A quantum device includes a resonator and a tuning structure. The tuning structure is made a material such as a chalcogenide and is positioned to interact with the electromagnetic radiation in the resonator so that a resonant mode of the first resonator depends on a characteristic of the tuning structure. The resonator is optically coupled so that a transition between quantum states associated with a defect produces electromagnetic radiation in the resonator. The characteristic of the tuning structure is adjustable after fabrication of the resonator and the tuning structure.