Numerous astrophysical and cosmological observations are best explained by the existence of dark matter, a mass density which interacts only very weakly with visible, baryonic matter. Searching for the extremely weak signals produced by this dark matter strongly motivate the development of new, ultra-sensitive detector technologies. Paradigmatic advances in the control and readout of massive mechanical systems, in both the classical and quantum regimes, have enabled unprecedented levels of sensitivity. In this white paper, we outline recent ideas in the potential use of a range of solid-state mechanical sensing technologies to aid in the search for dark matter in a number of energy scales and with a variety of coupling mechanisms.

We describe a variety of searches for new physics beyond the standard model of particle physics which may be enabled in the coming years by the use of optically levitated masses in high vacuum. Such systems are expected to reach force and acceleration sensitivities approaching (and possibly eventually exceeding) the standard quantum limit over the next decade. For new forces or phenomena that couple to mass, high precision sensing using objects with masses in the fg–ng range have significant discovery potential for new physics. Such applications include tests of fundamental force laws, searches for non-neutrality of matter, high-frequency gravitational wave detectors, dark matter searches, and tests of quantum foundations using massive objects.

The levitated sensor detector (LSD) is a compact resonant gravitational-wave (GW) detector based on optically trapped dielectric particles that is under construction. The LSD sensitivity has more favorable frequency scaling at high frequencies compared to laser interferometer detectors such as LIGO and VIRGO. We propose a method to substantially improve the sensitivity by optically levitating a multilayered stack of dielectric discs. These stacks allow the use of a more massive levitated object while exhibiting minimal photon recoil heating due to light scattering. Over an order of magnitude of unexplored frequency space for GWs above 10 kHz is accessible with an instrument 10 to 100 meters in size. Particularly motivated sources in this frequency range are gravitationally bound states of the axion from quantum chromodynamics with decay constant near the grand unified theory scale that form through black hole superradiance and annihilate to GWs. The LSD is also sensitive to GWs from binary coalescence of sub-solar-mass primordial black holes and as-yet unexplored new physics in the high-frequency GW window.

The applications of spin-based quantum sensors to measurements probing fundamental physics are surveyed. Experimental methods and technologies developed for spin-based quantum information science have rapidly advanced in recent years and these tools enable increasingly precise control and measurement of spin dynamics. Theories of beyond-the-standard-model physics predict, for example, discrete-symmetry-violating electromagnetic moments correlated with particle spins, exotic spin-dependent forces, and coupling of spins to ultralight bosonic dark-matter fields. Spin-based quantum sensors can be used to search for these myriad phenomena and offer a methodology for tests of fundamental physics that is complementary to particle colliders and large-scale particle detectors. Areas of technological development that can significantly enhance the sensitivity of spin-based quantum sensors to new physics are highlighted.

We present experimental results on optical trapping of Yb-doped $\beta$-NaYF subwavelength-thickness high-aspect-ratio hexagonal prisms with a micron-scale radius. The prisms are trapped in vacuum using an optical standing wave, with the normal vector to their face oriented along the beam propagation direction, yielding much higher trapping frequencies than those typically achieved with microspheres of similar mass. This platelike geometry simultaneously enables trapping with low photon-recoil-heating, high mass, and high trap frequency, potentially leading to advances in high frequency gravitational wave searches in the Levitated Sensor Detector, currently under construction. The material used here has previously been shown to exhibit internal cooling via laser refrigeration when optically trapped and illuminated with light of suitable wavelength. Employing such laser refrigeration methods in the context of our work may enable higher trapping intensity and thus higher trap frequencies for gravitational wave searches approaching the several hundred kilohertz range.