  Continuous-variable quantum key distribution (CV-QKD) protocols based on
coherent detection have been studied extensively in both theory and experiment.
In all the existing implementations of CV-QKD, both the quantum signal and the
local oscillator (LO) are generated from the same laser and propagate through
the insecure quantum channel. This arrangement may open security loopholes and
also limit the potential applications of CV-QKD. In this paper, we propose and
demonstrate a pilot-aided feedforward data recovery scheme which enables
reliable coherent detection using a "locally" generated LO. Using two
independent commercial laser sources and a spool of 25 km optical fiber, we
construct a coherent communication system. The variance of the phase noise
introduced by the proposed scheme is measured to be 0.04 (rad^2), which is
small enough to enable secure key distribution. This technology also opens the
door for other quantum communication protocols, such as the recently proposed
measurement-device-independent (MDI) CV-QKD where independent light sources are
employed by different users.

Quantum Physics