Nondistortion quantum interrogation using Einstein-Podolsky-Rosen entangled photons - art. no. 044103

We propose a scheme for nondistortion quantum interrogation defined as an i nteraction-free measurement that preserves the internal state of the object being detected. In our scheme. two Einstein-Podolsky-Rosen entangled photo ns are used as the probe and polarization-sensitive measurements are perfor med at the four ports of the Mach-Zehnder interferometer. In comparison wit h the previous single-photon scheme, it is shown that the two-photon approa ch has a higher probability of initial state preserving interrogation of an atom prepared in a quantum superposition. In the case that the presence of the atom is not Successfully detected, the experiment can be repeated sinc e the initial state of the atom is unperturbed.