(Received 3 February 1997)
The ``Which Path?'' interferometer consists of an Aharonov-Bohm ring with a quantum dot (QD) built in one of its arms, and an additional quantum point contact (QPC) located close to the QD. The transmission coefficient of the QPC depends on the charge state of the QD. Hence the point contact acts as a controllable measurement device for which path an electron takes through the ring. We calculate the suppression of the Aharonov-Bohm oscillations which is caused by both measurement dephasing and the orthogonality catastrophe, i.e., respectively, by real and virtual electron-hole pair creation at the QPC.
PACS: 73.23.Hk, 03.65.Bz, 73.23.Ad
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