QDev Seminar: Marcelo Goffman

Coherent manipulation of Andreev bound states in superconducting atomic-size contacts

M. F. Goffman, L. Tosi, H. Pothier, and C. Urbina

Quantronics Group

SPEC, Université Paris-Saclay, CEA Saclay 91191 Gif-sur-Yvette, France

The absorption of a photon by a superconductor is usually an incoherent process in which a Cooper pair is broken into a pair of independent quasiparticles. Here we show [1] that in an atomic-size contact between two superconductors it is possible to coherently excite a pair into a discrete localized bound state. By coupling the contact to the electromagnetic field of a microwave resonator we perform time resolved experiments of this particular excitation. Lifetimes of several microseconds are measured for the excited state of the localized pair. We also demonstrate coherent superpositions of this excited state and the ground state. We also detect the states in which a single quasiparticle occupies the bound state.

Our experimental strategy could be used to explore hybrid superconducting devices in the regime where Andreev states evolve into Majorana states [2].

[1] C. Janvier et al, Science 349, 1199 (2015).

[2] D. Chevallier, P. Simon, C. Bena, Phys. Rev. B 88, 165401 (2013).