High-speed polarization coding in a quantum key distribution system

We present a high-speed polarization-coding method, which makes use of phase modulation, for use in a quantum key distribution (QKD) system. This technique has been introduced into a QKD system for the first time. A completely quantum mechanical method is employed to describe quantum information processing here. Experiments on a balanced element for polarization coding by phase modulation are described in detail. The experimental results demonstrate that this technique can encode or decode polarization at high speed (with feasibility in the GHz range) and low voltage (a few volts) successfully.