Unlocking the quantum secret: Military applications of Chinese QSDC networks and the geopolitical challenge for the United States - ANALYSIS
- Gabriele Iuvinale
- 2 giu
- Tempo di lettura: 14 min
China's recent breakthroughs in Quantum Secure Direct Communication (QSDC) pose a direct risk to the United States and are a crucial strategic asset for Chinese national defense and economic security. The U.S. Congress has already acknowledged these innovations as a significant threat, underscoring the urgent need to protect sensitive data and critical infrastructure.
QSDC, pioneered by Professor Long Guilu's team, is an ultra-secure communication technology that directly encodes information into quantum states, making it inherently immune to attacks, even from future quantum computers. Unlike Quantum Key Distribution (QKD), QSDC transmits messages directly and covertly, offering superior secrecy and resilience vital for military and intelligence operations.
Teams led by Professor Chen Xianfeng (Shanghai Jiao Tong University) and Professor Li Yuanhua (Shanghai University of Electric Power) have driven pioneering advancements:
In 2021, they built a 15-user QSDC network over 40 km of optical fiber, demonstrating high fidelity.
They developed a one-way quasi-QSDC protocol, achieving a world-record secure transmission rate of 2.38 kilobits per second over 104.8 km, a 4,760-fold improvement over previous systems, sufficient for text, images, and voice.
Their most recent achievement is a 300 km fully-connected QSDC network in 2025, linking four users with high fidelity, enabled by innovations like a double-pumped structure and strategic introduction of extra noise for resilience.
These advancements transform QSDC from theory into practical technology with clear dual-use military implications. The ability to ensure secure, eavesdropping-resistant communications over long distances and among multiple users is fundamental for defense and intelligence operations.
China's massive and sustained investment (estimated over $15 billion) and strategic focus on quantum technologies, as outlined in its Five-Year Plans, position it at the global forefront. The lack of evidence that Chen and Li studied in the USA reinforces the notion that China is independently cultivating top talent in this strategic sector. This rapid progression underscores the necessity for the U.S. to understand and respond to this emerging national security threat.
Executive Summary
Recent and significant Chinese breakthroughs in quantum communication technologies, particularly in Quantum Secure Direct Communication (QSDC), have profound implications for national and military security, positioning these innovations as a crucial strategic asset. This report unequivocally confirms that the teams of Professor Chen Xianfeng from Shanghai Jiao Tong University and Professor Li Yuanhua from Shanghai University of Electric Power have conducted substantial and pioneering research that directly builds upon the fundamental theory of Secure Direct Quantum Communication (QSDC) developed by Professor Long Guilu. This collaboration represents a critical acceleration in the practical realization of QSDC. Their joint efforts have led to significant milestones, including the construction of a 15-user QSDC network , achieving record transmission speeds over long distances with one-way quasi-QSDC , and, notably, the recent demonstration of a 300 km fully-connected QSDC network. These advancements directly address long-standing challenges in quantum communication related to distance, scalability, and noise resilience. Such developments are fundamental for the transition of QSDC from a theoretical concept to an implementable technology, paving the way for ultra-secure communication infrastructures vital for future governmental, financial, and broader digital security applications.
1. Introduction to Quantum Secure Direct Communication (QSDC)
This section lays the groundwork by defining QSDC and highlighting Professor Long Guilu's pioneering contributions, establishing the theoretical foundation upon which subsequent research, including the collaborative work of Professors Chen and Li, is based.
1.1. Definition of Quantum Secure Direct Communication (QSDC)
Quantum Secure Direct Communication (QSDC) is an innovative secure communication paradigm, designed to transmit information directly and securely by encoding it into quantum states. Its intrinsic security is rooted in the fundamental principles of quantum mechanics, particularly superposition, entanglement, and the no-cloning theorem, which prevent eavesdropping without detection. Unlike traditional cryptographic methods that rely on computational complexity, QSDC's security is guaranteed by the laws of physics, making it immune even to attacks from future quantum computers. This characteristic makes it particularly valuable for applications requiring maximum confidentiality and resilience, such as those in military and intelligence contexts. Key features of QSDC include robust eavesdropping detection and prevention, seamless compatibility with existing network infrastructures, simplified management protocols, and the ability for covert data transmission.
