Observation of Prethermalization in Long-Range Interacting Spin Chains

TL;DR

This paper experimentally demonstrates that long-range interacting quantum spin chains can relax into novel prethermal states that retain initial conditions, challenging existing theories of thermalization and generalized Gibbs ensembles.

Contribution

It provides the first experimental observation of a new type of prethermal state arising from long-range interactions, not describable by traditional GGE models.

Findings

Prethermal states retain strong memory of initial conditions.

Long-range interactions lead to emergent double-well potentials.

Prethermalization occurs beyond previously understood regimes.

Abstract

Statistical mechanics can predict thermal equilibrium states for most classical systems, but for an isolated quantum system there is no general understanding on how equilibrium states dynamically emerge from the microscopic Hamiltonian. For instance, quantum systems that are near-integrable usually fail to thermalize in an experimentally realistic time scale and, instead, relax to quasi-stationary prethermal states that can be described by statistical mechanics when approximately conserved quantities are appropriately included in a generalized Gibbs ensemble (GGE). Here we experimentally study the relaxation dynamics of a chain of up to 22 spins evolving under a long-range transverse field Ising Hamiltonian following a sudden quench. For sufficiently long-ranged interactions the system relaxes to a new type of prethermal state that retains a strong memory of the initial conditions. In this case, the prethermal state cannot be described by a GGE, but rather arises from an emergent double-well potential felt by the spin excitations. This result shows that prethermalization occurs in a significantly broader context than previously thought, and reveals new challenges for a generic understanding of the thermalization of quantum systems, particularly in the presence of long-range interactions.