Quantum Parity Detectors with meV Resolution for Astroparticle Applications*

Next generation rare-event searches, such as those aimed at detecting low-mass dark matter, require the development of detectors sensitive to ultra-low O(meV) recoil energies. One promising candidate are charge-parity based sensors derived from the exquisite sensitivity of superconducting qubits to quasiparticle (QP) tunneling events. In the literature, Quantum Capacitance Detectors (QCDs) have proven capable of counting single THz photons and Offset-Charge Sensitive (OCS) transmons have proven effective at monitoring nonequilibrium QP dynamics at the single QP level. We seek to extend the applicability of these techniques to phonon-mediated detection schemes, for which Quantum Parity Detectors (QPDs) promise to enable counting of single O(meV) phonons. As envisioned, particle-like interactions generate phonons within a crystalline silicon substrate. Phonons break Cooper pairs in the superconducting qubit element patterned on the surface of the substrate. The resulting cascade of QP tunneling events switch the charge-parity of the device in a binary manner, which can be used to deduce the initial properties of the energy deposit. In this presentation, we will discuss progress towards O(meV) QPDs including device design, noise sources, and results from first generation phonon-mediated QCDs and OCS transmons.