By using a Raman-scattering process induced by optical pulses we create light-matter entanglement between the vibrational motion of two silicon optomechanical oscillators, each comprising the collective motion of approx. 100 billion atoms, and two optical modes. The relevant photon-phonon correlations are read out by mapping the single-phonon excitations onto single photons in the optomechanical cavity mode and consequently performing two-photon interferometry. This allows us to violate a Bell inequality by more than 4 standard deviations and directly confirms the nonclassical behavior of our optomechanical solid-state system without the need for a quantum description of our experiment. We also find a phonon-lifetime of several microseconds, which is an upper limit for the lifetime of the optomechanical entanglement.
Article: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.121.220404
Press release: https://physik.univie.ac.at/en/news/news-detail/news/probing-quantum-physics-on-a-macroscopic-scale-2
