First Laboratory Bounds on Ultralight Dark Photon Dark Matter from Precision Atomic Spectroscopy

Ultralight bosonic dark matter has come under increasing scrutiny as a dark matter candidate that has the potential to resolve puzzles in astronomical observation. We demonstrate that high-precision measurements of time variation in the frequency ratios of atomic transitions achieves leading sensitivity to ultralight vector portal dark matter at low masses. These bounds are the first laboratory-based bounds on this class of dark matter models. We propose further measurements that could enhance sensitivity to ultralight dark photons.