arXiv subjects

Daniel Comparat

Publications and source records attributed to Daniel Comparat.

At least 19 recordsLinked to original sources

arXiv2026

Simulation of Rydberg Ionization in Atomic Beams for FIB Optimization

This study explores the excitation and ionization of an atomic beam as a pathway to optimize focused ion beams (FIBs) for high-precision applications. Leveraging the unique advantages of Rydberg excitation followed by field ionization -- specifically its ability to minimize velocity and position dispersions -- we present a method to generate ion beams with good performance at low energies. A custom Lua program, integrated into the SIMION simulation platform, models the intricate processes of particle distributions, laser excitation, and Rydberg ionization. This integrated approach incorporates essential parameters such as excitation and ionization rates, Stark shifts, Doppler effects, and electric fields, enabling a detailed analysis of ion beam properties. Our simulations demonstrate the influence of critical factors such as the chosen Rydberg state, ionization region characteristics, and velocity dispersions on the final ion beam quality. By optimizing these parameters, we achieve significant reduction of the axial energy spread and the longitudinal extent of the ionization region. This framework bridges theoretical modeling and experimental validation, offering a comprehensive toolkit for the development of next-generation ion sources and advancing FIB technologies across various scientific domains.

physics.atom-ph↗

arXiv2025

Atomic Observables Induced by Cosmic Fields

The existence of cosmic fields made from yet unknown light bosons is predicted in many extensions to the Standard Model. They are especially of interest as possible constituents of dark matter. To detect such light and weakly interacting fields, atomic precision measurements offer one of the most sensitive platforms. In this work, we derive which atomic observables are sensitive to what kind of cosmic field couplings. For this we consider fields that couple either through scalar, pseudoscalar, vector, axial vector, or tensor couplings. We derive the corresponding non relativistic atomic potentials. Based on their symmetry properties, these can induce direct energy shifts or induce atomic electric dipole, magnetic dipole, electric quadrupole as well as nuclear Schiff and anapole moments.

hep-ph↗

arXiv2025

Demonstration of deuterium's enhanced sensitivity to symmetry violations governed by the Standard-Model Extension

We have performed hyperfine spectroscopy of two transitions in ground-state deuterium and searched for violations of CPT and Lorentz symmetry that would manifest as sidereal variations of the observed transition frequencies. Several nonrelativistic proton coefficients of the Standard-Model Extension framework have been addressed. The spin-independent coefficients with momentum power k=2,4 are constrained for the first time. Bounds on spin-dependent coefficients are improved by exploiting a sensitivity enhancement originating from the relative momenta of the nucleons in the deuteron. The best previous constraints by hydrogen maser measurements are surpassed by 4 and 14 orders of magnitude for coefficients with k=2 and 4, respectively.

hep-ex↗

arXiv2024

Polarizabilities as Probes for P, T, and PT Violation

Searches for violations of the fundamental symmetries of parity P and time reversal T in atomic and molecular systems provide a powerful tool for precise measurements of the physics of and beyond the standard model. In this work, we investigate how these symmetry violations affect the response of atoms and molecules to applied electric and magnetic fields. We recover well-known observables such as the P-odd, T-odd spin-electric field coupling that is used for searches of the electron electric dipole moment (eEDM) or the effect of P-odd, T-even optical rotation in atomic gases. Besides these, we obtain several other possible observables. This includes, in particular, effects that can only be seen when using oscillating or inhomogeneous fields.

physics.atom-ph↗

arXiv2024

Coherent laser cooling with trains of ultrashort laser pulses

We propose to extend coherent laser cooling from narrow-band to broad-band transitions by using trains of ultrashort broadband pulses. We study analytically two possible methods to reduce the momentum spread of a distribution by several units of photon momentum in a single spontaneous emission lifetime. We report on numerical simulations of one-dimensional laser cooling of a two-level system with realistic parameters. The technique introduced here is of high interest for efficient laser cooling of fast species with short lifetime such as positronium.

physics.optics↗

arXiv2023

Experimental perspectives on the matter-antimatter asymmetry puzzle: developments in electron EDM and antihydrogen experiments

In the search for clues to the matter-antimatter puzzle, experiments with atoms or molecules play a particular role. These systems allow measurements with very high precision, as demonstrated by the unprecedented limits down to $10^{-30}$ e.cm on electron EDM using molecular ions, and relative measurements at the level of $10^{-12}$ in spectroscopy of antihydrogen atoms. Building on these impressive measurements, new experimental directions offer potentials for drastic improvements. We review here some of the new perspectives in those fields and their associated prospects for new physics searches.

physics.atom-ph↗

arXiv2023

Comparative analysis of recirculating and collimating cesium ovens

We have performed a study of several cesium oven designs. A comparison between recirculating (or sticking-wall) or collimating (or reemitting-wall) ovens is made in order to extract the most efficient design in terms of beam brightness. Unfortunately, non-reproducible behaviors have been observed, and the most often observed output flux is similar to the sticking-wall case, which is the lowest theoretical value of the two cases, with a beam brightness close to $10^{18}$ at.sr$^{-1}$.s$^{-1}$.cm$^{-2}$. The reason of this universally observed behavior is unclear despite having tested several materials for the collimating tube. Conclusion on possible improved design based on sticking of cesium on several (un)cleaned surface is given.

