arXiv subjects

C. E. López

Publications and source records attributed to C. E. López.

13 recordsLinked to original sources

arXiv2021

Correlations transference and apparition of a metastable decoherence-free subspace in dissipative reservoirs

The dynamic of correlations in a system composed of a two-mode quantum field coupled with the environment is studied. The quantum field corresponds to two entangled coherent states whose amplitude we vary up to the mesoscopic regime. We show that under the onset of decoherence, correlations in the quantum field are not lost but transferred to the environment. We also found that sudden transitions in the decoherence regimes appear along with the dynamics depending on the coherent states' amplitude. Increasing the amplitude of the entangled coherence state results in the apparition of a metastable decoherence-free subspace (DFS) in the field subsystem, and the transference of classical correlations freezes. This subspace only exists during a time interval that depends on the average number of photons. Interestingly, the reservoir subsystem also experiences the apparition of a DFS. Only quantum correlations are transferred while the DFS exists.

quant-ph↗

arXiv2018

Study of simulated Bloch oscillations in strained graphene using neural networks

We consider a monolayer of graphene under uniaxial, tensile strain and simulate Bloch oscillations for different electric field orientations parallel to the plane of the monolayer using several values of the components of the uniform strain tensor, but keeping the Poisson ratio in the range of observable values. We analyze the trajectories of the charge carriers with different initial conditions using an artificial neural network, trained to classify the simulated signals according to the strain applied to the membrane. When the electric field is oriented either along the Zig-Zag or the Armchair edges, our approach successfully classifies the independent component of the uniform strain tensor with up to 90\% of accuracy and an error of $\pm1\%$ in the predicted value. For an arbitrary orientation of the field, the classification is made over the strain tensor component and the Poisson ratio simultaneously, obtaining up to 97\% of accuracy with an error that goes from $\pm5\%$ to $\pm10\%$ in the strain tensor component and an error from $\pm12.5\%$ to $\pm25\%$ in the Poisson ratio.

cond-mat.str-el↗

arXiv2018

Metastable decoherence-free subspace and pointer states in mesoscopic quantum systems

Two initially correlated coherent states, each interacting with its own independent dissipative environment exhibit a sudden transition from classical to quantum decoherence. This change in the dynamics is a turning point in the decoherence, in the sense that depending on the average number of photons of each cavity, decoherence can even be suppressed. Indeed, the quantum state is time-independent for a time span in the mesoscopic regime, revealing a decoherence-free subspace. Furthermore, the absence of decoherence is manifested in the apparition of a metastable pointer state basis.

quant-ph↗

arXiv2017

Bloch oscillations in graphene from an artificial neural network study

We develop an artificial neural network (ANN) approach to classify simulated signals corrsponding to the semi-classical description of Bloch oscillations in pristine graphene. After the ANN is properly trained, we consider the inverse problem of Bloch oscillations (BO),namely, a new signal is classified according to the external electric field strength oriented along either the zig-zag or arm-chair edges of the graphene membrane, with a correct classification that ranges from 82.6% to 99.3% depending on the accuracy of the predicted electric field. This approach can be improved depending on the time spent in training the network and the computational power available. Findings in this work can be straightforwardly extended to a variety of Dirac-Weyl materials.

cond-mat.mtrl-sci↗

arXiv2017

Stable and metastable freezing of classical correlations in qutrits

We study the dynamics of quantum and classical correlations in a two-qutrit system coupled to independent reservoirs. In particular, we addressed the differences in the dynamics of Markovian and non-Markovian regimes and show that for specific initial states, classical correlations exhibit abrupt changes along the dynamics. A particular sudden change occurs when the classical correlations freezes to a certain value at a given time, revealing the apparition of a pointer-state basis. After this given time, the decoherence only affects quantum correlations. Here we identify two regimes in the decoherence dynamics: a mixed regime when both classical and quantum correlations decay and a quantum regime when only quantum correlations decay. We show that the freezing of classical correlations can be stable or metastable depending on the system-reservoirs parameters. In the long-time limit, we find analytical expressions for the pointer-state basis the system settles in, and consequently for classical and quantum correlations.

