I argue that quantum optical experiments that purport to refute Bohr’s principle of complementarity fail in their aim. Some of these experiments try to refute complementarity by refuting the so called particle–wave duality relations, which evolved from the Wootters–Zurek reformulation of BPC. I therefore consider it important for my forgoing arguments to first recall the essential tenets of BPC, and to clearly separate BPC from WZPC, which I will argue is a direct contradiction of BPC. This leads to a need (...) to consider the meaning of particle–wave duality relations and to question their fundamental status. I further argue that particle and wave complementary concepts are on a different footing than other pairs of complementary concepts. (shrink)

Afshar et al. claim that their experiment shows a violation of the complementarity inequality. In this work, we study their claim using a modified Mach-Zehnder setup that represents a simpler version of the Afshar experiment. We find that our results are consistent with Afshar et al. experimental findings. However, we show that within standard quantum mechanics the results of the Afshar experiment do not lead to a violation of the complementarity inequality. We show that their claim originates from a particular (...) technique they use to analyze their results. In their analysis, they assume a classical concept, that particles have a definite trajectory before detection, thus, they obtain which-way information by particle detection plus path extrapolation by applying momentum conservation. This analysis technique is standard in experimental particle physics. Important discoveries such as the detection of vector bosons have been made through the application of this technique. We note that particle detection plus path extrapolation is a suitable technique within de Broglie-Bohm theory of quantum mechanics. (shrink)

A modified version of Young’s experiment by Shahriar Afshar indirectly reveals the presence of a fully articulated interference pattern prior to the post-selection of a particle in a “which-slit” basis. While this experiment does not constitute a violation of Bohr’s Complementarity Principle as claimed by Afshar, both he and many of his critics incorrectly assume that a commonly used relationship between visibility parameter V and “which-way” parameter K has crucial relevance to his experiment. It is argued here that this relationship (...) does not apply to this experimental situation and that it is wrong to make any use of it in support of claims for or against the bearing of this experiment on Complementarity. (shrink)

Complementarity can be considered as the weirdest idea associated with quantum mechanics. For Bohr, Complementarity is important in order to be able to convey successfully the non-classical features of quantum mechanics. This paper discusses the epistemic and ontological implications of different new experiments that attempt to detect complementarity. Complementarity has surely survived the attempts to overcome it, yet some of these experiments have led to a more general form of complementarity. Others claim to be able to differentiate among the different (...) interpretations of quantum physics. Nonetheless, such claims have revealed contradictory representations of the ontological picture of the universe. Hence, Bohr’s position is still valid. (shrink)

O experimento de Afshar foi proposto recentemente como sendo uma violação do princípio de complementaridade. Reconhecendo a novidade trazida pelo experimento, argumentamos que ele permite um refinamento de tal princípio, a partir do estabelecimento de dois pontos: (1) a possibilidade de modificar o "tipo" de fenômeno (onda ou partícula) sem alterar o estado quântico, e (2) a constatação de que o tipo de fenômeno, associado a um quantum detectado, refere-se a um trecho determinado percorrido pelo objeto quântico. O primeiro ponto (...) é explorado em interferômetros de Mach-Zehnder, com dispositivos de polarização e na montagem dupla de Unruh. O segundo ponto salienta que um fenômeno pode ser corpuscular com respeito a uma região e ondulatório com respeito a outra, estando a novidade de Afshar na proposta de uma maneira de constatar ambos simultaneamente. A restrição (1) acaba tendo um efeito desprezível no experimento de Afshar. Afshar's experiment was recently proposed as a violation of the principle of complementarity. Acknowledging the novelty brought by the experiment, we argue that it allows a refinement of this principle, with the establishment of two points: (1) the possibility of modifying the "type" of phenomenon (wave or particle) without changing the quantum-mechanical state, and (2) the recognition that the type of phenomenon, associated to a detected quantum, refers to a specific region traversed by the quantum object. The first point is explored in Mach-Zehnder interferometers, with polarization devices and in Unruh's double setup. The second point emphasizes that a phenomenon can be corpuscular with respect one region and undulatory with respect to another. Afshar's originality lies in his proposal of a way of ascertaining both simultaneously. Restriction (1) turns out having a negligible effect in Afshar's experiment. (shrink)