1.2. Professor Long Guilu's Fundamental Contributions to QSDC
Professor Long Guilu, a leading figure at Tsinghua University and Vice President of the Beijing Institute of Quantum Information Science, is widely recognized as the originator of QSDC. He proposed the first QSDC protocol, often referred to as the "efficient protocol," in 2000. His initial theoretical framework introduced the concept of direct communication using Einstein-Podolsky-Rosen (EPR) pairs without the prerequisite of a pre-established key. This represented a significant departure from existing quantum communication paradigms.
The consistent attribution of QSDC's origin to Professor Long Guilu across multiple sources highlights his seminal influence and establishes his theory as the undisputed conceptual foundation for subsequent research in this field.
1.3. Distinction between QSDC and Quantum Key Distribution (QKD)
While both QSDC and Quantum Key Distribution (QKD) leverage quantum principles for secure communication, they serve fundamentally different purposes. QKD's primary function is to establish a secure cryptographic key between two parties, which is then used for classical message encryption. It involves extracting secure keys from noisy quantum signals through post-processing techniques like privacy amplification, and typically requires the disclosure of all photon bases.
In contrast, QSDC directly encodes and transmits the actual information on quantum states, eliminating the need for a separate key establishment phase. It employs forward encoding before transmission and only reveals the bases of qubits used for eavesdropping checks, offering a more streamlined communication process and potentially fewer security vulnerabilities. This distinction underscores QSDC's unique advantage in direct message transmission, simplifying communication steps and reducing potential security loopholes. For military and intelligence applications, QSDC's ability to transmit secret messages directly, without the need for a pre-shared key and with the capability to detect any interception attempt, makes it a superior security technology for critical communications and sensitive data transfer. The clear differentiation between QKD and QSDC is not merely a defining point, but highlights QSDC's strategic advantage in scenarios requiring direct, keyless information transfer and enhanced secrecy. This positions QSDC as a distinct and complementary, rather than simply alternative, solution within the broader quantum communication landscape, justifying dedicated research efforts like those of Professors Chen and Li. This deeper insight into QSDC's distinctive value underscores the importance of collaborative research.
2. Profiles of Key Institutions and Research Teams
This section describes the individual strengths and contributions of the key institutions and researchers involved, providing context for their collaborative success.
2.1. Professor Chen Xianfeng's Team at Shanghai Jiao Tong University (SJTU)
Shanghai Jiao Tong University (SJTU) positions itself as a prominent global leader in quantum research in China, with significant contributions spanning quantum communication, quantum computing, and quantum metrology. The university actively fosters interdisciplinary collaboration and is a key player in China's national quantum initiatives.
Professor Chen Xianfeng is a leading researcher affiliated with the State Key Laboratory of Advanced Optical Communication Systems and Networks within the School of Physics and Astronomy at SJTU. His team's work includes significant research in integrated photonics, focusing on developing high-performance on-chip devices for simulating physical models. This expertise is directly relevant to building miniaturized, stable, and scalable quantum communication components, such as ultra-bright integrated Bragg reflection waveguide quantum sources. SJTU's broader quantum computing activities also include developing quantum algorithms for partial differential equations and continuous variable quantum information, with funding allocated to "quantum machine learning and quantum internet" initiatives. This indicates a comprehensive engagement with both fundamental and applied aspects of quantum networks.
2.2. Professor Li Yuanhua's Team at Shanghai University of Electric Power
Professor Li Yuanhua is a key researcher associated with the Department of Physics, Shanghai Key Laboratory of Materials Protection and Advanced Materials in Electric Power, at Shanghai University of Electric Power. His research interests encompass innovative approaches to quantum communication, particularly the application of machine learning frameworks, such as Bidirectional Encoder Representations from Transformers (BERT), to enhance the performance of noisy quantum communications, especially in superdense coding. This work directly addresses the critical challenge of noise in quantum channels. Professor Li has also contributed to the theoretical aspects of quantum communication complexity, exploring resource requirements for quantum communication models.
