Levitated Ferromagnetic Torque Sensors for Fundamental Physics Tests

Under conditions where intrinsic spin contributes significantly to the total angular momentum of a ferromagnet, the ferromagnet will behave as a gyroscope. If a ferromagnetic gyroscope (FG) can be sufficiently isolated from the environment, it is predicted to be far more sensitive to spin-dependent interactions than existing systems. Even when the intrinsic spin is a subdominant component of the total angular momentum, measurement of the oscillatory modes of the levitated ferromagnet can be used for precision measurements of spin-dependent interactions. In fact, such LEvitated Ferromagnetic Torque Sensors (LEFTS) can surpass the "energy resolution limit" for magnetic field measurements as well as the limit on measurement uncertainty imposed by the Heisenberg principle for independent particles. The remarkable sensitivity of LEFTS can be understood to be a result of rapid averaging of quantum noise. We discuss experimental progress toward realization of LEFTS and recent proposals to use LEFTS to search for new interactions and investigate physics at the intersection between quantum mechanics and general relativity.