Real-time dynamics of lattice gauge theories with a few-qubit quantum computer

TL;DR

This paper demonstrates the first digital quantum simulation of a lattice gauge theory, specifically 1+1-dimensional quantum electrodynamics, using a few-qubit trapped-ion quantum computer to explore real-time particle creation and entanglement.

Contribution

It presents the first experimental realization of a lattice gauge theory simulation on a quantum computer, implementing gauge invariance and local conservation laws efficiently.

Findings

Successful simulation of the Schwinger mechanism and particle-antiparticle creation.

Observation of entanglement dynamics related to particle generation.

Implementation of long-range interactions to simulate gauge fields on an ion trap.

Abstract

Gauge theories are fundamental to our understanding of interactions between the elementary constituents of matter as mediated by gauge bosons. However, computing the real-time dynamics in gauge theories is a notorious challenge for classical computational methods. In the spirit of Feynman's vision of a quantum simulator, this has recently stimulated theoretical effort to devise schemes for simulating such theories on engineered quantum-mechanical devices, with the difficulty that gauge invariance and the associated local conservation laws (Gauss laws) need to be implemented. Here we report the first experimental demonstration of a digital quantum simulation of a lattice gauge theory, by realising 1+1-dimensional quantum electrodynamics (Schwinger model) on a few-qubit trapped-ion quantum computer. We are interested in the real-time evolution of the Schwinger mechanism, describing the instability of the bare vacuum due to quantum fluctuations, which manifests itself in the spontaneous creation of electron-positron pairs. To make efficient use of our quantum resources, we map the original problem to a spin model by eliminating the gauge fields in favour of exotic long-range interactions, which have a direct and efficient implementation on an ion trap architecture. We explore the Schwinger mechanism of particle-antiparticle generation by monitoring the mass production and the vacuum persistence amplitude. Moreover, we track the real-time evolution of entanglement in the system, which illustrates how particle creation and entanglement generation are directly related. Our work represents a first step towards quantum simulating high-energy theories with atomic physics experiments, the long-term vision being the extension to real-time quantum simulations of non-Abelian lattice gauge theories.