arXiv subjects

Jérémie Caillat

Publications and source records attributed to Jérémie Caillat.

16 recordsLinked to original sources

arXiv2026

Quantum optical photoelectron interferometry

We present a general theoretical framework for multiphoton processes driven by quantum light fields, establishing a direct link between photon statistics and photoelectron observables. Our results show that the autocorrelation and cross-correlation functions, which quantify the underlying photon statistics, are directly mapped onto the resulting photoelectron spectra. Although our framework is broadly applicable, we demonstrate specifically in the example of reconstruction of attosecond beating by interference of two-photon transitions (RABBIT) the influence of the light statistical properties. In this approach, the amplitude, contrast and phase of the oscillations of the sideband signal as a function of pump-probe delay reveal the quantum nature of light. We analyze these observables across several quantum configurations, including correlated infrared and harmonic modes, as well as the uncorrelated case with non-classical harmonic statistics, thereby establishing a general framework for quantum-light RABBIT spectroscopy. We compare the analytical theory with numerical simulations for the case of classical harmonics and an infrared field in a squeezed coherent state, obtaining excellent agreement. Our results reveal how the interplay between classical and quantum correlations dictates the coherence of the photoemission process, providing a new window into the quantum-optical foundations of attosecond science.

quant-ph↗

arXiv2026

High-order harmonic generation from an atom in a disordered environment

Using one-dimensional simulations analyzed through the lens of open quantum systems, we study the photoelectron's strong-field dynamics from an atom surrounded by a scattering environment stochastically structured. We theoretically investigate high-order harmonic generation from this situation. We show that local dephasing of the photoelectron wavepacket induced by elastic scattering leads to global decoherence. This drives a transition from quantum to classical behavior, as witnessed by the photoelectron probability density localizing around specific trajectories of the classical analog system: unstable periodic orbits. This phenomenon mirrors quantum scars traditionally observed in the eigenfunctions of time-independent systems, such as quantum billiards. Here, it emerges in-situ within a time-dependent framework, manifesting directly in the real-time dynamics from the ground state rather than solely through spectral analysis.

quant-ph↗

arXiv2026

Roadmap on Attosecond Science

Twenty-five years have passed since the first experimental demonstration of attosecond pulses, marking the advent of our ability to resolve and control electron motion in real time. What began as a technological breakthrough - generating the shortest flashes ever produced - has evolved into a powerful approach for probing and steering electronic dynamics in atoms, molecules, and solids. This roadmap, authored by leading experts in the field, surveys the recent rapid progress in the generation and characterization of attosecond pulses, emerging attosecond measurement and control techniques, and their expanding range of applications. It reviews current and future developments in attosecond light sources, including novel laser technologies, waveform synthesizers, new schemes for high-order harmonic generation, attosecond pulse generation at free-electron lasers, and structured light. Advances in attosecond measurement methodologies are also discussed, encompassing all-attosecond pump-probe spectroscopy, attosecond four-wave mixing, attosecond microscopy, spectroscopy with light transients, and attosecond interferometry. Furthermore, the roadmap addresses applications of attosecond spectroscopy to reveal electron dynamics in molecules and condensed matter systems from both theoretical and experimental perspectives, and highlights emerging directions at the interface with quantum optics and quantum entanglement. Overall, this work aims to serve as a comprehensive resource for navigating the evolving landscape of attosecond science.

physics.optics↗

arXiv2025

Time-domain interferences as the source of electron-ion entanglement in Rabi-dressed photoemission

We investigate bipartite entanglement between a photoelectron and its parent ion when the latter undergoes Rabi oscillations, following the recent experiment of [Nandi et al. Science Advances 10, eado0668 (2024)]. Using numerical simulations on a model atom, we show that this entanglement results from ionization events occurring at different times, with the photoelectron leaving the ion in distinct superpositions of internal states due to the Rabi coupling. Our interpretation brings forward the possibility to access the purity of the photoion state from photoelectron spectra. Furthermore, we demonstrate a tomographic reconstruction of the dressed ionic state dynamics from the observable spectra.

physics.atom-ph↗

arXiv2025

Attosecond tunneling time measurements through momentum squeezing in strong field ionization

