Apparent quantum paradoxes as simple interference: Quantum violation of the pigeonhole principle and exchange of properties between quantum particles

It was recently argued that the pigeonhole principle, which states that if three pigeons are put into two pigeonholes then at least one pigeonhole must contain more than one pigeon, is violated in quantum systems [Proc. Natl. Acad. Sci. USA 113, 532 (2016), 10.1073/pnas.1522411112]. An experimental verification of this effect was recently reported [Proc. Natl. Acad. Sci. USA 116, 1549 (2019), 10.1073/pnas.1815462116]. In another recent experimental work, it was argued that two entities were observed to exchange properties without meeting each other [Nat. Commun. 11, 3006 (2020), 10.1038/s41467-020-16761-0]. Here we describe all these proposals and experiments as simple quantum interference effects where no such dramatic conclusions appear. Besides demystifying some of the conclusions of the cited works, we also present physical insights for some interesting behaviors present in these treatments. For instance, we associate the anomalous particles behaviors in the quantum pigeonhole effect to a quantum interference of force.