arXiv subjects

C. Tejedor

Publications and source records attributed to C. Tejedor.

At least 19 recordsLinked to original sources

arXiv2023

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

Multiphoton Emission

We describe the emission, detection and structure of multiphoton states of light. We include the effect of frequency filtering, which describes, at a fundamental level, physical detection of a quantum emitter. The case of the spontaneous emission of Fock states is treated fully and analytically. We stress this picture by contrasting it to the numerical simulation of two-photon bundles emitted from a two-level system in a cavity. We show that dynamical factors exist that allow for a more robust multiphoton emission than spontaneous emission. We also describe how this relates to thermal light.

quant-ph↗

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↗

arXiv2020

Determination of polariton condensates' critical temperature

We investigate the thermal robustness of traveling polariton condensates. We create remote condensates that have never been in contact, and study their interference in momentum space, when they travel with the same velocity, by means of time-resolved photoluminescence. We determine the condensed to thermal, uncondensed polariton fraction, which shows a gradual decay with increasing temperature, and obtain the critical temperature for the Bose-Einstein-like condensate (BEC) phase transition. We tentatively compare our experimental findings with theoretical models, developed for atomic condensates, to describe the condensates' coherence fading with temperature.

cond-mat.mes-hall↗

arXiv2020

Temperature dependence of the coherence in polariton condensates

We present a time-resolved experimental study of the temperature effect on the coherence of traveling polariton condensates. The simultaneous detection of their emission both in real- and reciprocal-space allows us to fully monitor the condensates' dynamics. We obtain fringes in reciprocal-space as a result of the interference between polariton wavepackets (WPs) traveling with the same speed. The periodicity of these fringes is inversely proportional to the spatial distance between the interfering WPs. In a similar fashion, we obtain interference fringes in real-space when WPs traveling in opposite directions meet. The visibility of both real- and reciprocal-space interference fringes rapidly decreases with increasing temperature and vanishes. A theoretical description of the phase transition, considering the coexistence of condensed and non-condensed particles, for an out of equilibrium condensate such as ours is still missing. Yet a comparison with theories developed for atomic condensates allows us to infer a critical temperature for the BEC-like transition when the visibility goes to zero.

cond-mat.mes-hall↗

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↗

arXiv2018

Spontaneous patterns in coherently driven polariton microcavities

We consider a polariton microcavity resonantly driven by two external lasers which simultaneously pump both lower and upper polariton branches at normal incidence. In this setup, we study the occurrence of instabilities of the pump-only solutions towards the spontaneous formation of patterns. Their appearance is a consequence of the spontaneous symmetry breaking of translational and rotational invariance due to interaction induced parametric scattering. We observe the evolution between diverse patterns which can be classified as single-pump, where parametric scattering occurs at the same energy as one of the pumps, and as two-pump, where scattering occurs at a different energy. For two-pump instabilities, stripe and chequerboard patterns become the dominant steady-state solutions because cubic parametric scattering processes are forbidden. This contrasts with the single-pump case, where hexagonal patterns are the most common arrangements. We study the possibility of controlling the evolution between different patterns. Our results are obtained within a linear stability analysis and are confirmed by finite size full numerical calculations.

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↗

arXiv2014

Quantum coherence in momentum space of light-matter condensates

We show that the use of momentum-space optical interferometry, which avoids any spatial overlap between two parts of a macroscopic quantum state, presents a unique way to study coherence phenomena in polariton condensates. In this way, we address the longstanding question in quantum mechanics: "\emph{Do two components of a condensate, which have never seen each other, possess a definitive phase?}" [P. W. Anderson, \emph{Basic Notions of Condensed Matter Physics} (Benjamin, 1984)]. A positive answer to this question is experimentally obtained here for light-matter condensates, created under precise symmetry conditions, in semiconductor microcavities taking advantage of the direct relation between the angle of emission and the in-plane momentum of polaritons.

cond-mat.mes-hall↗

arXiv2014

Reversible dynamics of single quantum emitters near metal-dielectric interfaces

Here we present a systematic study of the dynamics of a single quantum emitter near a flat metal-dielectric interface. We identify the key elements that determine the onset of reversibility in these systems by using a formalism suited for absorbing media and through an exact integration of the dynamics. Moreover, when the quantum emitter separation from the surface is small, we are able to describe the dynamics within a pseudomode description that yields analytical understanding and allows more powerful calculations.

cond-mat.mes-hall↗

arXiv2013

Emitters of $N$-photon bundles

We propose a scheme based on the coherent excitation of a two-level system in a cavity to generate an ultrabright CW and focused source of quantum light that comes in groups (bundles) of $N$ photons, for an integer $N$ tunable with the frequency of the exciting laser. We define a new quantity, the \emph{purity} of $N$-photon emission, to describe the percentage of photons emitted in bundles, thus bypassing the limitations of Glauber correlation functions. We focus on the case $1\le N\le3$ and show that close to 100% of two-photon emission and 90% of three-photon emission is within reach of state of the art cavity QED samples. The statistics of the bundles emission shows that various regimes---from $N$-photon lasing to $N$-photon guns---can be realized. This is evidenced through generalized correlation functions that extend the standard definitions to the multi-photon level.

