Magnetic torque enhanced by tunable dipolar interactions

We use tunable dipolar interactions between the spins of nitrogen-vacancy (NV) centers in diamond to rotate a diamond crystal. Specifically, we employ cross-relaxation between the electronic spin of pairs of NV centers in a trapped diamond to enhance the anisotropic NV paramagnetism and thus to increase the associated spin torque. Our observations open a path towards the use of mechanical oscillators to detect paramagnetic defects that lack optical transitions, to the investigation of angular momentum conservation in spin relaxation processes, and to different means of cooling the motion of mechanical oscillators.