Efficient Implementation of Time-Bin BB84-QKD Protocol with Phase-Randomized Weak Coherent States

Quantum key distribution (QKD) allows to share symmetric encryption keys between two remote parties, in an unconditionally secure way. Most of the QKD protocols rely on the usage of single photons, which however are difficult to produce in a practical way. The introduction of the decoy-method [1] allowed the usage of attenuated laser pulses whilst demonstrating unconditionally security. Since each qubit needs to carry a random global phase, this protocol relies on phase-randomized coherent states [2] which are normally produced exploiting gain switching mode [3].