title: Tensor representation of spin States.
abstract: We propose a generalization of the Bloch sphere representation for arbitrary spin states. It provides a compact and elegant representation of spin density matrices in terms of tensors that share the most important properties of Bloch vectors. Our representation, based on covariant matrices introduced by Weinberg in the context of quantum field theory, allows for a simple parametrization of coherent spin states, and a straightforward transformation of density matrices under local unitary and partial tracing operations. It enables us to provide a criterion for anticoherence, relevant in a broader context such as quantum polarization of light.
authors.affiliation: LPTMS, CNRS and Université Paris-Sud, UMR 8626, Bâtiment 100, 91405 Orsay, France.
authors.forename: O
authors.initials: O
authors.lastname: Giraud
authors.affiliation: Institut für theoretische Physik, Universität Tübingen, 72076 Tübingen, Germany.
authors.forename: D
authors.initials: D
authors.lastname: Braun
authors.affiliation: Institut de Physique Nucléaire, Atomique et de Spectroscopie, Université de Liège, 4000 Liège, Belgium.
authors.forename: D
authors.initials: D
authors.lastname: Baguette
authors.affiliation: Institut de Physique Nucléaire, Atomique et de Spectroscopie, Université de Liège, 4000 Liège, Belgium.
authors.forename: T
authors.initials: T
authors.lastname: Bastin
authors.affiliation: Institut de Physique Nucléaire, Atomique et de Spectroscopie, Université de Liège, 4000 Liège, Belgium.
authors.forename: J
authors.initials: J
authors.lastname: Martin