Professor Chen's expertise in integrated photonics focuses on hardware and infrastructure, creating compact, high-performance physical platforms for quantum communication. Conversely, Professor Li's work on machine learning for noise mitigation addresses the inherent fragility of quantum states in noisy environments, a fundamental challenge in long-distance quantum communication. When these two distinct yet complementary areas of expertise converge in collaborative research on QSDC networks (as observed in the 300 km network ), it enables a more comprehensive and robust approach to overcoming the multifaceted challenges of practical quantum communication. This integrated strategy, combining hardware innovation with advanced signal processing, is a deeper reason for their success.
3. Collaborative Progress in QSDC, Based on Long Guilu's Theory
This section forms the core of the report, detailing the specific achievements of the collaboration between Professors Chen and Li, explicitly linking them to Long Guilu's foundational work, and emphasizing their significance.
3.1. Initial Collaborative Milestone: The 15-User QSDC Network (2021)
A significant initial collaborative achievement involved Professor Chen Xianfeng (Shanghai Jiao Tong University) and Professor Li Yuanhua (then affiliated with Jiangxi Normal University ) in constructing a 15-user Quantum Secure Direct Communication (QSDC) network in 2021. This pioneering network enabled the direct transmission of confidential information among 15 distinct users, marking a crucial step towards multi-user quantum communication. Operating over 40 km of optical fiber, the network demonstrated high fidelity of entangled states (above 97% overall, and over 95% for 40 km transmissions) and maintained an information transmission rate exceeding 1 Kbp/s. This experimental demonstration explicitly built upon the efficient QSDC protocol originally proposed by Long and Liu , validating the scalability of Long's theoretical framework to complex multi-user scenarios.
The transition from theoretical protocols to a functional 15-user network represents a critical step in the evolution of QSDC. It demonstrates that Long Guilu's fundamental theory is not limited to simple point-to-point communication but can be scaled to support multiple users, a prerequisite for any practical communication network. This initial collaborative success provided empirical evidence of QSDC's networking potential, building confidence and laying the groundwork for even more ambitious, longer-distance, and higher-capacity systems. It showed that QSDC's "seamless network compatibility" attribute was achievable in practice.
3.2. Breakthrough in One-Way Quasi-QSDC
A major advancement in QSDC, involving Chinese researchers including those from Tsinghua University (Professor Long Guilu's institution), Beijing Academy of Quantum Information Sciences, and North China University of Technology, focused on developing a one-way quasi-QSDC protocol with single photons. This innovation directly addresses a significant limitation of previous QSDC protocols, which often required quantum states to travel back and forth, leading to substantial system loss and severely limiting communication performance and distance. By enabling one-way transmission, the protocol effectively halves the required quantum state transmission distance, drastically reducing loss.
The protocol also integrates techniques such as error correction and spectrum expansion, enhancing its robustness against noise and errors. It uniquely allows for simultaneous transmission of information and key exchange (STIKE) using the same single photons. In a proof-of-principle demonstration, this system achieved a world-record real-time secure transmission rate of 2.38 kilobits per second (kbps) over a 104.8-kilometer standard optical fiber network, representing a remarkable 4,760-fold improvement over a 2022 system that only achieved 0.5 bps over 100 km. This rate is sufficient for transmitting text, image files, and voice.
The shift to "one-way" QSDC is not merely a technical modification, but a fundamental engineering of the protocol to overcome the exponential loss inherent in bidirectional quantum state transmission. This directly addresses the "major hurdle" and "impracticality" identified in earlier QSDC development. The 4,760-fold increase in data rate transforms QSDC from a concept with extremely limited transmission capacity (0.5 bps) to a system capable of transmitting meaningful data (2.38 kbps ). This quantitative leap indicates a critical maturation, moving QSDC from purely theoretical demonstrations to a technology with tangible practical utility for real-world high-security applications. Professor Long Guilu's own comment on this breakthrough underscores its importance as a direct evolution of his foundational work.
