Microwave spectroscopy of interacting Andreev spins

Abstract

Andreev bound states are fermionic states localized in weak links between superconductors, which can be occupied with spinful quasiparticles. Recently, experiments embedding a nanowire Josephson junction into a superconducting circuit have enabled coherent manipulation of a single Andreev spin. However, these experiments remained limited to small magnetic fields. Here, the authors measure the microwave spectra of a nanowire Josephson junction in magnetic fields up to $\ensuremath{\sim}$ 250 mT and identify singlet, doublet, and triplet states of interacting Andreev spins.