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Chimie des processus biologiques: [résumé des cours et travaux : 2021-2022]
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Tailoring porphyrinic MOF-545 performances for CO 2 photocatalytic reduction through linker chlorination
No full textInternational audienceChlorinating porphyrin linkers in MOF-545 boosts photocatalytic CO 2 -to-formate conversion under visible light by tuning the electronic structure and the band gap
Reassessment of the global distribution and diversity of modern planktonic foraminifera from the FORCIS database
No full textInternational audiencePlanktonic foraminifera (PF) shells are ubiquitous archives used as proxies in paleoceanography and play a crucial role in paleoclimate reconstructions. Species respond differently to abiotic and biotic factors and have shifted habitats with recent ocean warming. We re-evaluate the biogeographic limits of major PF species in the modern ocean, using the FORCIS data to extend the data coverage and explore potentially overlooked distributions of (small) species from the seminal works from the 1950s to the 1970s that were based on > 200 µm mesh-size plankton tows. We present a comprehensive update of their modern biogeography, vertical habitat distribution, and thermal tolerance using the FORCIS database, which includes all available water-column-sourced data from the last century. Our analysis confirms that the higher PF diversity is in the tropical and subtropical oceans. PF are observed in temperatures ranging from −2 to 31 °C, highlighting their remarkable thermal tolerance and/or adaptability to a wide range of temperatures. In addition, species that displayed a preferential habitat in lower latitudes in the 1950-to-1970 time interval (e.g. G. ruber) have been observed at higher latitudes over the last 50 years. Since the 1970s, medium-sized species have increased in abundance across all latitudes, from the tropical to polar oceans, a trend particularly evident in the extensive data from the eastern North Atlantic. The analysis of the FORCIS database updates the evolving biogeography of modern PF and advances our understanding of their ecology, providing revised benchmarks for paleoceanographic interpretations and the ecology of modern planktonic calcifiers
Entre texte et temple : La transformation de la pratique monastique
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Terahertz Fourier Ptychographic Imaging
No full textInternational audienceHigh-resolution imaging in the terahertz (THz) spectral range remains fundamentally constrained by the limited numerical apertures of currently existing state-of-the-art imagers, which restricts its applicability across many fields, such as imaging in complex media or nondestructive testing. To address this challenge, we introduce a proof-of-concept implementation of THz Fourier Ptychographic imaging to enhance spatial resolution without requiring extensive hardware modifications. Our method employs a motorized kinematic mirror to generate a sequence of controlled, multi-angle plane-wave illuminations, with each resulting oblique-illumination intensity image encoding a limited portion of the spatial-frequency content of the target imaging sample. These measurements are combined in the Fourier domain using an aberration-corrected iterative phase-retrieval algorithm integrated with an efficient illumination calibration scheme, which enables the reconstruction of resolution-enhanced amplitude and phase images through the synthetic expansion of the effective numerical aperture. Our work establishes a robust framework for high-resolution THz imaging and paves the way for a wide array of applications in materials characterization, spectroscopy, and non-destructive evaluation
Quantum Simulation with Fluxonium Qutrit Arrays
No full textInternational audienceFluxonium superconducting circuits were originally proposed to realize highly coherent qubits. In this work, we explore how these circuits can be used to implement and harness qutrits, by tuning their energy levels and matrix elements via an external flux bias. In particular, we investigate the distinctive features of arrays of fluxonium qutrits, and their potential for the quantum simulation of exotic quantum matter. We identify four different operational regimes, classified according to the plasmon-like versus fluxon-like nature of the qutrit excitations. Highly tunable on-site interactions are complemented by correlated single-particle hopping, pair hopping and non-local interactions, which naturally emerge and have different weights in the four regimes. Dispersive corrections and decoherence are also analyzed. We investigate the rich ground-state phase diagram of qutrit arrays and propose practical dynamical experiments to probe the different regimes. Altogether, fluxonium qutrit arrays emerge as a versatile and experimentally accessible platform to explore strongly correlated bosonic matter beyond the Bose-Hubbard paradigm, and with a potential toward simulating lattice gauge theories and non-Abelian topological states
Looking elsewhere: improving variational Monte Carlo gradients by importance sampling
No full textInternational audienceNeural-network quantum states (NQS) offer a powerful and expressive ansatz for representing quantum many-body wave functions. However, their training via Variational Monte Carlo (VMC) methods remains challenging. It is well known that some scenarios -such as sharply peaked wave functions emerging in quantum chemistry -lead to high-variance gradient estimators hindering the effectiveness of variational optimizations. In this work we investigate a systematic strategy to tackle those sampling issues by means of adaptively tuned importance sampling. Our approach is explicitly designed to target the gradient estimator instead of the loss function and be computationally inexpensive. We benchmarked our approach across the ground-state search of a wide variety of hamiltonians, including frustrated spin systems and ab-initio quantum chemistry. Overall, our approach can reduce the computational cost of vanilla VMC considerably, up to a factor of 100x when targeting highly peaked quantum chemistry wavefunctions
Approaching Kasteleyn transition in frustrated quantum Heisenberg antiferromagnets
No full textWe show that the Kasteleyn transition, the abrupt proliferation of infinite strings of defects in classical dimer and related models, can also be relevant for frustrated 2d quantum magnets. This is explicitly demonstrated in a phase of the spin-1/2 Heisenberg diamond-decorated honeycomb lattice where a family of exact eigenstates built as products of dimer and plaquette singlets can be mapped onto the dimer coverings of the honeycomb lattice. The low-temperature properties of this phase are accurately described by an effective dimer model with anisotropic activities and a small, tunable density of monomers, leading to an arbitrarily sharp crossover version of the Kasteleyn transition. The generalization to other geometries and the possibility to realize this model in organo-metallic compounds are briefly discussed
