Remote entanglement of microwave cavities for enhanced scan rate in axion dark matter searches

The key figure of merit for cavity-based axion dark matter searches is the rate at which detectors can scan the vast parameter space made up of the particle’s unknown mass and coupling strength. Squeezed vacuum states have recently been used to circumvent the quantum limit, doubling the scan rate by widening the visibility bandwidth over that of the quantum-limited approach. We propose a method of further scan rate enhancement based on parametric coupling of an axion-sensitive cavity with an auxiliary readout circuit. By modulating the coupling at the difference and sum frequencies of the two cavity modes, we induce simultaneous two-mode squeezing (entangling) and state swapping interactions, resulting in amplification of an axion signal before it becomes polluted by vacuum noise introduced by measurement. Theoretical models of this system predict a 15-fold improvement in scan rate [1]. Here, we present the theoretical background for the technique as well as circuit simulation results.