arXiv subjects

M. F. Ciappina

Publications and source records attributed to M. F. Ciappina.

At least 19 recordsLinked to original sources

arXiv2026

Emergence of Gaussian entanglement and non-Gaussianity in high-harmonic generation driven by bright squeezed light

High harmonic generation (HHG) is a highly nonlinear optical process in which radiation from a strong driving field is up-converted into its high-order harmonics. In atomic systems, this nonlinearity manifests itself through the intensity scaling of the emitted harmonics with the driving field strength. Despite the highly nonlinear nature of HHG, when the driving field is prepared in a classical Gaussian state and atomic depletion remains negligible, the quantum statistical properties of the generated harmonics retains classical Gaussian quantum statistics. Driving HHG with bright squeezed vacuum (BSV) light challenges this paradigm, as its enhanced field fluctuations can modify the statistical properties of the generated harmonics. In this work, we investigate the conditions under which BSV-driven HHG gives rise to non-classical Gaussian states, and identify the regimes where this Gaussian description breaks down. For bichromatic driving by a strong coherent field at frequency $ω$ and a perturbative BSV field at $2ω$, the even-harmonic response is approximately linear in the BSV quadrature, leading to non-classical multimode Gaussian entanglement in the harmonic field. We show that this state can be described as a distributed collective squeezed mode over the even-harmonic manifold, and characterize its covariance matrix, entanglement structure, and quantum teleportation fidelity as an operational benchmark. Our results highlight the potential of non-classically driven HHG as a platform for engineering Gaussian and non-Gaussian states of light in the extreme ultraviolet regime.

quant-ph↗

arXiv2026

Attosecond Path Qubits in High-Harmonic Generation: Classical Dephasing and Trace-Out Decoherence

High-harmonic generation (HHG) is governed by interference between electron trajectories. We propose that the dominant short and long trajectories define an experimentally addressable two-level subsystem: an attosecond path qubit (APQ). We formulate a trajectory-resolved density matrix to identify two distinct coherence-loss mechanisms: classical dephasing from ensemble averaging and quantum decoherence arising from the trace-out of unobserved degrees of freedom. By investigating shot-to-shot fluctuations and unresolved transverse momentum, we demonstrate that while dephasing suppresses coherence through averaging, the ``trace-out'' channel produces mixed states even for fixed driving parameters. We explore how these mechanisms modify APQ purity and show that mode selection and conditioning provide operational routes to isolate them. These results establish a reduced-state framework for diagnosing coherence loss in HHG and for engineering trajectory-based quantum states in attosecond interferometry.

physics.optics↗

arXiv2025

Geometry-Driven Resonance and Localization of Light in Fractal Phase Spaces

Geometry can fundamentally govern the propagation of light, independent of material constraints. Here, we demonstrate that a fractal phase space, endowed with a non-Euclidean, scale-dependent geometry, can intrinsically induce resonance quantization, spatial confinement, and tunable damping without the need for material boundaries or external potentials. Employing a fractional formalism with a fixed scaling exponent, we reveal how closed-loop geodesics enforce constructive interference, leading to discrete resonance modes that arise purely from geometric considerations. This mechanism enables light to localize and dissipate in a controllable fashion within free space, with geometry acting as an effective quantizing and confining agent. Numerical simulations confirm these predictions, establishing geometry itself as a powerful architect of wave dynamics. Our findings open a conceptually new and experimentally accessible paradigm for material-free control in photonic systems, highlighting the profound role of geometry in shaping fundamental aspects of light propagation.

physics.optics↗

arXiv2025

Colloquium: Quantum optics of intense light--matter interaction

Intense light-matter interaction largely relies on the use of high-power light sources, creating fields comparable to, or even stronger than, the field keeping the electrons bound in atoms. Under such conditions, the interaction induces highly nonlinear processes such as high harmonic generation, in which the low-frequency photons of a driving laser field are upconverted into higher-frequency photons. These processes have enabled numerous groundbreaking advances in atomic, molecular, and optical physics, and they form the foundation of attosecond science. Until recently, however, such processes were typically described using semi-classical approximations, since the quantum properties of the light field were not required to explain the observables. This has changed in the recent past. Ongoing theoretical and experimental advances show that fully quantized descriptions of intense light-matter interactions, which explicitly incorporate the quantum nature of the light field, open new avenues for both fundamental research and technological applications at the fully quantized level. These advances emerge from the convergence of quantum optics with strong-field physics and ultrafast science. Together, they have given rise to the field of quantum optics and quantum electrodynamics of strong-field processes.

