• Type: Theoretical physics
• Advisors: Pascal Degiovanni (DR1 CNRS, ENS Lyon)
• Funding: To be determined
• Starting date: Internship in the Spring 2024, PhD studies in September 2024
• How to apply:
• Project : click here

  A decade of development in electron quantum optics have demonstrated our capability not only to generate but also to characterize individual electronic excitations in certain quantum conductors, including the edge channels of the entire quantum Hall effect, which serve as analogs to optical fibers in quantum photonic optics.

  Recent work within the European project SEQUOIA and the ANR QuSig4QuSense has explored the potential of electronic quantum optics for the detection and measurement of quantum electromagnetic fields on ultra-short time scales, such as radiation exhibiting fluctuations occasionally lower than those of vacuum fluctuations (compressed state).

  The so-called electron radar is dual to that of radar and LIDAR, which probe the properties of a material target using electromagnetic waves: here, an electronic interferometer is used to probe a quantum electromagnetic field. The existence of single-electron sources allows for quantum electric currents as probes that exert very weak quantum feedback on the probed electromagnetic field. Moreover, techniques for controlling single-electron sources enable the probing of the field over very short durations, with frequency resolution, or even in a combined manner.

  While recent work has established a general framework for predicting the signal observed by such an electronic radar, several important questions remain open, forming the focus of this thesis:

  1) The characterization of the signal-to-noise ratio of such a device is yet to be done. This will subsequently address the optimization of the single-electron source to maximize it, a classic problem in quantum metrology theory but unexplored in the context of electronic quantum optics.

  2) The analysis of expected signals in the case where the electromagnetic field is radiated by a single electronic excitation remains to be done. This case is crucial for realizing a "one-shot" single-electron detector and requires a detailed study of the collision between two single electrons propagating in two capacitively coupled chiral edge channels in a finite-length region.

  3) While in the case of optical interferometers, the gain provided by the use of entangled states involving multiple photons has long been characterized, the situation is not as clear in the electronic case. The exploration of the potential of entangled states involving two electrons for electronic radar will be the focus.

  A part of the work for aspects (2) and (3) will involve clarifying the concept of entanglement in electronic quantum optics and quantifying it based on experimentally measured quantities (such as current noise or, equivalently, second-order electronic coherences). This will be an important focus of the present project.

  5. Project Context and Planned Collaborations:

  This research project is part of the QuSig4QuSense research project funded by ANR, involving, in addition to the Lyon group, the experimental group of Gwendal Fève at ENS (Paris) and Inès Safi (Laboratoire de Physique des Solides in Orsay). Close attention will be given to the link with the experimental work, and regular exchanges are planned with the G. Fève group.

  Part (2) of this project is also part of the e-qubit-fly project funded by ANR under the "Quantum Computing on the Fly" call of the French national Quantum Plan. The e-qubit-fly project brings together key French groups involved in the development of electronic quantum optics.

• Type: Theoretical physics
• Advisors: Ines Safi (CR HDR CNRS) et Pascal Degiovanni (DR1 CNRS, ENS Lyon)
• Funding: To be determined
• Starting date: Internship in the Spring 2024, PhD studies in September 2024
• How to apply:
• Project : click here

  In recent years, a new field of research has emerged, aiming to study quantum electronic transport in its ultimate form, i.e., by manipulating one to a few coherent electronic excitations in a quantum conductor. A decade of work has led to demonstrating our ability not only to generate but also to characterize individual electronic excitations in certain quantum conductors, including the edge channels of the integer quantum Hall effect, which serve as analogs to optical fibers in quantum photonic optics.

  These progresses have opened the possibility to generate quantum electromagnetic fields in the microwave domain generated by quantum electrical currents propagating within edge channels of the quantum Hall effect. This will enable the fabrication of controlled on-chip quantum radiation sources. In these nano-circuits, photons are hybrid matter/light states involving charge density oscillation modes called "plasmons," whose propagation determines the finite-frequency electrical transport through the circuit.

  The proposed thesis aims to clarify how to use the plasmon modes of the edge channels of the Hall effect for microwave quantum optics. The questions addressed include:

  - What are the relationships between the properties of this radiation and the coherence properties of electrons?

  - Can we create nonlinear components that will generate non-classical states of radiation in the edge channels of the quantum Hall effect?

  - What is the electromagnetic radiation emitted by a source of single electrons, as well as by the interference of two electrons between such sources produced by an electron beam splitter?

  Note that a recent experiment has shown the possibility of generating non-classical (compressed) states of the electromagnetic field in the edge channels of the entire quantum Hall effect.

