Effect of Laser Illumination on Niobium Transmon Qubits for Quantum Transduction

A transducer that can coherently convert quantum states from the microwave to the optical domain is a key component in realizing long distance quantum networks that connect spatially separated quantum processors based on superconducting qubits. Recently, we demonstrated transduction of optical photons from a superconducting qubit using a piezoacoustic transduction scheme. This device operates in pulsed mode at a low repetition rate due to slow relaxation of quasiparticles (QPs) generated in the aluminum (Al) circuit upon optical illumination. We aim to address this issue by using niobium (Nb) qubits to leverage the short QP lifetime of Nb. In this work, we study the effects of pulsed laser light on a transmon qubit with a Nb capacitor and Al Josephson junctions. We use a lensed fiber to illuminate the qubit with laser light at 1.55um and extract a timescale for the recovery of qubit population and coherence after the laser pulse. We also study the effect of laser power and repetition rate on the population and coherence times of the qubit. Our measurements indicate that integrating our previously demonstrated piezoacoustic transducer with Nb qubits would allow for faster repetition rates, enabling experiments revealing the quantum coherent nature of the transduction process.