quant-ph↗

arXiv2025

Structured squeezed light allows for high-harmonic generation in classical forbidden geometries

High-harmonic generation (HHG) is a nonlinear process in which a strong driving field interacts with a material, resulting in the frequency up-conversion of the driver into its high-order harmonics. This process is highly sensitive to the field's polarization: circular polarization, for instance, inhibits HHG. In this work, we demonstrate that the use of non-classical structured light enables HHG in this otherwise prohibitive configuration for classical drivers. We consider circularly polarized light with non-classical fluctuations, introduced via squeezing along one polarization direction, and show that these non-classical features prompt the HHG process. We find that the spectral properties of the emitted harmonics depend on the type of squeezing applied and, by analyzing the inner electron dynamics, we relate the observed differences to modifications of the HHG three-step mechanism induced by the specific squeezing type. This approach opens new pathways for integrating quantum optics in HHG, providing novel means of controlling the light-matter interaction dynamics.

quant-ph↗

arXiv2025

Influence of Dark Matter on the Formation of Biogenic Elements in Early Universe Stars

We demonstrate that dark matter interactions can profoundly influence stellar nucleosynthesis in the early universe by altering thermodynamic gradients and modifying nuclear reaction rates within primordial stars. Incorporating a dark matter-modified Fermi-Dirac distribution and accounting for localized energy injection from annihilation heating, our model predicts enhanced production of carbon and nitrogen alongside reduced oxygen synthesis. These compositional shifts significantly reshape stellar structure and produce synthetic spectra that closely reproduce the observed characteristics of carbon-enhanced metal-poor (CEMP) stars. Our findings reveal a direct and previously overlooked role of dark matter in driving the chemical evolution of the early cosmos, offering a plausible link between fundamental particle physics and observable astrophysical signatures.

astro-ph.SR↗

arXiv2025

A spatiotemporal couplings perspective on harmonic vortices generation

The interaction of light with matter serves as a fundamental tool for probing material properties across a wide range of energy regimes. Recent breakthroughs in tailoring the topology of coherent electromagnetic fields have opened new avenues for exploring how matter uniquely responds to the topological characteristics of light. In this work, we conduct a comprehensive investigation of high-order harmonic generation (HHG) driven by spatiotemporal optical vortex (STOV) beams. We demonstrate how distinct STOV configurations imprint their signature on the HHG process and show that the intensity distribution of harmonic fields can be precisely controlled by tuning the beam parameters. Furthermore, by bridging microscopic calculations with far-field observations, we establish the consistency of our findings and offer fresh insights into this emerging nonlinear spatiotemporal regime.

physics.optics↗

arXiv2025

Recent developments in the generation of non-classical and entangled light states using intense laser-matter interactions

Non-classical and entangled light states are of fundamental interest in quantum mechanics and they are a powerful tool for the emergence of new quantum technologies. The development of methods that can lead to the generation of such light states is therefore of high importance. Recently, it has been demonstrated that intense laser-matter interactions can serve towards this direction. Specifically, it has been shown how the use of fully quantized approaches in intense laser-matter interactions and the process of high harmonic generation, can lead to the generation of high photon-number non-classical and entangled states from the far-infrared (IR) to the extreme-ultraviolet (XUV). Here, after a brief introduction on the fundamentals, we summarize the operation principles of these approaches and discuss the recent developments and future directions of non-classical light engineering using strong light fields with the potential application in ultrafast and quantum information science. These findings represent an important step in the development of novel quantum nonlinear spectroscopy methods, based on the interplay between the quantum properties of light and those of quantum matter.

quant-ph↗

arXiv2025

Squeezed states of light after high-harmonic generation in excited atomic systems

