Optical transmission of frequency-coded quantum bits with WDM synchronization

Quantum key distribution enables absolutely secure communication between two parties, making them able to share a secret that will be used in the posterior message encryption. Here we shall report the experimental implementation of an optical qubits transmission system compatible with BB84-based protocols. The photonic qubits preparation and measurement are performed by a double-modulation process according with the relative phase of a WDM carried synchronized radiofrequency signal, in the way that the quantum states are coded in the optical sidebands. A filtering scheme is applied to the further sidebands selection, delivering the qubits to single-photon detectors.