Is single-particle interference spooky?
One of the efforts in quantum foundations research is identification of those features which make the theory unique. It is often argued that quantum interference, collapse of the wave function or contextuality — which stand behind a host of paradoxes and weird effects — are unique to the quantum mechanical realm. While being certainly beyond the scope of our immediate intuitions, it is not at all clear to what extent these features discriminate against classical theories. In particular, it is not clear whether non-locality in the single-particle framework is on a par with the multi-particle case, i.e. does not admit existence of a local hidden variable model. A decisive answer would require either a rigorous no-go proof, like the Bell’s theorem is for two particles, or a counterexample encompassing all relevant aspects of quantum interferometric setups.
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 can be faithfully simulated with classical resources without violating the locality principle. We present 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. It is notably different form the multi-particle scenarios where entanglement is a source of non-local correlations on the ontological level.
arXiv: 1701.02552 [quant-ph]