Searching for Axion Dark Matter using Superconducting Qubits

A transmon qubit can be operated in a resonant cavity as a sensor of a single microwave photon produced by the interaction between axion dark matter and a laboratory magnetic field. The axion is a potential solution to the strong CP problem in QCD and could account for the abundance of dark matter observed in the universe. In the presence of an applied magnetic field, the axion field will source a current that can be harnessed to drive a resonant cavity to single photon occupation. When weakly coupled to the detection cavity through a dipole interaction, the qubit transition frequency shift is used to measure the cavity photon number. The use of a direct dispersive quantum non-demolition measurement of the photon number decouples the measurement induced back action from the experimental uncertainties.