  We report observations of the Electron Spin Resonance (ESR) of Nitrogen
Vacancy (NV) centers in diamonds that are levitating in an ion trap. Using a
needle Paul trap operating under ambient conditions, we demonstrate efficient
microwave driving of the electronic spin and show that the spin properties of
deposited diamond particles measured by the ESR are retained in the Paul trap.
We also exploit the ESR signal to monitor the rotation of levitating
monocrystals, a first step towards spin-controlled mechanical systems in
scattering-free traps.
