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Characterization ofparametric downconversion inthephoton number basis

Christine Silberhorn, Daryl Achilles, Konrad Banaszek

Published Jan 1, 2005• 0 citations

Abstract

Parametric downconversion inaquasi-phase matched KTPwaveguide offers thepossibility toimplement ahighly efficient source ofphotonic states. Weinvestigate thephoton statistics ofsuch asource with atime-multiplexed detector, which iscapable ofphoton number resolution. Parametric downconversion (PDC)sources havebecomeanestablished technique togenerate single photon states. InthePDCprocess pairs ofphotons canbeproduced indistinguishable modes(oforthogonal polarization) suchthat thedetection ofonephoton will herald thepresence oftheother intheconjugate mode.There have always beentwoproblems hindering progress inpreparing higher order photon number states: thelack ofhighly efficient PDCsources andphoton-number resolving detectors. Wedemonstrate approaches tostudy these problems, andshowtheexperimental generation oftwo-photon states withhighfidelity byconditional state preparation. Weutilize atime-multiplexed detector, whichisfiber based andoperates ontheprinciple ofdetector cascading, inconjunction with abright highly efficient waveguided, typeIIPDCsource, which wepumpwithultrashort pulses. ThePDCstate canbedescribed by 00

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•Jan 1, 2005•0 citations

Parametric downconversion inaquasi-phase matched KTPwaveguide offers thepossibility toimplement ahighly efficient source ofphotonic states. Weinvestigate thephoton statistics ofsuch asource with atime-multiplexed detector, which iscapable ofphoton number resolution. Parametric downconversion (PDC)sources havebecomeanestablished technique togenerate single photon states. InthePDCprocess pairs ofphotons canbeproduced indistinguishable modes(oforthogonal polarization) suchthat thedetection ofonephoton will herald thepresence oftheother intheconjugate mode.There have always beentwoproblems hindering progress inpreparing higher order photon number states: thelack ofhighly efficient PDCsources andphoton-number resolving detectors. Wedemonstrate approaches tostudy these problems, andshowtheexperimental generation oftwo-photon states withhighfidelity byconditional state preparation. Weutilize atime-multiplexed detector, whichisfiber based andoperates ontheprinciple ofdetector cascading, inconjunction with abright highly efficient waveguided, typeIIPDCsource, which wepumpwithultrashort pulses. ThePDCstate canbedescribed by 00

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.