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Long-Distance Quantum Key Distribution over Telecom Fiber

Leilei Huang

Published Jan 1, 2006• 0 citations
OpenAlex

Abstract

We present two long-distance quantum key distribution (QKD) systems over telecom fiber. The first one is the Sagnac QKD system implementing standard BB84 protocol. Novel polarization-insensitive phase modulators are used to simplify the conventional architecture. We are able to achieve a stable quantum bit error rate of 4-6.5% over 40km fiber loop over one hour without recalibration. The second one is the fiber-based QKD system using Gaussian-modulated coherent states. We have overcome the challenges imposed by the requirements for high detector sensitivity, long-term stability, and low signal crosstalk. Our GMCS QKD system is the first practical fiber-based one-way demonstration and is able to achieve a sifted secret key rate of 15.5 kbits/s over a transmission distance of 5km fiber. Experimental QKD is still in its infancy. The results presented in this thesis represent a significant step forward towards the practical QKD over conventional fiber networks.

Related papers

Sagnac quantum key distribution and secret sharing

Jan Bogdanski, Johan Ahrens, Mohamed Bourennane

We present the first Sagnac quantum secret sharing (in three- and four-party implementations) as well as Sagnac two-user quantum key distribution (QKD) over 1550 nm single mode fiber (SMF) networks, using the BB84- protocol with phase encoding. The secret sharing experiment has implemented a single qubit protocol, which allows for a practical secret sharing implementation over fiber telecom channels and in free-space. The previous quantum secret sharing proposals were based on multiparticle entangled states, not scalable and diffcult in the experimental implementations. Our experimental data show stable, in regards to birefringence drift, quantum secret sharing transmissions at the total Sagnac transmission loop distances of 45-55 km with the quantum bit error rates (QBER) of 3.0-3.7 % for the mean photon number μ = 0.1. In the QKD experiment we have achieved the total Sagnac transmission loop distances of 100-150 km with quantum bit error rates (QBER) of 5.84-9.79 % for μ = 0.1. The distances were much longer and rates much higher than in any other published Sagnac QKD experiments. The stability of quantum transmission in both secret sharing and QKD experiments has been achieved thanks to our new concept for compensation of SMF birefringence effects in Sagnac, based on a polarization control system and a polarization insensitive phase modulator. The measurement results have showed feasibility of quantum secret sharing and QKD over telecom fiber networks in Sagnac confi;guration, using standard fiber telecom components. Our birefringence compensation in SMF Sagnac open the door to other Sagnac-based applications over SMF links such as precise optical sensing, dispersion characteristics of optical fibers, acoustic and strain sensing, and generally sensing of any time varying phenomenon.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Dec 2, 2008•3 citations

Gaussian-modulated coherent state quantum key distribution experiment over 20km telecommunication fiber

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In most implementations of quantum-key-distribution (QKD) protocols the secure keys originate from single-photon signals. However, due to the unavoidable channel losses and the low efficiencies of single photon detectors, the key generation rate of a single-photon QKD system is low. Recently, there has been a growing interest in the Gaussian-modulated coherent state (GMCS) QKD protocol because it can be implemented with conventional laser sources and high efficiency homodyne-detectors. Here, we present our experimental results with a fully fiber-based one-way GMCS QKD system. Our system employed a double Mach-Zehnder interferometer (MZI) configuration in which the weak quantum signal and the strong local-oscillator (LO) go through the same fiber between Alice and Bob. We employed two novel techniques to suppress system excess noise. First, to suppress the LO's leakage, an important contribution to the excess noise, we implemented a scheme combining polarization and frequency multiplexing, achieving an extinction ratio of 70dB. Second, to further minimize the system excess noise due to phase drift of the double MZI, the sender simply remaps her data by performing a rotation operation. Under a realistic model, the secure key rates determined with a 5km and a 20km fiber link are 0.3bit/pulse and 0.05bit/pulse, respectively. These key rates are significantly higher than that of a practical BB84 QKD system.

