Causal modeling the delayed choice experiment

TL;DR

This paper analyzes delayed choice experiments using causal models, showing classical models can replicate quantum predictions in some cases, but certain variants reveal incompatibility with non-retrocausal hidden variables, supporting quantum non-classicality.

Contribution

It introduces a causal modeling framework for delayed choice experiments, demonstrating classical reproductions and identifying variants that challenge non-retrocausal hidden variable explanations.

Findings

Classical causal models can reproduce quantum predictions in some delayed choice setups.

A variant of Wheeler's experiment shows incompatibility with non-retrocausal hidden variables.

The proposed approach is robust to losses and suitable for loophole-free tests.

Abstract

Wave-particle duality has become one of the flagships of quantum mechanics. This counter-intuitive concept is highlighted in a delayed choice experiment, where the experimental setup that reveals either the particle or wave nature of a quantum system is decided after the system has entered the apparatus. Here we consider delayed choice experiments from the perspective of device-independent causal models and show their equivalence to a prepare-and-measure scenario. Within this framework, we consider Wheeler's original proposal and its variant using a quantum control and show that a simple classical causal model is capable of reproducing the quantum mechanical predictions. Nonetheless, among other results, we show that in a slight variant of Wheeler's Gedankenexperiment, a photon in an interferometer can indeed generate statistics incompatible with any non-retrocausal hidden variable model whose dimensionality is the same as that of the quantum system it is supposed to mimic. Our proposal tolerates arbitrary losses and inefficiencies making it specially suited to loophole-free experimental implementations.