Variable potentials for thermalized light and coupled condensates

Variable micropotentials for light are created by thermo-optic imprinting of a dye–polymer solution within a microcavity. A thermalized photon Bose–Einstein condensate as well as the coupling and eigenstate hybridization of sites are demonstrated. 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 , 3 , 4 , 5 . Advances towards photonic simulators of solid-state equilibrium effects include polariton lattice experiments 6 , 7 , 8 , 9 , 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.