Continuous Real-Time Detection of Quasiparticle Trapping in Aluminum Nanobridge Josephson Junctions

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 mu s. We describe initial measurements of quasiparticle behavior and discuss the possible optimization and application of such detector devices.& nbsp;Published under an exclusive license by AIP Publishing.