THE EFFECT OF PATH OBSERVATION ON QUANTUM INTERFERENCE PATTERN

A Gedankenexperiment is presented on the effect of imperfect detection of the electron path on the double slit interference pattern. Incorpo rating into our quantum system the detectors for the electron path and the observer who recognizes the response of the detectors, one can de compose the ensemble of electrons with their spots on the film into th ree subensembles according as the upper, lower or neither detector res ponds. Only the third ensemble shows the interference pattern. Negativ e result measurement is included as a special case. This Gedankenexper iment allows one to put the argument of Bohr's complementarity of the wave/particle duality on a quantitative basis. The realization of the experiment is well within the high technology of the present day.