ULTRAFAST SENSING BY ELECTRON AND MAJORANA FLYING QUBITS
An emerging pathway for quantum information is the use of flying electronic charges, such as single-electron excitations, as qubits.
These flying qubits present a key advantage: their intrinsic Coulomb interaction, which enables deterministic two-qubit gates and applications in quantum sensing.
Compared to photonic qubits, they therefore provide a natural means to overcome certain fundamental limitations.
Their main drawback lies in rapid decoherence, but this challenge can be mitigated by operating at ultrafast timescales, on the order of a picosecond.
An additional strategy involves exploiting the topological protection provided by Majorana modes, non-Abelian quasiparticles that are insensitive to local perturbations.
So far, most research has focused on localized 0D modes (at the ends of superconducting nanowires), with no conclusive experimental demonstrations.
This project proposes a new approach based on 1D chiral Majorana modes, offering a pathway toward topologically protected flying qubits.
The ambition is to establish a novel platform for quantum computing and quantum sensing.
This platform will exploit engineered multilayer graphene, combining the quantum anomalous Hall effect, superconductivity, and chiral Majorana modes.
Metallurgy under extreme conditions
The microstructure-properties relationship is a core concept of metallurgy, and of materials engineering in general. For instance, the hardness of quenched steels emerges from their martensitic microstructure, induced by a phase change in iron. Here we are concerned about metallurgy under extreme conditions in which metallic samples undergo pressurizations in the 100 GPa (=1 million atmospheres) range, making it possible to synthesise new crystalline phases with potentially interesting properties (hardness, magnetism, etc.).
Studied systems will include tin, then indium and cobalt. The three of them exhibit a rich polymorphism under high pressure and temperature. We will seek to elucidate the role of defects such as twinning and plasticity on the mechanism and kinetics of these transitions. This will be done by comparing experimental observations with microstructure predictions obtained through mesoscopic simulation. High pressure/ high temperature will be mainly generated by laser-heated diamond anvil cells, and characterisation tools will include in situ X-ray imaging by diffraction and tomography, as well as electron microscopy. The X-ray sources used will be synchrotron sources and the European free-electron X-ray laser.
microstructure informed kinetic model : application to solid explosives
When an explosive composition is subjected to an intense stress, such as a shock, the wave generated interacts with the microstructure and in particular with the defects it contains. Due to the nature of the defects, the energy can be localised, as when porosity is compacted, which can lead to the appearance of hot spots. Beyond a certain critical size, these hot spots grow as a result of the chemical decomposition of the explosive, and in some cases this can lead to the creation of a detonation wave. The role of these hot spots is therefore decisive in the initiation of solid explosives. The majority of macroscopic models used to study the shock-detonation transition (SDT) are phenomenological models calibrated on experiments (e.g. multi-strand gauge experiments) and therefore do not take into account the microstructural peculiarities specific to each explosive. It then becomes necessary to recalibrate a model for each composition, which limits any predictive capacity.
Microtomographic studies of real microstructures of explosive compositions have revealed that these deviate significantly from an average description based on a spherical pore. Through image segmentation, these microtomographs can provide essential ingredients for mesoscopic-scale simulation codes: these microstructures can be used directly as input for calculations or as a basis for generating virtual but realistic microstructures, thereby extending the accessible database given the experimental difficulties in generating this type of image in large numbers.
The computing power available today means that we can now envisage explicit simulations of realistic microstructures of explosive compositions. These simulations, in two or even three dimensions, will form the basis for the construction of a macroscopic kinetics model for modelling the shock-detonation transition. The results expected from this work are cross-disciplinary and can be transposed to all composite energetic materials. The effect of thermal or mechanical damage on the behaviour of an explosive or a solid propellant (vulnerability issues) could also benefit from this project. This more detailed knowledge of the role of microstructure (grain shape, porosity, etc.) could also improve filler manufacturing processes (e.g. ‘Very Insensitive’-RDX).
Thermally activated glide of screw dislocations in bcc metals
Thermally activated glide of dislocation is a key point for understanding the plastic deformation of metals. The screw dislocation in bcc metals is an archetypical case for which a large quantity of experimental data has been published in the scientific literature. It is then possible to compare these data to the theoretical predictions realized from the Vineyard statistical theory [1,2]. Such a theory is an essential tool allowing to perform a scale transition from atomistic computations [3] toward macroscopic scale at which are realized the deformation tests.
The aim of our research will be to test Vineyard theory in comparison with molecular dynamics simulations [4]. Some preliminary computations have shown a significant discrepancy that is not present when we repeat the comparison for point-like defect as vacancies or self-interstitial atoms. The discrepancy of the theory will have to be reduce within a new theoretical development. Our new theory should allow some predictions in agreement with macroscopic tensile test in bcc metals [5].
[1] Vineyard G.H., J. Phys. Chem. Solids 3, 121 (1957).
[2] Proville L., Rodney D., Marinica M-C., Nature Mater. 11, 845 (2012).
[3] Proville L., Ventelon L., Rodney D., Phys. Rev. B 87, 144106 (2013).
[4] Proville L., Choudhury A., Nature Mater. 23, 47 (2024).
[5] Caillard D., Acta Mater. 58, 3504 (2010).
Understanding the signals emitted by moving liquids
Elasticity is one of the oldest physical properties of condensed matter. It is expressed by a constant of proportionality G between the applied stress (s) and the deformation (?): s = G.? (Hooke's law). The absence of resistance to shear deformation (G' = 0) indicates liquid-like behavior (Maxwell model). Long considered specific to solids, shear elasticity has recently been identified in liquids at the submillimeter scale [1].
The identification of liquid shear elasticity (non-zero G') is a promise of discoveries of new liquid properties. For example, do we know that a confined liquid changes temperature under flow? Yet no classical model (Poiseuille, Navier-Stokes, Maxwell) predicts the effect because without long-range correlation between molecules (i.e. without elasticity), the flow is dissipative, therefore athermal. For a change in temperature to be flow induced (without a heat source), the liquid must have elasticity and this elasticity must be stressed [1,2].
The PhD thesis will explore how the mechanical energy of the flow is converted in a thermal response [2]. We will exploit the capacity of conversion to develop a new generation of microfluidic devices (patent FR2206312).
We will also explore the impact of the wetting on the liquid flow, and reciprocally, we will examine how the liquid flow modifies the solid dynamics (THz) of the substrate [3]. Powerful methods only available in Very Large Research Facilities such as the ILL will be used to probe the non-equilibrium state of solid phonons. Finally, we will strengthen our existing collaborations with theoreticians.
The PhD topic is related to wetting, macroscopic thermal effects, phonon dynamics and liquid transport.
1. A. Zaccone, K. Trachenko, “Explaining the low-frequency shear elasticity of confined liquids" PNAS, 117 (2020) 19653–19655. Doi:10.1073/pnas.2010787117
2. E. Kume, P. Baroni, L. Noirez, “Strain-induced violation of temperature uniformity in mesoscale liquids” Sci. Rep. 10 13340 (2020). Doi : 10.1038/s41598-020-69404-1.
3. M. Warburton, J. Ablett, P. Baroni, JP Rueff, L. Paolasini, L. Noirez, “Identification by Inelastic X-Ray scattering of bulk alteration of solid dynamics due to Liquid Wetting”, J. of Molecular Liquids 391 (2023) 123342202