Laboratoire de Chimie et Physique Quantiques

Group IV color centers in diamond are promising single-photon emitters for quantum information processing and networking. Among them, the tin-vacancy (SnV) center stands out due to its long spin coherence times at cryogenic temperatures above 1 K. While SnV centers have been realized using various fabrication routes, their in situ formation via microwave plasma-enhanced chemical vapor deposition (MW PE CVD) remains relatively unexplored. In this study, SnV centers, identified by a zero-phonon line (ZPL) near 620 nm, were synthesized in nanocrystalline diamond and free-standing microcrystalline diamond using tin oxide (SnO2) as a dopant source at substrate temperatures of 750°C and 850°C. Photoluminescence measurements reveal that lowering the substrate temperature enhances both the ZPL intensity and spatial uniformity of SnV centers. These results highlight substrate temperature as a key parameter for controlling SnV incorporation during MW PE CVD growth and provide insights into optimizing fabrication strategies for diamond-based quantum technologies.

Hydrogenated amorphous carbons (HACs) are complex, disordered forms of carbon that are of interest in various scientific fields, such as the study of air pollution from soot particles and astrochemistry. A new stochastic, structurally guided algorithm is presented for the large-scale generation of atomistic models of HACs. It consists of a two-step procedure: (i) the randomized generation of 2D structures using the SMILES (simplified molecular input line entry system) description, respecting user-predefined chemical constraints; (ii) the subsequent generation of 3D structures, making use of a stochastic sampling algorithm combined with local optimizations at the DFTB (density functional-based tight binding) level. The method was used to generate the ARMAGNHAC database (web site: https://armagnhac.laas.fr/) which provides structural (Cartesian coordinates, functional group ratios, Hill-Wheeler parameters, and aromaticity descriptors), energetic (HOMO-LUMO gap, ionization energy, and electronic affinity), and spectroscopic properties of 4366 HACs. Correlation plots between these descriptors can be generated on the web site, as well as IR spectra, possibly including their evolution as a function of a given property. Several illustrations are given, such as the dependence of the ionization potentials and electronic affinities on the size of the largest aromatic island of the HACs. The database (structures and properties) can be downloaded by users. This work paves the way for future studies aiming to derive relationships between structure, energetic, and spectral properties of HACs, as required to interpret spectral observations and experimental measurements.

Zwitterionic mixed-valence (MV) complexes offer a compelling strategy for designing charge-neutral molecular components for quantum-dot cellular automata (QCA). In this work, organometallic zwitterions 1a and 1b featuring two [Cp*(dppe)Fe] redox centers linked by a meta-phenylene ethynylene bridge and an internal carboxylate were generated and characterized. A comprehensive investigation combining cyclic voltammetry, IR, and vis–NIR spectroscopies unambiguously establishes that both 1a and 1b behave as charge-localized Robin–Day class-II MV systems. This crucial finding demonstrates that the covalently tethered counterion does not significantly alter the weak electronic communication inherent to the meta-substituted bridge. To rationalize these experimental results, density functional theory (DFT) calculations were performed. It is shown that while simplified gas-phase models inadequately predict a delocalized state, calculations incorporating a polarizable continuum model (PCM–CH2Cl2) successfully reproduce the experimentally observed charge localization. The agreement between the experimental data and the solvated theoretical model provides robust validation for the class-II description and confirms this zwitterionic design as a viable approach for creating charge-neutral molecular wires.

While photopharmacology enables precise spatiotemporal control over drug activity, its widespread reliance on UV‐responsive molecules often hinders preclinical and clinical advancements. Thus, alternative scaffolds can offer promising advantages over the commonly used azobenzene family. In this study, we introduce the first hemiindigo‐based photopharmacological agents, which are capable of isomer‐dependent human acetylcholinesterase inhibition in the nanomolar range. These hemiindigo photoswitches exhibit highly favorable properties: They are fully functional in aqueous medium with good photoisomerization quantum yields, respond exclusively to blue‐to‐orange visible light (415–590 nm), and maintain high stability in their metastable form, even in physiological buffers. Notably, indoxyl N ‐methylation emerged as a key structural feature for optimizing photophysical properties, as demonstrated through crystallography and a theoretical model describing the photochemical pathways governing photoisomerization. Overall, this study paves the way for broader exploration and future applications of the largely overlooked hemiindigo scaffold in photopharmacology.

