Experimental realization of causality-assisted Wheeler's delayed-choice experiment using single photons

Wave-particle duality is one of the most intriguing features in quantum physics. A well-known gedanken experiment that provides evidence for this is the Wheeler's delayed-choice experiment based on a Mach-Zehnder interferometer, and many different versions of delayed-choice experiments have been conducted with both classical and quantum detecting devices. A recent proposal suggests that the delayed-choice experiment can be considered in the perspective of device-independent causal model. Here, we experimentally realize this modified delayed-choice experiment with a deterministic high purity single-photon source, which plays a key role in the Wheeler's delayed-choice experiment. We examine that any two-dimensional nonretrocausal classical model can be excluded in a device-independent manner through our experimental results based on the violation of the dimension witness inequality. We also quantify the degree of retrocausality in our experiment and the results show that the amount of violating dimension witness inequality can be connected to the degree of quantum wave-particle superposition.