LAMPOST: First Constraints on Dark Photon Dark Matter with an Optical Haloscope

We demonstrate a proof-of-concept search for dark photon dark matter in the 0.7-0.8 eV mass range via coherent absorption in a multi-layer dielectric haloscope. This new experimental architecture optically focuses the signal from a compact target to a sub-mm-scale SNSPD, breaking conventional trade-offs in DM experiments requiring macroscopic panels of expensive and noisy detectors. Our SNSPD achieved a dark count rate of 6x10⁻⁶ counts/s, the lowest reported among all types of superconducting sensors, while still achieving close to 20% detection efficiency at 1700 nm wavelength. With less than one week of run time, our prototype constrains new dark photon DM parameter space in this mass range. After a rigorous analysis of the prototype’s strengths and shortcomings, we outline crucial improvements that could enable rapid searches over the meV to 10 eV mass range using this technology in the near future.