  We study dephasing of electrons induced by a which path detector and thus
verify Bohr's complementarity principle for fermions. We utilize a double path
interferometer with two slits, with one slit being replaced by a coherent
quantum dot (QD). A short one dimensional channel, in the form of a quantum
point contact (QPC), in close proximity to the QD, serves as a which path
detector. We find that by varying the properties of the QPC detector we affect
the visibility of the interference, inducing thus dephasing. We develop a
simple model to explain the dephasing due to the nearby detector and find good
agreement with the experiment.
