Abstract

Heralded pure single photons are an indispensable resource for linear optical quantum computing (LOQC), as the fidelity of single photon quantum gates depends critically on the state purity of the input ancilla photons. The heralded photon's purity requires the absence of any kind of entanglement between itself and the heralding photon, i. e. their joint amplitude function factorizes: $f({\overrightarrow{k}}_s,{\overrightarrow{k}}_i)=f_s({\overrightarrow{k}}_s)f_i({\overrightarrow{k}}_i)$ Several schemes for spontaneous parametric downconversion (SPDC) based heralded single photon sources have been proposed and demonstrated. In order to provide spectrally separable pairs, they typically rely heavily on narrow spatial [2] and/or spectral filtering [3], thus trading effective source brightness for purity.

© 2009 IEEE