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arXiv:1410.1936 · Physical Review A

Correlation control for pure and efficiently generated heralded single photons

Jefferson Flórez, Omar Calderón-Losada, Alejandra Valencia, Clara I. Osorio

Published Jan 9, 2015• 15 citations
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Abstract

We present a detailed study on the properties of single photons generated by spontaneous parametric down conversion (SPDC) when both the spectral and spatial degrees of freedom are controlled by means of filters. Our results show that it is possible to obtain pure heralded single photons with high heralding efficiency despite the use of filters. Moreover, we report an asymmetry on the single-photon properties exhibited in type-II SPDC sources that depends on choosing the signal or the idler photon as the heralding one.

DOI
10.1103/physreva.91.013819

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We present a detailed study on the properties of single photons generated by spontaneous parametric down conversion (SPDC) when both the spectral and spatial degrees of freedom are controlled by means of filters. Our results show that it is possible to obtain pure heralded single photons with high heralding efficiency despite the use of filters. Moreover, we report an asymmetry on the single-photon properties exhibited in type-II SPDC sources that depends on choosing the signal or the idler photon as the heralding one.
One method to produce pure heralded single photons (HSP) when using the optical process of spontaneous parametric down-conversion (SPDC) is by modifying the joint spectrum of the photon pairs by means of spectral filters. In this work, we characterize the dependence, with the bandwidth of such filters, of the spectral purity and heralding efficiency of the HSP generated in a bulk SPDC. The values we report for the purity and heralding efficiency are obtained from measurements of the joint spectrum. Our results are in agreement with the theoretical model that predicts a trade-off between the purity and heralding efficiency, and they complement similar measurements that have been done for HSP produced by other types of sources.
Abstract Evolving photonic quantum technologies and applications require higher and higher rates of single photon generation. In parallel, it is required that these generated photons are kept spectrally pure for multi-photon experiments and that multi-photon noise be kept to a minimum. In spontaneous parametric down-conversion sources, these requirements are conflicting, because spectral filtering to increase spectral purity always means lowering the rate at which photons are generated, and increasing the pump power means increasing the multi-photon noise. In this paper, we present a scheme, called extended heralding, which aims to mitigate the reduction of single-photon generation rate under spectral filtering by removing cases where we detect light in the rejection band of the heralding photon’s filter. Our experiment shows that this allows for higher single-photon generation rates with lower multi-photon noise than the standard approach of neglecting modes falling out of the filter bandwidth. We also show that by using active feed-forward control based on this extended heralding, it is possible to further improve the performance of the original source by physically eliminating uncorrelated photons from the output stream.
From quantum computation to quantum key distribution, many quantum-enhanced applications rely on the ability to generate pure single photons. Even though the process of spontaneous parametric downconversion (SPDC) is widely used as the basis for photon-pair sources, the conditions for pure heralded single-photon generation, taking into account both spectral and spatial degrees of freedom, have not been fully described. We present an analysis of the spatio-temporal correlations present in photon pairs produced by type-I, non-collinear SPDC. We derive a set of conditions for full factorability in all degrees of freedom—required for the heralding of pure single photons—between the signal and idler modes. In this paper, we consider several possible approaches for the design of bright, fiber-coupled and factorable photon-pair sources. We show through numerical simulations of the exact equations that sources based on: (i) the suppression of spatio-temporal entanglement according to our derived conditions and (ii) a tightly focused pump beam together with optimized fiber-collection modes and spectral filtering of the signal and idler photon pairs, lead to a source brightness of the same order of magnitude. Likewise, we find that both of these sources lead to a drastically higher factorable photon-pair flux, compared to an unengineered source.
The generation of high purity single photons and entangled photon pairs is a crucial first step in many quantum optics experiments, including those that require quantum teleportation [1], entanglement swapping [2], and the generation of multi-photon entanglement [3]. The most widely used and established approach for creating photon pairs is spontaneous parametric down conversion (SPDC) - where pump photons undergo a non-linear optical process to create a down-converted photon pair [4]. Traditionally, the generation of high-purity heralded single photons required severe spectral filtering, introducing additional loss. However, through careful engineering of spectral correlations of the down-converted photon pairs one can circumvent the need for filtering and avoid the accompanying reduction in heralding efficiency.