Coherence and Indistinguishability of Single Electrons Emitted by Independent Sources

The on-demand emission of coherent and indistinguishable electrons by independent synchronized sources is a challenging task of quantum electronics, in particular regarding its application for quantum information processing. Using two independent on-demand electron sources, we trigger the emission of two single-electron wavepackets at different inputs of an electronic beamsplitter. Whereas classical particles would be randomly partitioned by the splitter, we observe two-particle interferences resulting from quantum exchange. Both electrons, emitted in indistinguishable wavepackets with synchronized arrival time on the splitter, exit in different outputs as recorded by the low frequency current noise. The demonstration of two-electron interference provides the possibility to manipulate coherent and indistinguishable single-electron wavepackets in quantum conductors.Comment: Science Express of January 24 201

Velocity and confinement of edge plasmons in HgTe-based 2D topological insulators

High-frequency transport in the edge states of the quantum spin Hall (QSH) effect has to date rarely been explored, though it could cast light on the scattering mechanisms taking place therein. We here report on the measurement of the plasmon velocity in topological HgTe quantum wells both in the QSH and quantum Hall (QH) regimes, using harmonic GHz excitations and phase-resolved detection. We observe low plasmon velocities corresponding to large transverse widths, which we ascribe to the prominent influence of charge puddles forming in the vicinity of edge channels. Together with other recent works, it suggests that puddles play an essential role in the edge state physics and probably constitute a main hurdle on the way to clean and robust edge transport.Comment: 8 pages, 6 figures, + supplementary materia

Microwave studies of the fractional Josephson effect in HgTe-based Josephson junctions

The rise of topological phases of matter is strongly connected to their potential to host Majorana bound states, a powerful ingredient in the search for a robust, topologically protected, quantum information processing. In order to produce such states, a method of choice is to induce superconductivity in topological insulators. The engineering of the interplay between superconductivity and the electronic properties of a topological insulator is a challenging task and it is consequently very important to understand the physics of simple superconducting devices such as Josephson junctions, in which new topological properties are expected to emerge. In this article, we review recent experiments investigating topological superconductivity in topological insulators, using microwave excitation and detection techniques. More precisely, we have fabricated and studied topological Josephson junctions made of HgTe weak links in contact with two Al or Nb contacts. In such devices, we have observed two signatures of the fractional Josephson effect, which is expected to emerge from topologically-protected gapless Andreev bound states. We first recall the theoretical background on topological Josephson junctions, then move to the experimental observations. Then, we assess the topological origin of the observed features and conclude with an outlook towards more advanced microwave spectroscopy experiments, currently under development.Comment: Lectures given at the San Sebastian Topological Matter School 2017, published in "Topological Matter. Springer Series in Solid-State Sciences, vol 190. Springer

A Majorana mass production line

International audienc

Optique quantique électronique dans les canaux de bord de l'effet Hall quantique

This thesis is devoted to the implementation of quantum optics experiments in a ballistic quantum conductor, with single charge resolution. A mesoscopic capacitor produces on-demand single-electron excitations in the outermost edge channel of quantum Hall effect. We measure current fluctuations after partitioning of excitations on an electronic beamsplitter, in analogy with the Hanbury-Brown & Twiss experiment, so as to unveil neutral excitations (electron/holes pairs) that can accompany the emission of the charge. Thermal excitations in the Fermi sea are then responsible for two-particle interferences that yield information on the energy distribution of the generated quasiparticles. Using two independent and synchronized sources, we generate two indistinguishable quasiparticles that interfere on a beamsplitter as in the Hong-Ou-Mandel experiment. The visibility of this phenomenon could be limited by decoherence of the wavepackets due to interactions with the environment and especially with other co-propagating edge channels. By measuring the capacitive coupling between two co-propagating edge channels, we characterize the effects of Coulomb interaction on propagation and highlight a neutral mode of propagation. These experiments constitute the first implementations of electron quantum optics experiments with single charges. They pave the way to more complex experiments such as the tomography of a mono-electronic wavepacket.Cette thèse est consacrée à la manipulation d'excitations mono-électroniques dans un conducteur quantique balistique, par l'implémentation d'expériences d'optique quantique électronique avec la résolution d'une charge élémentaire. Une capacité mésoscopique produit à la demande des excitations monoélectroniques dans le canal de bord externe de l'effet Hall quantique. Nous mesurons les fluctuations de courant après partitionnement des excitations sur une lame séparatrice électronique, dans un analogue de l'expérience de Hanbury-Brown & Twiss, afin de révéler les excitations neutres (paires électron/trou) qui peuvent accompagner la charge produite. Les excitations thermiques dans la mer de Fermi sont alors responsables d'interférences à deux particules qui permettent d'obtenir des informations sur la distribution en énergie des quasiparticules émises par la source. A l'aide de deux sources indépendantes et synchronisées, nous générons deux quasi-particules indiscernables, qui interfèrent sur une lame séparatrice dans un analogue de l'expérience de Hong-Ou-Mandel. La visibilité de ce phénomène est possiblement limité par la décohérence des paquets d'ondes électroniques par interaction avec l'environnement, notamment les autres canaux de bords. En mesurant le couplage capacitif entre deux canaux de bords co-propageant, nous caractérisons les effets de l'interaction coulombienne et mettons en évidence un mode neutre de propagation. Ces expériences constituent les premières implémentations d'expériences d'optique quantique électronique avec des charges uniques, et permettent d'envisager des expériences plus complexes comme la tomographie d'un paquet d'onde mono-électronique

Optique quantique électronique dans les canaux de bord de l'effet Hall quantique

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