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Abstract: The generation of heralded pure Fock states via spontaneous parametric downconversion PDC relies on perfect photon-number correlations in the outputmodes. Correlations in any other degree of freedom, however, degrade the purityof the heralded state. In this paper, we investigate spectral entanglementbetween the two output modes of a periodically poled waveguide. With the intentof generating heralded 1- and 2-photon Fock states, we expand the output stateof the PDC to second order in photon number. We explore the effects of spectralfiltering and inefficient detection, of the heralding mode, on the count rate,g2 and purity of the heralded state, as well as the fidelity between theresulting state and an ideal Fock state. We find that filtering can decreasespectral correlations, however, at the expense of the count rate and increasedphoton-number mixedness in the heralded output state. As a physical example, wemodel a type II PP-KTP waveguide pumped by lasers at wavelengths of 400 nm, 788nm and 1930 nm. The latter two allow the fulfillment of extended phase matchingconditions in an attempt to eliminate spectral correlations in the PDC outputstate without the use of filtering, however, we find that even in these cases,some filtering is needed to achieve states of very high purity.

Autor: Agata M. Branczyk, T. C. Ralph, Wolfram Helwig, Christine Silberhorn

Fuente: https://arxiv.org/

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