Group Seminar at MPQ: A steady-state superradiant phase transition in free space: Atomic and photonic correlations from radiating two-level atomic ensembles.

Igor Ferrier-Barbut, Institut d’Optique
Group Seminar at MPQ, lecture hall and zoom
Tuesday, November 22nd, 09:00am (MEZ)

Abstract

We study collective spontaneous emission in dense ensembles of two-level atoms, that are indistinguishably coupled to a mode of the electromagnetic field, akin to cavity QED systems but here in free space. The power radiated by the ensemble depends on the atomic correlations inside of it, which is at the heart of Dicke superradiance. I will discuss our studies of the systems behaviour when continuously driven by a resonant laser that leads to a competition between laser driving and collective spontaneous emission. In a configuration that realizes a textbook model of a driven-dissipative many-body system, we observed that this competition induces a non-equilibrium phase transition between a magnetized phase and a steady-state superradiant phase.

Beyond measuring the field intensity, we measure photon-photon correlations. This precious tool of quantum optics allows us to question wether atomic correlations can impart non-trivial photonic correlations. I will show that indeed photonic correlations emerge, and despite the system’s simplicity, their description poses a challenge to many-body theories.