Campus Saint Jérome, 13013 Marseille
Aile 1, Niveau 6
The Magnetism group (MAG) is devoted to the study of exotic magnetic properties in condensed matter. We are specialized in electron spin resonance (ESR) in paramagnetic, ferromagnetic and antiferromagnetic materials.
We study materials for purely fundamental science like low-dimensional strongly correlated magnets (like spin chains, frustration, spin liquids) as well as material for potential applications in spintronics (ferromagnetic, multiferroic) and in quantum information processing (quantum coherence of electron spin in solid).
Our approach is based on three pillars: Experiment, Instrument, Theory
The Mn2+ ion (S=5/2), subjected to the very weak crystalline field of a cubic matrix, shows remarkable coherent quantum dynamics properties. When the pumping microwave field has an amplitude of the same order as the crystalline field, nonlinear dynamics appears. Population inversion can be achieved between transitions forbidden through the coherent absorption and emission of several photons. While a qubit is the superposition of two levels (i.e., S=1/2), its extension to a higher number of levels is called a qudit. In the case of the Mn2+ ion (S=5/2), we have been able to coherently manipulate six electronic levels and 36 levels by associating nuclear levels. In a series of articles, we have been able to show coherent control of up to five photons of the electronic levels, control of electron-nuclear transitions, and an experimental protocol for probing all 630 transitions. These results pave the way for the implementation of the Grover algorithm (an unstructured list quantum algorithm).
The study of quantum coherence in spin ensembles is a central theme, both for purely fundamental reasons and for potential applications in the field of quantum technologies. Our team is particularly interested in unconventional systems. Thus, our team's observation of the coherence of the magnetic resonance of strongly correlated defects opens the way to a whole new theme in quantum information: the realization and control of soliton qubits. To do this, we will use systems of strongly correlated organic spin chains (provided by the team of M. Foumigué of the ISCR) in which we will induce and control defects either by irradiation or by electrical control. In addition, by using magnetic field gradients, we will be able to locally address qubits.
The quantum coherence of a set of electron spins is very dependent on its environment. Phonons, magnetic dipoles and nuclear spin baths tend to destroy the coherent superposition state of spins. There are instrumental techniques that reduce these effects such as dynamic decoupling which consists in rapidly inverting several times the spin populations acting as noise filters. We have proposed and realized a new experimental protocol using two coherent electromagnetic waves, but of slightly different frequencies. The idea is the following: during the resonance, in the rotating reference frame, the spin acts as a damped oscillator. If we add a force of the same frequency as the Rabi frequency we should be able to force the set of spins to continue to oscillate. In the reference frame of the laboratory, this corresponds to having a second pumping frequency slightly different from that of the main source. Generally, to obtain such a configuration, an arbitrary function generator at microwave frequency is needed, often very expensive. In our case, a simple un-balanced mixer allowed us to realize the protocol. This protocol has been successfully tested on several electron spin systems (diamond, transition metals, rare earths) and it is probably applicable to many others such as quantum dots, superconductors or cold atoms.
Study of the formation, propagation and interaction of magnetic textures in nanostructures (nanowires, nanostrips, nanoplots):
Formation and propagation of magnetic excitations (magnons) in confined nanostructures Interactions between magnetic structures (magnons, domain walls, skyrmions) Systematic controlled displacement of magnetic textures for emergent magnetic technologies Complex non-linear domain wall dynamics under harmonic excitation: magnetic Duffing oscillator - neuromorphic computing.
Study of magnetic properties (magnetocrystalline anisotropy, magnetic relaxation, g-factor) and engeneering of ferromagnetic thin films (Mn5Ge3Cx, MnCoGe, Heussler alloys) by ferromagnetic resonance.
Generation and manipulation of optically-excited magnetic quantum states in semiconducting nanostructures. In particular, non-magnetic nanoparticles of ZnO have been recently proved by us to transit toward a localized quasi-stable magnetic excited state, when illuminated by a minimal wavelength of about 405 nm. After illumination removal, these surface magnetic states are non-radiatively relaxed by phonon scattering above 80 K and are permanent under this about 50 K. Pulse EPR has been successfully applied to this system, thus opening the way to the manipulation and monitoring of magnetic quantum states in stable and robust inorganic nanoparticles.
|Spectromètre RPE, Bruker EMX
Magnétomètre à SQUID,
Système de mesures de susceptibilité AC et DC MAGLAB 2000
Local : CINaM, ISM2, ICR, BIP, Madirel
National : LASIRE (Lille), IRCP (Paris), ISCR (Rennes), IRSN (Fontenay aux Roses), CEA (Sacclay), GREMAN (Tour).
International : NHMFL (USA), FSU (USA), U. Tokyo (Japan), U. Groningen (Germany), U. Stuttgart (Germany), Physikalishese Institut Dresden (Germany), Academy of Sciences Poznan (Poland), Jaypee University (India), LIU (Sweden).