quant-ph↗

arXiv2013

Bichromatic dressing of a quantum dot detected by a remote second quantum dot

We demonstrate an information transfer mechanism between two dissimilar remote InAs/GaAs quantum dots weakly coupled to a common photonic crystal microcavity. Bichromatic excitation in the s-state of one of the dots leads to the formation of dressed states due to the coherent coupling to the laser field, in resonance with the quantum dot. Information on the resulting dressed structure is read out through the photo-luminescence spectrum of the other quantum dot, as well as the cavity mode. The effect is also observed upon exchange of the excitation and detection quantum dots. This quantum dot inter-talk is interpreted in terms of a cavity-mediated coupling involving acoustic phonons. A master equation for a three level system coherently pumped by the two lasers quantitatively describes the behavior of our system. Our results present an important step towards scalable solid-state quantum networking based on coupled multi-quantum-dot-cavity systems, without the need of using identical quantum emitters.

cond-mat.mes-hall↗

arXiv2013

Theory of the strong coupling between quantum emitters and propagating surface plasmons

Here we present the theoretical foundation of the strong coupling phenomenon between quantum emitters and propagating surface plasmons observed in two-dimensional metal surfaces. For that purpose, we develop an ab-initio quantum framework that accounts for the coherent coupling be- tween emitters and surface plasmons and incorporates the presence of dissipation and dephasing. For both a single emitter and a disordered ensemble of emitters, our formalism is able to reveal the key physical mechanisms that explain the reported phenomenology and also to determine the physical parameters that optimize the strong coupling.

cond-mat.mes-hall↗

arXiv2013

Control and ultrafast dynamics of a two-fluid polariton switch

We investigate the cross-interactions in a two-component polariton quantum fluid coherently driven by two independent pumping lasers tuned at different energies and momenta. We show that both the hysteresis cycles and the ON/OFF threshold of one polariton signal can be entirely controlled by a second polariton fluid. Furthermore, we study the ultrafast switching dynamics of a driven polariton state, demonstrating the ability to control the polariton population with an external laser pulse, in less than a few picoseconds.

cond-mat.mes-hall↗

arXiv2012

Two-photon spectra of quantum emitters

We apply our recently developed theory of frequency-filtered and time-resolved N-photon correlations to study the two-photon spectra of a variety of systems of increasing complexity: single mode emitters with two limiting statistics (one harmonic oscillator or a two-level system) and the various combinations that arise from their coupling. We consider both the linear and nonlinear regimes under incoherent excitation. We find that even the simplest systems display a rich dynamics of emission, not accessible by simple single photon spectroscopy. In the strong coupling regime, novel two-photon emission processes involving virtual states are revealed. Furthermore, two general results are unraveled by two-photon correlations with narrow linewidth detectors: i) filtering induced bunching and ii) breakdown of the semi-classical theory. We show how to overcome this shortcoming in a fully-quantized picture.

quant-ph↗

arXiv2012

Multistability of a two component exciton-polariton fluid

We study the stability of a multicomponent exciton-polariton fluid under resonant excitation within the linear response approximation of a generalized Gross-Pitaevskii equation. We show that, two spatially homogeneous and independently tunable pumping lasers produce, for the same values of the system parameters, up to three stable solutions. Three-stability is understood by noting that the cavity can be either little or highly populated and, in this second case, the largest part of the population lies in either one of the two components. Moreover, we show that easily tunable multistable hysteresis loops can be performed by the system.

cond-mat.mes-hall↗

arXiv2012

Frictionless flow in a binary polariton superfluid

We study the properties of a binary microcavity polariton superfluid coherently injected by two lasers. The crossover from the supersonic to subsonic regime, where motion is frictionless, is described by evaluating the Bogoliubov spectra. We show that according to the Landau criteria, the coupling between the two components precludes the existence of superfluidity just for one component but not for the other. By analysing the drag force exerted on a defect, we give a recipe to experimentally address the crossover from the supersonic to the subsonic regime.

cond-mat.mes-hall↗

arXiv2011

Dissipation-driven generation of two-qubit entanglement mediated by plasmonic waveguides

We study the generation of entanglement between two distant qubits mediated by the surface plasmons of a metallic waveguide. We show that a V-shaped channel milled in a flat metallic surface is much more efficient for this purpose than a metallic cylinder. The role of the misalignments of the dipole moments of the qubits, an aspect of great importance for experimental implementations, is also studied. A careful analysis of the quantum-dynamics of the system by means of a master equation shows that two-qubit entanglement generation is essentially due to the dissipative part of the effective qubit-qubit coupling provided by the surface plasmons. The influence of a coherent external pumping, needed to achieve a steady state entanglement, is discussed. Finally, we pay attention to the question of how to get information experimentally on the degree of entanglement achieved in the system.

cond-mat.mes-hall↗