arXiv subjects

Francesco V. Pepe

Publications and source records attributed to Francesco V. Pepe.

At least 19 recordsLinked to original sources

arXiv2026

Superradiant decay in non-Markovian Waveguide Quantum Electrodynamics

An array of initially excited emitters coupled to a one-dimensional waveguide exhibits superradiant decay under the Born-Markov approximation, manifested as a coherent burst of photons in the output field. In this work, we employ tensor-network methods to investigate its non-Markovian dynamics induced by finite time delays in photon exchange among the emitters. We find that the superradiant burst breaks into a structured train of correlated photons, each intensity peak corresponding to a specific photon number. We quantify the emitter-photon and emitter-emitter entanglement generated during this process and show that the latter emerges in the long-time limit, as part of the excitation becomes trapped within the emitters' singlet subspace. We finally consider the decay of the system's most radiant state, the symmetric Dicke state, and show that time delay can lead to decay rates exceeding those predicted by the Markovian approximation.

quant-ph↗

arXiv2026

Quantum Walk on a Line with Absorbing Boundaries

Absorption of two-state coined quantum walks on a finite line with two sinks located at $N$ and $-N$ is investigated. Elaborating on the results of Konno et al., J. Phys. A: Math. Gen. {\bf 36} 241 (2003), we derive closed formulas for the absorption probabilities at the boundaries in the limit of large system size $N$. Two limiting cases are considered, with the starting position $k$ being independent of $N$, or kept at a constant distance $δ$ from one of absorbers. In the first scenario, the absorption probability is determined only by the coin parameter and polar angle of the initial coin state decomposed into the eigenbasis of the coin operator. In the second case, a correction depending exponentially on $δ$ is introduced. Finally, we perform an extensive numerical investigation for small system size $N$, showing excellent agreement between numerical and analytical results.

quant-ph↗

arXiv2026

Spontaneous emission from driven polar quantum systems

We investigate spontaneous radiative processes in a driven polar two-level system whose interaction with the laser field is dominated by broken inversion symmetry rather than by the usual transition dipole coupling. Using a polaron transformation, we derive the dressed eigenstates of the atom-laser system and show that their longitudinal coupling reshapes the spectrum into two displaced harmonic ladders. We then analyze spontaneous transitions induced by a bosonic reservoir, and obtain transition rates that depend on both the laser parameters and the overlap between displaced field states. In the few-photon regime, we identify conditions under which spontaneous emission from the excited state can be strongly suppressed, thereby extending its lifetime, as well as regimes where the ladder structure enables spontaneous absorption from the ground state. In the semiclassical limit of a strong coherent drive, we derive compact analytical expressions for the total transition rates and show that they are governed by Bessel-function weights associated with multiphoton channels. Our results show how broken inversion symmetry qualitatively modifies decay dynamics and radiative cascades, and they establish driven polar quantum systems as a platform for controlling spontaneous light emission beyond the standard inversion-symmetric setting.

quant-ph↗

arXiv2025

Non-Markovian dynamics of generation of bound states in the continuum via single-photon scattering

The excitation of bound states in the continuum (BICs) in two- or multi-qubit systems lies at the heart of entanglement generation and harnessing in Waveguide Quantum Electrodynamics platforms. However, the generation of qubit pair BICs through single-photon scattering is hindered by the fact that these states are effectively decoupled from propagating photons. We prove that scattering of a parity-invariant single photon on a qubit pair, combined with a properly engineered time variation of the qubit detuning, is not only feasible, but also more effective than strategies based on the relaxation of the excited states of the qubits when the distance between the qubits gives rise to non-negligible photon delays (non-Markovian regime). The use of tensor network methods to simulate the proposed scheme enables to include such photon delays in collision models, thus opening the possibility to follow the time evolution of the full quantum system, including qubits and field, and to efficiently implement and characterize the dynamics hence identifying optimal working points for the BIC generation.

quant-ph↗

arXiv2025

Quasi-degenerate resonant eigenstate doublets of two quantum emitters in a closed waveguide

