Quasiparticle Calorimetry using Dayem-Bridges

Quasiparticle poisoning in superconducting qubits is believed to be a limiting factor on coherence times. Addressing this challenge is complicated by the difficulty of measuring quasiparticle populations while deep in the superconducting state. In this talk, we discuss a generation and detection scheme for quasiparticles based on thermal relaxation of mesoscopic Dayem-bridges. In such bridges, the IV characteristics depend largely on the thermalization of the superconducting weak link by the quasiparticle population of the superconducting banks, due to the vanishing thermal conductance of the banks and substrate at low temperature. By bringing the bridge into the normal state via current bias, and measuring the thermal relaxation lifetime back into the zero resistance state as a function of temperature or applied field, one performs a calorimetric measurement of the entire device with the bridge acting as both heater and thermometer. From this, the lifetime of quasiparticles which contribute to cooling the bridge may be obtained. We report on our experiments to demonstrate efficacy of this technique, and explore implications of quasiparticle lifetimes for superconducting qubit operation.