Axion Dark Matter Detection with Superconducting Qubits

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 used to drive a resonant cavity to single photon occupation. A transmon qubit operating as a microwave photon sensor is a viable readout system at frequencies where the added noise of quantum limited amplifiers overwhelms the signal rate. The use of a direct dispersive quantum non-demolition measurement of the photon number decouples the measurement back action from the experimental uncertainties. In this regime background and dark counts become the dominant sources of detector error. For a transmon qubit operating as a photon counter, the dark rate is typically 1-10% and is orders of magnitude greater than the anticipated signal rate. In order to mitigate the effect of individual bit flip errors of the detector we operate multiple detectors in the same cavity volume. The error rate of the joint N-qubit detector could potentially have exponentially suppressed error rates as compared to the single detector. We will report theoretical performance and progress towards characterizing fidelity and correlations of multiqubit detectors.