Supercurrent Spectroscopy of Andreev States

L Bretheau (1) , C Ö Girit (1) , C Urbina (1) , D Esteve (1) , H Pothier (1)

1 QUANTRONICS - Quantronics Group

We measure the excitation spectrum of a superconducting atomic contact. In addition to the usual continuum above the superconducting gap, the single particle excitation spectrum contains discrete, spin-degenerate Andreev levels inside the gap. Quasiparticle excitations are induced by a broadband on-chip microwave source and detected by measuring changes in the supercurrent flowing through the atomic contact. Since microwave photons excite quasiparticles in pairs, two types of transitions are observed: Andreev transitions, which consists of putting two quasiparticles in an Andreev level, and transitions to odd states with a single quasiparticle in an Andreev level and the other one in the continuum. In contrast to absorption spectroscopy, supercurrent spectroscopy allows detection of long-lived odd states.

Domains: Physics [physics]

L Bretheau, C Ö Girit, C Urbina, D Esteve, H Pothier. Supercurrent Spectroscopy of Andreev States. Physical Review X, 2013, 3, ⟨10.1103/PhysRevX.3.041034⟩. ⟨cea-01479024⟩