Revealing spontaneous symmetry breaking in continuous time crystals

TL;DR

This paper experimentally demonstrates two types of continuous time crystals in atomic ensembles, revealing mechanisms behind spontaneous symmetry breaking and phase randomness, advancing understanding of this novel state of matter.

Contribution

It introduces and experimentally realizes two distinct mechanisms for continuous time crystals, expanding the understanding of spontaneous symmetry breaking in non-equilibrium systems.

Findings

Observation of two types of CTCs in atomic ensembles

Identification of manifold topology and chaos as mechanisms

Provision of general methods for realizing CTCs

Abstract

Spontaneous symmetry breaking plays a pivotal role in physics ranging from the emergence of elementary particles to the phase transitions of matter. The spontaneous breaking of continuous time translation symmetry leads to a novel state of matter named continuous time crystal (CTC). It exhibits periodic oscillation without the need for periodic driving, and the relative phases for repetitively realized oscillations are random. However, the mechanism behind the spontaneous symmetry breaking in CTCs, particularly the random phases, remains elusive. Here we propose and experimentally realize two types of CTCs based on distinct mechanisms: manifold topology and near-chaotic motion. We observe both types of CTCs in thermal atomic ensembles by artificially synthesizing spin-spin nonlinear interactions through a measurement-feedback scheme. Our work provides general recipes for the realization of CTCs, and paves the way for exploring CTCs in various systems.