Source of Single Photons on Pseudo-Demand from Stored Parametric Down-conversion

There are currently proposals for providing a single-photon from the spontaneous emission of an isolated two-state quantum system such as a single atom, ion or quantum dot. In principle, these approaches offer the possibility of a single-photon “on-demand” in the sense that the isolated two-state system can be excited at any time by any user. Although the probability of single-photon emission can be high in these approaches, there is no method for ensuring that a photon has actually been emitted.

In contrast, the Johns Hopkins University Applied Physics Lab has conceived an approach based on the production of pairs of photons through low-power, pulsed-pump, parametric down-conversion. Furthermore, the detection of one of the photons of a pair can signal the presence of the other photon with near certainty. This system provides a single-photon “pseudo-demand” in that a stored single photon can be released from the storage loop at a later time scheduled by the user. The pumping intervals and storage-loop round-trip time can be chosen to emulate a pseudo-demand source of this kind and is just as effective as a source in which the single photon can be produced on-demand at arbitrary times.

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