부산대학교 도서관

Summary: ``The notion of low-noise channels was recently proposed andanalysed in detail in order to describe noise processes driven by theenvironment [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-noiseparameters of channels hasalso been developed. In this paper, we address the low-noise parameterestimation problem for the $N$-body extension of the dissipativelow-noise channels. We perturbatively calculate the Fisher informationof the output states in order to evaluate the lower bound of themean-square error of the parameter estimation. We show that themaximum of the Fisher information over all input states can beattained by a factorized input state in the leading order of thelow-noise parameter. Thus, to achieve optimal estimation, it is notnecessary for there to be entanglement of the $N$ subsystems, as long asthe true low-noise parameter is sufficiently small and the channel isproperly dissipative.''