Tunneling of a particle through a potential barrier is a fundamental physical process and a major thought-provoking outcome of quantum physics. It is at the basis of multiple scientific and technological advances and strongly influences both the structuring and the dynamics of matter at the microscopic scale. Without a classical counterpart, it defies our intuitive perception and understanding of the motion of a particle. Thus, the temporal characterization of tunneling, typically in terms of the time spent "under the barrier", referred to as tunneling time, raises several debates and questions on its interpretation and measurability. Here we show that an electron wavepacket tunneling out of an atom through the potential barrier induced by a strong electric field, carries in its momentum profile the value of the corresponding tunneling time, in a self-probing manner. In a revisited interpretation of the attoclock setup, we view a circularly polarized light pulse as a temporal prism which maps the barrier configuration, and hence the tunneling dynamics, onto different photoelectron ejection directions. From our simulations, we find that tunneling times in the infrared regime are of the order of hundreds of attoseconds, in agreement with previous theories.

physics.atom-ph↗

arXiv2024

Complete retrieval of attosecond photoelectron dynamics from partially-coherent states in entangled photoemission

We show that the complete photoemission dynamics in situations of electron-ion entanglement can be retrieved from photoelectron spectral measurements without information on the ion. To this end, we develop an energy-time analysis of the photoelectron's reduced density matrix based on first principles. We test and assess our approach with numerical simulations on a low dimensional model molecule in interaction with broadband composite pulses occulting the vibrational resolution. Our method is directly applicable to recent experimental schemes measuring the photoelectron reduced density matrices in atomic and molecular photoemission. Therefore, it opens a new window on the dynamics of decoherence and entanglement at the attosecond timescale.

physics.chem-ph↗

arXiv2024

Probing Wigner time delays with photoelectron interferometry: Anisotropic long-range imprint of the short-range centrifugal potential

We consider the two-photon ionization of Hydrogen-like atoms. We find an approximate expression of the long-range phase based on an asymptotic expansion of the continuum eigenfunctions within the Wentzel-Kramers-Brillouin approximation. Combined with commonly used perturbative approaches, the resulting analytic formalism can treat, at the same time, the two-photon propensity rules, the anisotropy in the continuum-continuum photoionization time delay and the soft-photon regime.

physics.atom-ph↗

arXiv2024

Vibronic correlations in molecular strong field dynamics

We investigate ultrafast vibronic dynamics triggered by intense femtosecond infrared pulses in small molecules. Our study is based on numerical simulations performed with 2D model molecules, and analyzed in the perspective of the renown Lochfrass and Bond-Softening models. We give a new interpretation of the observed nuclear wave packet dynamics, with a focus on the phase of the bond oscillations. Our simulations also reveal intricate features in the field-induced nuclear motion that are not accounted for by existing models. Our analyses assign these features to strong dynamic correlations between the active electron and the nuclei, which significantly depend on the carrier envelope phase of the pulse, even for relatively ``long'' pulses, which should make them experimentally observable.

physics.chem-ph↗

arXiv2024

Anisotropic molecular photoemission dynamics: Interpreting and accounting for the nuclear motion

We investigate how vibration affects molecular photoemission dynamics, through simulations on two-dimension asymmetric model molecules including the electronic and nuclear motions in a fully correlated way. We show that a slight anisotropy in the electron-ion momentum sharing is sufficient to prevent one from unambigously characterizing the vibrationnaly averaged photoemission dynamics in terms of stereo Wigner delays. We further show that vibrational resolution can be retrieved in fixed-nuclei simulations, using effective molecular conformations that are specific to each vibrational channel. The optimal internuclear distances found empirically in 1-photon processes can be identified a priori using simple physical arguments. They also turn out to be efficient to simulate vibrationnally-resolved \rabbit measurements and to account for interchannel coherences in broadband 1-photon ionization.

physics.chem-ph↗

arXiv2023

Strong-field photoionization by circularly polarized light

We demonstrate that strong-field ionization of atoms driven by circularly polarized light becomes an adiabatic process when described in the frame rotating with the laser field. As a direct consequence, a conservation law emerges: in the rotating frame the energy of the tunneling electron is conserved for rotationally invariant potentials. This conservation law, arising from a classical picture, is retrieved through a proper classical-quantum correspondence when considering the full quantum system, beyond the Strong Field Approximation.

physics.atom-ph↗

arXiv2021

Anisotropic dynamics of two-photon ionization: An attosecond movie of photoemission

