A loophole-free Wheeler-delayed-choice experiment

TL;DR

This paper reports a loophole-free, device-independent Wheeler-delayed-choice experiment with space-like separated photon states, confirming quantum predictions and challenging two-dimensional hidden-variable theories, thus reinforcing the role of causality in quantum tests.

Contribution

It presents the first loophole-free, device-independent realization of Wheeler's delayed-choice experiment with space-like separated photons, challenging causal hidden-variable explanations.

Findings

Loophole-free confirmation of quantum predictions in delayed-choice experiment

Incompatibility of causal two-dimensional hidden-variable theories with experimental results

Demonstration of causality as a tool to test quantum theory

Abstract

Wheeler's delayed-choice experiment investigates the indeterminacy of wave-particle duality and the role played by the measurement apparatus in quantum theory. Due to the inconsistency with classical physics, it has been generally believed that it is not possible to reproduce the delayed-choice experiment using a hidden variable theory. Recently, it was shown that this assumption was incorrect, and in fact Wheeler's delayed-choice experiment can be explained by a causal two dimensional hidden-variable theory [R. Chaves, G. B. Lemos, and J. Pienaar, Phys. Rev. Lett. 120, 190401 (2018)]. Here, we carry out an experiment of a device-independent delayed-choice experiment using photon states that are space-like separated, and demonstrate a loophole-free version of the delayed-choice protocol that is consistent with quantum theory but inconsistent with any causal two-dimensional hidden variable theory. This salvages Wheeler's thought experiment and shows that causality can be used to test quantum theory in a complementary way to the Bell and Leggett-Garg tests.