  Since the early work by Ashkin in 1970, optical trapping has become one of
the most powerful tools for manipulating small particles, such as micron sized
beads or single atoms. The optical trapping mechanism is based on the
interaction energy of a dipole and the electric field of the laser light. In
atom trapping, the dominant contribution typically comes from the allowed
optical transition closest to the laser wavelength, whereas for mesoscopic
particles it is given by the bulk polarizability of the material. These two
different regimes of optical trapping have coexisted for decades without any
direct link, resulting in two very different contexts of applications: one
being the trapping of small objects mainly in biological settings, the other
one being dipole traps for individual neutral atoms in the field of quantum
optics. Here we show that for nanoscale diamond crystals containing artificial
atoms, so-called nitrogen vacancy (NV) color centers, both regimes of optical
trapping can be observed at the same time even in a noisy liquid environment.
For wavelengths in the vicinity of the zero-phonon line transition of the color
centers, we observe a significant modification ($10\%$) of the overall trapping
strength. Most remarkably, our experimental findings suggest that owing to the
large number of artificial atoms, collective effects greatly contribute to the
observed trapping strength modification. Our approach adds the powerful
atomic-physics toolbox to the field of nano-manipulation.
