Quantum secure direct communication (QSDC) enables the direct and secure transmission of messages without the need for prior key distribution, offering a groundbreaking paradigm in quantum communication. This paper presents a novel symmetric QSDC protocol that ensures immunity to collective-phase and collective-rotation noises while enabling efficient and two-way message transfer. The proposed protocol features an innovative approach where qubits are transmitted only during the initial entanglement sharing phase, eliminating the need to send message carrying qubits thereafter. By leveraging this design, the protocol minimizes vulnerability to external noise and eavesdropping attempts. The symmetry of the protocol allows both parties to exchange messages seamlessly and securely, ensuring equal communication procedure. Analytical analysis and theoretical proofs demonstrate the robustness and security of the protocol under non-secure quantum channel, marking a significant advancement in practical quantum communication systems. The proposed scheme follows an entanglement-based QSDC paradigm, where confidential information is embedded into quantum correlations rather than being directly transmitted over the quantum channel.
Quantum secure direct communication (QSDC) enables the direct and secure transmission of messages without the need for prior key distribution, offering a groundbreaking paradigm in quantum communication. This paper presents a novel symmetric QSDC protocol that ensures immunity to collective-phase and collective-rotation noises while enabling efficient and two-way message transfer. The proposed protocol features an innovative approach where qubits are transmitted only during the initial entanglement sharing phase, eliminating the need to send message carrying qubits thereafter. By leveraging this design, the protocol minimizes vulnerability to external noise and eavesdropping attempts. The symmetry of the protocol allows both parties to exchange messages seamlessly and securely, ensuring equal communication procedure. Analytical analysis and theoretical proofs demonstrate the robustness and security of the protocol under non-secure quantum channel, marking a significant advancement in practical quantum communication systems. The proposed scheme follows an entanglement-based QSDC paradigm, where confidential information is embedded into quantum correlations rather than being directly transmitted over the quantum channel.
Quantum secure direct communication (QSDC) is one of the most important branches of quantum communication. In contrast to the quantum key distribution (QKD) which distributes a secure key between distant parties, QSDC directly transmits secret message instead of sharing key in advance. To establish a secure QSDC protocol, on the one hand, the security of the quantum channel should be confirmed before the exchange of the secret message. On the other hand, the quantum state should be transmitted in a quantum data block since the security of QSDC is based on the error rate analysis in the theories on statistics. Compared with the deterministic quantum key distribution (DQKD) which can also be used to transmit deterministic information, QSDC schemes do not need extra classical bits to read the secret message except for public discussion. In this article, we introduce the basic principles of QSDC and review the development in this field by introducing typical QSDC protocols chronologically. The first QSDC protocol was proposed by Long and Liu, which can be used to establish a common key between distant parties. In their scheme, the method for transmitting quantum states in a block by block way and in multiple steps was proposed and the information leakage before eavesdropping detection was solved. Subsequently, Deng et al. presented two pioneering QSDC schemes, an entangled-state-based two-step QSDC scheme and a single-photon-state-based quantum one-time pad scheme, in which the basic principle and criteria for QSDC were pointed out. From then on, many interesting QSDC schemes have been proposed, including the high-dimension QSDC scheme based on quantum superdense coding, multi-step QSDC scheme based on Greenberger-Horne-Zeilinger states, QSDC scheme based on quantum encryption with practical non-maximally entangled quantum channel, and so on. We also introduce the anti-noise QSDC schemes which were designed for coping with the collective-dephasing noise and the collective-rotation noise, respectively. In 2011, Wang et al. presented the first QSDC which exploited the hyperentangled state as the information carrier and several QSDC schemes based on the spatial degree of freedom (DOF) of photon, single-photon multi-DOF state and hyperentanglement were proposed subsequently. In addition to the point-to-point QSDC schemes, we also review the QSDC networks. Finally, a perspective of QSDC research is given in the last section.
We present two novel quantum secure direct communication (QSDC) protocols over different collective-noise channels. Different from the previous QSDC schemes over collective-noise channels, which are all source-encrypting protocols, our two protocols are based on channel-encryption. In both schemes, two authorized users first share a sequence of EPR pairs as their reusable quantum key. Then they use their quantum key to encrypt and decrypt the secret message carried by the decoherence-free states over the collective-noise channel. In theory, the intrinsic efficiencies of both protocols are high since there is no need to consume any entangled states including both the quantum key and the information carriers except the ones used for eavesdropping checks. For checking eavesdropping, the two parties only need to perform two-particle measurements on the decoy states during each round. Finally, we make a security analysis of our two protocols and demonstrate that they are secure.
An improved quantum secure direct communication (QSDC) protocol is proposed in this paper. Blocks of entangled photon pairs are transmitted in two steps in which secret messages are transmitted directly. The single logical qubits and unitary operations under decoherence free subspaces are presented and the generalized Bell states are constructed which are immune to the collective noise. Two steps of qubit transmission are used in this protocol to guarantee the security of communication. The security of the protocol against various attacks are discussed.
Quantum secure direct communication (QSDC) enables the message sender to directly transmit messages to the message receiver through quantum channel without keys. Environmental noise is the main obstacle for QSDC's practicality. For enhancing QSDC's noise robustness, we introduce the quantum error correction (QEC) code into QSDC and propose the QSDC protocol based on the redundancy code. This QSDC protocol correlates atomic state with the electron–photon entangled pairs and transmits photons in quantum channels for two rounds. The parties can construct the remote atomic logical entanglement channel and decode messages with the heralded photonic Bell state measurement (BSM) and single electron measurement. This QSDC protocol is unconditionally secure in theory and has some advantages. First, benefiting from the heralded photonic BSM, it can eliminate the influence from photon transmission loss and has the potential to realize long-distance secure message transmission. Second, taking use of the error correction function of the repetition code, the error rate caused by the decoherence during the second round of photon transmission can be reduced, which can reduce the message error and increase the secret message capacity. Third, the whole protocol is feasible under current experimental condition. Our QSDC protocol can be extended to use other stronger QEC code. It provides a promising method to promote QSDC's practicality in the future.
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) can transmit secret messages directly from one user to another without first establishing a shared secret key, which is different from quantum key distribution. In this paper, we propose a novel quantum secure direct communication protocol based on signal photons and Bell states. Before the execution of the proposed protocol, two participants Alice and Bob exchange their corresponding identity IDA and IDB through quantum key distribution and keep them secret, respectively. Then the message sender, Alice, encodes each secret message bit into two single photons (| 01〉or|10〉) or a Bell state , and composes an ordered secret message sequence. To insure the security of communication, Alice also prepares the decoy photons and inserts them into secret message sequence on the basis of the values of IDA and IDB. By the secret identity IDA and IDB, both sides of the communication can check eavesdropping and identify each other. The proposed protocol not only completes secure direct communication, but also realizes the mutual authentication. The security analysis of the proposed protocol is presented in the paper. The analysis results show that this protocol is secure against some common attacks, and no secret message leaks even if the messages are broken. Compared with the two-way QSDC protocols, the presented protocol is a one-way quantum communication protocol which has the immunity to Trojan horse attack. Furthermore, our proposed protocol can be realized without quantum memory.