Mikio Fujiwara

We show joint propagation of CV-QKD with successful secret key generation over 24 hours with 100 state-of-the-art EDFA amplified coherent WDM channels amounting to a total classical bitrate of 18.3~Tbit/s.

We considered research and development aimed at improving the operability and scalability of large-scale QKD net-works (QKDNs) by introducing hierarchical control architecture. This paper focus on a distributed-control QKDN within such a hierarchical large scale QKDN and presents the design and implementation of a QKDN controller (QKDN-C) that selects appropriate key relay routes in response to control instructions from an orchestrator (QKDN-O). In particular, it describes a method for distributed key relay and routing table management, in which the routing tables of individual key managers (KMs) are dynamically updated on instructions from the QKDN-O. It also shows that, in a hierarchically structured QKDN, coordinated operation between the QKDN-O and distributed QKDNs enable key re-laying to be realized over optimal routes.

In quantum key distribution (QKD) networks, key resources are limited, and efficient key relay is essential for stable multi-site operation. However, evaluating how effective the key relay paths are requires large-scale and iterative verification using real networks, which entails substantial costs and practical constraints. This paper reports on a simulator that was developed to evaluate the performance and effectiveness of key relay path computation models in large-scale QKD networks. The simulator takes as input the results of key relay path selection obtained from various routing models and simulates fluctuations in the amount of key across the entire QKD network. Using this simulator, we confirmed that it is possible to systematically verify whether the key relay paths are suitable for efficient and stable operation of QKD networks under various network scales and operational conditions. The results provide a useful foundation for the design and evaluation of future QKD networks.

To construct a large-scale quantum key distribution network (QKDN) as future secure infrastructure, it is necessary interwork many QKDNs. Here, we demonstrate an interoperable key relay between two different types of QKDNs: a centralized QKDN and a distributed QKDN. In the demonstration, we build an experimental environment for interworking by using physical QKDNs and implement three fundamental functions (key relay, delivery confirmation, and status information collection) for performing key relay between heterogeneous QKDNs.

The key relay protocol (KRP) plays an important role in improving the performance and the security of quantum key distribution (QKD) networks. On the other hand, there is also an existing research field called secure network coding (SNC), which has similar goal and structure. We here analyze differences and similarities between the KRP and SNC rigorously. We found, rather surprisingly, that there is a definite gap in security between the KRP and SNC; that is, certain KRPs achieve better security than any SNC schemes on the same graph. We also found that this gap can be closed if we generalize the notion of SNC by adding free public channels; that is, KRPs are equivalent to SNC schemes augmented with free public channels.

We developed a genome sequence data storage system using a distributed storage system on a quantum key distribution (QKD) network and have successfully demonstrated secure storage and data reconstruction for genome sequence data. The proposed system thus has potential for use as a distributed storage system in genome analysis.