arXiv subjects

T. Rook

Publications and source records attributed to T. Rook.

7 recordsLinked to original sources

arXiv2026

Erasing photons from bright squeezed vacuum light via above-threshold ionization

While the interface between strong-field physics and quantum optics offers a unique regime for combining extreme nonlinearity with quantum optical resources, its potential for generating non-classical states of light remains largely unexplored. Standard protocols for generating optical Schr\"odinger cat states, such as photon subtraction from squeezed light, are inherently limited in the achievable macroscopicity of the state and its scalability. In this work, we bridge this gap by demonstrating that above-threshold ionization driven by bright squeezed light provides a strong-field analogue of photon subtraction, where photoelectron detection acts as a high-intensity heralding mechanism, enabling the generation of large amplitude optical Schr\"odinger cat states. We characterize the resulting non-Gaussian features and show that they can be tuned via the detected photoelectron momentum, and study their robustness against the experimental imperfections arising from finite momentum resolution at the heralding step. Despite the noise, we show that the generated states can be manipulated to violate a Bell inequality, thereby highlighting their potential for foundational and practical applications. Our results establish strong-field processes as a scalable platform for macroscopic quantum state engineering, opening a route to quantum optics in previously inaccessible regimes.

quant-ph↗

arXiv2026

Interferometrically Enhanced Asymmetry in Strong-field Ionization with Bright Squeezed Vacuum

We demonstrate that quantum light statistics can be used to control strong-field ionization at the tunneling step. Using a bichromatic linearly polarized field composed of a strong coherent driver and a weak bright squeezed vacuum (BSV), we show through simulation that photoelectron momentum distributions (PMDs) exhibit asymmetries that exceed those obtained with classical fields of comparable intensity by orders of magnitude. This enhancement is uniquely linked to the nonclassical statistics of the BSV field. A semiclassical analysis based on the strong-field approximation (SFA) reveals that the effect originates from fluctuations in the instantaneous field amplitude, which strongly modify the tunneling ionization probability while leaving the electron's continuum dynamics essentially unchanged. This selective control enables reconstruction of ionization pathways and provides a robust route to extract sub-cycle dynamics from strong-field observables.

quant-ph↗

arXiv2024

Energy-conservation conditions in saddle-point approximation for the strong-field-ionization of atoms

Orbit-based methods are widespread in strong-field laser-matter interaction. They provide a framework in which photoelectron momentum distributions can be interpreted as the quantum interference between different semi-classical pathways the electron can take on its way to the detector, which brings with it great predictive power. The transition amplitude of an electron going from a bound state to a final continuum state is often written as multiple integrals, which can be computed either numerically, or by employing the saddle-point method. If one computes the momentum distribution via a saddle-point method, the obtained distribution is highly dependent on the time window from which the saddle points are selected for inclusion in the "sum over paths". In many cases, this leads to the distributions not even satisfying the basic symmetry requirements and often containing many more oscillations and interference fringes than their numerically integrated counterparts. Using the strong-field approximation, we find that the manual enforcement of the energy-conservation condition on the momentum distribution calculated via the saddle-point method provides a unique momentum distribution which satisfies the symmetry requirements of the system and which is in a good agreement with the numerical results. We illustrate our findings using the example of the Ar atom ionized by a selection of monochromatic and bichromatic linearly polarized fields.

physics.atom-ph↗

arXiv2024

Influence of catastrophes and hidden dynamical symmetries on ultrafast backscattered photoelectrons

We discuss the effect of using potentials with a Coulomb tail and different degrees of softening in the photoelectron momentum distributions (PMDs) using the recently implemented hybrid forward-boundary CQSFA (H-CQSFA). We show that introducing a softening in the Coulomb interaction influences the ridges observed in the PMDs associated with backscattered electron trajectories. In the limit of a hard-core Coulomb interaction, the re-scattering ridges close along the polarization axis, while for a soft-core potential, they are interrupted at ridge-specific angles. We analyze the momentum mapping of the different orbits leading to the ridges. For the hard-core potential, there exist two types of saddle-point solutions that coalesce at the ridge. By increasing the softening, we show that two additional solutions emerge as the result of breaking a hidden dynamical symmetry associated exclusively with the Coulomb potential. Further signatures of this symmetry breaking are encountered in subsets of momentum-space trajectories. Finally, we use scattering theory to show how the softening affects the maximal scattering angle and provide estimates that agree with our observations from the CQSFA. This implies that, in the presence of residual binding potentials in the electron's continuum propagation, the distinction between purely kinematic and dynamic caustics becomes blurred.

