Why interference phenomena do not capture the essence of quantum theory

Quantum 7, 1119 (2023).

https://doi.org/10.22331/q-2023-09-25-1119

Quantum interference phenomena are widely viewed as posing a challenge to the classical worldview. Feynman even went so far as to proclaim that they are the $textit{only mystery}$ and the $textit{basic peculiarity}$ of quantum mechanics. Many have also argued that basic interference phenomena force us to accept a number of radical interpretational conclusions, including: that a photon is neither a particle nor a wave but rather a Jekyll-and-Hyde sort of entity that toggles between the two possibilities, that reality is observer-dependent, and that systems either do not have properties prior to measurements or else have properties that are subject to nonlocal or backwards-in-time causal influences. In this work, we show that such conclusions are not, in fact, forced on us by basic interference phenomena. We do so by describing an alternative to quantum theory, a statistical theory of a classical discrete field (the `toy field theory’) that reproduces the relevant phenomenology of quantum interference while rejecting these radical interpretational claims. It also reproduces a number of related interference experiments that are thought to support these interpretational claims, such as the Elitzur-Vaidman bomb tester, Wheeler’s delayed-choice experiment, and the quantum eraser experiment. The systems in the toy field theory are field modes, each of which possesses, at all times, $both$ a particle-like property (a discrete occupation number) and a wave-like property (a discrete phase). Although these two properties are jointly possessed, the theory stipulates that they cannot be jointly $known$. The phenomenology that is generally cited in favour of nonlocal or backwards-in-time $textit{causal influences}$ ends up being explained in terms of $inferences$ about distant or past systems, and all that is observer-dependent is the observer’s $knowledge$ of reality, not reality itself.

Contributed talk by Lorenzo Catani at QIP 2023:

Contributed talk by Robert Spekkens at the “Conference on Quantum Information and Quantum Control IX” — University of Toronto 2022:

Invited talk by Lorenzo Catani at the “Physics and the first-person perspective” Essentia Foundation conference 2022 :

Seminar by Lorenzo Catani at IQOQI Vienna 2022:

Contributed talk by Lorenzo Catani at QPL 2022: