arXiv subjects

L. Quiroga

Publications and source records attributed to L. Quiroga.

At least 19 recordsLinked to original sources

arXiv2025

Twisted light drives chiral excitations of interacting electrons in nanostructures with magnetic field

Twisted light (TL), a special kind of light carrying orbital angular momentum, provides a powerful tool for driving symmetry resolved transitions in quantum confined nanostructures. We study a realistic model where a TL pulse excites two interacting electrons in a nanostructure under a perpendicular magnetic field. To include image charge effects in layered systems, we use an effective electron electron potential of the form 1/r^n. For n = 2, the system exhibits an underlying su(1,1) dynamical symmetry, enabling analytical solutions and a clear interpretation of selection rules, parity changes, and angular momentum resolved absorption. We show that the bare Coulomb 1/r interaction produces similar spectra, indicating that twisted light driven excitations are robust against the precise interaction form. The excitation spectrum reveals strong chiral properties: TL pulses, unlike conventional dipolar fields, directly access interaction-driven transitions otherwise symmetry-forbidden. In particular, TL breaks the generalized Kohn theorem, exposing internal excitations through multi quanta orbital processes. More broadly, our results establish TL as a sensitive probe of correlations, symmetry, and magneto-optical dynamics in strongly interacting quantum systems, uncovering features that remain invisible to standard infrared absorption.

cond-mat.mes-hall↗

arXiv2023

Cavity-induced switching between Bell-state textures in a quantum dot

Nanoscale quantum dots in microwave cavities can be used as a laboratory for exploring electron-electron interactions and their spin in the presence of quantized light and a magnetic field. We show how a simple theoretical model of this interplay at resonance predicts complex but measurable effects. New polariton states emerge that combine spin, relative modes, and radiation. These states have intricate spin-space correlations and undergo polariton transitions controlled by the microwave cavity field. We uncover novel topological effects involving highly correlated spin and charge density that display singlet-triplet and inhomogeneous Bell-state distributions. Signatures of these transitions are imprinted in the photon distribution, which will allow for optical read-out protocols in future experiments and nanoscale quantum technologies.

cond-mat.mes-hall↗

arXiv2022

From edge to bulk: Cavity induced displacement of topological non-local qubits

We investigate the ability of selective cavity coupling to a topological chain for tailoring the connectivity of Majorana fermions. We show how topological qubits (TQs), associated with non-local Majorana fermion pairing, can be moved from the edge to the bulk of a topological chain through selective access to light-matter interaction with specific physical sites. In particular, we present a comprehensive DMRG study of ground-state features in different chain-cavity coupling geometries and validate analytical insights in the strong coupling regime. This new kind of Majorana fermion correlation generation process comes with new cavity photon features. Moreover, by considering the time evolution after a sudden quench of the cavity-matter coupling strength, we show that the development of high non-trivial matter (Majorana) correlations leaves off measurable non-classical photon imprints in the cavity. New ways to dynamically generate TQ nonlocal correlations in topological chains of arbitrary length are thus provided, opening alternative routes to controllable long-range entanglement in hybrid photonic solid-state systems.

cond-mat.mes-hall↗

arXiv2021

Ladder of Loschmidt anomalies in the deep strong-coupling regime of a qubit-oscillator system

We uncover a remarkably regular array of singularity-like structures within the deep strong-coupling limit of qubit-oscillator (e.g. light-matter) systems described by the quantum Rabi model, as a function of time and coupling strength. These non-analytic anomalies in the Loschmidt amplitude (echoes) suggest the existence of new forms of dynamical phase transition within this deep strong-coupling regime. The key feature whereby the initial state collapses into orthogonal states at select values of the interaction strength and select times, may be used to enhance - or attack - quantum information processing or computation schemes that rely on removing - or retaining - a given quantum state.

cond-mat.mes-hall↗

arXiv2020

Rényi Entropy Singularities as Signatures of Topological Criticality in Coupled Photon-Fermion Systems

We show that the topological phase transition for a Kitaev chain embedded in a cavity can be identified by measuring experimentally accessible photon observables such as the Fano factor and the cavity quadrature amplitudes. Moreover, based on density matrix renormalization group numerical calculations, endorsed by an analytical Gaussian approximation for the cavity state, we propose a direct link between those observables and quantum entropy singularities. We study two bipartite entanglement measures, the von Neumann and Rényi entanglement entropies, between light and matter subsystems. Even though both display singularities at the topological phase transition points, remarkably only the Rényi entropy can be analytically connected to the measurable Fano factor. Consequently, we show a method to recover the bipartite entanglement of the system from a cavity observable. Thus, we put forward a path to experimentally access the control and detection of a topological quantum phase transition via the Rényi entropy, which can be measured by standard low noise linear amplification techniques in superconducting circuits. In this way, the main quantum information features of Majorana polaritons in photon-fermion systems can be addressed in feasible experimental setups.

cond-mat.quant-gas↗

arXiv2019

Enhancing violations of Leggett-Garg inequalities in nonequilibrium correlated many-body systems by interactions and decoherence

