Reaching the Heisenberg Limit with VEBAX Multi-cavity Axion Haloscopes

The axion, first proposed to resolve the unobserved-yet-expected CP violation in QCD, is an excellent candidate for wave-like dark matter. The most successful experimental technique to search for galactic axions thus far, the cavity haloscope, is limited in both scan speed and accessible axion-mass- or frequency-range, particularly above 1.5 GHz. Next generation axion haloscopes will scan higher frequencies using arrays of identical cavities, presenting new opportunities to use quantum technologies to surpass the SQL beyond the squeezing and state-swapping techniques being explored for single-cavity searches. Inter-cavity multi-mode correlations have the potential to further elevate the scan rate of an array from linear scaling with cavity number to quadratic at the Heisenberg limit. This talk presents efforts at PNNL, WUSTL, & LLNL building capability to prepare and measure multi-mode states in cavity arrays, as part of the Very Entangled Bose Array eXperiment (VEBAX) pathfinder, forging a way for haloscope searches to reach the Heisenberg limit.