Correlations and linewidth of the atomic beam continuous superradiant laser

TL;DR

This paper introduces a minimal model for a continuous superradiant laser with a beam of atoms crossing a cavity, analyzing the effects of decoherence, atom correlations, and quantum fluctuations on laser properties.

Contribution

It presents an original Hamiltonian-based approach to model atomic dynamics in a superradiant laser, deriving conditions for sustained emission and analyzing linewidth limitations.

Findings

Linewidth is primarily determined by quantum fluctuations of the atomic dipole.

Atom-atom correlations grow in the superradiant regime but minimally affect linewidth.

Decoherence from transit time dominates over spontaneous emission in the studied regime.

Abstract

We propose a minimalistic model to account for the main properties of a continuous superradiant laser, in which a beam of atoms crosses the mode of a high-finesse Fabry-Perot cavity, and collectively emits light into the cavity mode. We focus on the case of weak single atom - cavity cooperativity, and highlight the relevant regime where decoherence due to the finite transit time dominates over spontaneous emission. We propose an original approach where the dynamics of atoms entering and leaving the cavity is described by a Hamiltonian process. This allows deriving the main dynamical equations for the superradiant laser, without the need for a stochastic approach. We derive analytical conditions for a sustained emission and show that the ultimate linewidth is set by the fundamental quantum fluctuations of the collective atomic dipole. We calculate steady-state values of the two-body correlators and show that the continuous superradiant regime is tied to the growth of atom-atom correlations, although these correlations only have a small impact on the laser linewidth.