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Anais de XXXV Simpósio Brasileiro de Telecomunicações e Processamento de Sinais

Stable polarization coded quantum communication through single mode optical fibers

GUILHERME BARRETO XAVIER, G. Vilela de Faria, Guilherme P. Temporão, Jean Pierre von der Weid, Hugo Zbinden, Nicolas Gisin

Published Jan 1, 2008• 0 citations

Abstract

We perform a transmission of polarization encoded quantum bits through 16 km of single mode optical fiber in the 1550 nm window.The polarization drift caused by the changing birefringence of the fiber is kept stable through the use of a polarization control system we developed.This system employs 2 classical reference signals with 0.8 nm spacing from the quantum channel.We also send through the same fiber an extra reference classical signal used to trigger the single-photon detector.To the best of our knowledge this is the first time a quantum channel is multiplexed with 3 classical signals in the same optical fiber.

DOI: 10.14209/sbrt.2008.42622

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We perform a transmission of polarization encoded quantum bits through 16 km of single mode optical fiber in the 1550 nm window.The polarization drift caused by the changing birefringence of the fiber is kept stable through the use of a polarization control system we developed.This system employs 2 classical reference signals with 0.8 nm spacing from the quantum channel.We also send through the same fiber an extra reference classical signal used to trigger the single-photon detector.To the best of our knowledge this is the first time a quantum channel is multiplexed with 3 classical signals in the same optical fiber.

Polarization-encoding provides a promising approach for the practical quantum key distribution (QKD) system due to the simple encoding and decoding method. Here we present a long-term stable polarization-encoding QKD with a real-time polarization control. The polarization of the signal photons in the optical fiber was maintained stable by using time-division-multiplexed reference pulses for feedback control. We implemented this technique in the QKD experiment in 50 km fiber to show that it could facilitate polarization-encoded quantum communication. The system operated stably for ∼460 min, and the quantum bit error rate was ∼5.27%. The raw key generating rate in this system was kept stable at ∼500 bits s -1 . The advantages and disadvantages of the previous polarization-control schemes were also rigorously analyzed.

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.

A real-time polarization control system employing two non-orthogonal reference signals multiplexed in either time or wavelength with the data signal is presented. It is shown, theoretically and experimentally, that complete control of multiple polarization states can be attained employing polarization controllers in closed-loop configuration. Experimental results on the wavelength multiplexing setup show that negligible added penalties, corresponding to an average added optical Quantum Bit Error Rate of 0.044%, can be achieved with response times smaller than 10 ms, without significant introduction of noise counts in the quantum channel.

Abstract We experimentally demonstrate the compatibility of wavelength multiplexed active polarization stabilization for quantum communication in an optical fiber carrying telecom traffic. One of the feedback control channels contains a 9.953 Gb/s datastream generated from a BER meter. We verify the ability to transmit single‐photons in the two opposite directions of a 23‐km optical fiber spool, while maintaining their state of polarization stable and a classical BER in the feedback channel error‐free, during 6 h of continuous operation. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:2661–2665, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop26320

We report the first long-term field test of a polarization-encoding QKD system in C-band coexistence with classical signals over the same standard optical fiber. The system combines a self-stable polarization transmitter with a polarization control unit that stabilizes the link based on quantum metrics. This enables robust QKD operation over a metropolitan fiber link for several days, without requiring knowledge or control of the classical channels. The system can produce positive secret key rates of 422 kbps while coexisting with 0.7 mW classical power along a 50-km deployed link, achieving more than 98% uptime in the quantum channel.

We have recently constructed a fiber-optic “plug and play” quantum cryptography system as shown in Fig.1, wherein a Faraday-Mirror was used to compensate the polarization mode dispersion and phase drifts. It worked at 1550 nm and was based on the B92 protocol[1]. We have achieved stable quantum key distribution in a standard telecom fiber with different working-distances of 10, 25 and 50 km, respectively, by using some specifically developed techniques to guarantee long-term stability of our system, such as polarization-independent phase-modulation for stable phase encoding and decoding, hybrid coincidence for efficient detection of single photons with coincidence-gated quenching of the single-photon detectors followed by coincident counting of the avalanche signals, and synchronized detection of single-photon pulses by coincidence counting gated with proper delay and width. These unique techniques greatly enhanced the fringe visibility of single-photon interference. And we have also demonstrated the application of our system in cryptographic communication by sending coded pictures from Alice to Bob using the sifted quantum keys.