Quantum sensing by the resonant transduction of photons to quasiparticles

Typical transmon qubit structures are the aperture duals of resonant wire loop antennas, with peak spectral response in the range from 100 GHz to 1 THz. Absorption by the qubits of background radiation generates nonequilibrium quasiparticles (QPs), a dominant source of qubit initialization errors. Here, we explore three schemes to exploit this physics to realize next-generation mm-wave sensors. First, we optimize the qubit structure itself for photon-to-QP transduction; a change in charge parity of the weakly charge-sensitive transmon is detected using Ramsey interferometry. Second, we take a modular approach involving a separate Josephson aperture antenna coupled to the qubit through a low-gap superconducting channel embedded in a higher-gap groundplane. QPs generated at the detector diffuse to the qubit and induce charge-parity switches. Finally, we embed Josephson antennas in microwave kinetic inductance detectors (MKIDs). We discuss limits to detector noise equivalent power and possible applications of these approaches to the detection of wavelike dark matter.