Hua-Lei Yin

Quantum digital signatures (QDS) provide information-theoretic security for data integrity, authenticity, and nonrepudiation by exploiting the laws of quantum mechanics. While existing QDS protocols have achieved significant efficiency improvements via one-time universal hashing, they rely on trusted quantum devices, requiring precise characterization and stable calibration of state preparation and measurement processes, which in practice cannot be fully guaranteed. Here, we propose a device-independent QDS protocol based on the violation of Bell inequalities and the entropy accumulation theorem, thereby ensuring information-theoretic security against general coherent attacks without assumptions on the internal functioning of the devices. We analyze the protocol performance under realistic noise and loss models and show that it is feasible with current experimental technology over multikilometer distances. Furthermore, by leveraging state-of-the-art single-photon sources, the achievable distance can be extended to several tens of kilometers. Our results establish device-independent QDS as a practical and scalable cryptographic primitive for secure applications in quantum networks with untrusted devices.

Zero-knowledge proofs (ZKPs) are widely applied in digital economies, such as cryptocurrencies and smart contracts, for establishing trust and privacy between untrusted parties. Classical ZKPs rely on computational assumptions and are vulnerable to quantum attacks. While a recent advance suggests quantum-sound symmetric relativistic ZKPs for the graph three-coloring problem without computational assumptions, the high round complexity, which leads to unachievable runtime and overall randomness cost, renders them impractical for real-life deployment. To overcome this, we develop an efficient asymmetric relativistic ZKP protocol using relativistic bit commitments, and prove its quantum soundness by relating it to the nonlocal Clauser-Horne-Shimony-Holt (CHSH) game. Our protocol achieves a linear relationship between the round complexity and the number of edges, and thus significantly improves practical feasibility. In addition, we implement a proof-of-principle experiment which completes all interactive rounds in about 0.22 seconds and requires an overall randomness cost of 430.81 MB. Our work illustrates the powerful potential of integrating special relativity with quantum theory in trustless cryptography, paving the way for robust applications against quantum attacks in distrustful Internet environments.

Quantum key distribution (QKD) theoretically offers information-theoretic security. The prevailing approach is the prepare-and-measure BB84 protocol, which implements QKD using a conventional laser rather than a single-photon source via the decoy-state method. However, side-channel attacks targeting sources severely threaten system security. Despite extensive efforts, including a fully passive scheme, this vulnerability persists even with a perfect single-photon source. Here, we propose a source-independent (SI) QKD protocol that resolves all known and unknown source-side attacks without pre-sending an entanglement source. Aligning with advances in quantum light sources, our protocol simultaneously doubles the transmission distance while remaining robust against imperfection of source. Theoretical analysis shows that non-classical light source provides practical security advantages unattainable with a conventional laser.

Resonance fluorescence arises from the coherent interaction of laser light with a two-level system and constitutes a quantum light source exhibiting single-photon emission and antibunching, making it a fundamental building block for future quantum networks. Our recent work [ Nat. Commun. 16 , 6453 ( 2025 ) 10.1038/s41467-025-61884-x ] demonstrates that under continuous-wave excitation and in the absence of pure dephasing, the single-time joint state of resonance fluorescence and the two-level system can be described by a pure entangled state. Here, we analyze the cross-correlation and auto-correlation properties of the quantum optical field generated by the interference of resonance fluorescence with laser light at the resonance excitation frequency. Simulation results indicate that by varying the intensity or phase of the interfering laser light, the higher-order coherence of the post-interference quantum optical field transitions from anti-bunching to super-bunching behavior, consistent with recent theoretical and experimental advances by mean-field engineering. This approach offers a complementary framework to characterize and manipulate the multiphoton quantum optical fields.

Quantum key distribution (QKD) with deterministic single photon sources has been demonstrated over intercity fiber and free-space channels. The previous implementations relied mainly on polarization encoding schemes, which are susceptible to birefringence, polarization-mode dispersion and polarization-dependent loss in practical fiber networks. In contrast, time-bin encoding offers inherent robustness and has been widely adopted in mature QKD systems using weak coherent laser pulses. However, its feasibility in conjunction with a deterministic single-photon source has not yet been experimentally demonstrated. In this work, we construct a time-bin encoded QKD system employing a high-brightness quantum dot (QD) single-photon source operating at telecom wavelength. Our proof-of-concept experiment successfully demonstrates the possibility of secure key distribution over fiber link of 120 km, while maintaining extraordinary long-term stability over 6 h of continuous operation, that is highest secure key rate among the time-bin QKDs based on single-photon sources. This work provides the first experimental validation of integrating a QD single-photon source with time-bin encoding in a telecom-band QKD system. This development signifies a substantial advancement in the establishment of a robust and scalable QKD network based on solid-state single-photon technology.

Quantum Byzantine Agreement (QBA), a cornerstone of quantum blockchain, offers inherent advantages in security and fault tolerance over classical protocols, guaranteed by the laws of quantum mechanics. However, existing multiparty QBA protocols face challenges for large-scale deployment due to exponential communication complexity or reliance on complex multi-particle entanglement. To address this, we propose a multiparty circular QBA protocol that adopts a semi-decentralized architecture, leveraging circular message gathering and quantum digital signatures to achieve quadratic communication complexity and enhanced fault tolerance. Our protocol is experimentally feasible, requiring only weak coherent states, and is compatible with existing star-shaped quantum networks. Simulations conducted on a global satellite-to-ground network demonstrate that the protocol sustains high consensus rates among multiple users, even when employing different key generation protocols under realistic conditions. This work presents a scalable framework for large-scale QBA networks, establishing the foundation for a practical quantum blockchain that enables secure and fault-tolerant decentralized services.

Photon-number superposition states are a valuable resource for quantum information processing and can be deterministically generated using advanced quantum-dot (QD) platforms. Here, we propose a twin-field quantum key distribution (TF-QKD) protocol that employs photon-number superposition states of the form 1− t |0⟩+ e ^{i ϕ} t |1⟩. Numerical simulations show that the protocol outperforms existing laser-based TF-QKD schemes in secret-key rate and transmission distance, surpasses the repeaterless bound, enabling secure communication beyond 210 km under experimentally achievable conditions. A key advantage is its direct compatibility with existing QD technology. As integrated, solid-state, on-demand single-photon sources, QDs inherently provide high stability, scalability, and photon indistinguishability, making them well suited for deployment in large-scale quantum networks. Overall, our work demonstrates a practical pathway toward high-performance long-distance TF-QKD and highlights the broader potential of solid-state non-classical light sources for quantum networking architectures.