A field-theoretic causal model of a Mach–Zehnder Wheeler delayed-choice experiment

We consider a Wheeler delayed-choice experiment based on the Mach–Zehnder Interferometer. Since the development of the causal interpretation of relativistic boson fields, there have not been any applications for which the equations of motion for the field have been solved explicitly. Here, we provide perhaps the first application of the causal interpretation of boson fields for which the equations of motion are solved. Specifically, we consider the electromagnetic field. Solving the equations of motion allows us to develop a relativistic causal model of the Wheeler delayed-choice Mach–Zehnder interferometer. We show explicitly that a photon splits at a beam splitter. We also demonstrate the inherent nonlocal nature of a relativistic quantum field. This is particularly revealed in a which-path measurement where a quantum is nonlocally absorbed from both arms of the interferometer. This feature explains how when a photon is split by a beam splitter it nevertheless registers on a detector in one arm of the interferometer. Bohm et al. [Nature 315 (1985) 294] have argued that a causal model of a Wheeler delayed-choice experiment avoids the paradox of creating or changing history, but they did not provide the details of such a model. The relativistic causal model we develop here serves as a detailed example which demonstrates this point, though our model is in terms of a field picture rather than the particle picture of the Bohm–de Broglie nonrelativistic causal interpretation.