What is nonclassical about quantum interference? - Matthew Leifer

Feynman famously said that quantum interference is, "impossible, absolutely impossible, to explain in any classical way". I use the acronym TRAP (Traditionally Regarded As Problematic) to describe aspects of quantum interference that Feynman built his argument on. Many other puzzling quantum phenomena, such as the Elitzur-Vaidman bomb, the delayed choice experiment, and the quantum eraser, have been built on top of the TRAP. I will briefly review a model for the Mach-Zehnder version of the TRAP phenomena that is classical in a very strong sense. This immediately leads to the question of whether other, more subtle, aspects of quantum interference, do provide evidence of non-classicality? I will give an affirmative answer by showing that the quantum which-path/visibility tradeoff in a Mach Zehnder interferometer and making an arbitrarily good interaction free measurement using the Quantum Zeno Effect both require quantum contextuality, which is arguably the most basic nonclassical resource.
This talk is based on: L. Catani et. al., Quantum 7, 1119 (2023) https://doi.org/10.22331/q-2023-09-25-1119 L. Catani et. al., Physical Review Letters 129, 240401 (2022) https://doi.org/10.1103/PhysRevLett.129.240401 L. Catani et. al., Physical Review A 108, 022207 (2023) (2023) https://doi.org/10.1103/PhysRevA.108.022207 and more recent work that is not yet published