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JSAP-OSA Joint Symposia

Real-time 70 Gbit/s, 128 QAM quantum noise stream cipher transmission over 100 km with secret keys delivered by continuous variable quantum key distribution system

Masataka Nakazawa

Published Jan 1, 2017• 3 citations
Publisher

Abstract

We have been intensively studying quantum noise stream cipher (QNSC) transmission technique using quadrature amplitude modulation (QAM) with a view to realizing a high-speed and long-distance secure communication system [1]. In this talk, we describe our recent demonstration of an on-line 70 Gbit/s, 128 QAM/QNSC transmission over 100 km with a continuous variable quantum key distribution (CV-QKD) system [2], in which a shared key is transmitted online via the CV-QKD so that the key is shared for a certain time period with absolutely no risk of being eavesdropped.

DOI
10.1364/jsap.2017.7p_a410_1

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We have been intensively studying quantum noise stream cipher (QNSC) transmission technique using quadrature amplitude modulation (QAM) with a view to realizing a high-speed and long-distance secure communication system [1]. In this talk, we describe our recent demonstration of an on-line 70 Gbit/s, 128 QAM/QNSC transmission over 100 km with a continuous variable quantum key distribution (CV-QKD) system [2], in which a shared key is transmitted online via the CV-QKD so that the key is shared for a certain time period with absolutely no risk of being eavesdropped.
We report the first on-line high-speed and large-capacity secure optical communication system. This was realized by combining a quadrature amplitude modulation/quantum noise stream cipher technology where a coherent multi-level optical signal is hidden in quantum noise and a quantum key distribution technology where secure key delivery is realized with an extremely weak laser light comparable to a single photon. In our security analysis, we adopt a realistic assumption, namely, that an adversary does not have a lossless fiber. To show the advantage of this scheme, we performed a 128 QAM, 70-Gbit/s single-channel transmission over 100 km with a spectral efficiency of as high as 10.3 bits/s/Hz. This is the fastest data rate and highest spectral efficiency yet achieved in quantum cryptography with a realistic assumption.
We describe in detail our recent demonstration of a 10 Tbit/s secure physical layer transmission that we achieved by using digital coherent QAM quantum noise stream cipher (QNSC) and injection-locked WDM techniques. We used an FPGA-based transmitter and receiver to demonstrate a 165 channel polarization-multiplexed WDM 5 Gbaud 128 QAM/QNSC (70 Gbit/s) on-line transmission over 160 km with a spectral efficiency of 6 bit/s/Hz. In the present system, the original 128 QAM data were encrypted in a 1024 × 1024 QAM format using basis information. The encrypted signal was then masked by a large ASE noise, which reduced the detection “success” probability for an eavesdropper to 0.13% for each symbol. Furthermore, the multiplicity of the original QAM data and the seed keys used to generate the basis information were arbitrarily changed with time, which makes the decryption much more difficult.