High-harmonic generation (HHG) has recently emerged as a promising method for generating non-classical states of light with frequencies spanning from the infrared up to the extreme ultraviolet regime. In this work, we theoretically investigate the generation of squeezed states of light through HHG processes in atomic systems that had been initially driven to their first excited state. Our study reveals significant single-mode squeezing in both the driving field and low-order harmonic modes. Additionally, we characterize two-mode squeezing features in the generated states, both between fundamental and harmonic modes, and among the harmonic modes themselves. Using these correlations, we demonstrate the generation of optical Schrödinger kitten states through heralding measurements, specifically via photon subtraction in one of the modes influenced by two-mode squeezing.

quant-ph↗

arXiv2024

Nondipole circularly polarized laser-assisted photoelectron emission

We theoretically study atomic laser-assisted photoelectric emission (LAPE) beyond the electric dipole approximation. We present a theoretical description for first-order nondipole corrections ($O(c^{-1})$ where $c$ is the speed of light) to the nonrelativistic description of the laser-atom interaction for a strong circularly polarized infrared (IR) laser field combined with a train of extreme-ultraviolet (XUV) laser pulses. We investigate the photoelectron momentum distribution (PMD) as the product of two main contributions: the intra- and interpulse factors. Whereas the interpulse factor gives rise to a sideband pattern with a shift opposite to the IR beam propagation direction, the intrapulse factor forms an angular streaking pattern following the IR time-dependent polarization direction. We explore the transition of the PMD from the dipole to the nondipole framework, showing the gradual break of the forward-backward symmetry as the laser parameters are varied. Furthermore, we find non-zero contributions in dipole forbidden directions independent of the IR polarization state, wherein Cooper-\textit{like} minima are observed. Our work lays a theoretical foundation for understanding time-resolved nondipole LAPE in cutting-edge ultrafast experiments.

physics.atom-ph↗

arXiv2024

Attosecond vortices in semiconductor materials

We present the first theoretical results on the generation of short-wavelength attosecond vortex beams in semiconductors through their interactions with an intense Laguerre-Gauss beam, in the limit where non-perturbative high-order harmonics are generated. We exploit the details of the novel microscopic mechanism for high-order harmonic generation (HHG) in condensed matter, such as the use of dephasing time included in semiconductor Bloch equations (SBE), the combination of the SBE model with the thin slab model, and the use of experimentally verified scaling laws for various harmonic orders. For our test, we use a zinc oxide crystal as our standard sample, and our vortex beam is characterized by a topological charge of $l=1$. Our time-domain analysis shows that harmonics within the plateau region specifically contribute to the generation of the attosecond vortex beam. Our findings have implications for advancing the understanding of solid-state HHG and leveraging its strengths, such as the use of thin and dense media, for the efficient generation of short-wavelength attosecond vortex beams.

physics.atom-ph↗

arXiv2024

Orbital Angular Momentum Beam assisted High-Order Harmonic Generation in Semiconductor Materials

We investigate the use of light beams carrying orbital angular momentum (OAM) in the context of high harmonic generation (HHG) within semiconductor crystals. Our contribution deals with the transfer and conservation of OAM in the strong-field regime, from the driving laser field to the generated harmonics. To this end, in this work, we combine the semiconductor Bloch equations with the thin slab model to simulate the generation of high-order harmonics in semiconductor media and to compute the features of the far-field harmonics. We demonstrate that this theoretical approach is capable of satisfactorily reproducing previously published experimental features of the generated harmonics in ZnO driven by a Laguerre-Gauss beam. Our research not only deepens the understanding of light-solid interactions but also heralds the dawn of bright, structured XUV coherent radiation sources with unparalleled potential across diverse technological areas, paving the way for enhanced functionalities in fields such as microscopy, spectroscopy, and optical communication.

physics.optics↗

arXiv2024

Quantum state engineering of light using intensity measurements and post-selection

Quantum state engineering of light is of great interest for quantum technologies, particularly generating non-classical states of light, and is often studied through quantum conditioning approaches. Recently, we demonstrated that such approaches can be applied in intense laser-atom interactions to generate optical "cat" states by using intensity measurements and classical post-selection of the measurement data. Post-processing of the sampled data set allows to select specific events corresponding to measurement statistics as if there would be non-classical states of light leading to these measurement outcomes. However, to fully realize the potential of this method for quantum state engineering, it is crucial to thoroughly investigate the role of the involved measurements and the specifications of the post-selection scheme. We illustrate this by analyzing post-selection schemes recently developed for the process of high harmonic generation, which enables generating optical cat states bright enough to induce non-linear phenomena. These findings provide significant guidance for quantum light engineering and the generation of high-quality, intense optical cat states for applications in non-linear optics and quantum information science.