3.3. World Record: The 300 km Fully-Connected QSDC Network (2025)
The most recent and impactful collaborative work directly involving Professor Chen Xianfeng (Shanghai Jiao Tong University) and Professor Li Yuanhua (Shanghai University of Electric Power) is detailed in their 2025 paper, "A 300-km fully-connected quantum secure direct communication network". This study, based on the quantum direct communication theory from the Beijing Institute of Quantum Information Science and Professor Long Guilu's team at Tsinghua University, specifically addresses the critical limitations of transmission distance and user count in realizing large-scale scalable quantum communication networks.
The team successfully demonstrated QSDC over an unprecedented distance of 300 km, connecting four users in a fully-connected network topology. This represents a substantial extension of the communication range for QSDC, far surpassing previous records. Key technical innovations that enabled this achievement include:
A double-pumped structure: The researchers innovatively utilized double-pumped light parameter sub-volume conversion technology to build a quantum entanglement distribution system with high anti-interference capability. This design enhances the generation of polarization-entangled photon pairs across multiple quantum correlation links, crucial for entangling multiple users.
The introduction of extra noise: Counterintuitively, this technique is employed before photon pair distribution to compensate for quantum noise, thereby improving the fidelity of shared entangled states between users and extending the transmission distance.
A custom-made on-chip periodically poled lithium niobate (PPLNOI): This integrated photonic component is vital for the efficient and stable generation of entangled photons.
The network maintained high fidelity of entangled states, consistently above 85%, between users even over the 300 km distance, verifying the reliability of the solution in long-distance communication. The photonic logarithm reaching the receiving node after 300 kilometers of transmission is still 300 x 400Hz (Hertz), which means that after encoding, the theoretical communication speed can reach several bits per second. This work is presented as a new foundation for the future realization of long-distance, large-scale quantum communications and explicitly cites Long Guilu's foundational work on QSDC, demonstrating a clear line of research.
The achievement of 300 km QSDC is a significant quantitative leap, but the methods employed reveal deeper implications. The "introduction of extra noise" is a sophisticated and non-obvious technique that indicates a mature understanding of quantum error management, moving from passive mitigation to active compensation. This suggests that researchers are now actively manipulating quantum channel characteristics to extend performance, rather than simply battling intrinsic limitations. Furthermore, the use of "on-chip periodically poled lithium niobate (PPLNOI)" underscores the critical role of integrated photonics in achieving compact, stable, and scalable quantum systems. This integration of advanced theoretical protocols with cutting-edge hardware engineering is the underlying causal relationship enabling these breakthroughs, directly addressing the "impracticality" of QSDC mentioned in and paving the way for compact integrated platforms.
Below, Table 1 offers a comparative overview of key QSDC experimental results, highlighting the progression and evolution of the technology.
Table 1: Key QSDC Experimental Results and Their Evolution
4. Technological Innovations and Impact
This section synthesizes the technological advancements and discusses their broader implications for the field of quantum communication.
4.1. Overcoming Key QSDC Limitations
The collaborative research, alongside independent advancements by Long Guilu, has addressed and largely overcome long-standing challenges that hindered the practical implementation of QSDC: specifically, significant photon loss over distance, limited communication range, and difficulties in scaling to multiple users. The development of one-way protocols drastically reduces photon loss by eliminating the need for bidirectional quantum state transmission, a major bottleneck in previous systems. The innovative use of noise introduction and robust error correction techniques demonstrate advanced strategies for maintaining quantum state fidelity over noisy and long-distance channels.
4.2. Transition from Theory to Practical Implementation
The achieved performance metrics, particularly the 2.38 kbps data rate over 104.8 km and the 300 km fully-connected network , unequivocally mark a crucial transition for QSDC. These results move the technology beyond theoretical demonstrations and into the realm of real-world applicability. The significant increase in data rate and distance makes QSDC practical for transmitting various forms of information, including text, image files, and even voice, expanding its potential utility beyond mere proof-of-concept.
4.3. Role of Integrated Photonics and Advanced Engineering
Professor Chen Xianfeng's broader expertise in integrated photonics is implicitly fundamental to the advancements in compact and scalable QSDC systems. The mention of "on-chip periodically poled lithium niobate (PPLNOI)" in the 300 km network paper highlights the direct application of integrated photonic technology in achieving high-performance quantum communications. This emphasis on on-chip devices and stable quantum sources is crucial for reducing the size, cost, and complexity of QSDC systems, making them more viable for widespread deployment.
