Continuous variable entanglement by radiation pressure

We show that when an intense and quasi-monochromatic laser field is incident on a single vibrating and perfectly reflecting mirror in free space, radiation pressure realizes an effective coupling between a mirror vibrational mode and the first two optical sidebands of the incident field. The two reflected sidebands are in fact entangled by the optomechanical interaction and the resulting continuous variable entanglement proves to be robust against the thermal noise acting on the vibrational mode. If the duration of the incident laser pulse is appropriately chosen, the resulting state of the two sideband modes becomes an exact two-mode squeezed state.