Photon thermalization via laser cooling of atoms
Light is a paradigmatic quantum field, with individual excitations -- photons -- that are the most accessible massless particles known. However, their lack of mass and extremely weak interactions means that typically the thermal description of light is that of blackbody radiation. As the temperature of the light decreases, the overall number of photons approaches zero. However, a peculiar non-equilibrium scenario emerges when one considers the light emitted during the laser cooling of atoms. Typically, one focuses on the atomic motion, and forgets the photons that carry away the excess energy. Here we show that those forgotten photons in fact have a very different, thermal description that is closer to that of an ideal gas than to black body radiation. This suggests that atomic laser cooling enables a new platform for the nascent field of quantum simulation with light, leading to the possibility of interacting photonic systems with a large number of photons while being also in equilibrium.
Featured in Physics-Synopsis: https://physics.aps.org/synopsis-for/10.1103/PhysRevA.98.013834