physics.atom-ph↗

arXiv2023

Cesium atoms in cryogenic argon matrix

This paper presents both experimental and theoretical investigations into the spectroscopy of dilute cesium (Cs) atoms within a solid argon (Ar) matrix at cryogenic temperatures. This system is relevant for matrix isolation spectroscopy and in particular for recently proposed methods for investigating phenomena that extend beyond the standard model of particle physics. We record absorption spectra at various deposition temperatures and examine the evolution of these spectra post-deposition with respect to temperature changes. Taking advantage of Cs-Ar and Ar-Ar pairwise interaction potentials, we conduct a stability study of trapping sites, which indicates a preference for T$_{\rm d}$ (tetrahedral, 4 vacancies) and O$_{\rm h}$ (cubic, 6 vacancies) symmetries. By implementing a mean-field analysis of the long-range Cs(6s,6p)-Ar-Ar triple dipole interaction, combined with a temperature-dependent shift in zero point energy, we propose effective Cs(6s,6p)-Ar pairwise potentials. Upon integrating these pairwise potentials with spin-orbit coupling, we achieve a satisfactory agreement between the observed and simulated absorption line positions. The observed line broadening is reasonably well reproduced by a semi-classical thermal Monte Carlo approach based on Mulliken-type differences between excited and ground potential curves. Additionally, we develop a simple, first-order crystal field theory featuring only 6 interaction mode coordinates. It uses the reflection approximation and incorporates quantized (phonon) normal modes. This produces a narrow triplet structure but not the observed amount of splitting.

physics.atom-ph↗

arXiv2022

A Rydberg hydrogen beam for studies of stimulated deexcitation

We present a Rydberg hydrogen beamline developed to commission techniques of stimulated deexcitation for application in antihydrogen experiments at CERN's Antiproton Decelerator. The stimulation of spontaneous decay is a key technology to enhance the number of ground-state anti-atoms available in a beam toward precision spectroscopy and gravity measurements.

physics.atom-ph↗

arXiv2021

Induced THz transitions in Rydberg caesium atoms for application in antihydrogen experiments

Antihydrogen atoms are produced at CERN in highly excited Rydberg states. However, precision measurements require anti-atoms in ground state. Whereas experiments currently rely on spontaneous emission only, simulations have shown that THz light can be used to stimulate the decay towards ground state and thus increase the number of anti-atoms available for measurements. We review different possibilities at hand to generate light in the THz range required for the purpose of stimulated deexcitation. We demonstrate the effect of a blackbody type light source, which however presents drawbacks for this application including strong photoionization. Further, we report on the first THz transitions in a beam of Rydberg caesium atoms induced by photomixers and conclude with the implications of the results for the antihydrogen case.

physics.atom-ph↗

arXiv2019

Stimulated decay and formation of antihydrogen atoms

Antihydrogen atoms are routinely formed at the Antiproton Decelerator at CERN in a wide range of Rydberg states. To perform precision measurements, experiments rely on ground state antimatter atoms which are currently obtained only after spontaneous decay. In order to enhance the number of atoms in ground state, we propose and assess the efficiency of different methods to stimulate their decay. First, we investigate the use of THz radiation to simultaneously couple all n-manifolds down to a low lying one with sufficiently fast spontaneous emission toward ground state. We further study a deexcitation scheme relying on state-mixing via microwave and/or THz light and a coupled (visible) deexcitation laser. We obtain close to unity ground state fractions within a few tens of microseconds for a population initiated in the n=30 manifold. Finally, we study how the production of antihydrogen atoms via stimulated radiative recombination can favourably change the initial distribution of states and improve the overall number of ground-state atoms when combined with the stimulated deexcitation proposed.

physics.atom-ph↗

arXiv2018

Laser stimulated deexcitation of Rydberg antihydrogen atoms

Antihydrogen atoms are routinely formed at CERN in a broad range of Rydberg states. Ground-state anti-atoms, those useful for precision measurements, are eventually produced through spontaneous decay. However given the long lifetime of Rydberg states the number of ground-state antihydrogen atoms usable is small, in particular for experiments relying on the production of a beam of antihydrogen atoms. Therefore, it is of high interest to efficiently stimulate the decay in order to retain a higher fraction of ground-state atoms for measurements. We propose a method that optimally mixes the high angular momentum states with low ones enabling to stimulate, using a broadband frequency laser, the deexcitation toward low-lying states, which then spontaneously decay to ground-state. We evaluated the method in realistic antihydrogen experimental conditions. For instance, starting with an initial distribution of atoms within the $n=20-30$ manifolds, as formed through charge exchange mechanism, we show that more than 80\% of antihydrogen atoms will be deexcited to the ground-state within 100 ns using a laser producing 2 J at 828 nm.

