Tensor Representation of Spin States

O. Giraud ¹ D. Braun ² D. Baguette ³ T. Bastin ³ J. Martin ³

Physical Review Letters, American Physical Society, 2015, 114, pp.080401

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.

• 1. LPTMS – Laboratoire de Physique Théorique et Modèles Statistiques
• 2. Tübingen Universität – Tübingen University
• 3. Institut de Physique Nucléaire, Atomique et de Spectrométrie