Probing Bell Diagonal State without Disturbing Its Correlations

In this paper, we propose a very simple scheme to probe the quantum and classical correlation including quantum entanglement of Bell diagonal state. In the probing process, the correlation of Bell diagonal state, even the state itself, is not disturbed, which means a non-destructive probing. In addition, our scheme can be performed even though the two qubits of the Bell diagonal state are separate in space. (general)