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Physical Review A

Increased polarization-entangled photon flux via thinner crystals

P. S. K. Lee, Martin P. van Exter, J. P. Woerdman

Published Oct 22, 2004• 11 citations
Publisher

Abstract

We analyze the scaling laws that govern the production of polarization-entangled photons via type-II spontaneous parametric down-conversion (SPDC). We demonstrate experimentally that thin nonlinear crystals can generate a higher number of entangled photons than thicker crystals, basically because they generate a broader spectrum.
DOI
10.1103/physreva.70.043818

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We develop and experimentally verify a theory of type II spontaneous parametric down-conversion (SPDC) in media with inhomogeneous distributions of second-order nonlinearity. As a special case, we explore interference effects from SPDC generated in a cascade of two bulk crystals separated by an air gap. The polarization quantum-interference pattern is found to vary strongly with the spacing between the two crystals. This is found to be a cooperative effect due to two mechanisms: the chromatic dispersion of the medium separating the crystals and spatiotemporal effects that arise from the inclusion of transverse wave vectors. These effects provide two concomitant avenues for controlling the quantum state generated in SPDC. We expect these results to be of interest for the development of quantum technologies and the generation of SPDC in periodically varying nonlinear materials.