Each photon is created by exciting a single “artificial atom” (a quantum dot) inside a semiconductor. Usually, these photons leave the quantum dot in all possible directions and thus a large fraction is lost. In the photon source now presented, the researchers have solved this problem by positioning the quantum dot inside a “funnel” to send all photons in a specific direction.
The funnel is a novel micro-cavity that represents the real innovation of the research team: The micro-cavity captures almost all of the photons and then directs them into an optical fiber. The photons, each about two centimeters long, emerge at the end of an optical fiber.
The efficiency of the entire system is 57 %, more than double that of previous single-photon sources.
This work has been presented in the journal Nature Nanotechnology.