title: Spectrum of Andreev bound states in a molecule embedded inside a microwave-excited superconducting junction.
abstract: Nondissipative Josephson current through nanoscale superconducting constrictions is carried by spectroscopically sharp energy states, the so-called Andreev states. Although theoretically predicted almost 40 years ago, no direct spectroscopic evidence of these Andreev bound states exists to date. We propose a novel type of spectroscopy based on embedding a superconducting constriction, formed by a single-level molecule junction, in a microwave QED cavity environment. In the electron-dressed cavity spectrum we find a polariton excitation at twice the Andreev bound state energy, and a superconducting-phase-dependent ac Stark shift of the cavity frequency. Dispersive measurement of this frequency shift can be used for Andreev bound state spectroscopy.
authors.affiliation: Department of Microtechnology and Nanoscience--MC2, Chalmers University of Technology, S-412 96 Göteborg, Sweden.
authors.forename: Jonas
authors.initials: J
authors.lastname: Sköldberg
authors.forename: Tomas
authors.initials: T
authors.lastname: Löfwander
authors.forename: Vitaly S
authors.initials: VS
authors.lastname: Shumeiko
authors.forename: Mikael
authors.initials: M
authors.lastname: Fogelström