差動4値位相シフト量子鍵配送(DQPS‐QKD)の鍵生成実験

Kyo Inoue, Yuuki Iwai, Tetsuya Kukita +1 more

A quantum key distribution (QKD) scheme named differential-quadrature-phase-shift (DQPS) QKD is presented. A transmitter sends a weak coherent pulse train with a phase of {0, π}{ π/2. 3π /2} for each pulse, and a receiver measures it with either one of two delay interferometers respectively having bias phases of 0 and π/2. The scheme introduces the idea of the BB84 protocol into differential-phase-shift (DPS) QKD, making the system robust against a sequential attack, and may guarantee the unconditional security as in BB84.

恵介 米良

駿 川上

Quantum key distribution (QKD) allows two distant parties to share a secret key and realizes a communication with information-theoretic security by combining it with one-time-pad encryption.Since the Bennett-Brassard 1984 (BB84) protocol was proposed, a large number of researches on QKD have been conducted from both aspects of theory and implementations.For implementations of QKD, weak coherent pulses (WCP) are heavily used as optical signals because they are easily generated by typical lasers and attenuators.The security for QKD with WCP has been also studied along the development of the implementations.In this thesis, the security analysis of the QKD with WCP is considered and further developed from two aspects.First, the security of the differential-quadrature-phase-shift (DQPS) protocol is proved.The DQPS protocol has essentially the same set up as the phase-encoding BB84 (PE-BB84) protocol, which is one of the most frequently demonstrated protocols.Since the known proof techniques for the BB84 protocol is not directly applicable, a modified approach is developed which is suitable for the DQPS protocol.As a result, the advantage of the DQPS protocol in the key generation rate over the PE-BB84 protocol is shown in the asymptotic limit where the size of communication data is assumed to be infinite.Second, a new method for security analysis with finite-key size is proposed as a suitable method for QKD protocols using WCP.Differently from the current method based on simple random sampling, the proposed method relies on Bernoulli sampling, which is associated with binomial distribution.The security of the BB84 protocol is proved by using the Bernoulli-sampling method, enabling a simpler analysis with a smaller number of parameters to be estimated compared to the method with simple random sampling.The required number of detected signals to generate a secret key is shown to be smaller than 10 4 , which is drastic improvement from the number ∼ 10 7 obtained in the previous result.The proposed method is also applied to the DQPS protocol, and its advantage over the PE-BB84 protocol is certified even in the finite-key regime.i

利守 本庄, 康弘 都倉

Kazuki Maeda

Muataz Alhussein, Kyo Inoue, Toshimori Honjo

This paper demonstrates phase-encoding BB84-based QKD experiments with active basis selection using one interferometer with no phase and polarization controls, unlike conventional BB84-QKD experiments. A countermeasure against detector blinding attack is also implemented. © 2019 The Author(s)