Microwave Susceptibility Observation of Interacting Many-Body Andreev States

Microwave spectroscopy of interacting Andreev spins

“…Previous microwave experiments probing Andreev states with superconducting circuits have traditionally used thick (150-nm) coplanar waveguides [5,9,12,15] or coplanar stripline resonators [8,10,11,14]. Here, we use thin-film (20-nm) lumped-element resonators due to their proven resilience to parallel fields shown earlier in fluxonium devices [44].…”

“…When two superconductors (S) are separated by a normal (N) material, the transport of Cooper pairs between them is mediated by Andreev reflections at the N-S interfaces. The consequent formation of current-carrying, discrete Andreev states in S-N-S junctions can be observed with microwave spectroscopy [4][5][6][7][8][9][10][11][12][13][14][15].…”

“…Embedding nanowire Josephson junctions in microwave superconducting circuits allows for probing of individual Andreev states with a remarkable energy resolution of ∼100 MHz (i.e., ∼0.4 µeV) [8][9][10][11][12][13][14][15] and with potential spin sensitivity [9][10][11][12][13]. Thus, such circuits provide an excellent platform to study the (spin) properties of Andreev bound states.…”

“…Thus, such circuits provide an excellent platform to study the (spin) properties of Andreev bound states. In fact, microwave spectroscopy has already revealed that spin-orbit coupling [9,10] and electron-electron interactions [14,15] are crucial ingredients that determine the many-body Andreev spectrum of hybrid nanowire Josephson junctions. However, so far, such experiments using superconducting circuits have been limited to zero or small magnetic fields.…”

Josephson tunnel junction arrays and Andreev weak links: what’s the difference?

“…† Here we focus on the even parity sector that is near resonance. Even-odd parity transitions are a subject of study for both CPT 9, 10 and S-QD-S,8,[11][12][13][14] in part due to quasiparticle poisoning 15. Proc.…”