Table of hyperfine anomaly in atomic systems

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1. Apparenté Pas pertinent

   Precision measurement of the n=2 triplet P J=1-to-J=0 fine structure of atomic helium using frequency-offset separated oscillatory fields

   F. Heydarizadmotlagh, T. D. G. Skinner, K. Kato et al. · 2023 · Physique atomique · Résumé IA disponible

   Résumé scientifique

   Increasing accuracy of the theory and experiment of the $n$$=$$2$ $^3$P fine structure of helium has allowed for increasingly-precise tests of quantum electrodynamics (QED), determinations of the fine-structure constant $\alpha$, and limitations on possible beyond-the-Standard-Model physics. Here we present a 2~part-per-billion (ppb) measurement of the $J$$=$$1$-to-$J$$=$$0$ interval. The measurement is performed using frequency-offset separated-oscillatory-fields. Our result of $29\,616\,955\,018(60)$~Hz represents a landmark for helium fine-structure measurements, and, for the first time, will allow for a 1-ppb determination of the fine-structure constant when QED theory for the interval i…

2. Apparenté Pas pertinent

   Cooperative non-equilibrium phase transition in a dilute thermal atomic gas

   Christopher Carr, Ralf Ritter, Kevin J Weatherill et al. · 2013 · Physique atomique · Résumé IA disponible

   Résumé scientifique

   We demonstrate a cooperative first-order non-equilibrium phase transition in an optically-driven atomic ensemble. The long-range correlation arises due to dipole-dipole interactions between Rydberg atoms. The macroscopic phase transition is observed in the optical domain as intrinsic optical bistability displaying hysteresis and critical slowing down. In the emitted fluorescence, the phase transition occurs between states characterized by single-atom decay and many-body superradiant decay. The demonstration of non-equilibrium phenomena in a controlled, non-destructive environment contributes important experimental evidence to the study of many-body dynamics in complex systems.

3. Apparenté Pas pertinent

   Charge Migration in Heterocyclic Five-Membered Rings

   Sucharita Giri, Gopal Dixit, Jean Christophe Tremblay · 2023 · Physique atomique · Résumé IA disponible

   Résumé scientifique

   This contribution presents numerical simulations of N-electron dynamics in heterocyclic five-membered ring molecules to shed light on the effect of molecular symmetry on charge migration. Laser-driven dynamics is studied using the hybrid time-dependent density functional theory/configuration methodology, and the ensuing field-free charge migration is investigated by means of transient electronic flux density maps. Our results demonstrate that the charge migration in aromatic rings is sensitive to the presence of heteroatoms such as oxygen and nitrogen. Their presence within the ring induces significant modifications of the character in the ground and low-lying electronic states, which is imp…

4. Apparenté Pas pertinent

   Optimization of the ionization time of an atom with tailored laser pulses: a theoretical study

   David Kammerlander, Alberto Castro, Miguel A. L. Marques · 2016 · Physique atomique · Résumé IA disponible

   Résumé scientifique

   How fast can a laser pulse ionize an atom? We address this question by considering pulses that carry a fixed time-integrated energy per-area, and finding those that achieve the double requirement of maximizing the ionization that they induce, while having the shortest duration. We formulate this double-objective quantum optimal control problem by making use of the Pareto approach to multi-objetive optimization, and the differential evolution genetic algorithm. The goal is to find out how much a precise time-profiling of ultra-fast, large-bandwidth pulses may speed up the ionization process with respect to simple-shape pulses. We work on a simple one-dimensional model of hydrogen-like atoms (…

5. Apparenté Pas pertinent

   Femtosecond pulse parameter estimation from photoelectron momenta using machine learning

   Tomasz Szołdra, Marcelo F. Ciappina, Nicholas Werby et al. · 2023 · New J. Phys. 25, 083039 (2023) · Résumé IA disponible

   Résumé scientifique

   Deep learning models have provided huge interpretation power for image-like data. Specifically, convolutional neural networks (CNNs) have demonstrated incredible acuity for tasks such as feature extraction or parameter estimation. Here we test CNNs on strong-field ionization photoelectron spectra, training on theoretical data sets to `invert' experimental data. Pulse characterization is used as a `testing ground', specifically we retrieve the laser intensity, where `traditional' measurements typically lead to 20% uncertainty. We report on crucial data augmentation techniques required to successfully train on theoretical data and return consistent results from experiments, including accountin…

6. Apparenté Pas pertinent

   Use of a Microcontroller for Fast Feedback Control of a Fiber Laser

   M. R. Dietrich, B. B. Blinov · 2009 · Physique atomique · Résumé IA disponible

   Résumé scientifique

   An inexpensive, easily programmed microcontroller is demonstrated for the fast frequency stabilization of an infrared fiber laser. The microcontroller manages all digitalization and processing, with external circuitry only providing buffering, amplification and overvoltage protection. Several convenient features are included to recover from common failure modes of a laser lock system, and a final Nyquist frequency of 200 kHz is obtained, corresponding to a usable bandwidth of 40-60 kHz.