Quantum Correlations in the Stokes-anti-Stokes Raman Scattering: Photonic Cooper Pairs

The production of correlated Stokes (S) and anti-Stokes (aS) photons (SaS process) mediated by real phonon is well known in the literature. However, in recent work we demonstrated that Photons can interact with each other in condensed matter through the same mechanism that forms Cooper pairs in superconductors—the exchange of virtual phonons [Phys. Rev. Lett. 119, 193603 (2017)]. We investigate the energy, momentum and production rate of correlated Stokes–anti-Stokes (SaS) photons in diamond and we show the rate of correlated SaS production depends on the energy shifts of the pair, which in the BCS theory determines whether there should be an attractive or repulsive interaction. With this view, we only observe correlated SaS in the case of attractive interactions [PRB 99, 100503 (2019)]. We also observe that the SaS photons crosses the sample following the same path as the noninteracting laser. Finally, we investigate the polarization of correlated SaS photons, demonstrating that they have mainly the same polarization of the excitation laser. By pump-probe experiments we measure the decay rate of the SaS pair production, evidencing the fundamental difference between the real and virtual phonon exchange processes.