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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Narrowband polarization-entangled photon pairs distributed over a WDM link for qubit networks

Sébastien Sauge, Marcin Świłło, Sebastian Albert‐Seifried, J. Waldebäck, Maria Tengner, Daniel Ljunggren, Anders Karlsson, GUILHERME BARRETO XAVIER

Published Jun 1, 2007• 4 citations
Publisher

Abstract

A brighter, more narrowband and portable source using two 50 mm long orthogonally oriented, quasi-phase-matched crystals is built. The new source generates polarization-entangled photon pairs at 809 nm and 1555 nm at a maximum rate of 1.2 x 106s-1THz-1mW-1after coupling to single-mode fiber. For transmission experiments, the quantum and synchronization channels are multiplexed in a WDM environment, and with only 0.8 nm spacing between them, a detected rate of 1.1 x 103 s-1photon pairs is achieved with a raw visibility of 85 % in all measurement bases after transmission over 27 km of single mode fiber. With the current isolation of about 100 dB achieved between channels, the quantum channel could even be multiplexed with a classical data channel.

DOI
10.1109/cleoe-iqec.2007.4387014

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A brighter, more narrowband and portable source using two 50 mm long orthogonally oriented, quasi-phase-matched crystals is built. The new source generates polarization-entangled photon pairs at 809 nm and 1555 nm at a maximum rate of 1.2 x 106s-1THz-1mW-1after coupling to single-mode fiber. For transmission experiments, the quantum and synchronization channels are multiplexed in a WDM environment, and with only 0.8 nm spacing between them, a detected rate of 1.1 x 103 s-1photon pairs is achieved with a raw visibility of 85 % in all measurement bases after transmission over 27 km of single mode fiber. With the current isolation of about 100 dB achieved between channels, the quantum channel could even be multiplexed with a classical data channel.
We present a bright, narrowband, portable, quasi-phase-matched two-crystal source generating polarization-entangled photon pairs at 809 nm and 1555 nm at a maximum rate of 1.2 x 10(6) s(-1) THz-1 mW(-1) after coupling to single-mode fiber. The quantum channel at 1555 nm and the synchronization signal gating the single photon detector are multiplexed in the same optical fiber of length 27 km by means of wavelength division multiplexers (WDM) having 100 GHz (0.8 nm) spacing between channels. This implementation makes quantum communication applications compatible with current high-speed optical networks.
We discuss recent work in quantum communication, and in some details present a bright, narrowband, portable, quasi-phase-matched two-crystal source generating polarization-entangled photon pairs at 809 nm and 1555 nm. We also show how the single-photon quantum channel at 1555 nm and a classical synchronization signal gating the single photon detector at the receiving side can be multiplexed in the same optical fiber of length 27 km by means of wavelength division multiplexers (WDM) having 100 GHz (0.8 nm) spacing between channels. This illustrates how single-photon quantum communication applications is compatible with current high-speed optical networks.
We demonstrate a bright, narrowband, compact, quasi-phase-matched single-crystal source generating path-polarization-entangled photon pairs at 810 nm and 1550 nm at a maximum rate of 3 x 10(6) s(-1) THz(-1) mW(-1) after coupling to single-mode fiber, and with two-photon interference visibility above 90%. While the source can already be used to implement quantum communication protocols such as quantum key distribution, this work is also instrumental for narrowband applications such as entanglement transfer from photonic to atomic qubits, or entanglement of photons from independent sources.
We demonstrate a bright, narrowband, compact, quasi-phase-matched single-crystal source generating path-polarization-entangled photon pairs at 810 nm and 1550 nm at a maximum rate of 3 × 10 6 s −1 THz −1 mW −1 after coupling to single-mode fiber, and with two-photon interference visibility above 90%. While the source can already be used to implement quantum communication protocols such as quantum key distribution, this work is also instrumental for narrowband applications such as entanglement transfer from photonic to atomic qubits, or entanglement of photons from independent sources.
Studies on telecom-band entangled photon-pair sources for entanglement distribution have so far focused on their narrowband operations. Fiber-based sources are seriously limited by spontaneous Raman scattering while sources based on quasi-phase-matched crystals or waveguides are usually narrowband because of long device lengths and/or operations far from degeneracy. An entanglement distributor would have to multiplex many such narrowband sources before entanglement distribution to fully utilize the available fiber transmission bandwidth. In this work, we demonstrate a broadband source of polarization-entangled photon-pairs suitable for wavelength-multiplexed entanglement distribution over optical fiber. We show that our source is potentially capable of simultaneously supporting up to forty-four independent wavelength channels.
We demonstrate a compact and stable source of polarization-entangled pairs of photons, one at 810 nm wavelength for high detection efficiency and the other at 1550 nm for long-distance fiber communication networks. Due to a novel Sagnac-based design of the interferometer no active stabilization is needed. Using only one 30 mm ppKTP bulk crystal the source produces photons with a spectral brightness of 1.13 x 10(6) pairs/s/mW/THz with an entanglement fidelity of 98.2%. Both photons are single-mode fiber coupled and ready to be used in quantum key distribution (QKD) or transmission of photonic quantum states over large distances.