We know from multiple astrophysical observations that the vast majority of matter in our galaxy is of totally unknown nature, and, as such, its direct detection promises to revolutionize our understanding of the universe. For a well-motivated range of “ultralight dark matter” (UDM) candidates (peV-scale particle mass), superfluid helium represents an ideal, extraordinarily low-noise acoustic sensor that will place new and deep constraints on UDM, notably outperforming long-running experiments (e.g., Eot-Wash and LIGO-Virgo) after just an hour of operation. The current prototype (HeLIOS) relies on helium’s high-Q mechanical resonance to place deep constraints over a needle-thin (swept) range of frequencies. However, using our group's specialized membrane and fiber-cavity systems, we can create a pressure transducer capable of achieving the prototype's resonant sensitivity over the broad band, thereby covering previously inaccessible masses while turning years-long frequency sweeps into hours-long single acquisitions that are sensitive to transients. Moreover, the sensitivity floor exhibits notches at special frequencies (due to destructive interference canceling the UDM drive) that can also be swept to help validate candidate signals. Our long-term goal is to realize a global array of these “UDM antennas” to reject local noise sources and provide new information about the UDM “wind” direction.

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