Widely Tunable Coupling between a Mechanical Mode and Cavity Photons via a Superconductor

Inducing strong coupling between a mechanical degree of freedom and optical modes has been of great scientific interest itself, but also important for the applications to the quantum information technology. However, photons and mechanical modes usually are weakly interacting due to very small momentum exerted by photons. Here, we demonstrate a scheme for coupling a resonance mode of a mechanical oscillator with an optical cavity, by utilizing the magneto-optical effect of a mesoscopic superconductor attached to the mechanical oscillator. The absorption of cavity photons by the superconductor in external magnetic fields gives rise to a retarded force that modifies the damping and frequency of the oscillator. Measurements using NbSe 2 achieved approximately a factor of 17 reduction in the mode temperature from 5.0 K to 260 mK.