Spin-cooling of the motion of a trapped diamond

Observing and controlling macroscopic quantum systems has long been a driving force in quantum physics research. In particular, strong coupling between individual quantum systems and mechanical oscillators is being actively studied^1-3. Whereas both read-out of mechanical motion using coherent control of spin systems^4-9 and single-spin read-out using pristine oscillators have been demonstrated^10,11, temperature control of the motion of a macroscopic object using long-lived electronic spins has not been reported. Here we observe a spin-dependent torque and spin-cooling of the motion of a trapped microdiamond. Using a combination of microwave and laser excitation enables the spins of nitrogen-vacancy centres to act on the diamond orientation and to cool the diamond libration via a dynamical back-action. Furthermore, by driving the system in the nonlinear regime, we demonstrate bistability and self-sustained coherent oscillations stimulated by spin-mechanical coupling, which offers the prospect of spin-driven generation of non-classical states of motion. Such a levitating diamond-held in position by electric field gradients   under vacuum-can operate as a 'compass' with controlled dissipation and has potential use in high-precision torque sensing^12-14, emulation of the spin-boson problem¹⁵ and probing of quantum phase transitions¹⁶. In the single-spin limit¹⁷ and using ultrapure nanoscale diamonds, it could allow quantum non-demolition read-out of the spin of nitrogen-vacancy centres at ambient conditions, deterministic entanglement between distant individual spins¹⁸ and matter-wave interferometry^16,19,20.