Observation of Time Crystal in a Spin Maser System

TL;DR

This paper reports the experimental observation of a time crystal in a hybrid spin maser system, demonstrating spontaneous time translation symmetry breaking through a retarded interaction-induced self-sustained oscillation.

Contribution

It introduces a novel realization of a time crystal using a retarded interaction in a spin maser system, highlighting a phase transition and robustness of oscillation amplitude.

Findings

Observation of a self-sustained oscillation with a characteristic frequency

Oscillation amplitude is robust against perturbations

Time phase distribution is random, indicating symmetry breaking

Abstract

Pair interaction potentials between atoms in a crystal are in general non-monotonic in distance, with a local minimum whose position gives the lattice constant of the crystal. A temporal analogue of this idea of crystal formation is still pending despite intensive studies on the time crystal phase. In a hybrid spin maser system with a time delay feedback, we report the observation of a time crystal induced by a retarded interaction with a characteristic time scale. This nonequilibrium phase features a self-sustained oscillation with an emergent frequency other than the intrinsic Larmor precession frequency of the spin maser system. It is shown that the amplitude of the oscillation is robust against perturbation, while its time phase randomly distributes from 0 to $2\pi$ for different realizations, a signature of spontaneous time translation symmetry breaking. This time crystal phase emerges only when the feedback strength exceeds a critical value, at which the system experiences a first order phase transition. Such a retarded interaction induced time crystal is closer to the idea of crystal, compared to other time crystal realizations.