An Eavesdropping Detecting Approach Based on Mode--Mode Correlation

We find that second-order coherence as well as a Hanbury--Brown--Twiss intensity interferometer may provide an optimal approach for eavesdropping detection in the quantum key distribution based on two-mode squeezed vacuum states. With this approach, eavesdropping can be easily detected without sacrificing extra secret bits as the test key. In addition, the efficiency of the quantum key distribution protocol is enhanced greatly.