Counterfactual quantum measurements
Phys. Rev. A 113, 042206 – Published 3 April, 2026
DOI: https://doi.org/10.1103/9836-q2q3
Abstract
Counterfactual reasoning plays a crucial role in exploring hypothetical scenarios, by comparing some consequent under conditions identical except as results from a differing antecedent. David Lewis' well-known analysis evaluates counterfactuals using a hierarchy of desiderata. These were, however, built upon a deterministic classical framework, and whether it could be generalized to indeterministic quantum theory has been an open question. In this article, we propose a formalism for quantum counterfactuals in which antecedents are measurement settings. Unlike other approaches, it nontrivially answers questions such as, “Given that a photon-detector, observing an atom's fluorescence, clicked at a certain time, what would a field-quadrature detector have measured, if it had been used instead?”
