Single photon source using laser pulses and two-photon absorption

Abstract

We have previously shown that two-photon absorption (TPA) and the quantum Zeno effect can be used to make deterministic quantum logic devices from an otherwise linear optical system. Here we show that this type of quantum Zeno gate can be used with additional two-photon absorbing media and weak laser pulses to make a heralded single photon source. A source of this kind is expected to have a number of practical advantages that make it well suited for large scale quantum information processing applications.Although two-photon absorption (TPA) is a nonlinear optical process, it is not typically considered a fundamental resource for optical quantum information processing (QIP). We have previously shown that TPA and the quantum Zeno effect can be used to make deterministic quantum logic devices (Zeno gates) from an otherwise linear optical system [1]. In a Zeno gate, TPA is used to suppress the failure events that would normally occur in a linear optics device [2-4] when multiple photons exit the device in the same optical mode. Here we show that additional two-photon absorbing media can be used in a more conventional manner along with a Zeno gate to convert weak laser pulses into heralded single photon pulses. Because recent theoretical results indicate that single photon losses can be much less than the rate of TPA [5], realistic devices of this kind could become critical components for future optical QIP systems.There have been many demonstrations of single photon sources over the past few years using a variety of physical systems, including parametric down conversion (PDC) [6], quantum dots [7], and single molecules [8]. Two metrics commonly used to categorize these sources are the heralding efficiency, which is the probability that the output contains a single photon given a trigger signal from the source, and the production efficiency, which is the probability that the source will produce a single photon on any given attempt. Although PDC sources have demonstrated heralding efficiencies approaching 85% [6], the conversion rate of the PDC process currently limits the overall production rate to much less than 1%. This would mean that a very large number of these types of sources would have to be combined with very low loss switches in order to make a deterministic single photon source.Unheralded sources, such as quantum dots, have demonstrated relatively high production rates ~20% [7], but their potential use in large QIP systems may be limited by the lack of a heralding signal. There have recently been several proposals to make heralding devices for these types of sources using linear [9] and nonlinear [10] optical techniques, including TPA; however, the maximum heralding efficiency using these techniques and assuming ideal nonlinearities, perfect detectors, and neglecting single photon loss, is under 85% [10]. The source we present here can be viewed as an unheralded source with an ideal production efficiency of 50% followed by a heralding circuit (Zeno gate) with an ideal heralding efficiency of 100%.The poten...

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