arXiv subjects

Lorena Rebón

Publications and source records attributed to Lorena Rebón.

At least 19 recordsLinked to original sources

arXiv2026

Quantum skyrmions in the antiferromagnetic triangular lattice

Magnetic skyrmions are topological quasiparticles potentially useful for memory and computing devices. Antiferromagnetic (AF) skyrmions present no transverse deflection, making them suitable candidates for data storage applications. After the discovery of skyrmions with length scales comparable to the lattice constant, several works presented quantum analogues of classical ferromagnetic skyrmions in spin systems. However, studies about quantum analogues of AF skyrmions are still lacking. Here, we explore the phases of the AF quantum spin-1/2 Heisenberg model with Dzyaloshinskii-Moriya interactions on the triangular lattice using the density matrix renormalization group (DMRG) algorithm. We study the magnetization profile, spin structure factor and quantum entanglement of the resulting ground states to characterize the corresponding phases and signal the emergence of quantum AF skyrmions. Moreover, we present calculations of the quantum analogs of the scalar chirality, and construct local chirality maps, to further explore the different phases. Our results support that three-sublattice quantum antiferromagnetic skyrmion textures are stabilized in a wide range of magnetic fields.

cond-mat.str-el↗

arXiv2025

"Chirpons": one-dimensional phase singularities as atypical local oscillations

In this work, phase singularities embedded in a wavepacket are shown to act as sources of atypical localized oscillations when the packet interacts with a linear system. We refer to these oscillations as \textit{chirpons}, since they arise as strong variations of the instantaneous frequency (chirp). A mathematical expression is then provided to describe \textit{chirpons}, and their behavior is explored through the interaction of a super-bandwidth wavepacket -- containing two singularities -- with a damped harmonic oscillator, a fundamental model for many physical systems. This interaction is analyzed theoretically, and the predictions are verified experimentally using a resonant electrical circuit as a realization of the oscillator. The results show that \textit{chirpons} evolve in a manner fundamentally different from standard Fourier oscillations, revealing features of linear systems that are otherwise inaccessible. This introduces a new approach to analyze and characterize system responses, with potential applications in high-resolution spectroscopy and signal sensing.

physics.gen-ph↗

arXiv2025

Parallelized projective measurements for spatial photonic qudits estimation

We present a quantum state tomography method that enables the reconstruction of \emph{arbitrary} $d-$dimensional quantum states encoded in the discretized transverse momentum of photons, by using \emph{only} $d+1$ experimental settings. To this end, we identify a family of bases with the property that the outcomes of a projective measurement are \emph{spatially multiplexed} on the interference pattern of the projected state. Using the proposed scheme we performed, as a proof-of-principle, an experimental reconstruction of $d=6-$dimensional states, for which a complete set of mutually unbiased bases does not exist. We obtained fidelity values above 0.97 for both pure and mixed states, reducing the number of experimental settings from $42$ to only $7$.

quant-ph↗

arXiv2025

Tomographic measurement data of states that never existed

Microscopic Schr{ö}dinger cat states are generated from quantum correlated fields using a probabilistic heralding photon subtraction event. Subsequent quantum state tomography provides complete information about the state with typical photon numbers of the order of one. Another approach strives for a larger number of quantum-correlated photons by conditioning the measurement analysis on events with exactly this number of photons. Here, we present a new approach to derive measurement data of quantum correlated states with average quantum-correlated photon numbers significantly larger than one. We produce an ensemble of a heralded, photon-subtracted squeezed vacuum state of light. We split the states at a balanced beam splitter and simultaneously measure a pair of orthogonal field quadratures at the outputs using tomographic `Q-function homodyne detection' (QHD). The final act is probabilistic two-copy data post-processing aiming for data from a new state with larger photon number. Evaluating the final tomographic data as that of a grown microscopic Schr{ö}dinger cat state shows that the probabilistic post-processing increased the photon number of $|α_0|^2 \approx 1.2$ to $|α_2|^2 \approx 6.8$. Our concept for obtaining tomographic measurement data of mesoscopic non-classical states that never existed might be a turning point in measurement-based quantum technology.

quant-ph↗

arXiv2025

Free temporal evolution of a superbandwidth wave packet: The quantum tale of the hare and the tortoise

