  Quantum key distribution (QKD) provides an attractive solution for secure
communication. However, channel disturbance severely limits its application
when a QKD system is transfered from the laboratory to the field. Here, a
high-speed Faraday-Sagnac-Michelson QKD system is proposed that can
automatically compensate for the channel polarization disturbance, which
largely avoids the intermittency limitations of environment mutation. Over a
50-km fiber channel with 30-Hz polarization scrambling, the practicality of
this phase-coding QKD system was characterized with an interference fringe
visibility of 99:35% over 24 hours, and a stable secure key rate of 306k bits/s
over 7 days without active polarization alignment.
