The Invisible Drummer: A search for vector ultralight dark matter with a membrane*

Optomechanical accelerometers have been proposed as detectors for vector ultralight dark matter [1] which would produce material-dependent accelerations. In this talk we present a cryogenic dark matter search using a resonant detector based on cm-scale nanomechanical membranes. Our accelerometer consists of  two silicon nitride membranes with different stiffnesses, vertically integrated onto the same chip and forming a Fabry-Perot cavity [2]. Operating in a closed-cycle cryostat, we implement a custom vibration isolation system to suppress acoustic vibrations and enable thermalization to 4 K, and use photothermal frequency tuning to improve resonant detection bandwidth. We perform an analysis of the detector’s measured acceleration spectra to search for dark matter signals around 40 kHz, corresponding to particle mass near 10^-10 eV/c². Although our prototype device does not surpass current dark-matter constraints, we report on ongoing improvements to the detector design, namely, Bayesian optimization of the test-mass geometry to reduce thermal acceleration noise and patterning photonic crystal mirrors onto the membranes to enhance readout sensitivity [3]. We also report on a demonstration of squeezing-enhanced readout of an array of membrane-based force sensors [4], which would benefit dark matter searches [5].

[1] J. Manley, M.D. Chowdhury, D. Grin, S. Singh and D.J. Wilson, Searching for vector dark matter with an optomechanical accelerometer, Phys. Rev. Lett. 126 (2021) 061301

[2] M.D. Chowdhury, A.R. Agrawal, and D.J. Wilson, Membrane-based optomechanical accelerometry. Physical Review Applied, 19(2) (2023) 024011.

[3] A.R. Agrawal, J. Manley, D. Allepuz-Requena, and D.J. Wilson, Focusing membrane metamirrors for integrated cavity optomechanics. Optica 11, no. 9 (2024): 1235-1241.

[4] Y. Xia, A.R. Agrawal, C.M. Pluchar, A.J. Brady, Z. Liu, Q. Zhuang, D.J. Wilson, and Z. Zhang, Entanglement-enhanced optomechanical sensing. Nature Photonics, (2023) 17(6), 470-477.

[5] A.J. Brady, et al. Entanglement-enhanced optomechanical sensor array with application to dark matter searches, Communications Physics 6.1 (2023): 237.