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Paradox in Wave-Particle Duality

We report on the simultaneous determination of complementary wave and particle aspects of light in a double-slit type “welcher-weg” experiment beyond the limitations set by Bohr’s Principle of Complementarity. Applying classical logic, we verify the presence of sharp interference in the single photon regime, while reliably maintaining the information about the particular pinhole through which each individual photon had passed. This experiment poses interesting questions on the validity of Complementarity in cases where measurements techniques that avoid Heisenberg’s uncertainty principle and quantum entanglement are employed. We further argue that the application of classical concepts of waves and particles as embodied in Complementarity leads to a logical inconsistency in the interpretation of this experiment.

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Correspondence to Shahriar S. Afshar.

Additional information

A Preliminary version of this paper was presented by S.S.A. at a Seminar titled “Waving Copenhagen Good-bye: Were the Founders of Quantum Mechanics Wrong?,” Department of Physics, Harvard University, Cambridge, MA 02138, 23 March, 2004.

Private communication by Einstein to his friend Michele Besso, 1951.

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Afshar, S.S., Flores, E., McDonald, K.F. et al. Paradox in Wave-Particle Duality. Found Phys 37, 295–305 (2007).

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  • principle of complementarity
  • wave-particle duality
  • non- perturbative measurements
  • double-slit experiment
  • Afshar experiment

PACS numbers:

  • 03.65.Ta
  • 42.50.Xa
  • 14.70.Bh