The transition of QSDC from a theoretical concept to practical application is not solely due to breakthroughs in quantum physics, but equally, if not more so, to sophisticated engineering. The available data reveals a clear trend: the theoretical insights from Long Guilu's work are being made practical through engineering innovations such as integrated photonics (Chen's expertise ), one-way transmission protocols , and advanced noise management techniques (Li's expertise and the "extra noise" technique in ). This causal relationship, where engineering prowess translates theoretical quantum advantages into implementable systems, is a key underlying theme. The ability to achieve high data rates and long distances is a direct consequence of this comprehensive engineering effort, making QSDC truly "practical for applications".
5. Implications and Future Prospects
This section will discuss the broader significance of these advancements and their potential future impact.
5.1. Potential Applications in High-Security Sectors
The significantly improved performance and scalability of QSDC systems make them ideal candidates for adoption in sectors requiring the highest levels of information security. This includes critical areas such as government affairs, national defense, and financial transactions. QSDC's intrinsic features, such as covert transmission and immunity to frequency licensing or radio frequency interference , make it a unique and highly desirable choice for sensitive applications where data protection is paramount.
In particular, quantum communication technologies, including QSDC, are considered a strategic asset for national defense and economic security. Chinese advancements in this field have clear dual-use military implications, extending to quantum cryptography, networks, computing, and space experiments. QSDC ensures secure, eavesdropping-resistant communications critical for defense operations. Its ability to transmit information directly without the need for pre-established key distribution and the use of secure relays that do not require trusted nodes are particularly advantageous for military and intelligence applications, where absolute secrecy and resilience are of primary importance. The drive towards such ultra-secure communications is also fueled by concerns about cyber espionage and the need to develop "post-quantum" or "quantum-resistant" cryptography to guard against future quantum computer threats.
5.2. Contribution to the Quantum Internet
The advancements in long-distance and multi-user QSDC networks are fundamental building blocks for the realization of a comprehensive quantum internet. The ability to distribute entangled states and securely communicate information among multiple detached users over extended distances is a prerequisite for a global quantum network. The research by Professors Chen and Li directly contributes to solving the challenges of transmission distance and user scalability that limit large-scale quantum communication networks.
5.3. China's Leadership in Quantum Technologies
The consistent progress in QSDC, particularly the world-record achievements by Chinese research teams, underscores China's significant and sustained investment in quantum technologies. This national commitment, formalized in initiatives like the 13th and 14th Five-Year Plans with billions of dollars in funding, positions China at the forefront of global quantum research and development.
The continuous and rapid progression of QSDC capabilities – from initial protocols to 15-user networks, then to one-way transmission with high data rates, and finally to 300 km fully-connected networks – is not merely a series of isolated academic achievements. This sustained and aggressive advancement, particularly in China, indicates a clear strategic imperative. Consistent government funding and explicit goals to build a "nationwide quantum communication infrastructure" reveal that QSDC is viewed as a critical component of national security and technological leadership. This is further contextualized by the "race to develop quantum-resistant encryption standards" , implying that QSDC is considered a proactive defense against the long-term threat of quantum computers to classical cryptography.
6. Conclusion
The collaborative research undertaken by Professor Chen Xianfeng's team at Shanghai Jiao Tong University and Professor Li Yuanhua's team at Shanghai University of Electric Power represents an undeniable and profound advancement in Quantum Secure Direct Communication. Their work directly and significantly builds upon the fundamental theory established by Professor Long Guilu.
Their joint efforts have not only validated and extended the theoretical foundations of QSDC but have also achieved critical experimental milestones, dramatically improving key performance indicators such as transmission distances, data rates, and network user capacity. These achievements are a testament to the power of inter-institutional collaboration in pushing the boundaries of quantum technology.
These advancements are crucial for accelerating QSDC's transition from a theoretical concept to a practical and implementable technology. They lay a robust foundation for the development of ultra-secure communication networks, which will be essential for safeguarding information in a future increasingly reliant on quantum-resistant cryptographic solutions and the ultimate realization of a global quantum internet.
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