A mesoscopic quantum eraser

Motivated by a recent experiment by Buks et al. (Nature 391 (1998) 871) we consider electron transport through an Aharonov-Bohm interferometer with a quantum dot in one of its arms. The quantum dot is coupled to a quantum sys tem with a finite number of states acting as a which-path detector. The Aha ronov-Bohm interference is calculated using a two-particle scattering appro ach for the joint transitions in detector and quantum dot. Tracing over the detector yields dephasing and a reduction of the interference amplitude. W e show that the interference can be restored by a suitable measurement on t he detector and propose a mesoscopic quantum eraser based on this principle .