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Dephasing in electron interference by a ‘which-path’ detector


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.

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Figure 1: The which-path device.
Figure 2: Conduction characteristics of the which-path device.
Figure 3: Measurements of visibility.


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We thank S. Gurvitz for presenting to us ref. 7, which initiated the present work. We also thank I. Imry, Y. Levinson, Y. Meir, A. Stern and N. Wingreen for discussions. This work was supported in part by a MINERVA grant and a MINERVA fellowship for one of us (R.S.).

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Correspondence to M. Heiblum.

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Buks, E., Schuster, R., Heiblum, M. et al. Dephasing in electron interference by a ‘which-path’ detector. Nature 391, 871–874 (1998).

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