title: Generalized limits for single-parameter quantum estimation.
abstract: We develop generalized bounds for quantum single-parameter estimation problems for which the coupling to the parameter is described by intrinsic multisystem interactions. For a Hamiltonian with k-system parameter-sensitive terms, the quantum limit scales as 1/Nk, where N is the number of systems. These quantum limits remain valid when the Hamiltonian is augmented by any parameter-independent interaction among the systems and when adaptive measurements via parameter-independent coupling to ancillas are allowed.
authors.affiliation: Department of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico 87131, USA.
authors.forename: Sergio
authors.initials: S
authors.lastname: Boixo
authors.forename: Steven T
authors.initials: ST
authors.lastname: Flammia
authors.forename: Carlton M
authors.initials: CM
authors.lastname: Caves
authors.forename: J M
authors.initials: JM
authors.lastname: Geremia