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Optics

Observation and Control of Sharp Many-Body Localization in Cold-Atom Optical Lattices

Xingbo Wei, Xuewei Zuo

Published Jun 30, 2026• 0 citations
Publisher

Abstract

We investigate the localization transition in a one-dimensional extended Aubry–André–Harper (AAH) model, emphasizing its implementation as a quantum simulator in ultracold atomic optical lattices. In the single-particle case, quasi-periodic hopping modulation allows the localization transition point to be clearly observed even for small system sizes. By driving the system into strongly Anderson localized states immediately after the transition, we observe a sharp many-body localization (MBL) transition upon introducing interactions, with the MBL transition point closely approaching that of Anderson localization. To demonstrate the effects of interactions, we map out a global phase diagram and find that critical states in this model are easily thermalized. Contrary to previous studies where enhanced interactions significantly promoted thermalization, we find that increasing interactions does not notably shift the MBL transition point. Importantly, our setup offers a practical and experimentally accessible platform for studying sharp MBL transitions using ultracold atoms in optical lattices, bridging MBL physics with advances in quantum optics and cold-atom technologies.

DOI
10.3390/opt7040046

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We investigate the localization transition in a one-dimensional extended Aubry–André–Harper (AAH) model, emphasizing its implementation as a quantum simulator in ultracold atomic optical lattices. In the single-particle case, quasi-periodic hopping modulation allows the localization transition point to be clearly observed even for small system sizes. By driving the system into strongly Anderson localized states immediately after the transition, we observe a sharp many-body localization (MBL) transition upon introducing interactions, with the MBL transition point closely approaching that of Anderson localization. To demonstrate the effects of interactions, we map out a global phase diagram and find that critical states in this model are easily thermalized. Contrary to previous studies where enhanced interactions significantly promoted thermalization, we find that increasing interactions does not notably shift the MBL transition point. Importantly, our setup offers a practical and experimentally accessible platform for studying sharp MBL transitions using ultracold atoms in optical lattices, bridging MBL physics with advances in quantum optics and cold-atom technologies.
Considering ultracold atoms in optical lattices, we propose experimental protocols to study many-body-localization (MBL) length and criticality in quench dynamics. Through numerical simulations with exact diagonalization, we show that in the MBL phase the perturbed density profile following a local quench remains exponentially localized in postquench dynamics. The size of this density profile after long-time-dynamics defines a localization length, which tends to diverge at the MBL-to-ergodic transition as we increase the system size. The determined localization transition point agrees with previous exact diagonalization calculations using other diagnostics. Our numerical results provide evidence for violation of the Harris-Chayes bound for the MBL criticality. The critical exponent $\ensuremath{\nu}$ can be extracted from our proposed dynamical procedure, which can then be used directly in experiments to determine whether the Harris-Chayes-bound holds for the MBL transition. These proposed protocols to detect localization criticality are justified by benchmarking to the well-established results for the noninteracting three-dimensional Anderson localization.
We study many-body localization (MBL) in the quasiperiodic ${t}_{1}\text{\ensuremath{-}}{t}_{2}$ model, focusing on the role of next-nearest-neighbor (NNN) hopping t2{t}_{2}t2​, which introduces a single-particle mobility edge. The calculated phase diagram can be divided into three distinct regimes, depending on the strength of the short-range interaction UUU. For weak interactions ($U\ensuremath{\ll}{t}_{1}$), this model is always nonthermal. For intermediate interactions ($U\ensuremath{\sim}{t}_{1}$), the thermal-MBL phase transition in this model is qualitatively the same as that of the Aubry-Andre (AA) model, which is consistent with existing experimental observations. For strong interactions $(U\ensuremath{\gg}{t}_{1})$, the NNN hopping produces qualitatively new physics because it breaks down the Hilbert space fragmentation present in the AA model. The NNN hopping is thus irrelevant when the interaction is intermediate but relevant for strong interactions.
