Stable differential phase shift quantum key distribution with a key creation efficiency of 3/4

In this letter, we demonstrate that a high key creation efficiency can be achieved in a stable differential phase shift quantum key distribution system by using three cascaded Mach-Zehnder interferometers. A pulse is split into four independent pulses, and the bit information is carried by one of the three phase differences between the sequential pulses. Any birefringence effects and polarization-dependent losses in the long-distance fiber are automatically compensated with a Faraday mirror. Due to the neatly use of three cascaded interferometers, the key creation efficiency reaches 3/4. (C) 2004 American Institute of Physics.