Quasiparticle dynamics in a superconducting qubit irradiated by a localized infrared source

One source of decoherence in superconducting qubits is the presence of broken Cooper pairs, or quasiparticles. These can be generated by high-energy radiation, either present in the environment or purposefully introduced out of necessity, as is the case for some hybrid quantum devices. Here, we systematically study the coherence properties of a transmon qubit under illumination by a focused infrared laser beam. We move the beam in-situ and observe how the position and power of continuous-wave light affects the qubit. Then we inject quasiparticles using a short pulse of laser light with various powers and durations and measure the recovery of the qubit coherence as a way of investigating the quasiparticle dynamics. Our experimental platform can be used to further study the response of superconducting circuits to catastrophic high-energy radiation events.