Subradiant-to-Subradiant Phase Transition in the Bad Cavity Laser

TL;DR

This paper uncovers a dissipative phase transition in a bad cavity laser that precedes superradiance, characterized by non-analytic changes in output power and atomic inversion, and reveals a macroscopic entangled state near criticality.

Contribution

It identifies a novel phase transition between subradiant phases in a bad cavity laser and characterizes the entangled steady state near the critical point.

Findings

Discontinuous change in cavity output power at the transition

Suppressed output power below critical repump rate

Macroscopic entanglement near the critical region

Abstract

We show that the onset of steady-state superradiance in a bad cavity laser is preceded by a dissipative phase transition between two distinct phases of steady-state subradiance. The transition is marked by a non-analytic behavior of the cavity output power and the mean atomic inversion, as well as a discontinuity in the variance of the collective atomic inversion. In particular, for repump rates below a critical value, the cavity output power is strongly suppressed and does not increase with the atom number, while it scales linearly with atom number above this value. Remarkably, we find that the atoms are in a macroscopic entangled steady state near the critical region with a vanishing fraction of unentangled atoms in the large atom number limit.