Quantum secure direct communication (QSDC) is an evolving quantum communication framework based on transmitting secure information directly through a quantum channel, without relying on key-based encryption such as in quantum key distribution (QKD). Optical QSDC protocols, utilizing discrete and continuous variable encodings, show great promise for future technological applications. We present the first table-top continuous-variable QSDC proof of principle, analyzing its implementation and comparing the use of coherent against squeezed light sources. A simple beam-splitter attack is analyzed by using Wyner wiretap channel theory. Our study illustrates the advantage of squeezed states over coherent ones for enhanced security and reliable communication in lossy and noisy channels. Our practical implementation, utilizing mature telecom components, could foster secure quantum metropolitan networks compatible with advanced multiplexing systems.
Quantum secure direct communication (QSDC) is an evolving quantum communication framework based on transmitting secure information directly through a quantum channel, without relying on key-based encryption such as in quantum key distribution (QKD). Optical QSDC protocols, utilizing discrete and continuous variable encodings, show great promise for future technological applications. We present the first table-top continuous-variable QSDC proof of principle, analyzing its implementation and comparing the use of coherent against squeezed light sources. A simple beam-splitter attack is analyzed by using Wyner wiretap channel theory. Our study illustrates the advantage of squeezed states over coherent ones for enhanced security and reliable communication in lossy and noisy channels. Our practical implementation, utilizing mature telecom components, could foster secure quantum metropolitan networks compatible with advanced multiplexing systems.
Quantum secure direct communication (QSDC) is a recently developed practical solution, which transmits secret messages between legitimate parties, without setting up a cryptographic key. The QSDC protocols are mainly classified into entanglement-based and single photon-based approaches. Their security has been analyzed using Wyner's wiretap channel theory, and their secrecy capacity has been calculated [1]. Hitherto, QSDC protocols have been implemented on optical fiber and free-space channels, all in discrete-variable (DV) encoding that employs single-photon detectors [1]–[2]. However, the implementation of continuous-variable (CV) QSDC, in which the keys are encoded into the quadratures of quantized electromagnetic fields (e.g., coherent states) and detected via homodyne techniques, is preferred due to: its lower costs, excellent integrability with existing optical communication systems, easy implementation from state preparation to measurement, and fast experimental realization. Furthermore, it has been proved that CV-QSDC protocols using squeezed states show higher tolerance in purely lossy channels and enhanced robustness against highly noisy ones, as well [3]. Nevertheless, none of the CV-QSDC protocols employing either coherent or squeezed quantum states have been implemented yet.
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.
Quantum secure direct communication (QSDC) can transmit secret messages without keys, making it an important branch of quantum communication. We present a hybrid entanglement-based quantum secure direct communication (HE-QSDC) protocol with simple linear optical elements, combining the benefits of both continuous variables (CV) and discrete variables (DV) encoding. We analyze the security and find that the QSDC protocol has a positive security capacity when the bit error rate is less than 0.073. Compared with previous DV QSDC protocols, our protocol has higher communication efficiency due to performing nearly deterministic Bell-state measurement. On the other hand, compared with CV QSDC protocol, this protocol has higher fidelity with large α. Based on these advantages, our protocol may provide an alternative approach to realize secure communication.
Quantum secure direct communication (QSDC) leverages quantum states to transmit information securely and reliably over a noisy, lossy, and wiretapped quantum channel. It has been proven to be information-theoretically secure. Recent experiments show that QSDC can enable long-distance communication and large-scale networking with existing technologies. In particular, free-space QSDC has the unique advantages and prospects for practical large-scale application. Here, we review the QSDC basics and the progress of free-space QSDC. The feasibility of satellite-based QSDC and the future directions of free-space QSDC are discussed. We propose a practical and feasible route that can make immediate application of QSDC in real life.
Abstract Quantum secure direct communication (QSDC) promises unconditional security for direct information transmission without pre-shared keys. However, practical implementations using weak coherent sources face critical challenges from device imperfections, such as emitting vacuum states and multiphoton states. Here, we introduce a heralded QSDC protocol leveraging squeezed-state superposition in a cross-Kerr nonlinear medium, where single-mode squeezed states interfere with coherent states to generate superposition states via post-measurement selection. We have considered three detector models to analyze the heralding performance of light sources under different conditions, including the ideal photon number detector, the practical photon number detector, and the practical photon detector. Our proposed protocol dramatically reduces the vacuum state ratio compared to weak coherent pulse sources, and the multiphoton ratio is still maintained at a low level, significantly enhancing the security information capacity and the maximum secure communication distance. We perform numerical simulations and compare our protocol with the optical single-photon-based QSDC protocol. At 7.5 km with an average photon number of 0.01, the security information capacity improves by 13.42 times, 12.20 times, and 8.64 times for three detector models. Extending to 17.5 km, these gains will be to 277.59 times, 251.58 times, and 172.91 times. Our work provides a robust framework for high-capacity, long-distance, secure quantum communication systems. PACS numbers: 03.67.Pp, 03.67.Hk, 03.65.Ud