Detecting High-Frequency Gravitational Waves with Optically Levitated Sensors

We propose a tunable resonant sensor to detect gravitational waves in the frequency range of 50–300 kHz using optically trapped and cooled dielectric microspheres or microdisks. The technique we describe can exceed the sensitivity of laser-based gravitational wave observatories in this frequency range, using an instrument of only a few percent of their size. Such a device extends the search volume for gravitational wave sources above 100 kHz by 1 to 3 orders of magnitude, and could detect monochromatic gravitational radiation from the annihilation of QCD axions in the cloud they form around stellar mass black holes within our galaxy due to the superradiance effect.

Figure 1

A dielectric nanosphere or microdisk is optically trapped in an antinode (solid red line) of a cavity of length ${\ell }_m$ at position $x_s$. A second light field with two different frequency components (dashed blue line) is used to cool and read out the axial position of the levitated object, respectively. Two additional beams perpendicular to the cavity axis (not shown) are used to cool the transverse motion of the sensor. A passing gravitational wave at frequency ${\omega }_{\mathrm{GW}}$ displaces the sensor from its equilibrium position in the optical trap and imparts a force as described in text. The resulting displacement is resonantly enhanced when ${\omega }_{\mathrm{GW}}$ coincides with the trap frequency ${\omega }_0$.

Figure 2

Strain sensitivity for optically levitated microdisks (black dashed line) or spheres (blue dashed line) for experimental parameters described in the text. For comparison, also shown are the LIGO and predicted Advanced LIGO sensitivity in the frequency range of 10–300 kHz [25, 28]. The shaded region denotes predicted signals due to black hole superradiance.