physics.atom-ph↗

arXiv2023

Impact of the continuum Coulomb interaction in quantum-orbit-based treatments of high-order above-threshold ionization

We perform a systematic comparison between photoelectron momentum distributions computed with the rescattered-quantum orbit strong-field approximation (RQSFA) and the Coulomb-quantum orbit strong-field approximation (CQSFA). We exclude direct, hybrid, and multiple scattered CQSFA trajectories, and focus on the contributions of trajectories that undergo a single act of rescattering. For this orbit subset, one may establish a one-to-one correspondence between the RQSFA and CQSFA contributions for backscattered and forward-scattered trajectory pairs. We assess the influence of the Coulomb potential on the ionization and rescattering times of specific trajectory pairs, kinematic constraints determined by rescattering, and quantum interference between specific pairs of trajectories. We analyze how the Coulomb potential alters their ionization and return times, and their interference in photoelectron momentum distributions. We show that Coulomb effects are not significant for high or medium photoelectron energies and shorter orbits, while, for lower momentum ranges or longer electron excursion times in the continuum, the residual Coulomb potential is more important. We also assess the agreement of both theories for different field parameters, and show that it improves with the increase of the wavelength.

physics.atom-ph↗

arXiv2023

Forward and hybrid path-integral methods in photoelectron holography: sub-barrier corrections, initial sampling and momentum mapping

We construct two strong-field path integral methods with full Coulomb distortion, in which the quantum pathways are mimicked by interfering electron orbits: the rate-based CQSFA (R-CQSFA) and the hybrid forward-boundary CQSFA (H-CQSFA). The methods have the same starting point as the standard Coulomb quantum-orbit strong-field approximation (CQSFA), but their implementation does not require pre-knowledge of the orbits' dynamics. These methods are applied to ultrafast photoelectron holography. In the rate-based method, electron orbits are forward propagated and we derive a non-adiabatic ionization rate from the CQSFA, which includes sub-barrier Coulomb corrections and is used to weight the initial orbit ensemble. In the H-CQSFA, the initial ensemble provides initial guesses for a subsequent boundary problem and serves to include or exclude specific momentum regions, but the ionization probabilities associated with individual trajectories are computed from sub-barrier complex integrals. We perform comparisons with the standard CQSFA and \textit{ab-initio} methods, which show that the standard, purely boundary-type implementation of the CQSFA leaves out whole sets of trajectories. We show that the sub-barrier Coulomb corrections broaden the resulting photoelectron momentum distributions (PMDs) and improve the agreement of the R-CQSFA with the H-CQSFA and other approaches. We probe different initial sampling distributions, uniform and otherwise, and their influence on the PMDs. We find that initial biased sampling emphasizes rescattering ridges and interference patterns in high-energy ranges, while an initial uniform sampling guarantees accurate modeling of the holographic patterns near the ionization threshold or polarization axis. Our results are explained using the initial to final momentum mapping for different types of interfering trajectories.

physics.atom-ph↗

arXiv2022

Exploring symmetries in photoelectron holography with two-color linearly polarized fields

We investigate photoelectron holography in bichromatic linearly polarized fields of commensurate frequencies $r\omega$ and $s\omega$, with emphasis on the existing symmetries and for which values of the relative phase between the two driving waves they are kept or broken. Using group-theoretical methods, we show that, additionally to the well-known half-cycle symmetry, which is broken for $r+s$ odd, there are reflection symmetries around the field zero crossings and maxima, which may or may not be kept, depending on how both waves are dephased. The three symmetries are always present for monochromatic fields, while for bichromatic fields this is not guaranteed, even if $r+s$ is even and the half-cycle symmetry is retained. Breaking the half-cycle symmetry automatically breaks one of the other two, while, if the half-cycle symmetry is retained, the other two symmetries are either \textit{both} kept or broken. We analyze how these features affect the ionization times and saddle-point equations for different bichromatic fields. We also provide general expressions for the relative phases $\phi$ which retain specific symmetries. As an application, we compute photoelectron momentum distributions for $\omega-2\omega$ fields with the Coulomb Quantum Orbit Strong-Field approximation and assess how holographic structures such as the fan, the spider and interference carpets behave, focusing on the reflection symmetries. The features encountered can be traced back to the field gradient and amplitude affecting ionization probabilities and quantum interference in different momentum regions.

physics.atom-ph↗