Spontaneous $\mathcal{T}$-symmetry breaking and exceptional points in cavity quantum electrodynamics systems

TL;DR

This paper theoretically demonstrates spontaneous time-reversal symmetry breaking and the existence of exceptional points in a cavity quantum electrodynamics system, revealing topological quantum state manipulation possibilities.

Contribution

It introduces a novel theoretical framework for symmetry breaking and exceptional points in cavity QED systems with atomic ensembles and cavity modes.

Findings

Symmetry breaking depends on atomic detuning and coupling strength.

Identification of an exceptional point where eigenstates coalesce.

Chiral mode switching enables topological control of quantum states.

Abstract

Spontaneous symmetry breaking has revolutionized the understanding in numerous fields of modern physics. Here, we theoretically demonstrate the spontaneous time-reversal symmetry breaking in a cavity quantum electrodynamics system in which an atomic ensemble interacts coherently with a single resonant cavity mode. The interacting system can be effectively described by two coupled oscillators with positive and negative mass when the two-level atoms are prepared in their excited states. The occurrence of symmetry breaking is controlled by the atomic detuning and the coupling to the cavity mode, which naturally divides the parameter space into the symmetry broken and symmetry unbroken phases. The two phases are separated by a spectral singularity, a so-called exceptional point, where the eigenstates of the Hamiltonian coalesce. When encircling the singularity in the parameter space, the quasi-adiabatic dynamics shows chiral mode switching which enables topological manipulation of quantum states.