Daylight operation of a free space, entanglement-based quantum key   distribution system
  Many quantum key distribution (QKD) implementations using a free space transmission path are restricted to operation at night time in order to distinguish the signal photons used for a secure key establishment from background light. Here, we present a lean entanglement-based QKD system overcoming that imitation. By implementing spectral, spatial and temporal filtering techniques, we were able to establish a secure key continuously over several days under varying light and weather conditions. 
Matthew P. Peloso, Ilja Gerhardt, Caleb Ho, Antia Lamas-Linares and   Christian Kurtsiefer