Spontaneous Symmetry Breaking of Time-Reversal-Symmetry and Time-Crystal States in Chiral Atomic Systems

TL;DR

This paper theoretically demonstrates how chiral atomic systems interacting with their environment can spontaneously break time-reversal symmetry or form time-crystal-like states due to intrinsic spin and virtual transitions, without external bias.

Contribution

It introduces a new mechanism for spontaneous time-reversal symmetry breaking and time-crystal formation driven solely by quantum vacuum fluctuations in chiral atomic systems.

Findings

Time-reversal symmetry can spontaneously break in chiral atomic systems.

Time-crystal-like states can emerge with long relaxation times.

The system's behavior depends on the handedness of spin precession.

Abstract

We present a theoretical study of the interaction between an atom characterized by a degenerate ground state and a reciprocal environment, such as a semiconductor nanoparticle, without the presence of external bias. Our analysis reveals that the combined influence of the electron's intrinsic spin magnetic moment on the environment and the chiral atomic dipolar transitions may lead to either the spontaneous breaking of time-reversal symmetry or the emergence of time-crystal-like states with remarkably long relaxation times. The different behavior is ruled by the handedness of the precession motion of the atom's spin vector, which is induced by virtual chiral-dipolar transitions. Specifically, when the relative orientation of the precession angular velocity and the electron spin vector is as in a spinning top, the system manifests time-crystal-like states. Conversely, with the opposite relative orientation, the system experiences spontaneous symmetry breaking of time-reversal symmetry. Our findings introduce a novel mechanism for the spontaneous breaking of time-reversal symmetry in atomic systems, and unveil an exciting opportunity to engineer a nonreciprocal response at the nanoscale, exclusively driven by the quantum vacuum fluctuations.