Experimental study on Gaussian-modulated coherent states quantum key distribution over standard telecom fiber

Abstract

In this paper, we present a fully fiber-based one-way Quantum Key Distribution (QKD) system implementing the Gaussian-Modulated Coherent States (GMCS) protocol. The system employs a double Mach-Zehnder Interferometer (MZI) configuration in which the weak quantum signal and the strong Local Oscillator (LO) go through the same fiber between Alice and Bob, and are separated into two paths inside Bob's terminal. To suppress the LO leakage into the signal path, which is an important contribution to the excess noise, we implemented a novel scheme combining polarization and frequency multiplexing, achieving an extinction ratio of 70dB. To further minimize the system excess noise due to phase drift of the double MZI, we propose that, instead of employing phase feedback control, one simply let Alice remap her data by performing a rotation operation. We further present noise analysis both theoretically and experimentally. Our calculation shows that the combined polarization and frequency multiplexing scheme can achieve better stability in practice than the time-multiplexing scheme, because it allows one to use matched fiber lengths for the signal and the LO paths on both sides of the double MZI, greatly reducing the phase instability caused by unmatched fiber lengths. Our experimental noise analysis quantifies the three main contributions to the excess noise, which will be instructive to future studies of the GMCS QKD systems. Finally, we demonstrate, under the "realistic model" in which Eve cannot control the system within Bob's terminal, a secure key rate of 0.3bit/pulse over a 5km fiber link. This key rate is about two orders of magnitude higher than that of a practical BB84 QKD system.

21 pages, 9 figures

References in corpus (5)

• Quantum key distribution over 25 km with an all-fiber continuous-variable system
• Security of coherent state quantum cryptography in the presence of Gaussian noise
• Quantum key distribution with "dual detectors"
• Quantum key distribution based on a Sagnac loop interferometer and polarization-insensitive phase modulators
• Asymptotic correctability of Bell-diagonal quantum states and maximum tolerable bit error rates

Cited by in corpus (2)

• Field test of a continuous-variable quantum key distribution prototype
• Feasibility of free space quantum key distribution with coherent polarization states