title: Quantum metrological limits via a variational approach.
abstract: The minimum achievable statistical uncertainty in the estimation of physical parameters is determined by the quantum Fisher information. Its computation for noisy systems is still a challenging problem. Using a variational approach, we present an equation for obtaining the quantum Fisher information, which has an explicit dependence on the mathematical description of the noise. This method is applied to obtain a useful analytical bound to the quantum precision in the estimation of phase-shifts under phase diffusion, which shows that the estimation uncertainty cannot be smaller than a noise-dependent constant.
authors.affiliation: Instituto de Física, Universidade Federal do Rio de Janeiro, 21.941-972 Rio de Janeiro, Brazil. bmescher@if.ufrj.br
authors.forename: B M
authors.initials: BM
authors.lastname: Escher
authors.forename: L
authors.initials: L
authors.lastname: Davidovich
authors.forename: N
authors.initials: N
authors.lastname: Zagury
authors.forename: R L
authors.initials: RL
authors.lastname: de Matos Filho