Probing the Quench Dynamics of Antiferromagnetic Correlations in a 2D Quantum Ising Spin System

Abstract

Simulating the real-time evolution of quantum spin systems far out of equilibrium poses a major theoretical challenge, especially in more than one dimension. We experimentally explore quench dynamics in a two-dimensional Ising spin system with transverse and longitudinal fields. We realize the system with a near unit-occupancy atomic array of over 200 atoms obtained by loading a spin-polarized band insulator of fermionic lithium into an optical lattice and induce short-range interactions by direct excitation to a low-lying Rydberg state. Using site-resolved microscopy, we probe antiferromagnetic correlations in the system after a sudden quench from a paramagnetic state and compare our measurements to numerical calculations using state-of-the-art techniques. We achieve many-body states with longer-range antiferromagnetic correlations by implementing a near-adiabatic quench of the longitudinal field and study the buildup of correlations as we vary the rate with which we change the field.

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Plain Language Summary

Quantum computation, quantum materials, and quantum chemistry all must deal with the challenging problem of calculating the complex nonequilibrium dynamics of an ensemble of many interacting particles. There have been many advances in techniques to compute the properties of equilibrium systems. However, the theoretical toolkit for tackling nonequilibrium dynamics is still very much a work in progress. These algorithms must be tested against data from real physical systems. Fortunately, the ability to create and control synthetic quantum systems that can serve as test beds has rapidly advanced over the past decade. Here, we experimentally explore out-of-equilibrium quantum dynamics in a synthetic two-dimensional magnet.

Specifically, we realize an array of interacting spins by trapping more than 200 cold atoms in a crystal by using interfering light beams. We couple the atoms to a highly excited electronic state known as a Rydberg state, where they interact strongly with each other. The interactions favor antiferromagnetic correlations; that is, an atom in the Rydberg state is more likely to be next to an atom in the ground state. Using a high-resolution microscope, we measure the evolution of these antiferromagnetic correlations after sudden changes in the strength of an effective magnetic field and compare our results to state-of-the-art theory.

Our results demonstrate that higher-dimensional arrays of Rydberg atoms can be used to explore quantum dynamics in regimes that are challenging for current theory. The data from such experiments will be useful for testing various approximations made in quantum dynamics algorithms.