A near-unity efficiency source of entangled guided waves
  Surface phonon polaritons are hybrid modes of photons and optical phonons that can propagate on the surface of a polar dielectric. In this work, we show that the precise combination of confinement and bandwidth offered by surface phonon polaritons allows for the ability to create highly efficient sources of entangled light in the IR/THz. Specifically, phonon polaritons can cause emitters to preferentially decay by the emission of pairs of surface phonon polaritons, instead of the previously dominant single-photon emission. We show that such two-photon emission processes can occur on nanosecond time-scales and can be nearly two orders of magnitude faster than competing single-photon transitions, as opposed to being as much as eight to ten orders of magnitude slower in free space. Our results suggest a fundamentally new design strategy for quantum light sources in the IR/THz: ones that prefer to emit a relatively broad spectrum of entangled photons, potentially allowing for new sources of both single and multiple photons. 
Nicholas Rivera, Ido Kaminer, Marin Soljacic
physics.optics