Experimental demonstration of counteracting imperfect sources in a practical one-way quantum-key-distribution system

In a practical quantum-key-distribution system, photon source and small operational errors cause intensity fluctuations inevitably, which cannot be ignored for a precise estimation on the single-photon fraction. In this paper, we demonstrated an efficient three-intensity decoy method scheme on top of the one-way Faraday-Michelson Interferometric system, combining an active monitoring with existing commercial apparatus to inspect fluctuations instantly. With this faithful detection for the upper bound of the fluctuation, the secure quantum key distribution is unconditionally realized with whatever type of intensity errors, which declares the utility and potential of decoy theory and active monitoring for quantum key distribution in practical use.