When every photon counts

Single-photon sources are desirable resources for a variety of applications, ranging from quantum information processing to metrology.  A single emitter, like a single atom or a quantum dot can, in principle, be used as the central element in such a device, and indeed, this has been demonstrated by many groups over the past two decades. However, the low efficiency in collecting the emitted photons makes its impossible to tell when a single photon will arrive. In other words, success of previous work has been more to ensure that one never has more than one photon at a time but not that one has a photon at a given time! In recent work we tackled the problem of photon collection by designing a metallo-dielectric antenna structure that allows >99% of the photons emitted from a single emitter to be collected by a microscope objective. In the experiment we use single CdSe/CdS quantum dots in a thin polymer film (PMMA/PVA) sandwiched between a sapphire substrate and a gold mirror. We measure the performance of the antenna by investigating the angular emission pattern from a quantum dot at room temperature. The experimental results show remarkable agreement with theoretical predictions, leading us to the conclusion that the antenna indeed has a photon collection efficiency exceeding 99%. Such an antenna might be the key element for realizing a deterministic single-photon source that can deliver several tens of millions of photons per second.

Experimental realization of an optical antenna designed for collecting 99% of photons from a quantum emitter

 X.-L. Chu, T. J. K. Brenner, X.-W. Chen, Y. Ghosh, J. A. Hollingsworth, V. Sandoghdar, and S. Götzinger; Optica 4, 203-208 (2014)