Yoshimichi Tanizawa

In this paper, we describe a key routing method for large-scale quantum key distribution (QKD) networks. The proactive and dynamic key routing method decides the amount of key for distribution which is based on the key usage history of each application and stored key status of each link. Furthermore, we also propose a key routing method which applies multiple routing protocols according to the network domain of destination. The method provides key usage efficiently and promotes scalability for large-scale QKD networks.

We improved secure bit rates by multiplexing QKD systems without any additional optical dark fibers.

As the volume of data and connections exchanged across telecom/datacom networks continues to increase, there is a growing need for technologies that deploy quantum key distribution (QKD) on a large scale in a practical and sustainable manner. To realize high-speed, real-time communication of large-volume data using one-time pad cryptography with QKD modules, it will be important to multiplex QKD modules in the future. Furthermore, it is necessary to consider the physical size of the device for the practical application of multiplexed QKD modules. In this study, we focused on miniaturizing the key distillation process required at the back end of the QKD chip. To reduce the size of the device, it is necessary to estimate as accurately as possible the minimum computing power required to run the key distillation process for the target secret key rate (SKR). However, the performance of the key distillation process requires computing power and involves the exchange of messages via classical channels. Therefore, we evaluate the performance by a network simulator before performing evaluations on the actual equipment. In this paper, we focus on the behavior of classical communication paths in the multiplexed QKD system, which is a problem in studying the key distillation process, and we evaluate it with the simulator. Specifically, we clarify the relationship between the required performance of the key distillation process (i.e., throughput) and the target SKR, which is necessary to realize a part of the key distillation process in hardware.

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.