Letters to Nature

Nature 391, 871-874 (26 February 1998) | doi:10.1038/36057; Received 17 September 1997; Accepted 16 December 1997

Dephasing in electron interference by a 'which-path' detector

E. Buks1, R. Schuster1, M. Heiblum1, D. Mahalu1 & V. Umansky1

  1. Braun Center for Submicron Research, Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100, Israel

Correspondence to: M. Heiblum1 Correspondence and requests for materials should be addressed to M.H. (e-mail address: Email: heiblum@wis.weizmann.ac.il).

Wave–particle duality, as manifest in the two-slit experiment, provides perhaps the most vivid illustration of Bohr's complementarity principle: wave-like behaviour (interference) occurs only when the different possible paths a particle can take are indistinguishable, even in principle1. The introduction of a which-path (welcher Weg) detector for determining the actual path taken by the particle inevitably involved coupling the particle to a measuring environment, which in turn results in dephasing (suppression of interference). In other words, simultaneous observations of wave and particle behaviour is prohibited. Such a manifestation of the complementarity principle was demonstrated recently using a pair of correlated photons, with measurement of one photon being used to determine the path taken by the other and so prevent single-photon interference2. Here we report the dephasing effects of a which-path detector on electrons traversing a double-path interferometer. We find that by varying the sensitivity of the detector we can affect the visibility of the oscillatory interference signal, thereby verifying the complementarity principle for fermions.