Research and Development

We were one of the members of Tokyo QKD Network Demonstration in October 2010, where we have successfully implemented a QKD system (Fig.1) over an installed fiber link of 24km (13 dB loss), as well as the QKD smart phones (Fig. 2) connected to it. In the new project starting in 2011, our main goal is to refine our QKD system further such that it can achieve simultaneously, a stable key generation rate for a long span of time, and a high-level security which is as close as possible to the theoretical one in practical environment. We also aim to develop new applications of the QKD smart phones, in which voice and video data are encrypted by one-time pad with secure keys shared by QKD. They would benefit potential customers such as governmental or financial institutions who demand high-end network security.

In order to realize the above purposes, we revise the optical block by installing dedicated planar light circuits (PLCs) and an active feedback control scheme to stabilize the visibility of quantum channel. Our recent theoretical results on privacy amplification and the finite size effect lead to an efficient algorithm will be applied for enabling fully software-based implementation of efficient key distillation. In this algorithm, hybrid automatic repeat request based on LDPC codes achieve high code rates of error correction, and the FFT-based multiplication algorithm of the Toeplitz matrices realizes a high-speed privacy amplification.

Fig. 1

Fig. 1

Fig. 2

Fig. 2