physics.atom-ph↗

arXiv2018

Phase space density limitation in laser cooling without spontaneous emission

We study the possibility to enhance the phase space density of non-interacting particles submitted to a classical laser field without spontaneous emission. We clearly state that, when no spontaneous emission is present, a quantum description of the atomic motion is more reliable than semi-classical description which can lead to large errors especially if no care is taken to smooth structures smaller than the Heisenberg uncertainty principle. Whatever the definition of position - momentum phase space density, its gain is severely bounded especially when started from a thermal sample. More precisely, the maximum phase space density, can only be improved by a factor M for M-level atoms. This bound comes from a transfer between the external and internal degrees of freedom. To circumvent this limit, one can use non-coherent light fields, informational feedback cooling schemes, involve collectives states between fields and atoms, or allow a single spontaneous emission even

quant-ph↗

arXiv2016

Bichromatic magneto-optical trapping for $ J\rightarrow J,J-1 $ configurations

A magneto-optical trap (MOT) of atoms or molecules is studied when two lasers of different detunings and polarization are used. Especially for $J\rightarrow J,J-1$ transitions, a scheme using more than one frequency per transition and different polarization is required to create a significant force. Calculations have been performed with the simplest forms of the $J\rightarrow J-1$ case (i.e. $J''=1 \rightarrow J'=0$) and $J\rightarrow J$ case (i.e. $J''=1/2 \rightarrow J'=1/2$). A one dimensional (1D) model is presented and a complete 3D simulation using rate equations confirm the results. Even in the absence of Zeeman effect in the excited state, where no force is expected in the single laser field configuration, we show that efficient cooling and trapping forces are restored in our configuration. We study this mechanism for the C$_2^-$ molecular anion as a typical example of the interplay between the two simple transitions $J \rightarrow J,J-1$.

quant-ph↗

arXiv2015

Laser Cooling of Molecular Anions

We propose a scheme for laser cooling of negatively charged molecules. We briefly summarise the requirements for such laser cooling and we identify a number of potential candidates. A detailed computation study with C$\_2^-$, the most studied molecular anion, is carried out. Simulations of 3D laser cooling in a gas phase show that this molecule could be cooled down to below 1 mK in only a few tens of milliseconds, using standard lasers. Sisyphus cooling, where no photo-detachment process is present, as well as Doppler laser cooling of trapped C$\_2^-$, are also simulated. This cooling scheme has an impact on the study of cold molecules, molecular anions, charged particle sources and antimatter physics.

physics.atom-ph↗

arXiv2014

A Study of molecular cooling via Sisyphus processes

We present a study of Sisyphus cooling of molecules: the scattering of a single-photon remove a substantial amount of the molecular kinetic energy and an optical pumping step allow to repeat the process. A review of the produced cold molecules so far indicates that the method can be implemented for most of them, making it a promising method able to produce a large sample of molecules at sub-mK temperature. Considerations of the required experimental parameters, for instance the laser power and linewidth or the trap anisotropy and dimensionality, are given. Rate equations, as well as scattering and dipolar forces, are solved using Kinetic Monte Carlo methods for several lasers and several levels. For NH molecules, such detailed simulation predicts a 1000-fold temperature reduction and an increase of the phase space density by a factor of 10^7 . Even in the case of molecules with both low Franck-Condon coefficients and a non-closed pumping scheme, 60% of trapped molecules can be cooled from 100 mK to sub-mK temperature in few seconds. Additionally, these methods can be applied to continuously decelerate and cool a molecular beam

physics.chem-ph↗

arXiv2012

Cooperative excitation and many-body interactions in a cold Rydberg gas

The dipole blockade of Rydberg excitations is a hallmark of the strong interactions between atoms in these high-lying quantum states. One of the consequences of the dipole blockade is the suppression of fluctuations in the counting statistics of Rydberg excitations, of which some evidence has been found in previous experiments. Here we present experimental results on the dynamics and the counting statistics of Rydberg excitations of ultra-cold Rubidium atoms both on and off resonance, which exhibit sub- and super-Poissonian counting statistics, respectively. We compare our results with numerical simulations using a novel theoretical model based on Dicke states of Rydberg atoms including dipole-dipole interactions, finding good agreement between experiment and theory.

cond-mat.quant-gas↗

arXiv2012

Triplet-singlet conversion by broadband optical pumping

We demonstrate the conversion of cold Cs_{2} molecules initially distributed over several vibrational levels of the lowest triplet state a^{3}\Sigma_{u}^{+} into the singlet ground state X^{1}\Sigma_{g}^{+}. This conversion is realized by a broadband laser exciting the molecules to a well-chosen state from which they may decay to the singlet state throug\textcolor{black}{h two sequential single-photon emission steps: Th}e first photon populates levels with mixed triplet-singlet character, making possible a second spontaneous emission down to several vibrational levels of the X^{1}\Sigma_{g}^{+} states. By adding an optical scheme for vibrational cooling, a substantial fraction of molecules are transferred to the ground vibrational level of the singlet state. The efficiency of the conversion process, with and without vibrational cooling, is discussed at the end of the article. The presented conversion is general in scope and could be extended to other molecules.

physics.atom-ph↗