Vivoli, V. CapraraBarnea, T.Galland, ChristopheSangouard, N.2017-02-272017-02-272017-02-27201610.1103/PhysRevLett.116.070405https://infoscience.epfl.ch/handle/20.500.14299/134843Photons of a laser beam driving the upper motional sideband of an optomechanical cavity can decay into photon-phonon pairs by means of an optomechanical parametric process. The phononic state can subsequently be mapped to a photonic state by exciting the lower sideband, hence creating photon-photon pairs out of an optomechanical system. Here we show that these pairs can violate a Bell inequality when they are measured with photon counting techniques preceded by small displacement operations in phase space. The consequence of such a violation as well as the experimental requirements are intensively discussed.text::journal::journal article::research article