  A first step will consists in studying the behavior of plasmonic cavities obtained by closing an edge channel of the quantum Hall effect on itself. By deforming such an incompressible droplet of electrons using electrodes that allow the introduction of a quantum point contact (QPC), a model of a nonlinear resonator for plasmon modes is obtained. Experiments are currently being developed within the G. Fève group to measure the reflection and transmission of such resonators. Particular attention will be paid to probing the effect of electronic quantum coherence within these resonators by varying the magnetic flux and thus the Aharonov-Bohm phase of electrons, studying its effect on the resonator's response. Recent unified theories of non-equilibrium nonlinear transport developed by I. Safi will be exploited. These theories have inspired, in particular, a method for determining fractional charge.

  Collaborations and Skills:

  This thesis is part of the ANR project "QuSig4QuSense," involving the Physics Laboratory at ENS Lyon (P. Degiovanni), the Physics Laboratory at ENS Paris (G. Fève), and the LPS (I. Safi). Therefore, it will be conducted collaboratively among the three groups.

  Co-supervision is proposed between I. Safi (LPS) and P. Degiovanni (ENS Lyon), who is the coordinator of the QuSig4QuSense project and whose expertise is relevant for bridging quantum electronic and photonic optics.

  The required skills include both analytical and numerical abilities.

• Type: Theoretical physics
• Advisors: Pascal Degiovanni (DR1 CNRS, ENS Lyon)
• Funding: To be determined
• Starting date: Internship in the Spring 2024, PhD studies in September 2024
• How to apply:
• Project : click here

  A decade of development in electron quantum optics have demonstrated our capability not only to generate but also to characterize individual electronic excitations in certain quantum conductors, including the edge channels of the integer quantum Hall effect which serve as analogs to optical fibers in quantum photonic optics [Physica Status Solidi B 254, 1600618 (2017)]. It is now possible to prepare and characterize quantum electrical currents involving one too few electronic excitations in these systems [see Nature Communications 10, 3379 (2019)], therefore bringing quantum electrical transport closer to quantum optics experiments that are have been routinely performed in optics laboratories for a long time.

  On the other hand, time dependent electrical currents are known to emit electromagnetic radiation in Maxwell’s theory. This remain true in quantum electrodynamics but was never really investigated due to the lack of control on quantum electrical currents. Photon sources thus involve atoms, molecule or artificial systems such as qubits. However, the degree of control on quantum electrical currents reached in electron quantum optics opens the possibility to use them as flexible controlled sources of quantum electromagnetic radiation. A first step in this direction is the the generation of radiation with sub-vacuum quantum fluctuation at a given frequency recently demonstrated in quantum Hall edge channels by G. Fève’s group at the ENS Paris [Phys. Rev. Lett 130, 106201 (2023)].

  The PhD project aims at developing a method based on the controlled interaction of a well defined quantum electrical current with an electromagnetic environment, followed by a generalized measurement performed on the current itself. This idea, similar to the one used by S. Haroche et al in their groundbreaking cavity QED experiments, is based on exploiting the quantum backaction of the electronic generalized quantum measurement on the quantum electromagnetic field. The project will consist in determining this quantum back action for electrons propagating within quantum Hall edge channels and explore the prospect for quantum state preparation of various electronic measurement schemes currently in development.

  Some experimental groups at the British (National Physics Laboratory) and German (PTB) metrology institutes are developing electron quantum optics experiments where the electronic excitations are well separated from their electromagnetic environment. However, one has to take into account the remaining decoherence effects. In order to provide a framework suitable for the experiments performed at the ENS Paris, the PhD student will rely on the formalism developed by P. Degiovanni et al to describe electronic decoherence effects in the presence of a non-separable quantum environment and discuss how this can be used to describe the experiments envisioned by the metrology institutes.

  Skills and background:

  This project is mainly theoretical but involves a close interaction with experimental groups. It involves quantum measurement theory, light matter interaction, quantum field theory techniques for 1D quantum systems such as bosonization, the Glauber coherence formalism for quantum optics. Part of the work will be purely analytical but at some point, numerical techniques will be needed to obtain explicit results.

  Project Context and Planned Collaborations:

  This research project will involve the experimental group of Gwendal Fève at ENS (Paris) as well as the theory group of Pr. Vyacheslavs Kashcheyevs (University of Latvia in Riga). Regular visits to these groups will take place during the course of the project. Possible interactions with the quantum electronic microscopy community (Pr. Armin Feist, Göttingen) may also take place as the project unfolds.

