Ultrahigh finesse Fabry-Pérot superconducting resonator

Abstract
The authors have built a microwave Fabry-Pérot resonator made of diamond-machined copper mirrors coated with superconductingniobium. Its damping time ( T c = 130 ms at 51 GHz and 0.8 K ) corresponds to a finesse of 4.6 × 10 9 , the highest ever reached for a Fabry-Pérot in any frequency range. This result opens many perspectives for quantum information processing, decoherence and nonlocality studies.