Ultralight scalars are an interesting dark matter candidate that may produce a mechanical signal by modulating the Bohr radius. Recently it has been proposed to search for this signal using resonant-mass antennas. Here, we extend that approach to a new class of existing and near term compact (gram to kilogram mass) acoustic resonators composed of superfluid helium or single crystal materials, producing displacements that are accessible with opto- or electromechanical readout techniques. We find that a large unprobed parameter space can be accessed using ultrahigh-$Q$, cryogenically cooled centimeter-scale mechanical resonators operating at 100 Hz–100 MHz frequencies, corresponding to ${10}^{-12}–{10}^{-6}\mathrm{eV}$ scalar mass range.

• Received 21 November 2019
• Accepted 18 March 2020

DOI:https://doi.org/10.1103/PhysRevLett.124.151301