Can the interplay between quantum mechanics and classical optics offer new perspectives on wavepacket dynamics? Building on this connection, we show that local momenta with both super-oscillatory and suboscillatory characteristics can arise during the free propagation of a quantum particle. This behavior is mathematically analogous to the propagation of a superbandwidth laser pulse in a dispersive medium, where the instantaneous frequencies of the electric field exhibit similar sub- and super-oscillatory features. This analogy is rooted in the equivalence between the wave description of light in classical optics and the formalism of quantum mechanics. In addition, we explore the phenomenon of wavepacket localization during free propagation within a bounded region. This localization is directly linked to the distribution of local momenta within the confined wavepacket region. To complement our quantum mechanical analysis, we also perform a classical analysis to provide further insights into this phenomenon. Our findings reveal that both the emergence of local momenta with sub- and super-oscillatory features and the wavepacket localization occur within a distinct timescale, which we define as the interference time.

quant-ph↗

arXiv2024

Group-invariant estimation of symmetric states generated by noisy quantum computers

The problem of quantum state estimation is crucial in the development of quantum technologies. In particular, the use of symmetric quantum states is useful in many relevant applications. In this work, we analyze the task of reconstructing the density matrices of symmetric quantum states generated by a quantum processor. For this purpose, we take advantage of an estimation technique that results to be equivalent to the quantum Maximum Entropy (MaxEnt) estimation, and which was recently adapted to quantum states with arbitrary symmetries. The smart use of prior knowledge of the quantum state symmetries allows for a reduction in both, the number of measurements that need to be made on the system, and the size of the computational problem to store and process the data, resulting in a better overall performance of the estimator as well. After performing numerical simulations, we implement some examples of symmetric states in IonQ quantum processors, and estimate them using the proposed technique. The results are in a good agreement with numerical simulations, showing that the proposed method is a good estimator that allows to save both, experimental and computational resources.

quant-ph↗

arXiv2023

Above-threshold ionization by polarization-crafted pulses

Coherent light has revolutionized scientific research, spanning biology, chemistry, and physics. To delve into ultrafast phenomena, the development of high-energy, high-tunable light sources is instrumental. Here, the photo-electric effect is a pivotal tool for dissecting electron correlations and system structures. Particularly, above-threshold ionization (ATI), characterized by simultaneous multi-photon absorption, has been widely explored, both theoretical and experimentally. ATI decouples laser field effects from the structural information carried by photo-electrons, particularly when utilizing ultra-short pulses. In this contribution we study ATI driven by polarization-crafted (PC) pulses, which offer precise control over the electron emission directions, through an accurate change of the polarization state. PC pulses enable the manipulation of electron trajectories, opening up new avenues for understanding and harnessing coherent light. Our work explores how structured light could allow a high degree of control of the emitted photo-electrons.

physics.atom-ph↗

arXiv2023

Superbandwidth laser pulses in a dispersive medium: oscillating beyond the Fourier spectrum with unexpected propagation features

The concept of superbandwidth refers to the fact that a band-limited signal can exhibit, locally, an increase of its bandwidth, i.e., an effective bandwidth greater than that predicted by its Fourier transform. In this work, we study the propagation of superbandwidth laser pulses in a dispersive medium, characterized by the group velocity dispersion. In particular, two important results arise from the analysis of the instantaneous frequency of the pulse obtained through the Wigner function distribution: First, it can be observed local oscillations of the electric field which are beyond the Fourier spectrum of the incoming pulse. Second, for a range of values of the pulse synthesis parameters, surprisingly, the dynamics of the instantaneous frequency within certain temporal regions, corresponds to that of a pulse propagating in a medium with a group velocity dispersion of opposite sign. This phenomenon is intrinsic to the special characteristics of the pulse and not to the dispersive properties of the medium.

physics.optics↗

arXiv2023

Inspecting the use of SLMs for the control of photonic quantum states

Spatial light modulators (SLMs) are widely used to coherently control quantum states of light. When carrying out these experiments, some assumptions are made. For instance, it is supposed that the position-momentum correlations between twin photon pairs are not affected by the use of a liquid crystal display (LCD) as a SLM. Furthermore, it is assumed that the characterization of such devices performed with an intense laser source, is still valid in the single photon regime. In this work, we show that such assumptions are acceptable, within the experimental uncertainties, for a liquid crystal on silicon (LCoS) display. This is especially important when considering the use of this kind of displays for the coherent control of quantum states based on twin photon sources.

physics.optics↗

arXiv2023

Selective and efficient quantum process tomography for non-trace preserving maps: a superconducting quantum processor implementation

