Figure 1

(a) Schematic of the setup: blue detuned drive pulses interact with the mechanical resonators (devices A and B ) producing entangled photon-phonon pairs. The light-matter entanglement is in the path basis ( A or B ), corresponding to the device in which the Stokes scattering event took place. The generated photons are detected in single-photon detectors giving the measurement results a b 1 and a b 2 . The detection of the phonons is done by transferring their states to another optical mode by using a red drive after some time Δ τ and, subsequently, obtaining the results a r 1 and a r 2 . Note that for technical reasons the photons created by the blue and red drives are detected on the same pair of detectors, but with a time delay Δ τ = 200 ns . Therefore we have time separation of the two parties of the Bell test instead of space separation (as commonly done). BS 1 / 2 represent beam splitter 1 / 2 . (b) Scanning electron microscope image of one of the optomechanical devices, represented with a star symbol in (a) and (c), next to the coupling waveguide (top). (c) Illustration of our experimental sequence: one party of the Bell test measures in which detector path the Stokes photon is found at time t = 0 , while the other performs the same measurement for the anti-Stokes photon after a time t = Δ τ . We probe their correlations in order to violate the CHSH inequality. Since the two photons never interacted directly (only through the mechanics), the observed correlations are a direct consequence of the correlations between the Stokes photons and phonons.