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Sagnac secret sharing over telecom fiber networks

Jan Bogdanski, Johan Ahrens, Mohamed Bourennane

We report the first Sagnac quantum secret sharing (in three-and four-party implementations) over 1550 nm single mode fiber (SMF) networks, using a single qubit protocol with phase encoding. Our secret sharing experiment has been based on a single qubit protocol, which has opened the door to practical secret sharing implementation over fiber telecom channels and in free-space. The previous quantum secret sharing proposals were based on multiparticle entangled states, difficult in the practical implementation and not scalable. Our experimental data in the three-party implementation show stable (in regards to birefringence drift) quantum secret sharing transmissions at the total Sagnac transmission loop distances of 55-75 km with the quantum bit error rates (QBER) of 2.3-2.4% for the mean photon number micro?= 0.1 and 1.7-2.1% for micro= 0.3. In the four-party case we have achieved quantum secret sharing transmissions at the total Sagnac transmission loop distances of 45-55 km with the quantum bit error rates (QBER) of 3.0-3.7% for the mean photon number micro= 0.1 and 1.8-3.0% for micro?= 0.3. The stability of quantum transmission has been achieved thanks to our new concept for compensation of SMF birefringence effects in Sagnac, based on a polarization control system and a polarization insensitive phase modulator. The measurement results have showed feasibility of quantum secret sharing over telecom fiber networks in Sagnac configuration, using standard fiber telecom components.

