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Photon-bunching measurement after 2x25km of standard optical fibers

M. Halder·S. Tanzilli·H. de Riedmatten·A. Beveratos·H. Zbinden·N. Gisin
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Abstract

To show the feasibility of a long distance partial Bell-State measurement, a Hong-Ou-Mandel experiment with coherent photons is reported. Pairs of degenerate photons at telecom wavelength are created by parametric down conversion in a periodically poled lithium niobate waveguide. The photon pairs are separated in a beam-splitter and transmitted via two fibers of 25km. The wave-packets are relatively delayed and recombined on a second beam-splitter, forming a large Mach-Zehnder interferometer. Coincidence counts between the photons at the two output modes are registered. The main challenge consists in the trade-off between low count rates due to narrow filtering and length fluctuations of the 25km long arms during the measurement. For balanced paths a Hong-Ou-Mandel dip with a visibility of 47.3% is observed, which is close to the maximal theoretical value of 50% developed here. This proves the practicability of a long distance Bell state measurement with two independent sources, as e.g. required in an entanglement swapping configuration in the scale of tens of km.

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M. Halder, S. Tanzilli, H. de Riedmatten, A. Beveratos, H. Zbinden, N. Gisin. 2005-03-18. Photon-bunching measurement after 2x25km of standard optical fibers. https://doi.org/10.1103/physreva.71.042335

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