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The authors have built a microwave Fabry-Pérot resonator made of diamond-machined copper mirrors coated with superconducting niobium. Its damping time (Tc=130ms at 51GHz and 0.8K) corresponds to a finesse of 4.6×109, 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.
Kuhr et al. (Mon,) studied this question.