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TERATEC 2020 Forum
Tuesday October 13, 2020

Workshop 3 - 16:00 to 17:30
Quantum computing: What's new in QuBits?
Chaired by Philippe Duluc, Chief Technology Officer, Atos

Topological Qubits: principles and advantages
By Vivien Londe, Quantum Software Engineer, Microsoft

Quantum computing is based on the manipulation of quantum degrees of freedom, called qubits when they are binary. These degrees of freedom are ubiquitous at the atomic scale, but it is difficult to isolate and control them with precision.

The topological approach consists in encoding a quantum degree of freedom in a non-local way. Thus, quantum computing can only be affected by global errors, which are much less likely than local errors.

If the existence of the Majorana fermion was postulated as early as 1937 by the Italian physicist Ettore Majorana, it was only in 2012 that we managed to create a collective excitation, or quasi-particle, which reproduces its properties. When two Majorana fermions meet, they can either annihilate or generate an electron. The probability of these two fusion channels depends on the history of the relative movements of Majorana fermions. This is how the binary quantum degree of freedom of a qubit is achieved.

To build a universal quantum computer, it is also necessary to be able to process quantum memory. This is called applying a quantum gate. The processing of topological qubits can be done by the simple relative movement of Majorana fermions. The use of auxiliary degrees of freedom and collective measurements leads to the same result: it makes it possible to implement a set of universal gates.

We propose to review certain theoretical aspects of the topological quantum computer. Then we will briefly discuss the experimental engineering of collective excitations that have the properties of the Majorana fermion.

Biographie : Après avoir étudié la physique théorique à l’Ecole Polytechnique et les mathématiques à l’Université de Jussieu, Vivien Londe réalise son doctorat à Inria sur la correction d’erreur quantique. La correction d’erreur quantique consiste à réaliser un compromis entre qualité et quantité de la mémoire quantique. A partir d’un grand nombre de qubits de qualité médiocre, on construit un nombre plus restreint de qubits de meilleure qualité. On dit qu’on encode des qubits logiques dans un système de qubits physiques. Cela revient à reproduire artificiellement ce que l’ordinateur quantique topologique cherche à faire au niveau du hardware quantique. A l’issue de son doctorat, il rejoint Microsoft en tant que spécialiste de l’informatique quantique.

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