Postponing the Past: An Operational Analysis of Delayed-Choice Experiments

Pieter Thyssen, Fifth Meeting on the Foundations of Quantum Physics

JOHN ARCHIBALD WHEELER

Marlan O. Scully, HERBERT WALTHER

Richard Wagner, Wenzel Kersten, Hartmut Lemmel +2 more

We report an experiment with neutrons in a silicon perfect crystal interferometer, that realizes a quantum Cheshire Cat in a delayed choice setting. In our setup the quantum Cheshire Cat is established by spatially separating the particle and its property (i.e. the neutron and its spin) into the two different paths of the interferometer. The condition for a delayed choice setting is achieved by postponing the choice of path assignment for the quantum Cheshire Cat, i.e. which path is taken by the particle and which by its property, until the point in time when the neutron wave function has already split and entered the interferometer. The results of the experiment suggest not only the fact that the neutrons and its spin are separated and take different paths in the interferometer, but also quantum-mechanical causality is implied, insomuch that the behavior of a quantum system is affected by the choice of the selection at a later point in time.

孙君, 孙永南, 李传锋 +1 more

Huei Peng

The interpretations of the delayed-choice experiments suggest that photons i°retroactively decidei± to travel as particles or as waves from the time of its emission. To test the interpretations thoroughly, we propose and perform novel extended-delayed-choice experiments. The experiments are designed for easier to set up, carry out and reach meaningful results without ambiguity. The experimental results show the following: (A) The present does not decide the past retroactively, i.e., the causality holds; (B) Bohri¯s complementarity principle is challenged; (C) photons behave as particle before striking on a double-slit/cross-double-slit; (D) Particle nature is intrinsic.