RLD Fisher information bound for multiparameter estimation of quantum channels

One of the fundamental tasks in quantum metrology is to estimate multiple parameters embedded a noisy process, i.e., channel. In this paper, we study limits channel estimation via concept amortization and right logarithmic derivative (RLD) Fisher information value. Our key technical result proof chain-rule inequality for RLD value, which implies that amortization, access catalyst state family, does not increase value channels. This leads efficiently computable limitation multiparameter sequential setting, terms As consequence, conclude if finite, then Heisenberg scaling unattainable setting.