Observation of atomic dipole forces in optically trapped nanodiamonds containing NV centres, in a liquid environment

We report on the observation of resonant forces in optically trapped diamond nanoparticles containing NV centres, in a liquid environment. We use a laser beam slightly detuned from the dipole transition of target colour NV centres to exert resonant (attractive and repulsive) forces onto them and, in turn, to the host diamond nanoparticles. When tuning the wavelength in the vicinity of the zero-phonon line of the NV centres, we observe a significant effect (~10%) on the overall trapping strength of conventional optical tweezers due to the resonant forces. We discuss using full optical resonant trapping as a method to manipulate, in liquid, nanodiamonds as small as ~tens of nanometers containing suitable colour centres (e.g. SiV centres) for biological applications.