Single Quasiparticle Trapping in Aluminum Nanobridge Josephson Junctions

Understand

We present microwave measurements of a high quality factor superconducting resonator incorporating two aluminum nanobridge Josephson junctions in a loop shunted by an on-chip capacitor.

• Trapped quasiparticles (QPs) shift the resonant frequency, allowing us to probe the trapped QP number and energy distribution and to quantify their lifetimes.
• We find that the trapped QP population obeys a Gibbs distribution above 75 mK, with non-Poissonian trapping statistics.
• Our results are in quantitative agreement with the Andreev bound state model of transport, and demonstrate a practical means to quantify on-chip QP populations and validate mitigation strategies in a cryogenic environment.