Variable potentials for thermalized light and coupled condensates

Quantum gases in lattice potentials have been a powerful platform to simulate phenomena from solid-state physics, such as the Mott insulator transition(1). In contrast to ultracold atoms, photon-based platforms, such as photonic crystals, coupled waveguides or lasers, usually do not operate in thermal equilibrium(2-5). Advances towards photonic simulators of solid-state equilibrium effects include polariton lattice experiments(6-10), and the demonstration of a photon condensate(11,12). Here, we demonstrate a technique to create variable micropotentials for light using thermo-optic imprinting of a dye-polymer solution within an ultrahigh-finesse microcavity. We study the properties of single-and double-well potentials, and find the quality of structuring sufficient for thermalization and Bose-Einstein condensation of light. The investigation of effective photon-photon interactions along with the observed tunnel coupling between sites makes the system a promising candidate to directly populate entangled photonic many-body states. The demonstrated scalability suggests that thermo-optic imprinting provides a new approach for variable microstructuring in photonics.