The physics of systems of quantum emitters in waveguide quantum electrodynamics is significantly influenced by the relation between their spatial separation and the wavelength of the emitted photons. If the distance that separates a pair of emitters meets specific resonance conditions, the photon amplitudes produced from decay may destructively interfere. In an infinite-waveguide setting, this effect gives rise to bound states in the continuum, where a photon remains confined between the emitters. In the case of a finite-length waveguide with periodic boundary conditions, there exist two such relevant distances for a given arrangement of the quantum emitters, leading to states in which a photon is confined to either the shorter or the longer path that connects the emitters. If the ratio of the shorter and the longer path is a rational number, these two kinds of resonant eigenstates are allowed to co-exist for the same Hamiltonian. In this paper, we investigate the existence of quasi-degenerate resonant doublets of a pair of identical emitters coupled to a linear waveguide mode. The states that form the doublet are searched among the ones in which a single excitation tends to remain bound to the emitters. We investigate the spectrum in a finite range around degeneracy points to check whether the doublet remains well separated from the closest eigenvalues in the spectrum. The identification of quasi-degenerate doublets opens the possibility to manipulate the emitters-waveguide system as an effectively two-level system in specific energy ranges, providing an innovative tool for quantum technology tasks.

quant-ph↗

arXiv2025

Condensation of vanishing photon emission rates in random atomic clouds

In the collective photon emission from atomic clouds both the atomic transition frequency and the decay rate are modified compared to a single isolated atom, leading to the effects of superradiance and subradiance. In this article, we analyse the properties of the Euclidean random matrix associated to the radiative dynamics of a cold atomic cloud, previously investigated in the contexts of photon localization and Dicke super- and subradiance. We present evidence of a new type of phase transition, surprisingly controlled by the cooperativeness parameter, rather than the spatial density or the diagonal disorder. The numerical results corroborate the occurrence of such a phase transition at a critical value of the cooperativeness parameter, above which the lower edge of the spectrum vanishes exhibiting a macroscopic accumulation of eigenvalues. Independent evaluations based on the two phenomena provide the same value of the critical cooperativeness parameter.

quant-ph↗

arXiv2025

A digital Rydberg simulation of dynamical quantum phase transitions in the Schwinger model

We present the simulation of the quench dynamics of the Z3 Schwinger model, that describes an approximation of one-dimensional Quantum Electrodynamics, on a digital noisy Rydberg atom platform, aiming at the observation of multiple dynamical quantum phase transitions. In order to reach long-time dynamics, we exploit an enconding dictated by the symmetries, combined with a circuit compression procedure. We focus on a quench that evolves the Dirac vacuum by means of a Hamiltonian depending on a negative mass parameter. This leads to resonant Rabi oscillations between the Dirac vacuum and mesonic states. The population concentration exhibits oscillations with negligible fluctuations of detuned states also with the inclusion of combined noise sources, from which we can clearly detect multiple dynamical phase transitions.

quant-ph↗

arXiv2025

Electromagnetism: an intrinsic approach to Hadamard's method of descent

We present a systematic geometric framework for the dimensional reduction of classical electromagnetism based on the concept of descent along vector fields of invariance. By exploring the interplay between the Lie derivative and the Hodge star operator, we implement descent conditions on differential forms that reduce Maxwell's equations in four-dimensional spacetime to electromagnetic theories in lower dimensions. We also consider multiple descent along pairwise commuting vector fields of invariance, yielding a finer decomposition of Maxwell's equations. Our results provide a unified and geometrically transparent interpretation of dimensional reduction, with potential applications to field theories in lower-dimensional spacetimes.

math-ph↗

arXiv2025

Quantum error mitigation in optimized circuits for particle-density correlations in real-time dynamics of the Schwinger model

