Theory of the effect of geomagnetic field on plug-and-play schemes for fiber-based quantum key distribution systems

Quantum key distribution based on phase encoding in long-distance communication fiber

A robust two-way quantum key distribution system based on phase encoding is demonstrated in 50 km and 100 km commercial communication fiber. The system can automatically compensate for birefringence effects and remain stable over 23 h. A low quantum bit error rate and high visibility are obtained. Furthermore, the storage fiber is unnecessary and train of pulses is only needed in the test with 100 km fiber.

Nonintrusive characterization of long-fiber-link birefringence

We propose a technique for estimating the birefringence correlation length and beat length of a long fiber link based on the measurement of two parameters only, the mean differential group delay and the mean Faraday rotation of a fiber with a small magnetic field applied. The two parameters can be measured without the need of cutting the fiber.