We identify different schemes to enhance the violation of Leggett-Garg inequalities in open many-body systems. Considering a nonequilibrium archetypical setup of quantum transport, we show that particle interactions control the direction and amplitude of maximal violation and that in the strongly-interacting and strongly-driven regime bulk dephasing enhances the violation. Through an analytical study of a minimal model, we unravel the basic ingredients to explain this decoherence-enhanced quantumness, illustrating that such an effect emerges in a wide variety of systems.

cond-mat.stat-mech↗

arXiv2018

Pulsed Generation of Quantum Coherences and Non-classicality in Light-Matter Systems

We show that a pulsed stimulus can be used to generate many-body quantum coherences in light-matter systems of general size. Specifically, we calculate the exact real-time evolution of a driven, generic out-of-equilibrium system comprising an arbitrary number N qubits coupled to a global boson field. A novel form of dynamically-driven quantum coherence emerges for general N and without having to access the empirically challenging strong-coupling regime. Its properties depend on the speed of the changes in the stimulus. Non-classicalities arise within each subsystem that have eluded previous analyses. Our findings show robustness to losses and noise, and have potential functional implications at the systems level for a variety of nanosystems, including collections of N atoms, molecules, spins, or superconducting qubits in cavities -- and possibly even vibration-enhanced light harvesting processes in macromolecules.

quant-ph↗

arXiv2018

Universal two-time correlations, out-of-time-ordered correlators and Leggett-Garg inequality violation by edge Majorana fermion qubits

In the present work we propose that two-time correlations of Majorana edge localized fermions constitute a novel and versatile toolbox for assessing the topological phases of 1D open lattices. Using analytical and numerical calculations on the Kitaev model, we uncover universal relationships between the decay of the short-time correlations and a particular family of out-of-time-ordered correlators, which provide direct experimental alternatives to the quantitative analysis of the system regime, either normal or topological. Furthermore we show that the saturation of two-time correlations possesses features of an order parameter. Finally, we find that violations of Leggett-Garg inequalities can indicate the topological-normal phase transition by looking at different qubits formed by pairing local and non-local edge Majorana fermions.

cond-mat.str-el↗

arXiv2017

Dynamics of Entanglement and the Schmidt Gap in a Driven Light-Matter System

The ability to modify light-matter coupling in time (e.g. using external pulses) opens up the exciting possibility of generating and probing new aspects of quantum correlations in many-body light-matter systems. Here we study the impact of such a pulsed coupling on the light-matter entanglement in the Dicke model as well as the respective subsystem quantum dynamics. Our dynamical many-body analysis exploits the natural partition between the radiation and matter degrees of freedom, allowing us to explore time-dependent intra-subsystem quantum correlations by means of squeezing parameters, and the inter-subsystem Schmidt gap for different pulse duration (i.e. ramping velocity) regimes -- from the near adiabatic to the sudden quench limits. Our results reveal that both types of quantities indicate the emergence of the superradiant phase when crossing the quantum critical point. In addition, at the end of the pulse light and matter remain entangled even though they become uncoupled, which could be exploited to generate entangled states in non-interacting systems.

quant-ph↗

arXiv2016

Quantum Hysteresis in Coupled Light-Matter Systems

We investigate the non-equilibrium quantum dynamics of a canonical light-matter system, namely the Dicke model, when the light-matter interaction is ramped up and down through a cycle across the quantum phase transition. Our calculations reveal a rich set of dynamical behaviors determined by the cycle times, ranging from the slow, near adiabatic regime through to the fast, sudden quench regime. As the cycle time decreases, we uncover a crossover from an oscillatory exchange of quantum information between light and matter that approaches a reversible adiabatic process, to a dispersive regime that generates large values of light-matter entanglement. The phenomena uncovered in this work have implications in quantum control, quantum interferometry, as well as in quantum information theory.

cond-mat.quant-gas↗

arXiv2016

Quantum Phase Transitions detected by a local probe using Time Correlations and Violations of Leggett-Garg Inequalities

In the present paper we introduce a way of identifying quantum phase transitions of many-body systems by means of local time correlations and Leggett-Garg inequalities. This procedure allows to experimentally determine the quantum critical points not only of finite-order transitions but also those of infinite order, as the Kosterlitz-Thouless transition that is not always easy to detect with current methods. By means of simple analytical arguments for a general spin-$1 / 2$ Hamiltonian, and matrix product simulations of one-dimensional $X X Z$ and anisotropic $X Y$ models, we argue that finite-order quantum phase transitions can be determined by singularities of the time correlations or their derivatives at criticality. The same features are exhibited by corresponding Leggett-Garg functions, which noticeably indicate violation of the Leggett-Garg inequalities for early times and all the Hamiltonian parameters considered. In addition, we find that the infinite-order transition of the $X X Z$ model at the isotropic point can be revealed by the maximal violation of the Leggett-Garg inequalities. We thus show that quantum phase transitions can be identified by purely local measurements, and that many-body systems constitute important candidates to observe experimentally the violation of Leggett-Garg inequalities.