Quantum computing gives direct access to the study of real-time dynamics of quantum many-body systems. In principle, it is possible to directly calculate non-equal-time correlation functions, from which one can detect interesting phenomena, such as the presence of quantum scars or dynamical quantum phase transitions. In practice, these calculations are strongly affected by noise, due to the complexity of the required quantum circuits. As a testbed for the evaluation of real-time evolution of observables and correlations, the dynamics of the Zn Schwinger model in a one dimensional lattice is considered. To control the computational cost, we adopt a quantum-classical strategy that reduces the dimensionality of the system by restricting the dynamics to the Dirac vacuum sector and optimizes the embedding into a qubit model by minimizing the number of three-qubit gates. We derive a digital circuit implementation of the time-evolution of particle-density correlation operators and their correlation, comparing results from exact evolution, bare noisy simulations and simulations with different error mitigation techniques. For the evolution of the particle-density operators we also perform runs on a physical IBM quantum device.

quant-ph↗

arXiv2025

Robustness of chaotic-light correlation imaging against turbulence

We consider an imaging scheme, inspired by microscopy, in which both correlation imaging and first-order intensity imaging can be performed simultaneously, to investigate the effects of strong turbulence on the two different kinds of images. The comparison between direct and correlation imaging in the presence of strong turbulence unambiguously revealed an advantage of the latter. Remarkably, this advantage, quantified by analyzing the visibility of periodic sample patterns, is more striking when the presence of turbulence becomes the dominant factor in determining the image resolution.

physics.optics↗

arXiv2024

Dressed atom revisited: Hamiltonian-independent treatment of the radiative cascade

The dressed atom approach provides a tool to investigate the dynamics of an atom-laser system by fully retaining the quantum nature of the coherent mode. In its standard derivation, the internal atom-laser evolution is described within the rotating-wave approximation, which determines a doublet structure of the spectrum and the peculiar fluorescence triplet in the steady state. However, the rotating wave approximation may fail to apply to atomic systems subject to femtosecond light pulses, light-matter systems in the strong-coupling regime or sustaining permanent dipole moments. This work aims to demonstrate how the general features of the steady-state radiative cascade are affected by the interaction of the dressed atom with propagating radiation modes. Rather than focusing on a specific model, we analyze how these features depend on the parameters characterizing the dressed eigenstates in arbitrary atom-laser dynamics, given that a set of general hypotheses is satisfied. Our findings clarify the general conditions in which a description of the radiative cascade in terms of transition between dressed states is self-consistent. We provide a guideline to determine the properties of photon emission for any atom-laser interaction model, which can be particularly relevant when the model should be tailored to enhance a specific line. We apply the general results to the case in which a permanent dipole moment is a source of low-energy emission, whose frequency is of the order of the Rabi coupling.

quant-ph↗

arXiv2024

Innovative schemes for Correlation Plenoptic Imaging

CPI is a novel imaging modality capable of addressing the intrinsic limitations of conventional plenoptic imaging - namely, the resolution loss and the sacrificed change of perspective, - while guaranteeing the typical advantages of plenotpic imaging: 3D imaging, refocusing of acquired pictures, in post-processing, and depth of field extension. In this work, we review a recently developed CPI scheme, named correlation plenoptic imaging between arbitrary planes, and derive the algorithm for image refocusing.

physics.optics↗

arXiv2024

Plenoptic microscopy and photography from intensity correlations

We present novel methods to perform plenoptic imaging at the diffraction limit by measuring intensity correlations of light. The first method is oriented towards plenoptic microscopy, a promising technique which allows refocusing and depth-of-field enhancement, in post-processing, as well as scanning free 3D imaging. To overcome the limitations of standard plenoptic microscopes, we propose an adaptation of Correlation Plenoptic Imaging (CPI) to the working conditions of microscopy. We consider and compare different architectures of CPI microscopes, and discuss the improved robustness with respect to previous protocols against turbulence around the sample. The second method is based on measuring correlations between the images of two reference planes, arbitrarily chosen within the tridimensional scene of interest, providing an unprecedented combination of image resolution and depth of field. The results lead the way towards the realization of compact designs for CPI devices.