We experimentally study many-body localization (MBL) with ultracold atoms in a weak one-dimensional quasiperiodic potential, which in the noninteracting limit exhibits an intermediate phase that is characterized by a mobility edge. We measure the time evolution of an initial charge density wave after a quench and analyze the corresponding relaxation exponents. We find clear signatures of MBL when the corresponding noninteracting model is deep in the localized phase. We also critically compare and contrast our results with those from a tight-binding Aubry-André model, which does not exhibit a single-particle intermediate phase, in order to identify signatures of a potential many-body intermediate phase.
Quasiperiodicity is easily realized with ultracold atoms in optical lattices and has been used to simulate the delocalization-localization transition. Random local potentials can also be implemented by spatial light modulators. Programmable hopping disorder, however, remains difficult to realize in conventional optical lattices. Momentum-space lattice (MSL) offers a platform to address this. We implement the MSL using an 87^{87}87Rb Bose-Einstein condensate via multiple Bragg diffraction and benchmark the platform by simulating wavepacket dynamics with hopping disorder on top of the generalized Aubry-André (GAA) model. We test programmable hopping disorder added to localized/delocalized backgrounds tunable by the Aubry-André potential strength, as well as systems with mobility edges. Uncorrelated hopping disorder smooths the AA transition into a crossover between weakly (large localization lengths) and strongly localized regimes; the resulting enhancement in localization suppresses wavepacket spreading. We also implement spatially correlated hopping disorder and compare its dynamics with uncorrelated disorder of the same final width, demonstrating a correlation-induced enhancement in spreading. Measured dynamics agrees with trends from ideal tight-binding simulations. Trends in non-universal features depending on microscopic structure and short-time dynamics as functions of quasiperiodic potential strength, hopping-disorder strength, and GAA deformation also match numerical results, with better agreement at larger hopping-disorder strengths. Numerical simulations of the MSL dynamics provide insights into sources of corrections. Our results demonstrate that MSL provides a versatile platform for realizing general disordered quantum systems with programmable hopping amplitudes beyond quasiperiodic models.
The many-body localization (MBL) transition is a quantum phase transition involving highly excited eigenstates of a disordered quantum many-body Hamiltonian, which evolve from “extended/ergodic" (exhibiting extensive entanglement entropies and fluctuations) to “localized" (exhibiting area-law scaling of entanglement and fluctuations). The MBL transition can be driven by the strength of disorder in a given spectral range, or by the energy density at fixed disorder – if the system possesses a many-body mobility edge. Here we propose to explore the latter mechanism by using “quantum-quench spectroscopy", namely via quantum quenches of variable width which prepare the state of the system in a superposition of eigenstates of the Hamiltonian within a controllable spectral region. Studying numerically a chain of interacting spinless fermions in a quasi-periodic potential, we argue that this system has a many-body mobility edge; and we show that its existence translates into a clear dynamical transition in the time evolution immediately following a quench in the strength of the quasi-periodic potential, as well as a transition in the scaling properties of the quasi-stationary state at long times. Our results suggest a practical scheme for the experimental observation of many-body mobility edges using cold-atom setups.
Ultracold atomic systems offer a highly controllable platform for investigating quantum state transfer through the precise dynamical manipulation of system parameters. While quantized Thouless pumping has been extensively explored in these systems, adiabatic edge-to-edge transfer of localized quantum states remains largely unexplored. Here, we consider a one-dimensional ultracold atomic gas confined in a bichromatic optical lattice realizing a quasiperiodic Aubry--André--Harper system. We use its edge-localized winding states to implement quantum state transfer between opposite boundaries. Starting from the instantaneous spectral properties of the corresponding tight-binding model, we construct locally adiabatic protocols and extend the approach to higher protocol orders. We then simulate their dynamics under the full continuum bichromatic-lattice Hamiltonian. Our results reveal a tradeoff between edge localization and the minimum spectral gap: strongly localized states require longer transfer times, but can benefit substantially from higher protocol orders. We are also able to capture the main fidelity trends and coherent oscillations over a broad parameter regime using an effective two-level Landau--Zener description. Our results provide practical guidelines for selecting experimentally accessible parameters and tailoring quantum transfer protocols in quasiperiodic ultracold atomic systems.