Controlling the temperature and chemical potential of light
Massless particles, including photons, are not governed by particle conservation law during their typical interaction with matter even at low energies, and thus have no chemical potential as described by the theory of blackbody radiation. However, the concept of a chemical potential is essential in understanding transport and phase transitions. Moreover, in the context of quantum simulations with light, photonic systems are usually driven far from equilibrium to obtain a sufficient photon number population because vacuum is the typical ground state for such systems. Here we build upon the general concept of generating an effective chemical potential by a coherent drive with an implementation appropriate for optical or microwave photon-based quantum simulators. We consider how laser cooling of a well-isolated mechanical mode can provide an effective low-frequency bath for the quantum photonic system. The use of auxiliary photonic modes, coupled by the mechanical system, enables control of both the chemical potential and temperature of the resulting photonic quantum simulator’s grand canonical ensemble. This approach not only provides tunable parameters in performing quantum simulations, enables preparation of near-equilibrium photonic states of interest, but also allows an analogous voltage bias for photonic circuit elements.