A magnetically levitated mass couples to gravity and can act as a gravitational wave detector. We show that when excited by a gravitational wave, a superconducting sphere levitated in a quadrupolar magnetic field will produce fluctuations in the background magnetic field that can be read out using a radio frequency quantum upconverter. With a readout operating at the standard quantum limit, such a system achieves broadband strain noise sensitivity of h ~ 10^-21 for frequencies of ~1 MHz -1 GHz, opening new corridors for cosmological and astrophysical probes of new physics.
