Quantum key distribution via frequency translation in a nonlinear optical fiber

We propose a simple and original implementation of the BB84 quantum key distribution protocol via a quantum frequency-translation process in a nonlinear optical fiber. Unlike most conventional quantum key distribution implementations, which rely on the photon polarization/phase, encoding quantum information in the photon frequency state is inherently more stable against mechanical and/or thermal fluctuations over transmission media such as optical fibers. We also show the proposed scheme to be naturally expandable to larger character sets, and demonstrate a straightforward extension to a four-character alphabet (qu-quarts), providing enhanced security for quantum key distribution applications.