Welcher weg experiments, duality and the orthodox Bohr's Complementarity Principle

Abstract

In its most orthodox form, Bohr's Complementarity Principle states that a quanton (a quantum system consisting of a Boson or Fermion) can either behave as a particle or as wave, but never simultaneosuly as both. A less orthodox interpretation of this Principle is the "duality condition" embodied in a mathematical inequality due to Englert [B-G Englert, Phys. Rev. Lett., 77, 2154Lett., 77, (1996] which allows wave and particle attributes to co-exist, but postulates that a stronger manifestation of the particle nature leads to a weaker manifestation of the wave nature and vice versa. In this Letter, we show that some recent welcher weg ("which path") experiments in interferometers and similar set-ups, that claim to have validated, or invalidated, the Complementarity Principle, actually shed no light on the orthodox interpretation. They may have instead validated the weaker duality condition, but even that is not completely obvious. We propose simple modifications to these experiments which we believe can test the orthodox Complementarity Principle and also shed light on the nature of wavefunction collapse and quantum erasure.

Entropic no-disturbance as a physical principle

“…Introduction.-It is common to assert that quantum mechanics (QM) is beyond the classical conception of nature. There are many phenomena which indicate that classical description of our universe is not suit for quantum world, for example, the uncertainty principle [1], principle of complementarity [2,3], nonlocality [4][5][6], contextuality [7,8], negativity of quasi-probability [9] and so on. Among which contextuality and its more restricted form, nonlocality, attract many interests for both their theoretical importance and broad applications.…”