Progress Report
Scalable and Robust Integrated Quantum Communication System[1] Development of new network architectures and protocols to realize robust and large-scale communication networks
Progress until FY2024
1. Outline of the project
To realize a distributed quantum computer, it is essential not only to interconnect multiple quantum computers but also to build an integrated distributed quantum information processing environment that fully utilizes their combined processing capabilities, enabling unified execution of quantum applications. Achieving this requires three critical components: quantum computers themselves, communication interfaces, and quantum communication networks. Quantum communication networks, in particular, must exhibit efficiency, scalability, fault tolerance, and operability without performance degradation, even when handling large quantities of quantum data.
Within the broader research and development program, this project provides foundational technologies necessary for practical distributed quantum computing. It aims to facilitate early realization of large-scale fault-tolerant quantum computation through networking quantum computers developed in other projects.
During this fiscal year, we began finalizing hardware metrics for quantum network demonstration and initiated implementation of classical aspects of quantum link protocols. We detailed inter-module interface specifications and advanced research toward implementation through simulations scaled up to 1000 nodes. Additionally, we clarified noise reduction technologies and dynamic network design guidelines, performing numerical analysis to compare performance across various purification protocols.
Specifically, this task aims to achieve optimal network design from architectural, protocol, and classical control perspectives. Through system design, testbed measurements, and corresponding network simulations, we elucidated the achievable system performance.
2. Outcome so far
This year, detailed evaluations of parameters such as error probabilities and photon loss rates were conducted to facilitate quantum network practical implementation, alongside the development of implementation models for quantum communication protocols and concrete error-handling strategies.
Furthermore, space-division and time-division schemes for link-layer construction were explored, initiating the implementation of high-precision timing synchronization methods, including FPGA-based Time-to-Digital Converters and Dragonfly-type synchronization (TidyFly). Focusing on Q-Fly architecture as a network interface, the first physical demonstration experiments using optical switches were performed. Correspondingly, quantum network specifications were established, device control software (PnPQ) was developed, and repeater graph-state-based architectures were designed, including preliminary silicon photonics chip development.
Additionally, efforts were directed towards developing quantum state purification algorithms and addressing job scheduling challenges. Regarding noise reduction, the quantum relay system employing bosonic codes was evaluated and improved significantly by integrating quantum memory into cat codes. Dynamic structural analysis of latency-affected networks was conducted, proposing optimal configurations and protocol designs. Tools for purifying bipartite and multipartite states were also developed, assessing modular approaches to surface code implementation feasibility. Research aimed at simplifying quantum computer implementation via direct GHZ state generation commenced. Finally, foundational patterns for fault-tolerant communication combining cryogenic superconducting qubits and optical quantum communication were defined, establishing various essential performance indicators for realization.
3. Future plans
Moving forward, intelligent network design combining theory, experimentation, and simulation will continue to be pursued to achieve efficient large-scale distributed quantum computers. Specifically, the goal is to integrate developments in quantum optical communication, quantum memory and relay technology, and distributed quantum applications using communication protocols and classical control techniques, operating testbeds as cohesive communication systems. Collaboration with other projects will also be emphasized to guide future developments from the perspective of large-scale distributed quantum computing architecture.