The Pathway Toward a Highly Tunable Single-Microwave Photon Detector for Axion Searches

I will provide an update on the Stanford quantum group’s current efforts on single-microwave photon detector (SMPD) development. Photon counting has significant advantages over the standard quantum limit readout in enhancing the scanning speed of the haloscope-style axion experiments at above 4 GHz, providing a critical path toward reaching the DFSZ benchmark at these frequencies.

We design our SMPD following the promising approach by the Quantronics group at Paris-Saclay University, which leverages principles of quantum information processing. The device employs a four-wave mixing process involving two superconducting coplanar waveguide (CPW) resonators, a tuning pump, and a transmon qubit. Existing devices from the Saclay group have demonstrated an impressive efficiency of up to 80% and a dark count rate on the order of 10/s across approximately 50 MHz around 7 GHz. However, a larger frequency range is essential for the practical implementation of SMPDs in axion searches. We made improvements on this front by exploring different tuning strategies while maintaining the high detection efficiency and low dark count rate. In this presentation, I will outline our roadmap toward a 5-7 GHz tunable SMPD for the volume-enhanced ADMX-VERA experiment. I will discuss our design, simulation, and testing results from our initial fabrications.