Acceleration sensing with magnetically levitated oscillators above a superconductor

We experimentally demonstrate the stable trapping of a permanent magnet sphere above a lead superconductor, at vacuum pressures of $4×10−8$ mbar. The levitating magnet behaves as a harmonic oscillator, with frequencies in the 4–31 Hz range detected, and shows promise to be an ultrasensitive acceleration sensor. We directly apply an acceleration to the magnet with a current carrying wire, which we use to measure a background noise of $∼10−10 m/Hz$ at 30.75 Hz frequency. With current experimental parameters, we find an acceleration sensitivity of $Sa1/2=1.2±0.2×10−10 g/Hz$⁠, for a thermal noise limited system. By considering a 300 mK environment, at a background helium pressure of $1×10−10$ mbar, acceleration sensitivities of $Sa1/2∼3×10−15 g/Hz$ could be possible with ideal conditions and vibration isolation. To feasibly measure with such a sensitivity, feedback cooling must be implemented.