Photon thermalization and Bose condensation via laser cooling of atoms

The advent of laser cooling and trapping techniques for neutral atoms has led to remarkable breakthroughs in exploring the interaction between light and matter at ultracold temperatures. Here we focus on laser cooling from the perspective of the light --- specifically, the scattering of light between different optical modes in the presence of the cooling beams. In high optical depth atomic ensembles, we show that photons reemitted during the laser cooling process can equilibrate with the atomic motion and reach a steady state, and a grand canonical ensemble of photons can arise directly via atomic laser cooling in an experimentally accessible regime, with a chemical potential controlled by the laser frequency. Moreover, by placing the atoms in a curved cavity, the transverse modes in the cavity can be mapped into 2D massive bosons inside a parabolic well and can lead to 2D Bose-Einstein condensate of light. We consider realization of this regime using two-level atoms in Doppler cooling, and construct a phase diagram in the laser frequency and intensity parameter space showing the gain, condensate, thermal and quasi-thermal regimes for cavity photons with simulated values appropriate for the Yb intercombination transition.