quant-ph↗

arXiv2024

Attosecond spectroscopy using vacuum-ultraviolet pulses emitted from laser-driven semiconductors

Strongly laser-driven semiconductor crystals offer substantial advantages for the study of many-body physics and ultrafast optoelectronics via the high harmonic generation process. While this phenomenon has been employed to investigate the dynamics of solids in the presence of strong laser fields, its potential to be utilized as an attosecond light source has remained unexploited. Here, we demonstrate that the high harmonics generated through the interaction of mid--infrared pulses with a ZnO crystal leads to the production of attosecond pulses, that can be used to trace the ultrafast ionization dynamics of alkali metals. In a cross--correlation approach, we photoionize Cesium atoms with the vacuum-ultraviolet (VUV) high-harmonics in the presence of a mid-infrared laser field. We observe strong oscillations of the photoelectron yield originating from the instantaneous polarization of the atoms by the laser field. The phase of the oscillations encodes the attosecond synchronization of the ionizing high-harmonics and is used for attosecond pulse metrology. This light source opens a new spectral window for attosecond spectroscopy, paving the way for studies of systems with low ionization potentials including neutral atoms, molecules and solids. Additionally, our results highlight the significance of the source for generating non--classical massively entangled light states in the visible--VUV spectral region.

physics.optics↗

arXiv2024

Interference of high-order perfect optical vortex beams

We investigate the interference of high-order perfect optical vortex (POV) beams with different topological charges. Through numerical simulations, we reveal a remarkable phenomenon: keeping the beam width, and beam radius fixed while changing the topological charge, the splitting of the composite POV beam into two distinct individual perfect vortices occurs exactly at the same inter-axial separation. The observed interference pattern exhibits pronounced sensitivity to factors such as axial separation, phase shift, beam radius, and topological charges of the constituent beams. Notably, our findings are contrasted with the interference of high-order Laguerre-Gauss (LG) beams, highlighting that the splitting of composite vortices into their individual components is more rapid in the case of LG beams. Our research provides significant insights into the distinct interference properties of high-order POV beams, presenting potential applications in the fields of optical manipulation and communication systems.

physics.optics↗

arXiv2023

Quantum optical analysis of high-order harmonic generation in H$_2^+$ molecular ions

We present a comprehensive theoretical investigation of high-order harmonic generation in H$_2^+$ molecular ions within a quantum optical framework. Our study focuses on characterizing various quantum optical and quantum information measures, highlighting the versatility of HHG in two-center molecules towards quantum technology applications. We demonstrate the emergence of entanglement between electron and light states after the laser-matter interaction. We also identify the possibility of obtaining non-classical states of light in targeted frequency modes by conditioning on specific electronic quantum states, which turn out to be crucial in the generation of highly non-classical entangled states between distinct sets of harmonic modes. Our findings open up avenues for studying strong-laser field-driven interactions in molecular systems, and suggest their applicability to quantum technology applications.

quant-ph↗

arXiv2022

Pulse length effects in long wavelength driven non-sequential double ionization

We present a joint experimental and theoretical study of non-sequential double ionization (NSDI) in argon driven by a 3100-nm laser source. The correlated photoelectron momentum distribution (PMD) shows a strong dependence on the pulse duration, and the evolution of the PMD can be explained by an envelope-induced intensity effect. Determined by the time difference between tunneling and rescattering, the laser vector potential at the ionization time of the bound electron will be influenced by the pulse duration, leading to different drift momenta. Such a mechanism is extracted through a classical trajectory Monte Carlo-based model and it can be further confirmed by quantum mechanical simulations. This work sheds light on the importance of the pulse duration in NSDI and improves our understanding of the strong field tunnel-recollision dynamics under mid-IR laser fields.

physics.atom-ph↗

arXiv2022

Attosecond Physics and Quantum Information Science

In this article, we will discuss a possibility of a symbiosis for attophysics (AP) and quantum information (QI) and quantum technologies (QT). We will argue that within few years AP will reach Technology Readiness Level (RTL) 4-5 in QT, and will thus become a legitimate platform for QI and QT.

quant-ph↗