quant-ph↗

arXiv2015

Large dynamic light-matter entanglement from driving neither too fast nor too slow

A significant problem facing next-generation quantum technologies is how to generate and manipulate macroscopic entanglement in light and matter systems. Here we report a new regime of dynamical light-matter behavior in which a giant, system-wide entanglement is generated by varying the light-matter coupling at \emph{intermediate} velocities. This enhancement is far larger and broader-ranged than that occurring near the quantum phase transition of the same model under adiabatic conditions. By appropriate choices of the coupling within this intermediate regime, the enhanced entanglement can be made to spread system-wide or to reside in each subsystem separately.

quant-ph↗

arXiv2015

Robust quantum correlations in out-of-equilibrium matter-light systems

High precision macroscopic quantum control in interacting light-matter systems remains a significant goal toward novel information processing and ultra-precise metrology. We show that the out-of-equilibrium behavior of a paradigmatic light-matter system (Dicke model) reveals two successive stages of enhanced quantum correlations beyond the traditional schemes of near-adiabatic and sudden quenches. The first stage features magnification of matter-only and light-only entanglement and squeezing due to effective non-linear self-interactions. The second stage results from a highly entangled light-matter state, with enhanced superradiance and signatures of chaotic and highly quantum states. We show that these new effects scale up consistently with matter system size, and are reliable even in dissipative environments.

quant-ph↗

arXiv2013

New dynamical scaling universality for quantum networks across adiabatic quantum phase transitions

We reveal universal dynamical scaling behavior across adiabatic quantum phase transitions (QPTs) in networks ranging from traditional spatial systems (Ising model) to fully connected ones (Dicke and Lipkin-Meshkov-Glick models). Our findings, which lie beyond traditional critical exponent analysis and adiabatic perturbation approximations, are applicable even where excitations have not yet stabilized and hence provide a time-resolved understanding of QPTs encompassing a wide range of adiabatic regimes. We show explicitly that even though two systems may traditionally belong to the same universality class, they can have very different adiabatic evolutions. This implies more stringent conditions need to be imposed than at present, both for quantum simulations where one system is used to simulate the other, and for adiabatic quantum computing schemes.

quant-ph↗

arXiv2012

Quantum-correlated two-photon transitions to excitons in semiconductor quantum wells

The dependence of the excitonic two-photon absorption on the quantum correlations (entanglement) of exciting biphotons by a semiconductor quantum well is studied. We show that entangled photon absorption can display very unusual features depending on space-time-polarization biphoton parameters and absorber density of states for both bound exciton states as well as for unbound electron-hole pairs. We report on the connection between biphoton entanglement, as quantified by the Schmidt number, and absorption by a semiconductor quantum well. Comparison between frequency-anti-correlated, unentangled and frequency-correlated biphoton absorption is addressed. We found that exciton oscillator strengths are highly increased when photons arrive almost simultaneously in an entangled state. Two-photon-absorption becomes a highly sensitive probe of photon quantum correlations when narrow semiconductor quantum wells are used as two-photon absorbers.

cond-mat.mes-hall↗

arXiv2008

Nonequilibrium dynamics of polariton entanglement in a cluster of coupled traps

We study in detail the generation and relaxation of quantum coherences (entanglement) in a system of coupled polariton traps. By exploiting a Lie algebraic based super-operator technique we provide an analytical exact solution for the Markovian dissipative dynamics (Master equation) of such system which is valid for arbitrary cluster size, polariton-polariton interaction strength, temperature and initial state. Based on the exact solution of the Master equation at T=0K, we discuss how dissipation affects the quantum entanglement dynamics of coupled polariton systems.

cond-mat.mes-hall↗

arXiv2008

Control of non-Markovian effects in the dynamics of polaritons in semiconductor microcavities

We report on time-resolved photoluminescence from semiconductor microcavities showing that an optically controllable mechanism exists to turn on and off memory effects in a polariton system. By increasing the laser pumping pulse intensity we observe revivals of the decaying time-resolved photoluminescence signal, a manifestly non-Markovian behavior of the optically active polaritons. Based on an open quantum system approach we perform a comprehensive analytical and numerical study of the coupling of optically active polaritons to a structured reservoir to confirm the origin of the observed features. Our findings show that negative detunings and strong excitation should occur simultaneously for memory effects to take place.

cond-mat.mes-hall↗

arXiv2007

A non-Markovian optical signature for detecting entanglement in coupled excitonic qubits

We identify an optical signature for detecting entanglement in experimental nanostructure systems comprising coupled excitonic qubits. This signature owes its strength to non-Markovian dynamical effects in the second-order temporal coherence function of the emitted radiation. We calculate autocorrelation and cross-correlation functions for both selective and collective light excitation, and prove that the coherence properties of the emitted light do indeed carry information about the entanglement of the initial multi-qubit state. We also show that this signature can survive in the presence of a noisy environment.

cond-mat.mes-hall↗