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Acta Physica Sinica

Optical preamplifier based simultaneous quantum key distribution and classical communication scheme

Hai Zhong, Wei Ye, Xiaodong Wu, Ying Guo

Published Jan 1, 2021• 6 citations
Publisher

Abstract

That the simultaneous quantum key distribution and classical communication (SQCC) scheme are combined with the continuous variable quantum key distribution (CVQKD) and the classical communication together, will provide an effective method to implement the simultaneous CVQKD and the classical communication in the existing optical networks in the future. However, superimposing a classical signal on the quantum signal will introduce excess noise into the CVQKD system, thus greatly reducing the performance of the system. In this paper, a novel scheme of SQCC based on optical preamplifier (OPA) is proposed, that is, the OPA is inserted into the receiver to improve the performance of the system. On the one hand, under the condition of the same bit error rate, the amplification of the signal by the OPA can reduce the requirement for the modulation amplitude of the classical signal at the sending end, thereby reducing the noise effect of the classical signal on the quantum signal. On the other hand, the OPA can compensate for the imperfection of the receiver detector. Moreover, in the case of locally generated local oscillator, the amplifier can also amplify the weak phase reference pulse, and thus reducing the phase excess noise caused by the shot noise of the weak phase reference pulse. Numerical simulation results show that the proposed scheme has better performance than the original scheme in the sense of security key rate and transmission distance. These results show that this scheme provides an effective and practical method for the further development and practical application of the SQCC scheme.

DOI
10.7498/aps.70.20200855

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That the simultaneous quantum key distribution and classical communication (SQCC) scheme are combined with the continuous variable quantum key distribution (CVQKD) and the classical communication together, will provide an effective method to implement the simultaneous CVQKD and the classical communication in the existing optical networks in the future. However, superimposing a classical signal on the quantum signal will introduce excess noise into the CVQKD system, thus greatly reducing the performance of the system. In this paper, a novel scheme of SQCC based on optical preamplifier (OPA) is proposed, that is, the OPA is inserted into the receiver to improve the performance of the system. On the one hand, under the condition of the same bit error rate, the amplification of the signal by the OPA can reduce the requirement for the modulation amplitude of the classical signal at the sending end, thereby reducing the noise effect of the classical signal on the quantum signal. On the other hand, the OPA can compensate for the imperfection of the receiver detector. Moreover, in the case of locally generated local oscillator, the amplifier can also amplify the weak phase reference pulse, and thus reducing the phase excess noise caused by the shot noise of the weak phase reference pulse. Numerical simulation results show that the proposed scheme has better performance than the original scheme in the sense of security key rate and transmission distance. These results show that this scheme provides an effective and practical method for the further development and practical application of the SQCC scheme.
Continuous variable quantum key distribution (CVQKD) based on a simultaneous quantum and classical communication (SQCC) protocol can use a single coherent communication system for multiple purposes. In this paper, we propose an inter-satellite SQCC-CVQKD scheme in the terahertz (THz) band. This scheme performs classical modulation at the sending end, followed by quantum Gaussian modulation operations. At the receiving end, an amplifier is used to amplify and demultiplex the received signal, and, finally, a homodyne detector or heterodyne detector is selected for decoding. We have demonstrated the security of the SQCC-CVQKD system in the THz band, and a performance analysis of the scheme is given in the finite-size regime. The simulation results show that this scheme has a higher secret key rate and stronger anti-interference ability in practice. This work provides an effective way to construct wireless quantum communication networks.
Abstract We propose a passive continuous-variable quantum key distribution (CVQKD) protocol based on simultaneous quantum and classical communication (SQCC) under indoor environments and in inter-satellite links within the terahertz band. In our PSQCC-CVQKD scheme, classical modulation is performed at the transmitter, followed by passive quantum modulation operations. At the receiver, an amplifier is utilized to amplify and demultiplex the received signal, and a homodyne or heterodyne detector is subsequently selected for decoding. We derive the security bounds of the protocol and evaluate its performance in both indoor environments and inter-satellite links. Furthermore, by considering finite-size effects, we achieve tighter agreement constraints, which are more practical than those obtained in the asymptotic limit. Simulation results indicate that this scheme exhibits a high secret key rate and strong jamming resistance in practical applications, providing a more efficient pathway for the construction of future quantum networks.
The simultaneous quantum and classical communication (SQCC) protocol is an appealing protocol since it allows continuous-variable quantum key distribution (CV-QKD) and classical communication to be implemented simultaneously by using the same communication infrastructure and on a single wavelength. However, the main challenge of the SQCC protocol is its low tolerance of phase noise, limiting the transmission distance under the real local oscillator (LO) design. To eliminate the phase drift without the aid of the reference signal, the classical carrier phase estimation (CPE) algorithm in the field of coherent optical communication is employed for phase recovery and data extraction. Besides, the power of the residual phase noise in classical communication and the power of the excess phase noise in CV-QKD are derived, including the effects of the employed laser linewidth, the transversal filter length, and the classical signal power. On this basis, the performances of the SQCC protocol under the trusted and the untrusted phase noise model are discussed, respectively. Our work confirms the feasibility of the CPE algorithm in the SQCC protocol and demonstrates the conditions required for this protocol to operate on a coherent optical communication system.
At first sight, quantum key distribution (QKD) working at single-photon levels seems very different from classical optical communication using strong laser pulses. Surprisingly, in the simultaneous QKD and classical communication (SQCC) protocol, a single, coherent system can both transmit classical information and distribute a quantum key, but implementation has been impeded by its low tolerance of phase noise. The authors identify ``trusted'' noise from the coherent receiver, which cannot be accessed by an eavesdropper, and greatly improve the phase-noise tolerance of the SQCC protocol. Their findings suggest that the SQCC protocol could be truly practical for secure communication.
We propose a novel scheme for measurement-device-independent (MDI) continuous-variable quantum key distribution (CVQKD) by simultaneously conducting classical communication and QKD, which is called “simultaneous MDI-CVQKD” protocol. In such protocol, each sender (Alice, Bob) can superimpose random numbers for QKD on classical information by taking advantage of the same weak coherent pulse and an untrusted third party (Charlie) decodes it by using the same coherent detectors, which could be appealing in practice due to that multiple purposes can be realized by employing only single communication system. What is more, the proposed protocol is MDI, which is immune to all possible side-channel attacks on practical detectors. Security results illustrate that the simultaneous MDI-CVQKD protocol can secure against arbitrary collective attacks. In addition, we employ phase-sensitive optical amplifiers to compensate the imperfection existing in practical detectors. With this technology, even common practical detectors can be used for detection through choosing a suitable optical amplifier gain. Furthermore, we also take the finite-size effect into consideration and show that the whole raw keys can be taken advantage of to generate the final secret key instead of sacrificing part of them for parameter estimation. Therefore, an enhanced performance of the simultaneous MDI-CVQKD protocol can be obtained in finite-size regime.
The simultaneous classical and continuous variable quantum communication can allow classical communication and continuous variable quantum key distribution with a local local oscillator (LLO CVQKD) to be implemented simultaneously using the same communication architecture. Such scheme enables LLO CVQKD to be integrated with classical communication at the minimum cost, but the existence of reference pulses will bring security loopholes to the simultaneous communication system, allowing eavesdroppers to launch attacks. In this paper, we analyze and simulate the performance of the system by introducing the trusted noise model under the phase reference pulse intensity attack, where Eve can hide her attack by manipulating the intensity of the reference pulse using a phase insensitive amplifier. A reconstructed noise model is proposed to solve this problem. Moreover, we show that the reconstructed noise model can strengthen the security of the practical simultaneous communication system.