title: Maximal Holevo Quantity Based on Weak Measurements.
abstract: The Holevo bound is a keystone in many applications of quantum information theory. We propose " maximal Holevo quantity for weak measurements" as the generalization of the maximal Holevo quantity which is defined by the optimal projective measurements. The scenarios that weak measurements is necessary are that only the weak measurements can be performed because for example the system is macroscopic or that one intentionally tries to do so such that the disturbance on the measured system can be controlled for example in quantum key distribution protocols. We evaluate systematically the maximal Holevo quantity for weak measurements for Bell-diagonal states and find a series of results. Furthermore, we find that weak measurements can be realized by noise and project measurements.
authors.affiliation: 1] Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China [2] College of Mathematics, Tonghua Normal University, Tonghua, Jilin 134001, China.
authors.forename: Yao-Kun
authors.initials: YK
authors.lastname: Wang
authors.affiliation: 1] School of Mathematical Sciences, Capital Normal University, Beijing 100048, China [2] Max-Planck Institute for Mathematics in the Sciences, 04103 Leipzig, Germany.
authors.forename: Shao-Ming
authors.initials: SM
authors.lastname: Fei
authors.affiliation: School of Mathematical Sciences, Capital Normal University, Beijing 100048, China.
authors.forename: Zhi-Xi
authors.initials: ZX
authors.lastname: Wang
authors.affiliation: 1] Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China [2] Collaborative Innovation Center of Quantum Matter, Beijing 100190, China.
authors.forename: Jun-Peng
authors.initials: JP
authors.lastname: Cao
authors.affiliation: 1] Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China [2] Collaborative Innovation Center of Quantum Matter, Beijing 100190, China.
authors.forename: Heng
authors.initials: H
authors.lastname: Fan