Quantum Parity Detectors: A New Approach for Sub-GeV Dark Matter

Lack of strong evidence of a direct detection in GeV-TeV dark matter experiments has motivated the search for keV-MeV dark matter candidates. At such masses, we expect recoil energies as low as meV, with phonons being the dominant (or only) energy excitation. We present a promising phonon-mediated detector based on charge qubits' sensitivity to quasiparticle tunneling, dubbed the Quantum Parity Detector (QPD). Operation of the detector is as follows: a particle interaction in the substrate generates phonons, which travel through the substrate and break cooper pairs and generate quasiparticles in the superconducting qubit patterned on the surface. As quasiparticles tunnel in and out of the qubit's superconducting island, the energy spectrum of the qubit shifts according to whether an even or odd number of quasiparticles have tunneled onto the island. These binary shifts in the qubit energy can be monitored through a coupled readout resonator's frequency and hence translated into a measurement of the energy deposited in the qubit. We will discuss the physical realizations of QPDs, the expected noise sources, numerical estimates forecasting O(meV) energy thresholds, as well as current progress in device testing.