• Type: Theoretical physics, Quantum information
• Advisors: Feller Alexandre (CPJ, PhLAM Lille), Adam Rançon (MCF, PhLAM Lille)
• Funding: Funded
• Starting date: Internship in Spring 2024, PhD studies in September 2024
• How to apply: alexandre.feller@univ-lille.fr
• Project : click here

  The measurement problem and the quantum-to-classical transition are major conceptual problems since the advent of quantum theory and have become central practical problems since the developments in quantum technologies in recent years. The physics of decoherence, coming from the entanglement between the system and its environment, made it possible to lay the theoretical foundations to understand these problems in depth. However, despite many successes, the quantum-to-classical problem is still not completely clarified. A central missing element in the traditional approach of decoherence is the study of the physics of observers themselves, and not just that of the system, in order to understand how a network of observers, equipped with specific resources, can reconstruct a common classic image, if it exists at all. This question was highlighted by the work of Zurek on quantum Darwinism where the tools of quantum information theory are predominant. However, theses ideas are still in their infancy and tools are needed to assess the existence of a classical image and the reconstruction abilities of a network of observers. This project aims to build a general resource-based quantum information framework allowing us to precisely analyze the problem of the emergence and reconstruction of a classical description. A specific aim of this work is to put these general ideas to the test via the study measurement signals.

  The present project will tackle the following questions:

  1. Bosonic signals: How to define and test the role of resources available to observers in the emergence of a classical consensus remains a largely open question. A simple case study to properly define and test it experimentally is through the study of bosonic signals (multimode light), in the spirit of quantum Darwinism, from circuit electrodynamics and quantum optics experiments. It will help lay the foundations of the "one-shot" quantum information approach to the problem, a necessary step to get closer to experimental reality.

  2. Fermionic signals: Analysis of this problem for fermionic degrees of freedom, especially their entanglement, remains largely to be done. It’s a major issue for fermionic quantum technologies. An important part of the proposed work is to clarify what we mean by fermionic entanglement and to understand howto characterize it through experimental quantum signals, like those of optics quantum optics.

  3. N-body signals and correlations: Finally, the final objective of the proposed work will be to bridge the gap between the "practical point of view" (measurement signals) and the N-body correlations structure of the quantum state. The central question to address is to determine what kind of correlations are needed between N-bodies for a classical description to exit and being recovered at a certain scale.

  Planned collaborations: This project will be carried out in collaboration with Pascal Degiovanni (Laboratoire de Physique, ENS de Lyon) as well as Benjamin Roussel (Aalto University) who are both experts in electronic quantum optics but also on quantum information theory and quantum signal processing.

Les étudiantes et étudiants de l'ENS de Lyon intéressés par une école d'hiver ou d'été sur le thème des sciences et technologies quantiques peuvent demander un financement pour y participer. De nombreuses écoles d'une semaine ou deux ont lieu chaque année notamment en Europe. N'hésitez pas à écrire à pour demander une participation financière dans la limite de 300€.

Les bourses France Excellence Quantum de l’Institut français NL financent la mobilité d’étudiants et de jeunes chercheurs de l’enseignement supérieur néerlandais dans le domaine du quantique qui souhaitent poursuivre leurs études ou effectuer des recherches en France. Les bourses France Excellence Quantum se destinent également aux étudiants et jeunes chercheurs de l’enseignement supérieur français, dans les mêmes domaines, souhaitant se rendre aux Pays-Bas. En partenariat avec : QuantEduFrance & Quantum Delta NL. Tous les détails ici.

Le vendredi 12 janvier 2024, la compagnie Les ateliers du spectacle est venue présenter un Impromptu Scientifique autour de la supraconductivité.

Un métal refroidi à l’extrême devient supraconducteur : il transporte le courant électrique sans résistance, sans perte d’énergie. Mais que se passe-t-il dans ce métal pour qu’un tel phénomène ait lieu ? Pour le comprendre, on suivra, au milieu des vapeurs d’azote et des métaux volants, le chercheur en physique quantique Hugues Pothier. A la rencontre de ces électrons qui n’ont pas choisi entre l’ici et l’ailleurs.
Hugues Pothier est chercheur en physique quantique au sein du groupe Quantronique, Service de physique de l'état condensé (SPEC) du CEA-Paris- Saclay.

Une production de la compagnie Les ateliers du spectacle.Coproduction CEA Paris Saclay avec le soutien de QuantEdu France et du programme de l’Union Européenne – Horizon 2020 recherche et innovation (No 828948), de la Région Île de France – La Science pour tous et de la Diagonale Paris-Saclay.

Les étudiantes et étudiants de l'ENS de Lyon peuvent participer à l'organisation de la fête de la science. Le projet QuantEdu permet de financer la construction d'ateliers autour des sciences et technologies quantiques.