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Frontiers in Optics

Characterization of the non-classical nature of conditionally-prepared single photon states

Alfred B. U’Ren, Jonathan L. Ball, Christine Silberhorn, Konrad Banaszek, Ian A. Walmsley

Published Jan 1, 2005• 6 citations
Publisher

Abstract

We report the generation of high-fidelity single photons by conditional preparation from parametric downconversion in a KTP waveguide as experimentally verified by a novel criterion specifically designed for heralded single photon sources.
DOI
10.1364/fio.2005.fwd6

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arXiv:quant-ph/0412184•Physical Review A•Aug 25, 2005•60 citations
The reliable generation of true single-photon wavepackets with well-defined modal structure is a crucial ingredient for the realization of linear optical quantum computing. In this paper we present experimental results indicating the efficient generation of conditionally prepared single photons from parametric downconversion in a KTP nonlinear waveguide. In addition we present, theoretically and experimentally, a novel criterion for the assessment of conditional single photon sources which takes into account the contributions of heralded vacuum due to optical losses, of higher photon numbers and of the binary response of typical single photon detectors. Utilizing this criterion, we show that our KTP nonlinear waveguide represents a high fidelity source of conditionally prepared single photons.
The reliable generation of true single‐photon wavepackets with well‐defined modal structure is a crucial ingredient for the realization of linear optical quantum computing. We have implemented a highly efficient waveguided parametric downconversion source pumped by ultrashort pulses, which is characterized by the spatial decoupling of the signal and idler photon while exhibiting a conditional detection efficiency of 51%, corresponding to a preparation efficiency of 85%. We have performed various tests to confirm the single‐photon character of the conditionally prepared state.
A reliable single photon source is a prerequisite for linear optical quantum computation and for secure quantum key distribution. A criterion yielding a conclusive test of the single photon character of a given source, attainable with realistic detectors, is therefore highly desirable. In the context of heralded single photon sources, such a criterion should be sensitive to the effects of higher photon number contributions, and to vacuum introduced through optical losses, which tend to degrade source performance. In this Rapid Communication we present, theoretically and experimentally, a criterion meeting the above requirements.