Hua-Lei Yin

Asynchronous measurement-device-independent quantum key distribution (AMDI-QKD) stands out for its experimental simplicity and high key rate generation. To simplify the system further, we devise a post-measurement compensation scheme to accurately estimate the mutual frequency offset between two compact lasers using just the announced quantum-signal detection results, thereby obviating the need for optical reference light. As a result, we demonstrate an AMDI-QKD system operating at 2.5 GHz and achieving secure key rates (SKRs) of 537 and 101 kbit/s at distances of 100 and 201 km, respectively. By leveraging ultra-stable lasers, we achieve the highest SKRs with measurement-device-independent security within the 100 to 400 km range.

The development of quantum networks is paramount towards practical and secure communications. Quantum digital signatures (QDS) offer an information-theoretically secure solution for ensuring data integrity, authenticity, and nonrepudiation, rapidly growing from proof-of-concept to robust demonstrations. However, previous QDS systems relied on expensive and bulky optical equipment, limiting large-scale deployment and reconfigurable networking construction. Here, we introduce and verify a chip-based QDS network, placing the complicated and expensive measurement devices in the central relay while each user needs only a low-cost transmitter. We demonstrate the network with a three-node setup using an integrated encoder chip and decoder chip. By developing a 1-decoy-state one-time universal hashing-QDS protocol, we achieve a maximum signature rate of 0.0414 times per second for a 1 Mbit messages over fiber distances up to 200 km, surpassing all current state-of-the-art QDS experiments. This study validates the feasibility of chip-based QDS, paving the way for large-scale deployment and integration with existing fiber infrastructure.

A post-measurement coincidence pairing technique is proposed to hold a repeater-like advantage and simultaneously mitigate the global phase tracking. Here, we demonstrate a practical asynchronous MDI-QKD system with an excellent long-term stability. With the use of two independent economical acetylene-stabilized fiber lasers, we achieve a secure key rate (SKR) of 14.65 bit/s over 504 km fiber, beating the absolute repeaterless bound by 1.18 times. Our work will advance the development of economical and efficient quantum network.

Quantum fingerprinting (QF) enables exponential reduction of information transmission in communication complexity tasks. Coherent QF implementations rely upon a direct optical link to maintain coherence between the users, violating the no-shared-randomness rule. Here, we propose and experimentally demonstrate a novel QF protocol based on asynchronous coincidence pairing from the interference results between independent, remotely prepared coherent fields. Over a length of 20 km telecom fiber, our setup has outperformed the classical algorithm, for the first time without being susceptible to shared randomness. This work advances the practical application of QF in communication complexity.

Quantum conference key agreement facilitates the secure communication among multiple parties through multipartite entanglement, which is anticipated as an important cryptographic primitive for future quantum networks. However, the experimental complexity and low efficiency associated with synchronous detection of multipartite entanglement state have significantly hindered the practical application. Here, we propose a measurement-device-independent conference key agreement protocol utilizing asynchronous Greenberger-Horne-Zeilinger state measurement and achieve a linear scaling of the conference key rate among multiple parties, which has the similar performance with the single-repeater scheme in quantum network. The asynchronous measurement strategy bypasses the necessity for complex global phase-locking technologies, concurrently extending the intercity transmission distance with composable security in finite key regime. Our work also showcases the advantages of the asynchronous pairing concept in multiparty quantum entanglement.

Quantum network allows for multi-user applications that bring advantages that are unattainable with a classical network. A crucial application of quantum networks is quantum conference key agreement (QCKA), which enables remote nodes to efficiently share information-theoretic secure group key by leveraging the laws of quantum mechanics. However, the efficacy of QCKA is hampered by inherent losses in optical fibers and the increasing number of users, impacting both bit rate and range. Here we introduce multi-field (MF) QCKA scheme, where independently sets of phase-randomized optical fields are generated at remote locations, later combining them at a central measuring station. Employing the post-measurement pairing technique, we post-select optical fields with the same random phase, establishing Greenberger-Horne-Zeilinger correlations to distill a secret conference key. This method ensures that the communication efficiency of MF-QCKA scales linearly with communication transmittance and remains independent of the number of users. Using components similar to twin-field quantum key distribution, MF-QCKA can be implemented in a practial and scalable fashion. For three-user scenario, our protocol can overcome the performance limitation of QCKA without quantum memory in the finite regime. By mitigating the impact of optical fiber losses and accommodating a larger user base, MF-QCKA protocol represents a promising step forward in the realm of quantum communication, ensuring secure and efficient parallel communication in complex quantum networks.

E-commerce, a type of trading that occurs at a high frequency on the Internet, requires guaranteeing the integrity, authentication and non-repudiation of messages through long distance. As current e-commerce schemes are vulnerable to computational attacks, quantum cryptography, ensuring information-theoretic security against adversary's repudiation and forgery, provides a solution to this problem. However, quantum solutions generally have much lower performance compared to classical ones. Besides, when considering imperfect devices, the performance of quantum schemes exhibits a notable decline. Here, we demonstrate the whole e-commerce process of involving the signing of a contract and payment among three parties by proposing a quantum e-commerce scheme, which shows resistance of attacks from imperfect devices. Results show that with a maximum attenuation of 25 dB among participants, our scheme can achieve a signature rate of 0.82 times per second for an agreement size of approximately 0.428 megabit. This proposed scheme presents a promising solution for providing information-theoretic security for e-commerce.

In this presentation, I will introduce two of our recent works: experimental realization of measurement-device-independent (MDI) quantum key distribution (QKD) [arXiv:1209.6178] and unambiguous-state-discrimination (USD) attack on a decoy-state QKD system without phase randomization [arXiv:1304.2541]. On one hand, the MDI-QKD is able to shield all practical attacks realized so far. We experimentally demonstrate the MDI-QKD protocol by implementing high-speed and low-noise up-conversion single photon detectors. The security of MDI-QKD relies on a trusted source scenario, where the decoy-state method is assumed. On the other hand, phase randomization is commonly ignored from the decoy-state method. We demonstrate a USD attack on a decoy-state QKD system when the phase randomization is ignored.