SQUATs

Qubit Based Sensors

Superconducting qubits have demonstrated sensitivity to environmental radiation. Particle interactions in a device can influence a qubit’s state. These interactions are problematic for computing applications; however, our group seeks to leverage this sensitivity to design next-generation detectors. The Superconducting QUasiparticle Amplifying Transmon (SQUAT) is one such example.

Energy deposition events can break Cooper pairs into quasiparticles, either directly in the superconductor or indirectly through phonon-mediated pathways. When this occurs, SQUATs are designed to confine quasiparticles in the region surrounding a Josephson junction, where the quasiparticles may undergo multiple tunneling events. A transmon circuit is constructed around the junction and is designed to be weakly charge-sensitive. When a tunneling event occurs, the transmon’s charge parity flips, causing a discrete jump in the transition frequency. By monitoring these frequency jumps, we can detect an elevated tunneling rate following an energy deposition event [arXiv:2310.01345v3].

This configuration makes SQUATs a promising sensor for dark matter detection, with sensitivity projected down to meV phonons and THz photons. Our group focuses on detector research and development, which involves iterative cycles of design, fabrication, and cryogenic testing.