Indefinite causal order with fixed temporal order for electrons and positrons

Abstract

We provide an analysis of indefinite causal orders in relativistic quantum mechanics based on the electron–positron picture of Feynman involving negative energy electrons ‘moving backward in time’ (i.e., involving a retrocausal link). We show that genuine implementations of the paradigmatic quantum switch, but here violating some causal inequalities and with a fixed temporal order, become possible in extreme external electromagnetic field conditions.