Session Q54: Non-Equilibrium Physics with AMO Systems

Alkaline-earth atom arrays: from quantum-enhanced optical clocks to programmable Hubbard systems

In recent years, atom arrays have emerged as a versatile experimental platform enabling many exciting research directions in quantum science. In the strontium tweezer array experiment at JILA, we combine techniques from this novel platform with optical lattice potentials. In this way, we can not only engineer entangled many-body states of immobile particles, but also study the dynamics of itinerant and interacting particles. I will present our work on both of these frontiers in this talk. In particular, I will describe how we use non-equilibrium dynamics of an Ising and transverse-Ising model to create entangled states, which we use to demonstrate quantum-enhanced metrology in an optical clock. In the second part of the talk, I discuss our recent efforts to realize interacting Bose-Hubbard systems assembled from individually trapped and laser-cooled atoms. With such a system, we aim to explore questions concerning the preparation of many-body ground states and the emergence of dynamics strongly dependent on the initial state.   

Two-mode squeezing and entanglement dynamics for power-law interactions in two-dimensional bi-layer spin ½ system

We study the non-equilibrium dynamics of a quantum spin ½ XXZ model realized in a two-dimensional bi-layer system, with couplings mediated by inverse power-law interactions, falling off with distance r as 1/r^a.

Starting from an initial state of spins with opposite magnetization in the two layers we find exponential growth of correlated pairs of excitations. We demonstrate that for a broad range of parameters, the system shows collective behavior resulting in exponential generation of entanglement. Specifically, we study the effects of the range of the interactions via the inverse power, a, and the interlayer spacing a_z on the entanglement dynamics.

This work demonstrates that metrologically useful entanglement in the form of two-mode squeezed states separated in bilayers can be generated via power-law interactions, making it accessible in a wide variety of experimental atomic, molecular, and optical platforms, with potential applications in quantum enhanced sensing.   

Experimental realizations of bosonic dipolar quantum walks in optical lattice

Understanding emergent phenomena in strongly correlated system is one of the most important questions in physics. When it comes to quantum many-body systems, it is always challenging to understand interacting systems, especially understand their non-equilibrium dynamics. In this talk, I will discuss our recent demonstration of dipolar quantum walks using Rb atoms in optical lattice. Using linear tilting potential, we experimentally realize tilted Bose-Hubbard model, in which dipolar Bose-Hubbard model arises as an effective model. We experimentally observe quantum dynamics of finite density of bosons, which is an example of a fully interacting many-body nonequilibrium quantum dynamics. Using optical lattice, we observe constrained dynamics with a prethermal behavior due to emergent dipole conservation from a strong tilting potential. Despite that the dynamics is fully quantum and interacting in nature, the dynamics have a succinct description in term of quantum walks of emergent dipolar particles. I will highlight similarities and differences between the usual quantum walk and the dipolar quantum walk, and the experimental demonstration of the dipolar quantum walks in optical lattice. ​   

Strong Spin-Motion Coupling in the Ultrafast Quantum Many-body Dynamics of Rydberg Atoms in a Mott-insulator Lattice

Rydberg atoms in optical lattices and tweezers is now a well established platform for simulating quantum spin systems. However, the possible role of the atoms' spatial wavefunction has not been examined in detail experimentally. Here, we show a strong spin-motion coupling emerging from the large variation of the interaction potential over the wavefunction spread. We observe its clear signature on the ultrafast, out-of-equilibrium, many-body dynamics of atoms excited to a Rydberg S state from an unity-filling atomic Mott-insulator. We also propose a novel approach to tune arbitrarily the strength of the spin-motion coupling relative to the motional energy scale set by trapping potentials. Our work provides a new direction for exploring the dynamics of strongly correlated quantum system by including the motional degree of freedom into the Rydberg simulation toolbox.   

Unraveling hydrodynamization with Bragg-scattering pulses in 1D Bose gases

The term “hydrodynamization” was introduced to describe the notably short period of time after the start of a relativistic heavy ion collision before hydrodynamics can be used to describe the time evolution of the system. This fastest time scale and the following local prethermalization was recently observed in a system of 1D bose gases after a Bragg-scattering pulse quench [1]. In this work, we explore the conditions for hydrodynamization with different types of pulse sequences experimentally and theoretically (in the Tonks-Girardeau limit). We show that a quantum Newton’s cradle setup can undo the features of hydrodynamization that was previously observed. We further construct a nonequilibrium initial state that captures the main characteristics of the Bragg scattering pulse quenches. With this setup, we systemically study the dependence on the center and spread of the post-quench state energies for the hydrodynamization and local prethermalization time scales.

 

[1] Le, et al. Observation of hydrodynamization and local prethermalization in 1D Bose gases. Nature 618, 494–499 (2023).   

Quantum and classical coarsening and their interplay with the Kibble-Zurek mechanism

Understanding the out-of-equilibrium dynamics of a closed quantum system driven across a quantum phase transition is an important problem with widespread implications for quantum state preparation and adiabatic algorithms. While the quantum Kibble-Zurek mechanism elucidates part of these dynamics, the subsequent and significant coarsening processes lie beyond its scope. Here, we develop a universal description of such coarsening dynamics—and their interplay with the Kibble-Zurek mechanism—in terms of scaling theories. Our comprehensive theoretical framework applies to a diverse set of ramp protocols and encompasses various coarsening scenarios involving both quantum and thermal fluctuations. Moreover, we highlight how such coarsening dynamics can be directly studied in today's "synthetic" quantum many-body systems, including Rydberg atom arrays, and present a detailed proposal for their experimental observation.   

