Il est bien connu que les propriétés d'un émetteur de lumière ponctuel, tel qu'un atome ou une boîte quantique, peuvent être drastiquement modifiées à l'aide d'une cavité optique. Je passerai en revue les principales stratégies pour y parvenir, en évoquant notamment le cas des nano-antennes métalliques avec lesquelles nous travaillons au laboratoire pour façonner l'émission de LEDs à boîtes quantiques colloïdales. Nous verrons à travers ces différents exemples que l'intuition que possède la communauté sur ces systèmes repose pour l'essentiel sur des modèles et expériences impliquant des émetteurs uniques. Je présenterai ensuite des mesures nouvelles qui montrent que cette intuition n'est en fait pas pertinente dès lors que le système comprend un ensemble d'émetteurs en interaction. Je rationaliserai ces observations et discuterai des potentialités de ce régime d'émission pour l'optique et l'optoélectronique à l'échelle nano.

The strength of the electroweak symmetry breaking at high temperatures of the early Universe could substantially differ from the present day value. The Standard Model predicts the electroweak symmetry to get restored above the temperatures of about 160 GeV. I will discuss the recently proposed scenarios where the situation is reversed, and the breaking survives even at high temperatures. I will also discuss the implications of such a behaviour for one of the popular scenarios explaining the matter-antimatter asymmetry -- electroweak baryogenesis.

Understanding the structure and mechanical behavior of materials on the microscopic scales is crucial for the design of products with desired properties. This thesis focuses on obtaining microscopic insights into the properties, notably fracture, of oxide glasses which are among the most widely used materials in the world. To this end, we use state-of-the-art atomistic simulation techniques to investigate silica and sodium silicates, i.e., the prototypical compositions for many oxide glasses. Using large-scale molecular dynamics simulations, the dynamic fracture of the glasses is studied in depth. We show that the mechanical properties of the glasses are considerably more sensitive to the used interaction potential and simulation protocol than the structural properties. Fracture of silica glass is found to be pure bond rupturing at the crack tip, whereas fracture of Na-rich glasses is accompanied by the growth and coalescence of cavities. We also reveal that the nonaffine atomic displacement is the microscopic reason for the composition induced transition behavior in the stiffness of these glasses. It is found that the surfaces generated by the fracture are considerably rougher than the melt-formed surfaces and exhibit logarithmic-scaling at the nanoscale (≤ 10 nm). By using first-principles simulations, the vibrational and electronic signatures of some structural units that are abundant on the glass surface are identified. In addition, the ionicity and strength of various types of bonds are inferred from these simulations. Finally, we introduce a novel method to characterize the structure in liquids and glasses. Our analysis shows that these systems have a three-dimensional structure that is surprisingly ordered.

Keywords:
Oxide glasses, silica, sodium silicate, deformation, fracture, surface, atomistic computer simulations, molecular dynamics, first-principle calculations, chemical bonding, structural order

$T^4$ visio-conf*

Karsten will entertain us with the possibility that primordial magnetic fields could resolve the present-day Hubble tension

https://arxiv.org/abs/2004.09487

*bring your own tea/coffee/biscuits; visio-break around 3:30pm

$T^4$ visio-conf*

PART II of:
Karsten will entertain us with the possibility that primordial magnetic fields could resolve the present-day Hubble tension

https://arxiv.org/abs/2004.09487

*bring your own tea/coffee/biscuits; visio-break around 3:30pm

** This defense will take place online due to the current UM rules -- please contact me and I send you the link for the visioconference **
Biology offers new systems for Physics, namely proteins and molecular motors in interaction with biopolymers like DNA and messenger RNA. This field is at the interface between active matter, polymer physics, and physics of colloids. Interestingly, cells also need to increase locally concentrations of proteins in a phase transition-like mechanism to realize vital function like cell division, DNA repair, DNA segregation etc.

During this HDR defense, I will offer a physical perspective of intracellular phase transition with the example of bacterial DNA segregation. I will also discuss the motion of ribosomes along messenger RNA, an example of unidimensional inhomogeneous transport giving rise to different dynamical regimes.

The most impressive aspect of 2D materials is not the fact that they include vast variety of electronic and optical properties (metals, large band gap semiconductors, superconductors, ferromagnetic, ...). Their specificity is that they can be combined or stacked on top of other materials, quantum light sources or photonic elements, they can even be twisted in plane from another 2D materials. In my talk I will present some illustrations of that unique degree of freedom within the context of material science, optomechanics and quantum nano-photonics.
In particular I will present a graphene NEMS suspended a few tens of nanometers above nitrogen-vacancy centres (NVCs), which are stable single-photon emitters embedded in nanodiamonds [1]. The optomechanical coupling between the graphene displacement and the NVC emission is based on near-field dipole–dipole interaction, making it suitable for nanoscale devices. Semiconducting NEMS (WSe2, MoSe2) also show high mechanical Q-factors, which can be used to study the thermal properties of such materials[4]. Then, I will show a slightly different hybrid system consisting in lifetime-limited single emitters [2,3] (linewidth ~40 MHz) and 2D materials at sub-wavelength separation without degradation of the emission properties [4]. Our device’s nanoscale dimensions enable ultra-broadband tuning (tuning range > 400 GHz) and fast modulation (frequency ~ 100 MHz) of the emission energy, which renders it an integrated, ultra-compact tuneable SPS [5]. Conversely, this offers a novel approach to optical sensing of 2D material properties using a single emitter as a nanoprobe.

References
[1] Reserbat-Plantey A., Schädler K., Gaudreau L., Navickaite G., Güttinger J., Chang D.,Toninelli C., Bachtold A., and Koppens F. Electromechanical control of nitrogen- vacancy defect emission using graphene NEMS. Nature Communication. 7, 10218. 2016
[2] N. Morell, S. Tepsic, A. Reserbat-Plantey, A. Cepellotti, M. Manca, I. Epstein, A. Isacsson, X. Marie, F. Mauri, and Adrian Bachtold. Optomechanical Measurement of Thermal Transport in Two-Dimensional MoSe2 Lattices. Nano Letters. 19-5, 3141. 2019
[3] Morell*, N., Reserbat-Plantey*, A., Tsioutsios, I., Schädler, K., Dubin, F., Koppens, F., Bachtold, A. High Quality Factor Mechanical Resonators Based on WSe2 Monolayers.
Nano Letters. 16, 5102–5108. 2016
[4] K. Schädler,C. Ciancico, S.Pazzagli, P. Lombardi, A. Bachtold, C. Toninelli, A. Reserbat- Plantey, and F. Koppens. Electrical Control of Lifetime-Limited Quantum Emitters Using 2D Materials. Nano Letters. 19-6. 3789. 2019
[5] C. Ciancico, K. Schädler, S. Pazzagli, M. Colautti, P. Lombardi, J. Osmond, C. Dore, A. Mihi, A. Ovvyan, W. Pernice, E. Berretti, A. Lavacchi, C. Toninelli, F. Koppens and A. Reserbat- Plantey. Narrow Line Width Quantum Emitters in an Electron-Beam-Shaped Polymer. ACS Photonics, 6, 12, 3120. 2019