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Vendredi 21 avril à 14h00,
Salle des séminaires bât. A

Orateur : Clément GODFRIN
"Quantum information processing using a molecular magnet single nuclear spin qudit""


The application of quantum physics to the information theory turns out to be full of promises for our information society. Aware of this potential, groups of scientists all around the world have this common goal to create the quantum version of the computer. The first step of this ambitious project is the realization of the basic block that encodes the quantum information, the qubit. Among all existing qubits, spin based devices are very attractive since they reveal electrical read-out and coherent manipulation. Beyond this, the more isolated a system is, the longer its quantum behaviour remains, making of the nuclear spin a serious candidate for exhibiting long coherence time and consequently high numbers of quantum operation. In this context I worked on a molecular spin transistor. This setup enabled us to read-out electrically both the electronic and the nuclear spin states and to coherently manipulate the nuclear spin of the Terbium ion. I focus during my Ph.D. on the study of the spins dynamic and mainly the 3/2 nuclear spin under the influence of a microwave pulse. The first step was to measure the energy difference between these states leading in a second time to the coherent manipulation of the three nuclear spin transitions using only a microwave electric field. To further characterize the decoherence processes that break the phase of the nuclear spin states, I performed Ramsey and Hahn-echo measurements revealing coherence times of the order of 0.3ms. More than demonstrating the qubit dynamic, I demonstrated that a nuclear spin embedded in the molecular magnet transistor is a four quantum states system that can be fully controlled, a qudit. Theoretical proposal demonstrated that quantum information processing could be implemented using a 3/2 spin. I focused on the Grover algorithm. It allows a quadratic speed-up to find an element in an unordered list compared to classical algorithm. During my Ph.D., I demonstrated the experimental proof of feasibility of this algorithm applied to a multi-levels system.

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