(Phys.org)—In a quantum superposition,a quantum thing can be in two incompatible states at the same time, which is famously illustrated by Schrödinger's dead-and-alive cat. Recent research has shown that it's possible to absorb a superposition not only of incompatible states, and but also of incompatible orders of events. We often think of events occurring in a definite chronological order,with event A happening (and causing) event B, or vice versa. But in certain quantum processes, or events don't happen in a single definite order,but instead both orders (A before B, and B before A) occur at the same time. This counterintuitive superposition-like phenomenon is called "causal nonseparability."
Source: phys.org