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arXiv:quant-ph/0208174 · Physical Review A

Quantum interference with photon pairs created in spatially separated sources

Hugues de Riedmatten, I. Marcikic, Wolfgang Tittel, Hugo Zbinden, Nicolas Gisin

Published Feb 6, 2003• 111 citations
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Abstract

We report on a quantum interference experiment to probe the coherence between two photons coming from nondegenerate photon pairs at telecom wavelength created in spatially separated sources. The two photons are mixed on a beam splitter and we observe a reduction of up to 84% in the net coincidence count rate when the photons are made indistinguishable. This experiment constitutes an important step towards the realization of quantum teleportation and entanglement swapping with independent sources.

DOI
10.1103/physreva.67.022301

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We report on a quantum interference experiment to probe the coherence between two photons coming from nondegenerate photon pairs at telecom wavelength created in spatially separated sources. The two photons are mixed on a beam splitter and we observe a reduction of up to 84% in the net coincidence count rate when the photons are made indistinguishable. This experiment constitutes an important step towards the realization of quantum teleportation and entanglement swapping with independent sources.
We report on two-photon quantum interference experiments in the standard telecommunication band. Two identical photons in the 1.5 mm wavelength band were generated in spatially separated modes by a type-I spontaneous parametric down-conversion process, and injected into a fiber-optic Hong-Ou-Mandel interferometer. Two-photon interference patterns of dip and spatial beating in the coincidence counting rate were observed by varying the difference in optical path lengths. The visibilities obtained in the net coincidences were close to the theoretical value of 100%. The raw visibilities were also well above the classical limit.
Abstract The interference between two independent photons stands as a crucial aspect of numerous quantum information protocols and technologies. In this work, we leverage fiber-coupled devices, which encompass fibered photon pair-sources and off-the-shelf optics, to demonstrate Hong-Ou-Mandel interference. We employ two distinct single photon sources, namely a heralded single-photon source and a weak coherent laser source, both operating asynchronously in continuous-wave regime. We record two-photon coincidences, showing a state-of-art visibility of 91.9(5)%. This work, compliant with telecom technology, provides realistic backbones for establishing long-range communication based on quantum teleportation in hybrid quantum networks.
Entanglement swapping at telecom wavelengths is at the heart of quantum networking in optical fiber infrastructures. Although entanglement swapping has been demonstrated experimentally so far using various types of entangled photon sources both in near-infrared and telecom wavelength regions, the rate of swapping operation has been too low to be applied to practical quantum protocols, due to limited efficiency of entangled photon sources and photon detectors. Here we demonstrate drastic improvement of the efficiency at telecom wavelength by using two ultra-bright entangled photon sources and four highly efficient superconducting nanowire single photon detectors. We have attained a four-fold coincidence count rate of 108 counts per second, which is three orders higher than the previous experiments at telecom wavelengths. A raw (net) visibility in a Hong-Ou-Mandel interference between the two independent entangled sources was 73.3 ± 1.0% (85.1 ± 0.8%). We performed the teleportation and entanglement swapping, and obtained a fidelity of 76.3% in the swapping test. Our results on the coincidence count rates are comparable with the ones ever recorded in teleportation/swapping and multi-photon entanglement generation experiments at around 800 nm wavelengths. Our setup opens the way to practical implementation of device-independent quantum key distribution and its distance extension by the entanglement swapping as well as multi-photon entangled state generation in telecom band infrastructures with both space and fiber links.
Entanglement swapping at 1550 nm was experimentally demonstrated based on two polarization‐entangled photon pairs, which were created in two independent PPLN waveguides. Mandel dip was measured by using fourfold coincidences to yield a visibility of 71.8% and verify quantum interference between photons from two separated sources. By making Bell‐state measurement, the two initially independent photons were projected into an entanglement state. An interference visibility of 37.5% was observed for these two photons indicating the entanglement state was successfully swapped by using polarization‐entangled photon pairs in the telecom band.