Observation of a non-equilibrium superradiant phase transition in free space

Giovanni Ferioli (1) , Antoine Glicenstein (1) , Igor Ferrier-Barbut (1) , Antoine Browaeys (1)

1 Laboratoire Charles Fabry / Optique Quantique

We observe a non-equilibrium phase transition in a driven dissipative quantum system consisting of an pencil-shape cloud of up to $N\approx 2000$ laser-cooled atoms in free space, optically excited along its main axis. We find that our data are well reproduced by the Driven Dicke model, which assumes a sub-wavelength sample volume, by simply using an effective atom number. By measuring the excited state population of the atoms and the light emitted in the superradiant mode, we characterize the dynamics of the system and its steady-state properties. In particular, we observe the characteristic $N^2$ scaling of the photon emission rate in the superradiant phase, thus demonstrating steady-state superradiance in free space. Finally, we observe a modification of the statistics of the superradiant light as we cross the phase transition.

Keywords: photon: flux, superradiance, critical phenomena, atom, statistics, excited state, scaling, dissipation, cloud

Domains: Physics [physics]; Quantum Physics [quant-ph]; Atomic Physics [physics.atom-ph]

Giovanni Ferioli, Antoine Glicenstein, Igor Ferrier-Barbut, Antoine Browaeys. Observation of a non-equilibrium superradiant phase transition in free space. 2022. ⟨hal-03836768⟩