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Acta Physica Sinica

Experimental quantum key distribution with double protocol

Hu Hua-Peng, Jing Zhang, Jindong Wang, Huang Yu-Xian, Lu Yi-Qun, Songhao Liu, Wei Lü, (1)华南师范大学信息光电子科技学院,光子信息技术广东省高校重点实验室,广州 510006; (2)中国科学院合肥智能研究所，合肥 230031

Published Jan 1, 2008• 7 citations
Publisher

Abstract

We propose one kind of improved QKD scheme based on time coding and phase coding. The pulse which had been discarded on the BB84 protocol phase coding QKD system is used to realize the time coding protocol, thus the useful bits rate in the present scheme can be doubled. At the same time, the phase coding keys and the time coding keys are obtained, we may combine both as new keys which can enhancethe generated rate and the sensitivity of monitor. At Bob’s side, a Fraday-Michelson is used instead of a traditional M-Z interferometer, which improves the stability of the interference visibility. With the proposed experimental setup, a stable quantum key distribution was performed over 90 km fiber. It is shown in our experiment that the characteristics of our system are as follows: secure, stable and economical.

DOI
10.7498/aps.57.5605

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We propose one kind of improved QKD scheme based on time coding and phase coding. The pulse which had been discarded on the BB84 protocol phase coding QKD system is used to realize the time coding protocol, thus the useful bits rate in the present scheme can be doubled. At the same time, the phase coding keys and the time coding keys are obtained, we may combine both as new keys which can enhancethe generated rate and the sensitivity of monitor. At Bob’s side, a Fraday-Michelson is used instead of a traditional M-Z interferometer, which improves the stability of the interference visibility. With the proposed experimental setup, a stable quantum key distribution was performed over 90 km fiber. It is shown in our experiment that the characteristics of our system are as follows: secure, stable and economical.
A new quantum key distribution scheme is proposed to realize both phase coding and time coding based on two unbalanced Mach-Zehnder interferometers. The pulses which are discarded in the phase coding scheme can be coded in time coding, so the useful bit rate in the present scheme can be doubled. At the same time, the phase coding keys and the time coding keys are obtained. We can use one group of keys to communicate and the other one to guard against eavesdropping, or combine both of them to form new keys. This scheme has favorable application prospect.
An improved DPS-QKD scheme is proposed and demonstrated in this paper. At Alice's site，we use a M-Z interferometer to produce two coherent pulses. At Bob's site，a Faraday-mirrors-based Michelson interferometer is used instead of a M-Z interferometer to auto-compensate for the phase drifts and polarization mode dispersions in the fiber. It enhances the security of the whole system to use the two quantum cryptography protocols (namely the two pulse DPS-QKD scheme associated with the BB84 scheme). It is shown in our experiment that such a system features perfect stability with a quantum bit error rate less than 5% and high key generation rate. This scheme has been implemented successfully during the 80km fiber transmission.
We propose an improved scheme of hybrid quantum key distribution based on the combination of differential phase shift and BB84 polarization encoding. By adjusting the polarization properly and routing all the probability amplitudes to interfere, a higher protocol efficiency of 3/2 is obtained. A better stability can be achieved with the birefringence effects and polarization-dependent losses at the transmitter compensated automatically by employing Faraday mirrors and quantum bit error rate can be smaller by reducing single photon detectors with fewer time slots introducing dark counts. Moreover, the condition for stable interference at the receiver is provided and the security performance is demonstrated, specifically.
By tracking phase drift and distributing key at suitable times,the quantum key distribution based on double M-Z interferometer was performed over a fiber length of 80 km with a quantum bit-error rate of 6%,and it had been working stably for several days.In addition,we demonstrate that the quantum bit-error rate is less than 3.5% within a fiber length of 50 km.Through the local-area network,the key exchange and document transmission were achieved.The scheme applicable to other QKD systems can also improve the stability of interference,which has made progress in the practical application.
In this work, we present a new time-bin phase-encoding quantum key distribution (QKD), where the transmitter utilizes an inherently stable Sagnac-type interferometer, and has comparable electrical requirements to existing polarization or phase encoding schemes. This approach does not require intensity calibration and is insensitive to environmental disturbances, making it both flexible and high-performing. We conducted experiments with a compact QKD system to demonstrate the stability and secure key rate performance of the presented scheme. The results show a typical secure key rate of 6.2 kbps@20 dB and 0.4 kbps@30 dB with channel loss emulated by variable optical attenuators. A continuous test of 120-km fiber spool shows a stable quantum bit error rate of the time-bin basis within 0.4%∼0.6% over a consecutive 9-day period without any adjustment. This intrinsically stable and compatible scheme of time-bin phase encoding is extensively applicable in various QKD experiments, including BB84 and measurement-device-independent QKD.
We present an improved differential phase shift quantum key distribution schemewhich features auto-compensation，high efficiency，and excellent practicality. Alice modulates continuous laser using an intensity modulator based on polarization to generate coherent pulse train. Bob employs a Fraday-Michelson interferometer instead of a traditional M-Z interferometer，which automatically compensates for the polarization mode dispersion caused by the changes of environment and improves the stability of the interference visibility. The present scheme not only has a simpler configuration，but also offers a higher key creation efficiency than traditional schemes. Furthermore，it enhances the security of the system. With the proposed experimental setup，a stable quantum key distribution was performed over 80km fiber with a quantum bit-error rate of less than 4%.