effect of disorder and system size Keyi Liu, Emily A Townsend, Garnett W Bryant, Mark-yves Gaunin One-dimensional atomic chains with long-range Coulomb interactions are ideal models for studying many-body behavior. Quantized plasmonic excitations can be identified in chains as short as 8 atoms and can be launched and transferred across the chain by coupling to quantum emitters. By varying the amount of disorder in both the strength of the hopping between nearest neighbor sites and the electron-electron Coulomb interaction, we observe the localization landscape of the plasmon. We characterize the effects of disorder using a combination of exact diagonalization and machine learning algorithms and establish relations between distortion of the quantization and specific types of disorder using parameters such as the inverse participation ratio. We establish different regimes of disorder where phenomena such as Many Body Localization will onset. Additionally, we will discuss the application of Matrix Product State (MPS) algorithms on larger systems, which are infeasible for exact diagonalization, to understand quantization, disorder and localization in larger systems. |
Monday, March 14, 2022 9:12AM - 9:48AM |
A33.00007: Non-ergodicity and emergent Hilbert-space fragmentation in tilted Fermi-Hubbard chains Invited Speaker: Monika Aidelsburger Well-controlled synthetic quantum systems, such as ultracold atoms in optical lattices, offer intriguing possibilities to study complex many-body problems relevant to a variety of research areas. In particular, out-of-equilibrium phenomena constitute natural applications of quantum simulators, which have already successfully demonstrated simulations in regimes that are beyond reach using state-of-the-art numerical techniques. While generic models are expected to thermalize according to the eigenstate thermalization hypothesis (ETH), violation of ETH is believed to occur mainly in two types of systems: integrable models and many-body localized systems (MBL). In between these two extreme limits there is, however, a whole range of models that exhibit more complex dynamics. |
Monday, March 14, 2022 9:48AM - 10:00AM |
A33.00008: Multiphase dynamics in certain quasiperiodic systems Sambuddha Sanyal, Dintomon Joy, Parvathy S Nair In recent years quasiperiodic systems have been studied extensively as an ideal template for understanding localization transition and associated critical phenomena. In this talk we will demonstrate that competition between different phases near the critical regime of certain quasiperiodic systems can exhibit a rich range of dynamical properties. We will further show that the interplay between localized, delocalized and critical states in such systems can lead to novel emergent scale in the system. Finally we will discuss possible experimental signatures of these dynamical properties in certain quasiperiodic systems that have been realised in recent experiments. |
Monday, March 14, 2022 10:00AM - 10:12AM |
A33.00009: Many-body-localized discrete time crystal with a programmable spin-based quantum simulator Conor Bradley, Joe Randall, Floris V van der Gronden, Asier Galicia, Mohamed Abobeih, Matthew Markham, Daniel Twitchen, Francisco Machado, Norman Y Yao, Tim Hugo Taminiau Disorder-induced many-body-localization (MBL) is the only known mechanism by which to stabilize discrete-time-crystalline (DTC) order across the many-body spectrum. However, an experimental observation of this robust order has remained elusive due to the need for disordered interactions, varied state preparation, site-selective read-out and long coherence times. In this work, we use the electron spin of a single nitrogen-vacancy centre to perform dynamic-nuclear-polarization and selective spin-read-out of naturally interacting 13C spins in diamond [1]. Using selective radio-frequency controls [2], we isolate and manipulate a 1D chain of 9 spins from a precisely characterized 27-spin cluster [3]. We create a DTC via a Floquet unitary and observe long-lived period-doubled oscillations of the system autocorrelation up to N=800 Floquet cycles, and confirm its robustness for generic initial states, a hallmark of the MBL DTC. Our results are consistent with the realization of an out-of-equilibrium Floquet phase of matter and introduce a programmable quantum simulator based on solid-state spins for exploring many-body physics. |