Heterostructures involving transition metal dichalcogenides (TMDs) have attracted significant research interest due to the richness and versatility of the underlying physical phenomena. In this work, we investigate a heterostructure consisting of a rare-earth material, specifically a Gd monolayer, interfaced with WSe$_2$. We explore its electronic structure, magnetic properties, and transport behavior, with particular emphasis on the emergence of the anomalous Hall effect (AHE). Both Gd and W are heavy elements, providing strong spin-orbit coupling (SOC), which plays a crucial role in triggering the AHE. The combination of strong SOC and inversion symmetry breaking leads to pronounced asymmetries between the $\Gamma-K$ and $\Gamma-K^\prime$ directions in the Brillouin zone. Our calculations reveal a substantial anomalous Hall conductivity (AHC) at the ferromagnetic interface, primarily originating from numerous avoided crossings involving the d-states of both Gd and W near the Fermi level. Moreover, we demonstrate that the AHC is highly tunable, either by adjusting the in-plane lattice constant or by reducing the separation between Gd and WSe$_2$.

A linear fluid model defined by the continuity equation, and the momentum and energy balance equations, valid for describing high temperature and collisionless plasmas in the presence of an electromagnetic (EM) wave is proposed. The collisionless closure relations, the ponderomotive force, and the absorption rate of the EM wave are calculated for a relativistic temperature regime while assuming non-relativistic electron oscillation velocities in the laser electric field. The model equations coupled with the Maxwell's equations are used to study the filamentation instability (FI) in the context of inertial confinement fusion. Both the stationary and non-stationary filamentation instabilities are investigated. It is shown that the ponderomotive source of the instability is preponderant compared to the thermal source, and that the ponderomotive spatial growth rate increases significantly with the plasma temperature. The FI growth rates are compared to those of stimulated Brillouin and Raman scattering. At high temperatures, significant amplification of the filamentation instability is expected, potentially leading to non-uniform target compression, which could be detrimental for fusion.

The Coherent Backscattering (CBS) peak is a well-known interferential signature of weak localization in disordered or chaotic systems. More recently, a second interference feature -- the Coherent Forward Scattering (CFS) peak -- was predicted to emerge in the regime of strong localization. However, it has never been directly observed. Here we report the first direct observation of the CFS peak and demonstrate its dual role as a signature of non-ergodicity and as a probe of symmetries in quantum chaotic systems. Using a shaken rotor model realized with a Bose-Einstein condensate (BEC) of ultracold atoms in a modulated optical lattice, we investigate dynamical localization in momentum space. The CFS peak emerges in the position distribution as a consequence of non-ergodic dynamics, while its growth timescale reveals the underlying localization length. By finely tuning the modulation, we control time-reversal and parity symmetries and measure their distinct effects on both CBS and CFS peaks. Our results highlight the strong link of both the temporal growth and contrast of the CFS with symmetry and localization, making it a robust probe of these properties. This work opens new directions for characterizing non-ergodicity and symmetries in quantum chaotic or disordered systems, with possible applications in many-body localization and chaos.

Pentagonal bipyramidal complexes with a first-order spin–orbit coupling contribution can be readily obtained by chemical design optimization.

A series of windmill-shape heterocyclic molecules containing three N-B←N units, TBN and its derivatives, with quasi-planar C3 symmetric backbone, are synthesized. The parent TBN exhibits a strongly allowed, doubly degenerate lowest excited state but suffers from very low fluorescence, due to very fast nonradiative decay rate through a conical intersection (CI) as revealed by femtosecond transient absorption spectroscopy and quantum-chemical calculations. Introducing peripheral phenyl- or thienyl-groups (Ph-TBN or Th-TBN) induces pronounced bathochromic shifts and enhances fluorescence, which is beneficial from inhibited nonradiative pathway by the increased energy barriers to access the CI at excited state. The understanding of this rather uncommon behaviour may open routes for the design of novel fluorescence materials.

The intermediate scattering function is interpreted as a correlation function of thermal wave packets of the scattering centers perturbed by the scattering particles at different times. A proof of concept is given at the example of ballistic moving centers. The ensuing numerical method is then illustrated at the example of CO adsorbed on Cu(100).