Unbounded separation between definite and indefinite causal order in finite-dimensional quantum metrology
The research investigated if an Indefinite Causal Order (ICO) strategy can yield an unbounded advantage over a Definite Causal Order (DCO) strategy when estimating a geometric phase for finite-dimensional quantum systems. The findings confirm that arbitrarily large advantages exist in the finite sample regime, showing ICO requires significantly lower initial probe energy than DCO.