Optics Express•Jan 15, 2009•13 citations
We present two long-distance quantum key distribution (QKD) systems over telecom fiber. The first one is the Sagnac QKD system implementing standard BB84 protocol. Novel polarization-insensitive phase modulators are used to simplify the conventional architecture. We are able to achieve a stable quantum bit error rate of 4-6.5% over 40km fiber loop over one hour without recalibration. The second one is the fiber-based QKD system using Gaussian-modulated coherent states. We have overcome the challenges imposed by the requirements for high detector sensitivity, long-term stability, and low signal crosstalk. Our GMCS QKD system is the first practical fiber-based one-way demonstration and is able to achieve a sifted secret key rate of 15.5 kbits/s over a transmission distance of 5km fiber. Experimental QKD is still in its infancy. The results presented in this thesis represent a significant step forward towards the practical QKD over conventional fiber networks.
We present the first Sagnac quantum secret sharing (in three- and four-party implementations) as well as Sagnac two-user quantum key distribution (QKD) over 1550 nm single mode fiber (SMF) networks, using the BB84- protocol with phase encoding. The secret sharing experiment has implemented a single qubit protocol, which allows for a practical secret sharing implementation over fiber telecom channels and in free-space. The previous quantum secret sharing proposals were based on multiparticle entangled states, not scalable and diffcult in the experimental implementations. Our experimental data show stable, in regards to birefringence drift, quantum secret sharing transmissions at the total Sagnac transmission loop distances of 45-55 km with the quantum bit error rates (QBER) of 3.0-3.7 % for the mean photon number μ = 0.1. In the QKD experiment we have achieved the total Sagnac transmission loop distances of 100-150 km with quantum bit error rates (QBER) of 5.84-9.79 % for μ = 0.1. The distances were much longer and rates much higher than in any other published Sagnac QKD experiments. The stability of quantum transmission in both secret sharing and QKD experiments has been achieved thanks to our new concept for compensation of SMF birefringence effects in Sagnac, based on a polarization control system and a polarization insensitive phase modulator. The measurement results have showed feasibility of quantum secret sharing and QKD over telecom fiber networks in Sagnac confi;guration, using standard fiber telecom components. Our birefringence compensation in SMF Sagnac open the door to other Sagnac-based applications over SMF links such as precise optical sensing, dispersion characteristics of optical fibers, acoustic and strain sensing, and generally sensing of any time varying phenomenon.
In most implementations of quantum-key-distribution (QKD) protocols the secure keys originate from single-photon signals. However, due to the unavoidable channel losses and the low efficiencies of single photon detectors, the key generation rate of a single-photon QKD system is low. Recently, there has been a growing interest in the Gaussian-modulated coherent state (GMCS) QKD protocol because it can be implemented with conventional laser sources and high efficiency homodyne-detectors. Here, we present our experimental results with a fully fiber-based one-way GMCS QKD system. Our system employed a double Mach-Zehnder interferometer (MZI) configuration in which the weak quantum signal and the strong local-oscillator (LO) go through the same fiber between Alice and Bob. We employed two novel techniques to suppress system excess noise. First, to suppress the LO's leakage, an important contribution to the excess noise, we implemented a scheme combining polarization and frequency multiplexing, achieving an extinction ratio of 70dB. Second, to further minimize the system excess noise due to phase drift of the double MZI, the sender simply remaps her data by performing a rotation operation. Under a realistic model, the secure key rates determined with a 5km and a 20km fiber link are 0.3bit/pulse and 0.05bit/pulse, respectively. These key rates are significantly higher than that of a practical BB84 QKD system.
Unconditionally secure multiuser quantum key distribution (QKD) over long distance switched telecom fiber networks will have a revolutionary impact on people's, companies', and governmental exchange of confidential information. We report five-user QKD over switched fiber networks in both star and tree configurations, using the BB84-protocol with phase encoding. Both setups implement polarization insensitive phase modulators, necessary for birefringent single mode fiber networks. In both configurations, for the mean photon number μ=0.1, we have achieved raw rates between 50Hz and 300Hz at distances between 25km to 50km with quantum bit error rates between 1.24% to 5.56%. The measurements have showed feasibility of multiuser QKD over switched telecom fiber networks, using standard fiber telecom components.
Twin-field (TF) quantum key distribution (QKD) offers a promising approach to long-distance QKD networks due to its superior performance over large channel losses. Due to specialized hardware requirements, nearly all long-distance TFQKD demonstrations have only two users exchanging keys, rather than a network with three or more users. In this work, we experimentally demonstrate a proof-of-principle three-user-pair Sagnac TFQKD network spanning 127-km using single-photon avalanche detectors without any active phase stabilization or postcompensation. We implement efficient procedures for maintaining polarization stability and circumventing Rayleigh backscattering noise to achieve a stable Sagnac interference visibility of 93±193\pm193±1% over one hour. A secure key rate of 1.398×10−51.398\times10^{-5}1.398×10−5 bits per pulse is achieved over an asymmetric communication channel with 102-km fiber and 45-dB overall loss. To our knowledge, this is the first TFQKD network without active phase stabilization or postcompensation achieved over long fibers. Our results represent a highly practical and cost-effective approach to long-distance QKD networks.
We report the first Sagnac quantum secret sharing (in three-and four-party implementations) over 1550 nm single mode fiber (SMF) networks, using a single qubit protocol with phase encoding. Our secret sharing experiment has been based on a single qubit protocol, which has opened the door to practical secret sharing implementation over fiber telecom channels and in free-space. The previous quantum secret sharing proposals were based on multiparticle entangled states, difficult in the practical implementation and not scalable. Our experimental data in the three-party implementation show stable (in regards to birefringence drift) quantum secret sharing transmissions at the total Sagnac transmission loop distances of 55-75 km with the quantum bit error rates (QBER) of 2.3-2.4% for the mean photon number micro?= 0.1 and 1.7-2.1% for micro= 0.3. In the four-party case we have achieved quantum secret sharing transmissions at the total Sagnac transmission loop distances of 45-55 km with the quantum bit error rates (QBER) of 3.0-3.7% for the mean photon number micro= 0.1 and 1.8-3.0% for micro?= 0.3. The stability of quantum transmission has been achieved thanks to our new concept for compensation of SMF birefringence effects in Sagnac, based on a polarization control system and a polarization insensitive phase modulator. The measurement results have showed feasibility of quantum secret sharing over telecom fiber networks in Sagnac configuration, using standard fiber telecom components.