Optica 1, 203–208 (2014)

One of the main components of any quantum network is a source of single photons emitted in a deterministic way. However, a serious obstacle to hurdle is the collection of such photons, which can be emitted in any direction within a 4π solid angle. Xiao-Liu Chu and co-workers from the Universities of Erlangen and Potsdam in Germany and the Los Alamos National Laboratory in the USA now claim to have solved the problem. The team built a planar, metallo-dielectric antenna that directs the photons with an efficiency exceeding 99% — just as theoretically predicted. In their experimental configuration, a sapphire cover glass is coated with two polymer layers of PMMA/PVA, which contain light-emitting quantum dots with a CdSe core within a CdS shell. A movable metallic mirror is then positioned in free space a small distance above the planar structure. Investigation of the angular emission pattern from the structure when it is optically excited with the gold mirror at various distances from the quantum dots revealed that part of the emission was reflected at the mirror interface and then interfered with the emission direct from the dot. The resulting fluorescence emission patterns were heavily modulated, with a 10% larger intensity when the mirror was in place. The team says that the result is an important building block towards the development of an ultrabright single-photon source that can deterministically deliver several tens of millions of photons per second.