Non-equilibrium critical scaling and universality in a quantum simulator

TL;DR

This paper demonstrates that a quantum simulator can explore universal non-equilibrium critical scaling laws, revealing new universality classes and critical exponents following quantum quenches in a long-range Ising model.

Contribution

The study uncovers universal non-equilibrium scaling laws and critical exponents in a quantum simulator, extending the concept of universality beyond equilibrium phase transitions.

Findings

Post-quench fluctuations scale with system size with universal exponents.

Double quenches reveal a new non-equilibrium universality class.

Quantum simulators can explore critical phenomena beyond equilibrium.

Abstract

Universality and scaling laws are hallmarks of equilibrium phase transitions and critical phenomena. However, extending these concepts to non-equilibrium systems is an outstanding challenge. Despite recent progress in the study of dynamical phases, the universality classes and scaling laws for non-equilibrium phenomena are far less understood than those in equilibrium. In this work, using a trapped-ion quantum simulator with single-spin resolution, we investigate the non-equilibrium nature of critical fluctuations following a quantum quench to the critical point. We probe the scaling of spin fluctuations after a series of quenches to the critical Hamiltonian of a long-range Ising model. With systems of up to 50 spins, we show that the amplitude and timescale of the post-quench fluctuations scale with system size with distinct universal critical exponents, depending on the quench protocol. While a generic quench can lead to thermal critical behavior, we find that a second quench from one critical state to another (i.e.~a double quench) results in a new universal non-equilibrium behavior, identified by a set of critical exponents distinct from their equilibrium counterparts. Our results demonstrate the ability of quantum simulators to explore universal scaling beyond equilibrium.