Spatial distinguishability of photons produced by spontaneous parametric down-conversion with a focused pump

Abstract

It is known that photons produced by spontaneous parametric down-conversion can be coupled into optical fibers more efficiently by focusing the pump field. We find that focusing the pump in type-II down-conversion causes photons of ordinary and extraordinary polarization to acquire very different angular spreads, which amounts to spatial information that distinguishes between the polarization states. Numerical studies predict that the photons collected by a detector or quantum channel will be of predominantly one polarization and that the degree of polarization entanglement will be lessened in some cases.

Heralded single photon sources: a route towards quantum communication technology and photon standards

“…The maximum mode-matching efficiency is achieved with a large pump waist, with respect to the preparation and collection beam waist at the crystal. Similar results have been reported in reference [67], where the analysis of distinguishability of the polarized entangled photons is performed versus the pump focusing in the cases of a multi-mode or single mode channel collection. The results show that in multi-mode collection, a collimated pump is preferable both in terms of detection of single and coincidence events, while the single mode operation requires a focused pump to allow higher coincidence rate.…”

Anisotropically and High Entanglement of Biphoton States Generated in Spontaneous Parametric Down-Conversion

“…(12) is performed numerically, whereas in the case n ′ p = 0 ( -geometry) we used the analytical expression of Eq. (17). On the other hand, as in the case n ′ p = 0 the sincfunction (Fig.…”

“…The single-particle angular distribution in the -geometry is determined by Eq. (17) and is shown in Fig. 3(b) in the dashed-line curve.…”

“…That is why it seems that in order to generate well-localized biphoton wave packets in the k-domain one has to use good laser sources with a very small angular divergency and/or long crystals. At the same time forming particular angular profile of the pump is needed for coupling biphotons into the optical fibers [16,17], that is very important for some applications. So the question arises whether it's possible to get a good biphoton wave packet localization with a poor laser having a relatively high angular divergence?…”

Observation of non-diffracting behavior at the single-photon level

“…see Ref. [17]). The distinct properties resulting from a BG beam pump are, however, more evident when we analyze spatially-resolved coincidence counts.…”