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Research

Realization of Quantum Secure Direct Communication with Continuous Variable

Zhengwen Cao, Yuan Lu, Geng Chai, Hao Cheng Yu, Kexin Liang, Lei Wang

Published Jan 1, 2023• 64 citations
Publisher

Abstract

With the progress of theoretical and applied technologies, the communication system based on the classical encryption is seriously threatened by quantum computing and distributed computing. A communication method that directly loads confidential information on the quantum state, quantum secure direct communication (QSDC), came into being for resisting security threats. Here, we report the first continuous-variable QSDC (CV-QSDC) experimental demonstration for verifying the feasibility and effectiveness of the CV-QSDC protocol based on Gaussian mapping and propose a parameter estimation for signal classification under the actual channels. In our experiment, we provided 4 × 10 2 blocks, where each block contains 10 5 data for direct information transmission. For the transmission distance of 5 km in our experiment, the excess noise is 0.0035 SNU, where SNU represents the unit of shot-noise units. The 4.08 × 10 5 bit per second experimental results firmly demonstrated the feasibility of CV-QSDC under the fiber channel. The proposed grading judgment method based on parameter estimation provides a practical and available message processing scheme for CV-QSDC in a practical fiber channel and lays the groundwork for the grading reconciliation.

DOI
10.34133/research.0193

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With the progress of theoretical and applied technologies, the communication system based on the classical encryption is seriously threatened by quantum computing and distributed computing. A communication method that directly loads confidential information on the quantum state, quantum secure direct communication (QSDC), came into being for resisting security threats. Here, we report the first continuous-variable QSDC (CV-QSDC) experimental demonstration for verifying the feasibility and effectiveness of the CV-QSDC protocol based on Gaussian mapping and propose a parameter estimation for signal classification under the actual channels. In our experiment, we provided 4 × 10 2 blocks, where each block contains 10 5 data for direct information transmission. For the transmission distance of 5 km in our experiment, the excess noise is 0.0035 SNU, where SNU represents the unit of shot-noise units. The 4.08 × 10 5 bit per second experimental results firmly demonstrated the feasibility of CV-QSDC under the fiber channel. The proposed grading judgment method based on parameter estimation provides a practical and available message processing scheme for CV-QSDC in a practical fiber channel and lays the groundwork for the grading reconciliation.
Quantum secure direct communication (QSDC) realizes the transmission of secret messages directly in a quantum channel. A continuous-variable- (CV) based quantum-communication system allows high-speed, large-capacity information transmission in optical telecommunication systems. In this work, we propose a QSDC protocol based on Gaussian mapping. As for Gaussian modulation, the designed Gaussian-mapping scheme effectively solves the problem, which results from the nonuniformity of the secret-message bitstream, and is applicable to different modulation variances. The system performance analysis shows that the proposed scheme can realize inerrant Gaussian modulation of secret messages, and secure transmission of messages under information theory. Moreover, our work hopes to stimulate discussion on experimental realization and practical advance of CV-QSDC protocol.
Abstract Quantum secure direct communication (QSDC) enables the direct transmission of secret messages over a quantum channel without prior key sharing. QSDC implemented in the continuous-variable (CV) regime allows high-capacity information transmission using simple optical communication technologies. In this work, we propose a novel CV-QSDC protocol with a quantum one-time pad, which achieves secure message transmission based on coherent states and unitary operations, and the receiver can directly obtain the secret messages after measuring the coherent states. The security of this protocol is jointly guaranteed by one-time pad encryption and a CV quantum key distribution (QKD) protocol. Performance analysis shows that the proposed scheme can achieve a quantum bit error rate (QBER) lower than 1% by adjusting the modulation variance and unitary operation parameters. With the optimal modulation variance, the secure transmission distance of the proposed protocol can exceed 150 km.
Abstract Quantum secure direct communication (QSDC) allows secret messages to be directly communicated over a quantum channel; its further development could lead to many practical applications. In this paper, we propose a novel continuous-variable (CV)-based QSDC which could be compatible with fully developed optical telecommunication technologies to minimize the implementation costs. Through a security analysis we show that the proposed scheme can effectively resist an eavesdropper’s attacks on the light intensity. Furthermore, our work should inspire the improvement, development and application of CV-based QSDC.
Continuous-variable quantum secure communication encoded by Gaussian mapping offers high-capacity and high transmission rates. For the theoretically secure encryption scheme of a 1-time pad, a highly reliable coherent-state quantum secure communication system has been established, and its security has been quantitatively evaluated using Wyner’s wiretap channel theory. We also propose an information reconstruction scheme based on multidimensional rotation to extract secret messages at low-to-medium signal-to-noise ratios. Meanwhile, to address the unbalanced optical path, we design a self-balanced homodyne detector based on a programmable gain amplifier, achieving an electronic noise variance of 1.624 × 10 − 7 V 2 and a bandwidth of 715 MHz. In 10-km optical fiber transmission, the system successfully achieved secure transmission of the dichroic image, processed 1,536 information blocks, each containing 2 10 continuous variables, with a block error rate of approximately 8.78 × 10 − 5 , and ultimately achieved the secrecy capacity of 2.44 × 10 5 bits per second.
Abstract Quantum secure direct communication (QSDC) is a communication method based on quantum mechanics and it is used to transmit secret messages. Unlike quantum key distribution, secret messages can be transmitted directly on a quantum channel with QSDC. Higher channel capacity and noise suppression capabilities are key to achieving long-distance quantum communication. Here, we report a continuous-variable QSDC scheme based on mask-coding and orbital angular momentum, in which the mask-coding is employed to protect the security of the transmitting messages and to suppress the influence of excess noise. The combination of orbital angular momentum and information block transmission effectively improves the secrecy capacity. In the 800 information blocks ×1310 bits length 10-km experiment, the results show a statistical average bit error rate of 0.38%, a system excess noise value of 0.0184 SNU, and a final secrecy capacity of 6.319 × 10 6 bps. Therefore, this scheme reduces error bits while increasing secrecy capacity, providing a solution for long-distance large-scale quantum communication, which is capable of transmitting text, images and other information of reasonable size.
Quantum secure direct communication (QSDC) is convenient for the direct transmission of secure messages without requiring a prior key exchange by two participants, offering an elegant advantage in transmission security. The traditional implementations usually focus on the discrete-variable (DV) system, whereas its continuous-variable (CV) counterpart has attracted much attention due to its compatibility with existing optical infrastructure. In order to address its practical deployment in harsh environments, we propose a microwave-based scheme for the CV-QSDC that leverages entangled microwave quantum states through free-space channels in cryogenic environments. The two-step scheme is designed for the secure direct communication, where the classical messages can be encoded by using Gaussian modulation and then transmitted via displacement operations on microwave quantum states. The data processing procedures involve microwave entangled state generation, channel detection, parameter estimation, and so on. Simulation results demonstrate the feasibility of the microwave-based CV-QSDC, highlighting its potential for secure communication in integrated superconducting and solid-state quantum technologies.