Cryogenic optical beam steering for characterizing response of superconducting quantum devices to radiation events*

Particle interactions in the substrate of superconducting devices can generate phonons and liberate charge carriers. On a multi-qubit chip, propagation of these events can cause multiple qubits in close spatial proximity to decohere. Correlated decoherence events disrupt error correction, limiting the use of superconducting qubits in quantum computers. Novel applications in the field of particle physics seek to use these events as indicators of energy deposition, allowing quantum devices to serve as particle detectors. The low energy threshold of these proposed detectors makes them particularly well suited for a next-generation dark matter search. Further study of radiation sensitivity is required to advance the use of these devices for both quantum computing and particle detection. We have developed a cryogenic scanning apparatus capable of producing photon deposits with energies of 0.62 - 6.89eV across the surface of any quantum device. This can be used to characterize detector efficiency, and to investigate phenomena such as position sensitivity, phonon propagation, quasiparticle poisoning, and background-induced decoherence. In this talk, I will present the design overview and specifications of this calibration unit, along with current status and plans of the testing program.