Quantum sensing for DMRadio with Radio-frequency Quantum Upconverters

The DMRadio suite of experiments probes dark matter axion masses below 1 μeV. These axion detectors require extremely high sensitivity over a broad frequency tuning range, and will require novel quantum sensor architectures to reach DFSZ coupling for frequencies 0.1-30MHz in the GUT-scale DMRadio experiment. I will discuss backaction evasion (BAE), a quantum protocol that increases the frequency-integrated sensitivity beyond the Standard Quantum Limit (SQL) by widening the measurement sensitivity bandwidth. BAE protocols will be implemented in DMRadio using the radio-frequency quantum upconverter (RQU), a device that upconverts kHz-MHz flux signals onto microwave-frequency drive tones using a parametric interaction between a Josephson-junction interferometer and a superconducting resonator. DMRadio-50L (5kHz-5MHz) will be used as a testbed for developing RQU sensor technology, before its implementation in the DMRadio-GUT experiment. I will present designs, modeling, and data from first-generation RQUs with three-junction interferometer, including phase-sensitive measurements that demonstrate the first steps towards BAE protocol implementation. I will also describe current device limitations, future plans, and device requirements for implementation in DMRadio experiments.