Continuous real-time detection of quasiparticle trapping in aluminum nanobridge Josephson junctions

Abstract

Nonequilibrium quasiparticles are ubiquitous in superconducting electronics. These quasiparticles can trap in the internal Andreev bound states of a phase-biased Josephson junction, providing a mechanism for studying their presence and behavior. We characterize a quasiparticle trapping detector device based on a two junction aluminum nanobridge superconducting quantum interference device incorporated into a transmission line resonator. When the device is flux-biased, distinct resonant frequencies develop depending on the trapped quasiparticle number. We demonstrate continuous detection of up to 3 trapped quasiparticles, with detection of a trapped quasiparticle with a signal-to-noise ratio of 27 in 5 μs. We describe initial measurements of quasiparticle behavior and discuss the possible optimization and application of such detector devices.

Dynamical Polarization of the Fermion Parity in a Nanowire Josephson Junction

“…While microwave photons are only allowed to drive transitions that preserve parity, they should be able to polarize the fermion parity of a JJ by exciting one QP into the continuum of states above the superconducting gap in the leads [15,[41][42][43][44]. However, so far microwaves have only been observed to increase the rate of QP escape [19,45,46] or trapping [47] from the junction, while deterministic polarization toward either parity has not yet been demonstrated.…”