Dynamical signatures of conventional and asymptotic quantum many-body scars on a trapped ion simulator

TL;DR

This paper explores the experimental signatures of asymptotic quantum many-body scars (AQMBS) on a trapped ion quantum processor, demonstrating their stability and impact on thermalisation times in many-body quantum systems.

Contribution

It establishes a connection between gapless excitations and AQMBS, and demonstrates their preparation and observation in a 20-qubit trapped ion system using logarithmic-depth circuits.

Findings

Slower thermalisation times observed with increasing system size.

First experimental signatures of asymptotic scars in a quantum processor.

Preparation of AQMBS states with logarithmic circuit depth.

Abstract

One of the promising applications of digital quantum processors is the simulation of many-body quantum systems. They have been already used to investigate several ergodicity violating mechanisms, which were initially discovered in synthetic quantum matter, such as many-body localisation, Hilbert space fragmentation and quantum many-body scars (QMBS). In addition to conventional QMBS, a recently discovered mechanism for ergodicity violation are the so-called asymptotic quantum many-body scars (AQMBS). These become more stable as system size is increased, leading to progressively longer thermalisation timescales. In this work, we show a connection between gapless excitations and AQMBS in certain qudit-based models. We then consider a 2-local model, hosting both conventional and asymptotic scars, in which the AQMBS states are gapless excitations of a ground state localisation transition. By exploiting the structure of the found AQMBS states and the all-to-all connectivity of the Quantinuum H1-1 quantum processor, we prepare these states in logarithmic circuit depth, and probe their thermalisation behaviour under Floquet dynamics. Performing simulations on up to N = 20 qubits and up to 418 entangling ZZ gates, we find slower thermalisation times as the system size is increased, providing the first experimental signatures of asymptotic scars.