The Delayed-Choice Quantum Eraser Leaves No Choice

A realizable delayed-choice quantum eraser, using a modified Mach-Zehnder (MZ) interferometer and polarization entangled photons, is theoretically analyzed here. The signal photon goes through MZ interferometer, the of idler provides path information for photon. setup very similar to eraser experimentally studied by Vienna group. In class erasers with discrete output states, it easy see that delayed mode leaves no choice experimenter. which-way always erased, every detected fixes state idler, thus gives on precisely how traversed two paths. analysis shows first experimental demonstration fact experimenter, erased. Additionally shown this argument holds even in conventional two-slit eraser. Every registered anywhere screen, two-state detector unique mutually unbiased basis. experiments, role basis sets detector, has been overlooked till now.