physics.optics↗

arXiv2024

GPU-based data processing for speeding-up correlation plenoptic imaging

Correlation Plenoptic Imaging (CPI) is a novel technological imaging modality enabling to overcome drawbacks of standard plenoptic devices, while preserving their advantages. However, a major challenge in view of real-time application of CPI is related with the relevant amount of required frames and the consequent computational-intensive processing algorithm. In this work, we describe the design and implementation of an optimized processing algorithm that is portable to an efficient computational environment and exploits the highly parallel algorithm offered by GPUs. Improvements by a factor ranging from 20x, for correlation measurement, to 500x, for refocusing, are demonstrated. Exploration of the relation between the improvement in performance achieved and actual GPU capabilities, also indicates the feasibility of near-real time processing capability, opening up to the potential use of CPI for practical real-time application.

eess.IV↗

arXiv2024

Correlation Hyperspectral Imaging

Hyperspectral imaging aims at providing information on both the spatial and the spectral distribution of light, with high resolution. However, state-of-the-art protocols are characterized by an intrinsic trade-off imposing to sacrifice either resolution or image acquisition speed. We address this limitation by exploiting light intensity correlations, which are shown to enable overcoming the typical downsides of traditional hyperspectral imaging techniques, both scanning and snapshot. The proposed approach also opens possibilities that are not otherwise achievable, such as sharper imaging and natural filtering of broadband spectral components that would otherwise hide the spectrum of interest. The enabled combination of high spatial and spectral resolution, high speed, and insensitivity to undesired spectral features shall lead to a paradigm change in hyperspectral imaging devices and open-up new application scenarios.

physics.optics↗

arXiv2024

3D correlation imaging for localized phase disturbance mitigation

Correlation plenoptic imaging is a procedure to perform light-field imaging without spatial resolution loss, by measuring second-order spatio-temporal correlations of light. We investigate the possibility to use correlation plenoptic imaging to mitigate the effect of a phase disturbance in the propagation from the object to the main lens. We assume that this detrimental effect, that can be due to a turbulent medium, is localized at a specific distance from the lens, and is slowly varying in time. The mitigation of turbulence effects has already fostered the development of both light-field imaging and correlation imaging procedures. Here, we aim at merging these aspects, proposing a correlation light-field imaging method to overcome the effects of slowly varying turbulence, without the loss of lateral resolution, typical of traditional plenoptic imaging devices.

physics.optics↗

arXiv2024

Light-field imaging from position-momentum correlations

Correlation plenoptic imaging (CPI) is a light-field imaging technique employing intensity correlation measurements to simultaneously detect the spatial distribution and the propagation direction of light. Compared to standard methods, in which light-field images are directly encoded in intensity, CPI provides a significant enhancement of the volumetric reconstruction performance in terms of both achievable depth of field and 3D resolution. In this article, we present a novel CPI configuration where light-field information is encoded in correlations between position and momentum measurements, namely, points on a given object plane and points of the Fourier plane of the imaging lens. Besides the fundamental interest in retrieving the properties of position-momentum correlation, the proposed scheme overcomes practical limitations of previously proposed setups, providing higher axial homogeneity and robustness with respect to the identification of reference planes.

physics.optics↗

arXiv2023

Cooperative photon emission rates in random atomic clouds

We investigate the properties of the cooperative decay modes of a cold atomic cloud, characterized by a Gaussian distribution in three dimensions, initially excited by a laser in the linear regime. We study the properties of the decay rate matrix $S$, whose dimension coincides with the number of atoms in the cloud, in order to get a deeper insight into properties of cooperative photon emission. Since the atomic positions are random, $S$ is a Euclidean random matrix whose entries are function of the atom distances. We show that, in the limit of a large number of atoms in the cloud, the eigenvalue distribution of $S$ depends on a single parameter $b_0$, called the cooperativeness parameter, which can be viewed as a quantifier of the number of atoms that are coherently involved in an emission process. For very small values of $b_0$, we find that the limit eigenvalue density is approximately triangular. We also study the nearest-neighbour spacing distribution and the eigenvector statistics, finding that, although the decay rate matrices are Euclidean, the bulk of their spectra mostly behaves according to the expectations of classical random matrix theory. In particular, in the bulk there is level repulsion and the eigenvectors are delocalized, therefore exhibiting the universal behaviour of chaotic quantum systems.

quant-ph↗