  We show how entanglement between two optically levitated nanoparticles can be
generated and detected by coherent scattering of tweezer photons into a single
cavity mode. Triggered by the detection of a Stokes photon, the tweezer
detuning is switched from the blue to the red; entanglement is then verified by
the conditioned anti-Stokes photon flux, which oscillates with the mechanical
beat frequency. The proposed setup is realizable with near-future technology
and opens the door to the first experimental observation of non-classical
center-of-mass correlations between two or more levitated nanoscale objects.
