As a popular decentralized and distributed database exhibiting transparency and unforgeability, blockchain has received widespread attention. At the time of writing, its security hinges on classical cryptography, which maintains a high grade of security by exploiting the potentially excessive computational complexity of mathematical problems to be solved by state-of-the-art computers. However, as computational technology develops, this encryption philosophy is likely to be challenged and there is a risk of ’store now and decrypt later’ attacks. A compelling solution to this security threat is to intrinsically integrate blockchain with quantum technology. Against this background, we propose a quantum blockchain scheme relying on quantum secure direct communication (QSDC). Specifically, we conceive QSDC-based blockchain for identity verification, message encryption, and consensus. We also propose an optical network based realization of the proposed QSDC-aided blockchain using present-day technology. Our simulations quantify the benefits of the scheme, especially in terms of its resource utilization. This work provides a new prospect for the intrinsic fusion of quantum information technology and blockchain technology, paving the way for its rapid commercialization.

Quantum network extends the ability to transmit information securely from two-party communication to multi-party communication with arbitrarily long distances. The efficiency of secure communication in a quantum network depends on both the topology of the network and the strategy of communication relays. In this paper, we propose a strategy to build a quantum network integrating various types of quantum secure direct communication (QSDC) schemes. A cost optimization model is presented to measure the cost of transmitting secure messages in a quantum network. Within the model, two types of quantum network strategies, the quantum circuit switching strategy and the quantum packet switching strategy, are proposed and compared. Numerical simulations in a specific network show that the quantum packet switching strategy is more favorable in future quantum networks taking into account robustness and cost required when using different types of QSDC schemes.

Quantum networks leverage the principles of quantum mechanics for information transmission and processing, providing attractive functionalities absent in classical networks. Realizing entanglement distribution among network nodes is one of the important tasks in quantum network applications. Meanwhile, as free-space quantum communication technology advances, protocols adaptable to mobile terminal resource allocation become practical. Here, we propose the message-oriented quantum entanglement distribution protocol called quantum stream control transmission protocol (QSCTP) and illustrate its application within the entanglement distribution network. Through prototype network testing, we validate its efficacy in the intended application, offering a promising avenue for the seamless integration of quantum networks and paving the path toward their application.

Quantum secure direct communication (QSDC) directly transmits confidential information over a quantum channel. In this context, it is important to take into account the multi-photon effect when using weak coherent laser pulses as the quantum source. Here we propose a multi-intensity QSDC (MI-QSDC) protocol where laser pulses having different intensities are used for secure communication in a fashion reminiscent of decoy states, where only signal intensity pulses are used for key exchange. Pulses of all intensities are used both for information transmission and eavesdropping detection in the MI-QSDC. The statistical fluctuations associated with practical finite block-length in QSDC are also considered and a tight secrecy capacity bound is given. The simulation results show that the proposed protocol is capable of communicating over a distance on the order of 100 km by relying on a finite block-length of sending 1014pulses.

Solving systems of linear equations is important both in classical and quantum computing. Harrow-Hassidim-Lloyd algorithm (HHL algorithm), a quantum algorithm for solving systems of linear equations, has achieved exponentially improved performance compared with corresponding classical algorithm. We will show in this article that the HHL algorithm is actually a duality quantum algorithm with non- unitary transformation from initial to the final state. We present a detailed realization of the HHL algorithm in a duality quantum computing formalism that allows the construction of non- unitary operations. The divider structure, combinor structure, and the total quantum circuit for the HHL algorithm in the duality quantum computing formalism are given explicitly.