Hilbert space signatures of non-ergodic glassy dynamics

TL;DR

This study uses superconducting qubits to explore the transition between ergodic and non-ergodic phases in disordered quantum systems, revealing a glass-like intermediate regime with slow dynamics and partial freezing.

Contribution

First experimental observation of a finite-temperature quantum glass transition in a two-dimensional disordered quantum many-body system.

Findings

Identification of a non-ergodic, glass-like regime with broad observable distributions.

Detection of slow power-law decay in Hilbert-space return probability.

Observation of a transition characterized by the onset of Edwards-Anderson order and halted spin diffusion.

Abstract

Disorder in quantum many-body systems can drive transitions between ergodic and non-ergodic phases, yet the nature--and even the existence--of these transitions remains intensely debated. Using a two-dimensional array of superconducting qubits, we study an interacting spin model at finite temperature in a disordered landscape, tracking dynamics both in real space and in Hilbert space. Over a broad disorder range, we observe an intermediate non-ergodic regime with glass-like characteristics: physical observables become broadly distributed and some, but not all, degrees of freedom are effectively frozen. The Hilbert-space return probability shows slow power-law decay, consistent with finite-temperature quantum glassiness. In the same regime, we detect the onset of a finite Edwards-Anderson order parameter and the disappearance of spin diffusion. By contrast, at lower disorder, spin transport persists with a nonzero diffusion coefficient. Our results show that there is a transition out of the ergodic phase in two-dimensional systems.