01390nas a2200145 4500008004100000245007200041210006900113520091900182100002201101700002101123700001801144700002601162700001901188856003701207 2018 eng d00aBose Condensation of Photons Thermalized via Laser Cooling of Atoms0 aBose Condensation of Photons Thermalized via Laser Cooling of At3 a

A Bose-Einstein condensate (BEC) is a quantum phase of matter achieved at low temperatures. Photons, one of the most prominent species of bosons, do not typically condense due to the lack of a particle number-conservation. We recently described a photon thermalization mechanism which gives rise to a grand canonical ensemble of light with effective photon number conservation between a subsystem and a particle reservoir. This mechanism occurs during Doppler laser cooling of atoms where the atoms serve as a temperature reservoir while the cooling laser photons serve as a particle reservoir. Here we address the question of the possibility of a BEC of photons in this laser cooling photon thermalization scenario and theoretically demonstrate that a Bose condensation of photons can be realized by cooling an ensemble of two-level atoms (realizable with alkaline earth atoms) inside a Fabry-Perot cavity.

1 aWang, Chiao-Hsuan1 aGullans, Michael1 aPorto, J., V.1 aPhillips, William, D.1 aTaylor, J., M. uhttps://arxiv.org/abs/1809.0777701932nas a2200157 4500008004100000245005300041210005300094260000900147520147500156100002201631700002101653700001801674700002601692700001901718856003701737 2018 eng d00aPhoton thermalization via laser cooling of atoms0 aPhoton thermalization via laser cooling of atoms c20183 a

Laser cooling of atomic motion enables a wide variety of technological and scientific explorations using cold atoms. Here we focus on the effect of laser cooling on the photons instead of on the atoms. Specifically, we show that non-interacting photons can thermalize with the atoms to a grand canonical ensemble with a non-zero chemical potential. This thermalization is accomplished via scattering of light between different optical modes, mediated by the laser cooling process. While optically thin modes lead to traditional laser cooling of the atoms, the dynamics of multiple scattering in optically thick modes has been more challenging to describe. We find that in an appropriate set of limits, multiple scattering leads to thermalization of the light with the atomic motion in a manner that approximately conserves total photon number between the laser beams and optically thick modes. In this regime, the subsystem corresponding to the thermalized modes is describable by a grand canonical ensemble with a chemical potential set by the energy of a single laser photon. We consider realization of this regime using two-level atoms in Doppler cooling, and find physically realistic conditions for rare earth atoms. With the addition of photon-photon interactions, this system could provide a new platform for exploring many-body physics.

1 aWang, Chiao-Hsuan1 aGullans, Michael1 aPorto, J., V.1 aPhillips, William, D.1 aTaylor, J., M. uhttps://arxiv.org/abs/1712.08643