Quantum oscillations and decoherence in different types of materials

3^rd International Conference and Exhibition on Materials Science & Engineering

October 06-08, 2014 Hilton San Antonio Airport, USA

Bernard Barbara

Accepted Abstracts: Material Sci Eng

Abstract :

In a short introduction we recall how large spins systems, such as Single Molecular Magnets (SMMs) or diluted Rare- Earth ions (REs) interacting through weak dipolar interactions only, can be reversed by quantum tunneling along quantized hysteresis loops (incoherent at the measurement scale). Then we describe the first coherence measurements in a SMM (socalled V15) and a RE system (Er:CaWO4). The study of Rabi oscillations enables the study of decoherence mechanisms in particular with the evidence of a mechanism of ?driven? spin-bath decoherence where the stochastic noise of the excitation microwave pulse, amplified by magnetic dipolar interactions, constitutes a severe roadblock for quantum computation. At lower temperatures, when thermal or quantum fluctuations become smaller than weak dipolar interactions, quantum phase transitions take place, as this is shown for example in the Fe8 SMM. Magnetic order should suppress Rabi oscillation unless more sophisticated mechanisms take place (such as quantum oscillations of spin waves). Finally, the classical counterpart of the Landau-Zener model - the most famous and useful model to describe quantum dynamics is shown to be identical to the quantum model. This surprising but easy to understand result enables, in particular, an intuitive understanding of the above mentioned aspects of quantum spin dynamics. We shall end this talk by the demonstration of the existence of a new concept of spin-qubits in anti ferromagnetic spin-chains for which the first coherent measurements are given which should enable simpler implementation of a spin-based quantum computer.

Biography :

Bernard Barbara, Director of Research at the CNRS has also been till 2012 a Scientific Adviser at the Atomic Energy Center (CEA-Grenoble), at the French Ministry of Science (ANR grants, Aeres) and the European Research Council (for advanced ERC grants). He is now Director of Research Emeritus and a board member of the European Academy of Sciences (EURASC.org). He defended his PhD in 1972 under the supervision of Remy Lemaire and Louis Néel, Nobel Prize of Physics. All along his career he has initiated and developed pioneering works on different subjects of magnetism and magnetic materials, some of them having been distinguished by international prizes.