Trond Andersen, Nikita Astrakhantsev, Xiao Mi and Dmitry Abanin
Understanding how interacting particles approach thermal equilibrium is a major goal of quantum simulation. Analog quantum simulators (AQS) are appealing platforms for achieving this goal since they directly implement Hamiltonian dynamics, which are faster and less constrained by decoherence than in digital Trotter schemes. We here present a hybrid digital-analog quantum simulator comprising 69 superconducting qubits which exhibits very low analog evolution errors and performance beyond the reach of classical simulation in cross-entropy benchmarking experiments. Simulating an XY quantum magnet, we observe clear signatures of the Kosterlitz-Thouless transition – including the emergence of algebraically decaying correlations with an exponent near the expected universal value of ¼ – as well as a consequent breakdown of Kibble-Zurek scaling. We substantiate our interpretations by injecting variable energy density into the initial state, which enables studying the effects of the eigenstate thermalization hypothesis in targeted parts of the spectrum. Finally, we digitally prepare the system in pairwise-entangled dimer states and image the transport of energy and vorticity during thermalization. These results establish the efficacy of superconducting analog-digital quantum processors for preparing states across many-body spectra and unveiling their thermalization dynamics.