Entangling one polariton with a photon: effect of interactions on a   single-polariton quantum state
  Polaritons are quasi-particles originating from the coupling of light with matter that demonstrated quantum phenomena at the many-particle mesoscopic level, such as BEC and superfluidity. A highly sought and long-time missing feature of polaritons is a genuine quantum manifestation of their dynamics at the single-particle level. Although they are conceptually perceived as entangled states and theoretical proposals abound for an explicit manifestation of their single-particle properties, so far their behaviour has remained fully accountable for by classical and mean-field theories. In this Article, we report the first experimental demonstration of a genuinely-quantum manifestation of microcavity polaritons, by swapping, in a two-photon entangled state generated by parametric down-conversion, a photon for a polariton. Furthermore, we show how single polaritons are affected by polariton-polariton interactions in a propaedeutic demonstration of their qualities for quantum information applications. 
\'Alvaro Cuevas, Blanca Silva, Juan Camilo L\'opez Carre\~no, Milena   de Giorgi, Carlos S\'anchez Mu\~noz, Antonio Fieramos...
cond-mat.mes-hall physics.optics quant-ph