Superconducting Levitated Detector of Gravitational Waves

A magnetically levitated mass couples to gravity and can act as an effective gravitational wave detector. We show that a superconducting sphere levitated in a quadrupolar magnetic field, when excited by a gravitational wave, will produce magnetic field fluctuations that can be read out using a flux tunable microwave resonator. With a readout operating at the standard quantum limit, such a system could achieve broadband strain noise sensitivity of $h \lesssim 10^{-20}/\sqrt{\rm Hz}$ for frequencies of $1~\mathrm{kHz}~-~1~\mathrm{MHz}$, opening new corridors for astrophysical probes of new physics.