Comment on "Revisiting dynamics of quantum causal structures --when can causal order evolve?''

Understand

In the last few years, there has been increasing interest in quantum processes with indefinite causal order.

• Process matrices are a convenient framework to study such processes.
• Ref.
• [1] defines higher order transformations from process matrices to process matrices and shows that no continuous and reversible transformation can change the causal order of a process matrix.