Next Seminar (online)

Coulomb interaction and electronic quantum coherence in solid-state interferometers

Wednesday Decembre 16th 2020, 14h – Online

Invited speaker:
Hadrien Duprez

Team QPC

Electronic transport in low temperature and low scale solid-state devices is governed by the laws of quantum mechanics, where the wavelike nature of electrons cannot be overlooked. The resulting effects are well explained when electronic transport is expressed in terms of elementary conductive channels, that are analogous to optical modes in a waveguide. Quantum Hall edge channels are a direct implementation of such electronic channels and consequently are a platform of choice to study electrical transport at the fundamental level. Notably, they can be used to implement electronic interferometers and in particular, the analogue of a Mach-Zehnder interferometer, which among other realizations, illustrates a promising route toward reproducing quantum optics experiments with electrons. A crucial difference with optics is that Coulomb interaction is ubiquitous in electronic circuits, which both limits the electron quantum coherence and gives rise to exotic correlated phenomena.

In this thesis, quantum Hall edge channels were arranged in a Mach-Zehnder geometry in order to study the effect of Coulomb interaction on the electronic quantum coherence. The obtained results are two-fold. First, a strategy based on the suppression of the Coulomb mediated coupling between co-propagating edge channels to highly increase the coherence length was demonstrated. This resulted in an observed coherence length enhanced by over one order of magnitude, reaching a macroscopic length of 0.25mm, a distance visible to the naked eye, at low temperature (10mK). In a second experiment, a small metallic island was introduced on one of the two paths of an electronic Mach-Zehnder interferometer. An electron remains within such an island much longer than its quantum lifetime, which normally prohibits any quantum coherent propagation of electrons across it. However, when a single channel is connected to this island, and if the latter’s capacitance is small enough to freeze any fluctuation of its global charge, a perfect transmission of the electron quantum state across the island is predicted. This striking prediction was experimentally demonstrated in this thesis. While the first result illustrates how Coulomb interaction can be detrimental to quantum coherence, the second one, on the contrary, shows that it can be harnessed to preserve quantum coherence.

Jury :
Christopher Bäuerle – Directeur de recherche Institut Néel, CNRS - Rapporteur
Xavier Waintal – Directeur de recherche Quantum Photonics Electronics and Engineering Laboratory, CEA Grenoble - Rapporteur
Mitali Banerjee – Professeure assistante École Polytechnique Fédérale de Lausanne - Examinatrice
Piet Brouwer – Professeur Université Libre de Berlin - Examinateur
Patrice Roche – Directeur de Recherche Service de Physique de l’État Condensé, CEA Saclay - Examinateur
Anne Anthore – Enseignante-chercheuse Centre de Nanosciences et Nanotechnologies, Université de Paris - Co-directrice
Frédéric Pierre – Directeur de Recherche Centre de Nanosciences et Nanotechnologies, CNRS - Co-directeur


Upcoming seminars

  • Hugues Pothier (TBA)
  • Alois Arrighi (TBA)



Past seminars 2020

  • Kamran Behnia (ESPCI)

  • Pierre Capiod (Debye institute for Nanomaterials)

  • Audrey Bienfait (ENS-Lyon)

  • Sebastien Toussain (UCL)

  • David Goldhaber-Gordon (Stanford)

  • Javad Shabani (NYU)

  • Olivier Maillet (Aalto)

  • Mitali Banerjee (EPFL)

  • Anais Dreau (L2C) 

  • Klaus Ensslin (ETH- Zurich) 

  • Xavier Waintal (CEA- Grenoble) 

  • Gwendal Feve (LPENS) 

  • Shuoying Yang (MPI-Halle) 

  • Yann Gallais (MPQ) 

  • Carles Altimiras (CEA - Saclay)

  • Alexandra Palacio- Morales ( LPS) 

  • Everton Arrighi (Neel Institute)