Experimental investigation of Popper's proposed ghost-diffraction experiment

TL;DR

This study experimentally tests Popper's ghost-diffraction proposal, finding that the entangled partner does not exhibit increased diffraction, thereby providing insights into entanglement and challenging certain interpretations of quantum mechanics.

Contribution

The paper presents the first experimental implementation of Popper's ghost-diffraction experiment, clarifying its implications for quantum entanglement and the Copenhagen interpretation.

Findings

Partner beam does not undergo increased diffractive spreading

Results support the non-local nature of entanglement

Insights into the relationship between entanglement and the uncertainty principle

Abstract

In an effort to challenge the Copenhagen interpretation of quantum mechanics, Karl Popper proposed an experiment involving spatially separated entangled particles. In this experiment, one of the particles passes through a very narrow slit, and thereby its position becomes well-defined. This particle therefore diffracts into a large divergence angle; this effect can be understood as a consequence of the Heisenberg uncertainty principle. Popper further argued that its entangled partner would become comparably localized in position, and that, according to his understanding of the Copenhagen interpretation of quantum mechanics, the \qo{mere knowledge} of the position of this particle would cause it also to diffract into a large divergence angle. Popper recognized that such behaviour could violate the principle of causality in that the slit could be removed and the partner particle would be expected to respond instantaneously. Popper thus concluded that it was most likely the case that in an actual experiment the partner photon would not undergo increased diffractive spreading and thus that the Copenhagen interpretation is incorrect. Here, we report and analyze the results of an implementation of Popper's proposal. We find that the partner beam does not undergo increased diffractive spreading. Our work resolves many of the open questions involving Popper's proposal, and it provides further insight into the nature of entanglement and its relation to the uncertainty principle of correlated particles.