Imaging in real time the complete dynamics of a process as fundamental as photoemission has long been out of reach due to the difficulty of combining attosecond temporal resolution with fine spectral and angular resolutions. Here, we achieve full decoding of the intricate angle-dependent dynamics of a photoemission process in helium, spectrally and anisotropically structured by twophoton transitions through intermediate bound states. Using spectrally- and angularly-resolved attosecond electron interferometry, we characterize the complex-valued transition probability amplitude towards the photoelectron quantum state. This allows reconstructing in space, time and energy the complete formation of the photoionized wavepacket.

physics.atom-ph↗

arXiv2021

Self-probing of Molecules with High Harmonic Generation

This tutorial presents the most important aspects of the molecular self-probing paradigm, which views the process of high harmonic generation as "a molecule being probed by one of its own electrons". Since the properties of the electron wavepacket acting as a probe allow a combination of attosecond and Ångström resolutions in measurements, this idea bears great potential for the observation, and possibly control, of ultrafast quantum dynamics in molecules at the electronic level. Theoretical as well as experimental methods and concepts at the basis of self-probing measurements are introduced. Many of these are discussed on the example of molecular orbital tomography.

physics.atom-ph↗

arXiv2020

Attosecond-resolved photoionization of chiral molecules

Chiral light-matter interactions have been investigated for two centuries, leading to the discovery of many chiroptical processes used for discrimination of enantiomers. Whereas most chiroptical effects result from a response of bound electrons, photoionization can produce much stronger chiral signals that manifest as asymmetries in the angular distribution of the photoelectrons along the light propagation axis. Here we implement a self-referenced attosecond photoelectron interferometry to measure the temporal profile of the forward and backward electron wavepackets emitted upon photoionization of camphor by circularly polarized laser pulses. We found a delay between electrons ejected forward and backward, which depends on the ejection angle and reaches 24 attoseconds. The asymmetric temporal shape of electron wavepackets emitted through an autoionizing state further reveals the chiral character of strongly-correlated electronic dynamics.

physics.chem-ph↗

arXiv2018

Dynamical distortions of structural signatures in molecular High Harmonic Spectroscopy

We study the signature of two-center interferences in molecular high-order harmonic spectra, with an emphasis on the spectral phase. With the help of both ab initio computations based on the time-dependent Schrödinger equation and the molecular Strong-Field Approximation (SFA) as developed by Chirila et al. [Physical Review A, 73, 023410 (2006)] and Faria [Physical Review A, 76, 043407 (2007)], we observe that the phase behavior is radically different for the short and the long trajectory contributions. By means of Taylor expansions of the molecular SFA, we link this effect to the dynamics of the electron in the continuum. More precisely, we find that the value of the electric field at recombination time plays a crucial role on the shape of the destructive interference phase-jump.

physics.atom-ph↗

arXiv2018

Ionisation dynamics through a Fano resonance: Time domain interpretation of spectral amplitudes

We investigate a conjecture used in recent experiments to reconstruct the complete dynamics of Fano autoionisation processes out of measured spectral amplitudes [Gruson et al, Science 354 734 (2016); Beaulieu el al, Science 358 1288 (2017); Busto et al, J. Phys. B: At. Mol. Opt. Phys. 51 044002 (2018)]. The validity of the conjecture is established analytically within the formalism of Fano, and tested numerically on model atoms displaying adjustable autoionising states. A general condition for which the conjecture is valid, beyond the Fano case, is then derived.

physics.atom-ph↗

arXiv2016

Gaussian continuum basis functions for calculating high-harmonic generation spectra

We explore the computation of high-harmonic generation spectra by means of Gaussian basis sets in approaches propagating the time-dependent Schr{ö}dinger equation. We investigate the efficiency of Gaussian functions specifically designed for the description of the continuum proposed by Kaufmann et al. [J. Phys. B 22, 2223 (1989)]. We assess the range of applicability of this approach by studying the hydrogen atom, i.e. the simplest atom for which "exact" calculations on a grid can be performed. We notably study the effect of increasing the basis set cardinal number, the number of diffuse basis functions, and the number of Gaussian pseudo-continuum basis functions for various laser parameters. Our results show that the latter significantly improve the description of the low-lying continuum states, and provide a satisfactory agreement with grid calculationsfor laser wavelengths $λ$0 = 800 and 1064 nm. The Kaufmann continuum functions therefore appear as a promising way of constructing Gaussian basis sets for studying molecular electron dynamics in strong laser fields using time-dependent quantum-chemistry approaches.

physics.comp-ph↗