Nonclassical oscillations in pre- and post-selected quantum walks

TL;DR

This paper demonstrates nonclassical oscillations in quantum walks through a photonic experiment, revealing phenomena that cannot be mimicked by classical light and confirming quantum nonclassicality via Bell-like inequality violation.

Contribution

It introduces a novel experimental test of nonclassical oscillations in quantum walks using pre- and post-selection, and confirms their quantum nature through Bell inequality violation.

Findings

Experimental violation of Bell-like inequality up to eight standard deviations.

Observation of long-distance oscillations in quantum walks.

Demonstration of nonclassical behavior distinct from classical light simulations.

Abstract

Quantum walks are counterparts of classical random walks. They spread faster, which can be exploited in information processing tasks, and constitute a versatile simulation platform for many quantum systems. Yet, some of their properties can be emulated with classical light. This rises a question: which aspects of the model are truly nonclassical? We address it by carrying out a photonic experiment based on a pre- and post-selection paradox. The paradox implies that if somebody could choose to ask, either if the particle is at position x = 0 at even time steps, or at position x = d (d > 1) at odd time steps, the answer would be positive, no matter the question asked. Therefore, the particle seems to undergo long distance oscillations despite the fact that the model allows to jump one position at a time. We translate this paradox into a Bell-like inequality and experimentally confirm its violation up to eight standard deviations.