Precision Metrology Meets Cosmology: Improved Constraints on Ultralight Dark Matter from Atom-Cavity Frequency Comparisons

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We conduct frequency comparisons between a state-of-the-art strontium optical lattice clock, a cryogenic crystalline silicon cavity, and a hydrogen maser to set new bounds on the coupling of ultralight dark matter to Standard Model particles and fields in the mass range of $10^{-16}$ $-$ $10^{-21}$ eV.

• The key advantage of this two-part ratio comparison is the differential sensitivities to time variation of both the fine-structure constant and the electron mass, achieving a substantially improved limit on the moduli of ultralight dark matter, particularly at higher masses than typical atomic spectroscopic results.
• Furthermore, we demonstrate an extension of the search range to even higher masses by use of dynamical decoupling techniques.
• These results highlight the importance of using the best performing atomic clocks for fundamental physics applications as all-optical timescales are increasingly integrated with, and will eventually supplant, existing microwave timescales.