Alternatively to the full reconstruction of an unknown quantum process, the so-called selective and efficient quantum process tomography (SEQPT) allows estimating, individually and up to the required accuracy, a given element of the matrix that describes such an operation with a polynomial amount of resources. The implementation of this protocol has been carried out with success to characterize the evolution of a quantum system that is well described by a trace preserving quantum map. Here, we deal with a more general type of quantum process that does not preserve the trace of the input quantum state, which naturally arises in the presence of imperfect devices and system-environment interactions, in the context of quantum information science or quantum dynamics control. In that case, we show that with the aid of {\it a priori} information on the losses structure of the quantum channel, the SEQPT reconstruction can be adapted to reconstruct the non-trace-preserving map. We explicitly describe how to implement the reconstruction in an arbitrary Hilbert space of finite dimension $d$. The method is experimentally verified on a superconducting quantum processor of the IBM Quantum services, by estimating several non trace-preserving quantum processes in dimensions up to $d=6$. Our results show that it is possible to efficiently reconstruct non trace-preserving processes, with high precision, and with significantly higher fidelity than when the process is assumed to be trace-preserving.

quant-ph↗

arXiv2022

Principal frequency, super-bandwidth, and low-order harmonics generated by super-oscillatory pulses

An alternative definition to the main frequency of an ultra-short laser pulse, named principal frequency ($ω_P$), was recently introduced in E.G. Neyra, et al. Phys. Rev. A 103, 053124 (2021), resulting in a more transparent description of the nonlinear dynamics of a system driven by this coherent source. In this work, we extend the definition of $ω_P$ incorporating the spectral phase of the pulse. This upgraded definition allow us to deal with super-oscillatory pulses as well as to characterize sub-cycle pulses with a complex spectral content. Simultaneously, we study the nonlinear interaction between a few-cycle super-oscillatory pulse with a gaseous system, analysing the spectral characteristics of the fundamental, third and fifth harmonics. Here, we make use of an \textit{ab-initio} quantum mechanical approach, supplemented with a wavelet analysis. We show that the spectral characteristics of the low-order harmonics are very well explained in terms of $ω_P$, as well as the effective bandwidth of the super-oscillatory pulse. Our findings reinforce previous results that showed an increase of the effective bandwidth in the super-oscillatory region and the possibility to generate unique frequencies by a linear synthesis. We open, thus, not only new perspectives in ultrafast optics, exploring novel pathways towards the generation of fully tunable strong and short coherent sources, but also discuss possible extensions of the concepts presented here to other wave phenomena, that can be found in acoustics, signal processing or quantum mechanics.

physics.optics↗

arXiv2022

Parameterizing density operators with arbitrary symmetries to gain advantage in quantum state estimation

In this work, we show how to parameterize a density matrix that has an arbitrary symmetry, knowing the generators of the Lie algebra (if the symmetry group is a connected Lie group) or the generators of its underlying group (in case it is finite). This allows to pose MaxEnt and MaxLik estimation techniques as convex optimization problems with a substantial reduction in the number of parameters of the function involved. This implies that, apart from a computational advantage due to the fact that the optimization is performed in a reduced space, the amount of experimental data needed for a good estimation of the density matrix can be reduced as well. In addition, we run numerical experiments and apply these parameterizations to quantum state estimation of states with different symmetries.

quant-ph↗

arXiv2022

Performance of the quantum MaxEnt estimation in the presence of physical symmetries

When an informationally complete measurement is not available, the reconstruction of the density operator that describes the state of a quantum system can be accomplish, in a reliable way, by adopting the maximum entropy principle (MaxEnt principle), as an additional criterion, to obtain the least biased estimation. In this paper, we study the performance of the MaxEnt method for quantum state estimation when there is prior information about symmetries of the unknown state. We explicitly describe how to work with this method in the most general case, and present an algorithm that allows to improve the estimation of quantum states with arbitrary symmetries. Furthermore, we implement this algorithm to carry out numerical simulations estimating the density matrix of several three-qubit states of particular interest for quantum information tasks. We observed that, for most states, our approach allows to considerably reduce the number of independent measurements needed to obtain a sufficiently high fidelity in the reconstruction of the density matrix. Moreover, we analyze the performance of the method in realistic scenarios, showing that it is robust even when considering the effect of finite statistics, and under the presence of typical experimental noise.

quant-ph↗

arXiv2022

Optimization for maximum modulation of a double-pass twisted nematic liquid crystal display

