Instabilities of the continuous superradiant laser

We investigate the intensity stability of a superradiant laser in the configuration where a continuous beam of atoms in an electronically excited state crosses the mode of a high-finesse Fabry-Perot cavity. We show that such superradiant laser can become unstable and develop chaotic behavior.
arXiv:2606.21675 (2026)

We investigate the intensity stability of the superradiant laser. Our study focuses on the architecture where a continuous beam of atoms in an electronically excited state crosses the mode of a high-finesse Fabry-Perot cavity, which has been proposed as a new architecture of an active optical clock. We show that such superradiant laser can become unstable and develop chaotic behavior.

We derive an analytical criterion for this instability and find that it may only occur when the lifetime of photons in the cavity is significantly shorter than the lifetime of atoms. This criterion allows for refining the necessary parameters to run a superradiant laser as a frequency reference in the optical domain. In particular, we point-out the consequences of the instability on intensity fluctuations and laser linewidth.

On the other hand, we also point out that the superradiant laser, when in the unstable regime, can become an interesting playground for studying chaos. At the mean-field level, there is a direct mapping to the Bénard instability associated with fluid turbulence; however quantum fluctuations associated with photon out-coupling and atom re-filling substantially modify the expected behaviors.

Finally, we point-out the existence of a regular self-pulsing regime at large atom numbers.

Trajectories during the superradiant laser dynamics, in the unstable regime. We represent the real and imaginary parts of the photon field b versus the imaginary part of atomic coherences S−. The blue dots are within the mean-field approximation, while orange dots take into account atomic variable fluctuations using the TWA approximation. Mean-field trajectories oscillate between two strange attractors, while TWA trajectories show that phase drifts are stronger for small amplitudes of b and S-.