부산대학교 도서관

Summary: ``The notion of low-noise channels was recently proposed and analysed in detail in order to describe noise processes driven by the environment [M. Hotta, T. Karasawa and M. Ozawa, Phys. Rev. A (3) {\bf 72} (2005), no. 5, part A, 052334, 11 pp.]. An estimation theory of low-noise parameters of channels has also been developed. In this paper, we address the low-noise parameter estimation problem for the $N$-body extension of the dissipative low-noise channels. We perturbatively calculate the Fisher information of the output states in order to evaluate the lower bound of the mean-square error of the parameter estimation. We show that the maximum of the Fisher information over all input states can be attained by a factorized input state in the leading order of the low-noise parameter. Thus, to achieve optimal estimation, it is not necessary for there to be entanglement of the $N$ subsystems, as long as the true low-noise parameter is sufficiently small and the channel is properly dissipative.''