Highly efficient heralding of entangled single photons
  Single photons are an important prerequisite for a broad spectrum of quantum optical applications. We experimentally demonstrate a heralded single-photon source based on spontaneous parametric down-conversion in collinear bulk optics, and fiber-coupled bolometric transition-edge sensors. Without correcting for background, losses, or detection inefficiencies, we measure an overall heralding efficiency of 83 %. By violating a Bell inequality, we confirm the single-photon character and high-quality entanglement of our heralded single photons which, in combination with the high heralding efficiency, are a necessary ingredient for advanced quantum communication protocols such as one-sided device-independent quantum key distribution. 
Sven Ramelow, Alexandra Mech, Marissa Giustina, Simon Groeblacher,   Witlef Wieczorek, Adriana Lita, Brice Calkins, Thomas G...
quant-ph