Monday, March 14, 2022 10:12AM - 10:24AM |
A33.00010: Quasi-Periodic Topological Bulk-Bulk Localization Dan S Borgnia, Robert-Jan Slager, Ashvin Vishwanath We report on a direct connection between quasi-periodic topology and the Almost Mathieu (Andre-Aubry) metal-insulator transition. By constructing quasi-periodic transfer matrix equations from the limit of rational approximate projected Green's functions, we reduce results from SL(2,R) co-cycle theory (transfer matrix eigenvalue scaling) to consequences of translation invariant band theory. This reduction links the eigenfunction localization of the metal-insulator transition to the chiral edge modes of the Hofstadter Hamiltonian. Our analysis shows the localized phase roots in a topological "bulk-bulk" correspondence rather than self-duality, differentiating quasi-periodic localization from Anderson localization in disordered systems. These results and methods are widely relevant to systems beyond this paradigmatic model, including 2D cold atom realizations, and have direct application to Barry Simon's "Dry Ten Martini Problem" at criticality. |
Monday, March 14, 2022 10:24AM - 10:36AM |
A33.00011: Quantifying Unitary Flow Efficiency and Entanglement for Many-Body Localization Greg A Hamilton, Bryan K Clark We probe the bulk geometry of the Wegner Wilson Flow (WWF) in the context of many-body localization, by addressing efficiency and bulk entanglement growth measures through approximating upper bounds on the boundary entanglement entropy. We connect these upper bounds to the Fubini-Study metric and clarify how a central quantity, the information fluctuation complexity, distinguishes bulk unitary rotation from entanglement production. We also give a short new proof of the small incremental entangling theorem in the absence of ancillas, achieving a dimension-independent, universal factor of $c=2$. |
Monday, March 14, 2022 10:36AM - 10:48AM |
A33.00012: Borel-Padé analysis of the critical exponent of Anderson transition in Bogoliubov-de Gennes symmetry classes Tong Wang, Zhiming Pan, Keith Slevin, Tomi Ohtsuki Disorder and the associated localization phenomenon are ubiquitous in physical systems. The realization of quantum kicked rotor model in chaotic atom-optic system [1] opened up the possibility of direct observation of dynamic localization in higher dimensions. The scaling theory and universality classes of Anderson transition are at the heart of the study of disordered systems. In this study, we apply Borel-Padé resummation to the β-function [2] of four Boguliubov-de Gennes symmetry classes corresponding to disordered superconductors. From the approximated β-function we derive the critical conductance and critical exponent of each symmetry class in different dimensions. We compare our three-dimensional results with a recent numerical study [3]. We also discuss the applicability of Borel-Padé resummation to the epsilon-expansion of critical exponent. |
Monday, March 14, 2022 10:48AM - 11:00AM |
A33.00013: Dynamical signatures of thermal spin-charge delocalization in doped antiferromagnets Fabian Grusdt, Lauritz Hahn, Annabelle Bohrdt The mechanism underlying charge transport in strongly correlated quantum systems, such as doped antiferromagnetic Mott insulators, remains poorly understood. Here we study the expansion dynamics of an initially localized hole inside two-dimensional (2D) antiferromagnets at variable temperatures. Using a combination of classical Monte Carlo and a truncated basis method, we reveal two dynamically distinct regimes in a doped Ising model: A spin-charge confined region below a critical temperature $T^*$, characterized by slow spreading, and a spin-charge deconfined region above $T^*$, characterized by an unbounded diffusive expansion. The deconfinement temperature $T^* \approx 0.65 J_z$ we find is around the N\'eel temperature $T_N = 0.567J_z$ of the Ising background in 2D, but we expect $T^* < T_N$ in higher dimensions. In both regimes we find that the mobile hole does not thermalize with the Ising spin background on the considered time scales, indicating weak effective coupling of spin- and charge degrees of freedom. Our results can be qualitatively understood by an effective parton model, and can be tested experimentally in state-of-the-art quantum gas microscopes. |
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