Spatial light modulators are widely used to perform modulations of different properties of the electromagnetic field. In this work, a simple optimization method for general double-pass setups was developed. It takes into account the involved polarizing elements and displays, and a numerical simulation based on an exhaustive search routine finds the optimal optical axes orientation of the polarizing elements for the desired modulation. By simultaneously considering both impingements, we are able to take full advantage of the modulation capabilities of the chosen spatial light modulators. In particular, different polarization modulations and complex amplitude modulations were studied for twisted nematic liquid crystal displays and passive linear optical elements. Examples for different optimization criteria are shown and compared with experimental results, supporting the feasibility of this approach. This method offers the possibility of independent modulation of two properties of the input light state, outperforming the use of a single screen.

physics.optics↗

arXiv2021

Effective super-bandwidth in laser pulses

We present here a theoretical analysis of the interaction between an ideal two-level quantum system and a super-oscillatory pulse, like the one proposed and successfully synthesized in https://doi.org/10.1088/2040-8986/abfedf and arXiv:2106.09192. As a prominent feature, these pulses present a high efficiency of the central super-oscillatory region in relation to the unavoidable side-lobes. Besides, our study shows an increase of the effective bandwidth of the pulse, in the super-oscillatory region, and not only the appearance of a local frequency higher than its highest Fourier-frequency component, as in the usual description of the phenomenon of super-oscillations. Beyond introducing the concept of effective super-bandwidth, the presented results could be relevant for experimental applications and opening new perspectives for laser-matter interaction.

physics.optics↗

arXiv2020

Experimental characterization of quantum processes: a selective and efficient method in arbitrary finite dimension

The temporal evolution of a quantum system can be characterized by quantum process tomography, a complex task that consumes a number of physical resources scaling exponentially with the number of subsystems. An alternative approach to the full reconstruction of a quantum channel allows selecting which coefficient from its matrix description to measure, and how accurately, reducing the amount of resources to be polynomial. The possibility of implementing this method is closely related to the possibility of building a complete set of mutually unbiased bases (MUBs) whose existence is known only when the dimension of the Hilbert space is the power of a prime number. However, an extension of the method that uses tensor products of maximal sets of MUBs, has been introduced recently. Here we explicitly describe how to implement this algorithm to selectively and efficiently estimate any parameter characterizing a quantum process in a non-prime power dimension, and we conducted for the first time an experimental verification of the method in a Hilbert space of dimension $d=6$. That is the small space for which there is no known a complete set of MUBs but it can be decomposed as a tensor product of two other Hilbert spaces of dimensions $D_1=2$ and $D_2=3$, for which a complete set of MUBs is known. The $6$-dimensional states were codified in the discretized transverse momentum of the photon wavefront. The state preparation and detection stages are dynamically programmed with the use of only-phase spatial light modulators, in a versatile experimental setup that allows to implement the algorithm in any finite dimension.

quant-ph↗

arXiv2020

Determination of spatial quantum states by using Point Diffraction Interferometry

We present a method to reconstruct pure spatial qudits of arbitrary dimension $d$, which is based on a point diffraction interferometer. In the proposed scheme, the quantum states are codified in the discretized transverse position of a photon field, once they are sent through an aperture with $d$ slits, and a known background is added to provide a phase reference. To characterize these photonic quantum states, the complete phase wavefront is reconstructed through a phase-shifting technique. Combined with a multipixel detector, the acquisition can be parallelized, and only four interferograms are required to reconstruct any pure qudit, independently of the dimension $d$. We tested the method experimentally, for reconstructing states of dimension $d=6$ randomly chosen. A mean fidelity values of $0.95$ is obtained. Additionally, we develop an experimental scheme that allows to estimate phase aberrations affecting the wavefront upon propagation, and thus improve the quantum state estimation. In that regard, we present a proof-of-principle demonstration that shows the possibility to correct the influence of turbulence in a free-space communication, recovering mean fidelity values comparable to the propagation free of turbulence.

quant-ph↗

arXiv2019

Parallel-in-time optical simulation of history states

We present an experimental optical implementation of a parallel-in-time discrete model of quantum evolution, based on the entanglement between the quantum system and a finite dimensional quantum clock. The setup is based on a programmable spatial light modulator which entangles the polarization and transverse spatial degrees of freedom of a single photon. It enables the simulation of a qubit history state containing the whole evolution of the system, capturing its main features in a simple and configurable scheme. We experimentally determine the associated system-time entanglement, which is a measure of distinguishable quantum evolution, and also the time average of observables, which in the present realization can be obtained through one single measurement.

quant-ph↗