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Edited by* Marlan O. Scully, Texas A&M and Princeton Universities, College Station, TX, and Princeton, NJ, and approved April 16, 2012 (received for review January 23, 2012)
Abstract
The precise knowledge of one of two complementary experimental outcomes prevents us from obtaining complete information about the other one. This formulation of Niels Bohr’s principle of complementarity when applied to the paradigm of wave-particle dualism—that is, to Young’s double-slit experiment—implies that the information about the slit through which a quantum particle has passed erases interference. In the present paper we report a double-slit experiment using two photons created by spontaneous parametric down-conversion where we observe interference in the signal photon despite the fact that we have located it in one of the slits due to its entanglement with the idler photon. This surprising aspect of complementarity comes to light by our special choice of the TEM01 pump mode. According to quantum field theory the signal photon is then in a coherent superposition of two distinct wave vectors giving rise to interference fringes analogous to two mechanical slits.
Footnotes
- ↵1To whom correspondence should be addressed. E-mail: photonics{at}uni-potsdam.de.
Author contributions: R.M. designed research; R.M., D.P., A.H., and W.P.S. performed research; and R.M. and W.P.S. wrote the paper.
The authors declare no conflict of interest.
*This Direct Submission article had a prearranged editor.
*As single-photon counting modules we employ PerkinElmer SPCM-AQR-15 avalanche photo diodes coupled by a multimode graded index fiber of a core diameter 62.5 μm
Freely available online through the PNAS open access option.
Wave-particle dualism
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