Quantum nanomagnet

A single crystal made of nanomagnets is a macroscopic quantum object. The first of this class to have been discovered is the so-called molecular complex Mn-12-ac with a spin S = 10 per molecule. With vanishingly small tunneling gaps this system opened the field of slow quantum dynamics (incoherent), with the study of interplays between classical and quantum magnetism in particular. The first part of this article gives an overview of this new type of mesoscopy. An extension to the case of non-interacting rare-earth ions is presented in the second part, showing that mesoscopic magnetism can reach the atomic scale. Modifications occur in the spin-bath, allowing the observation of two- and four-spins entanglements. This field is narrowly connected with the one of solid-state spin qubits for quantum computation. To cite this article: B. Barbara, C R. Physique 6 (2005). (c) 2005 Academie des sciences. Published by Elsevier SAS. All rights reserved.