Quantum secure direct communication (QSDC) based on entanglement can directly transmit confidential information. However, the inability to simultaneously distinguish the four sets of encoded entangled states limits its practical application. Here, we explore a QSDC network based on time-energy entanglement and sum-frequency generation. In total,15 users are in a fully connected QSDC network, and the fidelity of the entangled state shared by any two users is >97%. The results show that when any two users are performing QSDC over 40 km of optical fiber, the fidelity of the entangled state shared by them is still >95%, and the rate of information transmission can be maintained above 1 Kbp/s. Our result demonstrates the feasibility of a proposed QSDC network and hence lays the foundation for the realization of satellite-based long-distance and global QSDC in the future.
Quantum secure direct communication (QSDC) based on entanglement can directly transmit confidential information. However, the inability to simultaneously distinguish the four sets of encoded entangled states limits its practical application. Here, we explore a QSDC network based on time-energy entanglement and sum-frequency generation. In total,15 users are in a fully connected QSDC network, and the fidelity of the entangled state shared by any two users is >97%. The results show that when any two users are performing QSDC over 40 km of optical fiber, the fidelity of the entangled state shared by them is still >95%, and the rate of information transmission can be maintained above 1 Kbp/s. Our result demonstrates the feasibility of a proposed QSDC network and hence lays the foundation for the realization of satellite-based long-distance and global QSDC in the future.
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.
In this paper, a Quantum Secure Direct Communication (QSDC) network is proposed and investigated. The protocol allows four independent users to exchange their confidential information pairwise, with the help of a central controller that regulates authorization and separation among concurrent communication flows. Quantum channels are used only in the preliminary distribution of the entangled states; afterward, no quantum-encoded message is transmitted. All message extraction is local, through direct measurements. This drastically reduces reliance on quantum transmission, constrains photon-loss effects, minimizes quantum hardware overhead, and increases the achievable message throughput compared to previous QSDC protocols. Given that the protocol utilizes entanglement distribution instead of consecutive quantum modulation, a very promising perspective is opened for scalability in future multi-party quantum communication systems. The simulation results confirm the strong robustness against classical and quantum adversarial strategies, testified by high detection probabilities and abort conditions that prevent information leakage.
Quantum secure direct communication (QSDC) offers a practical way to realize a quantum network which can transmit information securely and reliably. Practical quantum networks are hindered by the unavailability of quantum relays. To overcome this limitation, a proposal has been made to transmit the messages encrypted with classical cryptography, such as post-quantum algorithms, between intermediate nodes of the network, where encrypted messages in quantum states are read out in classical bits, and sent to the next node using QSDC. In this paper, we report a real-time demonstration of a computationally secure relay for a quantum secure direct communication network. We have chosen CRYSTALS-KYBER which has been standardized by the National Institute of Standards and Technology to encrypt the messages for transmission of the QSDC system. The quantum bit error rate of the relay system is typically below the security threshold. Our relay can support a QSDC communication rate of 2.5 kb/s within a 4 ms time delay. The experimental demonstration shows the feasibility of constructing a large-scale quantum network in the near future.
Quantum communication has developed into various classes, including recent novel quantum secure direct communication (QSDC) schemes. The QSDC method transmits confidential information directly between parties over a quantum channel without requiring a shared private key. Even though QSDC offers improved security guarantees and reduces the possibility of security loopholes, practical applications such as secure information rates, long-distance quantum communication and networking, and integration with existing technologies still requires improvement. Meanwhile, advances in artificial intelligence (AI) and machine learning (ML) continue to revolutionize several fields, including quantum communication, which is challenging to control and maintain effectively for optimum performance. Various ML techniques have been applied to quantum communication systems to mitigate noise-induced errors, analyze communication protocols, and optimize secure key generation rates. While this represents a significant development and has the potential to address challenges facing QSDC applications, we are unaware of ML applications specifically improving QSDC systems. Due to this, we bring forward the discussion and unveil the critical need to integrate AI and ML models into QSDC to enhance security, improve fault tolerance, increase communication distance, and optimize resource allocation. Consequently, this work establishes a practical framework for unlocking the full potential of QSDC protocols and, more broadly, practical quantum communication.
Quantum communication provides an absolute security advantage, and it has been widely developed over the past 30 years. As an important branch of quantum communication, quantum secure direct communication (QSDC) promotes high security and instantaneousness in communication through directly transmitting messages over a quantum channel. The full implementation of a quantum protocol always requires the ability to control the transfer of a message effectively in the time domain; thus, it is essential to combine QSDC with quantum memory to accomplish the communication task. In this Letter, we report the experimental demonstration of QSDC with state-of-the-art atomic quantum memory for the first time in principle. We use the polarization degrees of freedom of photons as the information carrier, and the fidelity of entanglement decoding is verified as approximately 90%. Our work completes a fundamental step toward practical QSDC and demonstrates a potential application for long-distance quantum communication in a quantum network.
Quantum communication realizes information-theoretic security using photonic quantum states, for example, quantum secure direct communication (QSDC), which can achieve secure and reliable communication in a channel with both noise and eavesdroppers. However, QSDC suffers from large losses and short communication distances, thus being impractical for applications. Here, we have proposed a one-way quasi-QSDC protocol with single photons. This protocol enables the simultaneous transmission of information and key exchange using the same single photons and is robust against loss and error because it uses error correction and spectrum expansion techniques. In a proof-of-principle demonstration using weak coherent pulses, the system achieved a real-time secure transmission rate of 2.38 kilobits per second over a 104.8-kilometer standard telecommunication fiber, which set world records in both aspects. This system paved the way for the practical application of QSDC and offers a unique method to detect eavesdropping online, which is crucial in certain circumstances.