Regular and bistable steady-state superradiant phases of an atomic beam traversing an optical cavity

TL;DR

This paper explores various superradiant emission regimes of an atomic beam passing through an optical cavity, revealing phase transitions and bistability influenced by atomic motion and beam orientation.

Contribution

It introduces the concept of bistable superradiant phases and analyzes the critical behavior and spectral features near phase boundaries.

Findings

Identification of continuous superradiance for small beam tilt

Prediction of a bistable superradiant phase with frequency detuning

Spectral linewidth exhibits critical scaling near phase transitions

Abstract

We investigate the different photon emission regimes created by a preexcited and collimated atomic beam passing through a single mode of an optical cavity. In the regime where the cavity degrees of freedom can be adiabatically eliminated, we find that the atoms undergo superradiant emission when the collective linewidth exceeds the transit-time broadening. We analyze the case where the atomic beam direction is slanted with respect to the cavity axis. For this situation, we find that a phase of continuous light emission similar to steady-state superradiance is established providing the tilt of the atomic beam is sufficiently small. However, if the atoms travel more than half a wavelength along the cavity axis during one transit time we predict a dynamical phase transition to a new bistable superradiant regime. In this phase the atoms undergo collective spontaneous emission with a frequency that can be either blue or red detuned from the free-space atomic resonance. We analyze the different superradiant regimes and the quantum critical crossover boundaries. In particular we find the spectrum of the emitted light and show that the linewidth exhibits features of a critical scaling close to the phase boundaries.