Visualizing Dynamics of Charges and Strings in (2+1)D Lattice Gauge Theories

TL;DR

This paper demonstrates the experimental simulation of charge and string dynamics in a (2+1)D lattice gauge theory using superconducting qubits, revealing confinement effects and string behavior in a quantum processor.

Contribution

It introduces a variational circuit approach to simulate and image string dynamics and confinement phenomena in a (2+1)D lattice gauge theory on a quantum device.

Findings

Observation of transition from deconfined to confined dynamics with increasing electric field

Identification of two regimes of string fluctuations within the confining phase

Detection of a resonance condition facilitating string breaking

Abstract

Lattice gauge theories (LGTs) can be employed to understand a wide range of phenomena, from elementary particle scattering in high-energy physics to effective descriptions of many-body interactions in materials. Studying dynamical properties of emergent phases can be challenging as it requires solving many-body problems that are generally beyond perturbative limits. Here, we investigate the dynamics of local excitations in a $\mathbb{Z}_2$ LGT using a two-dimensional lattice of superconducting qubits. We first construct a simple variational circuit which prepares low-energy states that have a large overlap with the ground state; then we create charge excitations with local gates and simulate their quantum dynamics via a discretized time evolution. As the electric field coupling constant is increased, our measurements show signatures of transitioning from deconfined to confined dynamics. For confined excitations, the electric field induces a tension in the string connecting them. Our method allows us to experimentally image string dynamics in a (2+1)D LGT from which we uncover two distinct regimes inside the confining phase: for weak confinement the string fluctuates strongly in the transverse direction, while for strong confinement transverse fluctuations are effectively frozen. In addition, we demonstrate a resonance condition at which dynamical string breaking is facilitated. Our LGT implementation on a quantum processor presents a novel set of techniques for investigating emergent excitations and string dynamics.