Proposal for the experimental detection of many-body quantum chaos via dynamics

Recently, there has been a resurgence of interest in quantum chaos, especially when caused by interactions between particles. A common diagnostic tool of quantum chaos is the presence of correlated eigenvalues and level statistics comparable to those of random matrices. However, the spectrum is not easily accessible to current experiments with cold atoms and ion traps, which are designed to investigate many-body quantum dynamics. For these experiments, we propose a way to detect many-body quantum chaos directly through the dynamics. We show that the spectral correlations are manifested in the form a the dip-ramp-plateau structure (aka correlation hole) in two exerimental quantities, the survival probability (dynamical version of the spectral form factor) and the spin autocorrelation function (density imbalance). Our results suggest that observation of this structure is within reach of current experimental capabilities.   

Proposal for realizing quantum spin models with Dzyaloshinskii-Moriya interaction using Rydberg atoms

Recently, quantum simulators using Rydberg atoms have attracted much attention. Various quantum spin models, such as Ising [1], XY [2], and XXZ [3] models have been realized experimentally. In this work, we propose a method for realizing highly controllable quantum spin models with Dzyaloshinskii-Moriya interaction (DMI) in Rydberg atom quantum simulators [4]. Our scheme is based on a two-photon Raman transition and transformation to the spin-rotating frame. The advantage of our scheme is that the ratio between the exchange interaction and DMI can be tuned in a wide range. We investigate the quantum dynamics of the Hamiltonian that includes only the DMI and magnetic field term, dubbed the DH model [5]. We show that the dynamics are quite different from the classical case. That is, the magnetization curve becomes smooth as a function of the magnetic field in contrast to the classical case. We also find that the DH model has quantum many-body scar states under the periodic boundary condition and the open boundary condition with the edge magnetic field.

[1]H. Bernien, et al.,  Nature 551, 579 (2017).

[2]S. de Léséleuc, et al, Phys. Rev. Lett. 120, 113602 (2018).

[3]A. Signoles, et al., Phys. Rev. X 11, 011011 (2021).

[4]M. Kunimi, et al., arXiv:2306.05591 (2023).

[5]S. Kodama, et al., Phys. Rev. B 107, 024403 (2023).    

Bose stimulated dynamics of an atom-molecule superfluid

The recent observations [1,2] of a stable molecular condensate emerging from a condensate of bosonic atoms and related “super-chemical” dynamics have raised an intriguing set of questions. Here we provide a microscopic theory of these phenomena showing one essential feature of these experiments is the extreme narrowness of the Feshbach resonance at B=19.849G in 133Cs. Comparing theory and experiment we demonstrate [3] how this narrow resonance enables the creation of a large fraction of closed-channel molecules in post-quench dynamics, appearing in the vicinity of unitarity. The inclusion of atom-molecule correlations is shown to lead to a substantial fraction of non-condensed closed-channel molecules, which participate in coherent oscillations along with the atomic and molecular condensates, as well as the excited Cooper pairs of atoms in the steady state. Using the time-resolved momentum distribution of atoms and molecules, we contrast this prethermal dynamics with that reported by Makotyn et al [Nat. Phys. 10, 116 (2014)] and Eigen et al [Nature 563, 221 (2018)] at unitarity showing new, resolvable oscillations.

Ref. [1]: Zhendong Zhang, Liangchao Chen, Kai-Xuan Yao, and Cheng

Chin, Nature 592, 708 (2021).

Ref. [2]: Zhendong Zhang, Shu Nagata, Kai-Xuan Yao, and Cheng Chin,

Nature Physics 19, 1466 (2023).

Ref. [3]: Zhiqiang Wang, Ke Wang, Zhendong Zhang, Shu Nagata, Cheng

Chin, K. Levin, arXiv:2310.01639 (2023)   

Controlled flow of excitations and source-to-drain transport in circuits of Rydberg atoms

We study chiral currents of Rydberg excitations in closed circuits of Rydberg atoms. The currents flowing in the circuit can be controlled by a phase pattern imprinted via a Raman scheme and can persist even in the presence of dephasing. Depending on the interplay between the Rabi coupling of Rydberg states and the dipole-dipole atom interaction, the current shows markedly different features. Attaching leads to a ring circuit, we study the source-to-drain transport through the system. Inspired by the rf-and c-SQUIDs we consider rings with one and two local energy offsets or detunings. As a combination of specific phase shifts in going though the localized detunings and as a result of coherent tunneling, we demonstrate how the transport of excitations can be controlled, with a distinctive dependence on the range of interaction.   

Quantum Quenches in the Two-Component Bose-Hubbard Model

Cold atoms in optical lattices can be used as quantum simulators to study the temporal evolution of quantum systems, which has lead to increasing interest in the out-of-equilibrium dynamics of multi-component bosons in optical lattices. We study the Bose-Hubbard model for two-component bosons using a strong-coupling approach within the closed time path formalism and develop an effective theory for the action of this problem. We obtain equations of motion for the superfluid order parameter and study these in the low-frequency, long wavelength limit during a quantum quench for various initial conditions.