By Hugues Pothier (CEA Saclay)
Abstract : Andreev states are localized quasiparticle states that arise at phase-biased Josephson junctions. With microwaves, a Cooper pair from the superconducting condensate can be excited and create a pair of quasiparticles in an Andreev state1. In transparent junctions, like the ones obtained in atomic contacts or nanowires, the two-level system spanned by the states with 0 and 2 quasiparticles is well decoupled from other excitations. I will report experiments in which the dynamics and the coherence of this system is probed by coupling it to a microwave resonator2.
Joint work with L. Tosi, C. Metzger, M. Goffman and C. Urbina, Quantronics group SPEC, CEA Saclay, CNRS, Université Paris-Saclay, France.

1. L. Bretheau et al., Exciting Andreev pairs in a superconducting atomic contact, Nature 499, 312-315
(2013).
2. C. Janvier et al., Coherent manipulation of Andreev states in superconducting atomic contacts, Science 349, 1199 (2015).
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