Abstract
Phase drift is an inevitable problem in the practical implementation of phase-coding quantum key distribution (QKD) systems. Conventional active phase tracking and compensation solutions cannot be implemented during the key transmission process, resulting in reduced efficiency of the system. In this paper, we propose a single-photon level real-time phase tracking scheme using only the estimated quantum bit error rate (QBER) and mismatched-basis data to acquire the phase drift parameter instead of a phase scanning process or reference light pulses, without extra hardware or interrupting the transmission of quantum signals. This scheme is applied into a phase-coding QKD system with active phase disturbance and obtains an average QBER of $1.01\%$ with a standard derivation of $0.37\%$ over 50 h of continuous operation. Experimental results show that this scheme enables QKD systems to operate continuously with long-term stability and keep a low level of QBER even with rapid phase drift, suggesting its suitability for practical applications.
Highlights
Quantum key distribution (QKD) provides information-theoretic secure keys between two remote parties over a non-protected communication channel
In order to evaluate the practical performance of the proposed phase tracking scheme, an active phase disturbance achieved by changing V0a with time is added in the quantum key distribution (QKD) system
Compared to the traditional active phase compensation scheme, the requirement of reference light pulses or scanning process is removed in our scheme, leading to an improvement of practicality of QKD systems
Summary
Quantum key distribution (QKD) provides information-theoretic secure keys between two remote parties over a non-protected communication channel. A fiber-stretcher [16], [17] is placed in the receiver’s interferometer to actively adjust the optical path difference, which is driven based on a feedback control algorithm These schemes can continually compensate phase drift though, reference light pulses with higher intensity are required to obtain the feedback signal, resulting in an increase of the fabrication difficulty of interferometers and system complexity. An active phase compensation scheme based on the machine learning algorithm is proposed [21] This scheme enables QKD systems to predict the parameter variations beforehand and actively perform real-time control on corresponding devices to perform the phase tracking, increasing the efficiency of the QKD system. Experimental results show that the system can be operated stably over 50 hours, the obtained average QBER is 1.01% with a standard deviation of 0.37%
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