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Acta Physica Sinica

Quantum key distribution system based on combined modulation

Banghong Guo, Yang Li, Chong Xiang, Guan Chong, Ling-An Wu, Songhao Liu

Published Jan 1, 2013• 7 citations
Publisher

Abstract

We suggest a combined modulation quantum key distribution (QKD) system which encodes each single-photon signal with both phase modulation and polarization modulation. With the aid of dual-velocity protocol of hybrid QKD system, we construct a scheme to realize this combined modulation QKD which generates two-bit key with one signal for increasing the efficiency of QKD. We also develop a combined modulation Michelson QKD system, then solve the stability problem of the combined modulation QKD system in principle.

DOI
10.7498/aps.62.130303

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We suggest a combined modulation quantum key distribution (QKD) system which encodes each single-photon signal with both phase modulation and polarization modulation. With the aid of dual-velocity protocol of hybrid QKD system, we construct a scheme to realize this combined modulation QKD which generates two-bit key with one signal for increasing the efficiency of QKD. We also develop a combined modulation Michelson QKD system, then solve the stability problem of the combined modulation QKD system in principle.
We propose a scheme for quantum key distribution, in which single photons are encoded with polarization states and then divided and delayed to encode phase differences between two sequential pulses. In an example, the BB84 and DPS (differential phase shift) protocols are combined to achieve single-photon two-qubit quantum key distribution. This scheme can increase the key generation efficiency up to 7/6, higher than that of the conventional single-photon one-qubit quantum key distribution scheme.
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.
Based on the hypothesis that the velocity of light in vacuum is the maximum velocity possible for any signal, we present a dual-velocity protocol for a hybrid quantum key distribution (QKD) system, and prove that its security is the same as that for the BB84 protocol. We show that this protocol can improve the efficiency of quantum key generation from 50% to 100%, and, at the same time, reduce Eve's information. Because it breaks the symmetry between Bob and Eve before open discussion, the dual-velocity protocol extends the concept of QKD and increases our choice of protocol bases. We present three application examples and analyze in detail their security under intercept/resend attacks.
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.
Abstract Round-robin differential-phase-shift (RRDPS) quantum key distribution (QKD) protocol is a practical QKD protocol without monitoring the signal disturbance. However, how to further increase the secure key rate is still a challenge in practice. In the paper, we propose a high efficient QKD protocol based on RRDPS-QKD, where the photon-states are encoded in two degrees of freedom (DOFs), phase and polarization. The key generation rate and the security of the proposal protocol are analyzed. The simulation results show that the secure key rate is greatly improved in comparison with the original RRDPS-QKD protocol by breaking the limitation of quantum state in a single DOF. Moreover, our protocol can still maintain the high error tolerance of RRDPS-QKD protocol.
Based on the analysis of the security performance and existing problems of quantum key distribution (QKD) protocol and measurement device independent quantum key distribution protocol (MDI-QKD), this article proposes a four-dimensional MDI-QKD scheme based on phase polarization hybrid encoding, combining phase polarization encoding, quantum state fusion and segmentation principles, and high-dimensional MDI-QKD scheme, and designs a matching four-dimensional simulation model. The simulation results show that under different polarization dismatch parameters, the performance of the four-dimensional MDI-QKD scheme based on hybrid encoding has been significantly improved in terms of key generation rate and secure communication distance.