Is single-particle interference spooky?

TL;DR

This paper demonstrates that single-particle quantum interference in multi-path interferometers can be simulated classically with a local ontological model, suggesting the true quantum mystery lies in multi-particle phenomena.

Contribution

It introduces a local classical model for single-particle interference that reproduces quantum predictions, challenging the notion of non-locality as fundamental.

Findings

Single-particle interference can be explained classically.

The model reproduces quantum predictions without non-locality.

Non-locality appears as an epistemic effect, not a fundamental feature.

Abstract

It is said about quantum interference that "In reality, it contains the only mystery". Indeed, together with non-locality it is often considered as the characteristic feature of quantum theory which can not be explained in any classical way. In this work we are concerned with a restricted setting of a single particle propagating in multi-path interferometric circuits, that is physical realisation of a qudit. It is shown that this framework, including collapse of the wave function, can be simulated with classical resources without violating the locality principle. We present a local ontological model whose predictions are indistinguishable from the quantum case. 'Non-locality' in the model appears merely as an epistemic effect arising on the level of description by agents whose knowledge is incomplete. This result suggests that the real quantum mystery should be sought in the multi-particle behaviour, since single-particle interferometric phenomena are explicable in a classical manner.