quant-ph↗

arXiv2017

Generation of maximally correlated states in the absence of entanglement

We study the generation of maximally correlated states of two qubits in the absence of quantum entanglement. We show that stationary maximally correlated states can be generated under the assistance of a collective dissipative dynamics. The absence of entanglement necessarily requires maximal entanglement to an environment. The conditions under which two qubits can be maximally correlated to a finite environment are studied. We find the existence of maximally correlated states without entanglement for $3 \otimes 3$ bipartite quantum states

quant-ph↗

arXiv2014

Emergence of metastable pointer states basis in non-Markovian quantum dynamics

We investigate the dynamics of classical and quantum correlations between two qubits. Each qubit is implemented by a pair of phosphorous impurities embedded in a silicon substrate. The main decoherence mechanism affecting these types of qubits is provided by the coupling of the phosphorous impurities to the acoustical vibrations of the silicon lattice. We find that depending on the temperature of the substrate and the initial state, three different dynamics can be found. These are characterized by the number of abrupt changes in both classical and quantum correlations. We also show that the correlations do not disappear. Moreover, before the classical correlations reach a constant value, they may experience successive abrupt changes associated with the apparition of metastable pointer states basis. Then, a constant value for the classical correlations is reached when the preferred basis is established.

quant-ph↗

arXiv2011

Multipartite Entanglement Generation Assisted by Inhomogeneous Coupling

We show that controllable inhomogeneous coupling between two-level systems and a common data bus provides a fast mechanism to produce multipartite entanglement. Our proposal combines resonant interactions and engineering of coupling strengths---between the qubits and the single mode---leading to well defined entangled states. Furthermore, we show that, if the two-level systems interact dispersively with the quantized mode, engineering of coupling strengths allows the controlled access of the symmetric Hilbert space of qubits.

quant-ph↗

arXiv2011

Entanglement of formation for a class of $(2\otimes d)$-dimensional systems

Currently the entanglement of formation can be calculated analytically for mixed states in a $(2\otimes2)$-dimensional Hilbert space. For states in higher dimensional Hilbert space a closed formula for quantifying entanglement does not exist. In this regard only entanglement bounds has been found for estimating it. In this work, we find an analytical expression for evaluating the entanglement of formation for bipartite ($2\otimes d$)-dimensional mixed states.

quant-ph↗

arXiv2010

Dynamics of Entanglement Transfer Through Multipartite Dissipative Systems

We study the dynamics of entanglement transfer in a system composed of two initially correlated three-level atoms, each located in a cavity interacting with its own reservoir. Instead of tracing out reservoir modes to describe the dynamics using the master equation approach, we consider explicitly the dynamics of the reservoirs. In this situation, we show that the entanglement is completely transferred from atoms to reservoirs. Although the cavities mediate this entanglement transfer, we show that under certain conditions, no entanglement is found in cavities throughout the dynamics. Considering the entanglement dynamics of interacting and non-interacting bipartite subsystems, we found time windows where the entanglement can only flow through interacting subsystems, depending on the system parameters.

quant-ph↗

arXiv2007

Space Velocities of Southern Globular Clusters. V. A Low Galactic Latitude Sample

We have measured the absolute proper motions of globular clusters NGC 2808, 3201, 4372, 4833, 5927 and 5986. The proper motions are on the Hipparcos system and they are the first determinations ever made for these low Galactic latitude clusters. The proper motion uncertainties range from 0.3 to 0.5 mas/yr. The inferred orbits indicate that 1) the single metal rich cluster in our sample, NGC 5927, dynamically belongs to the thick disk, 2) the remaining metal poor clusters have rather low-energy orbits of high eccentricity; among these, there appear to be two "pairs" of dynamically associated clusters, 3) the most energetic cluster in our sample, NGC 3201 is on a highly retrograde orbit -- which had already been surmised from its radial velocity alone -- with an apocentric distance of 22 kpc, and 4) none of the metal poor clusters appear to be associated with the recently detected SDSS streams, or with the Monoceros structure. These are the first results of the Southern Proper-Motion Program (SPM) where the second-epoch observations are taken with the CCD camera system recently installed on the double astrograph at El Leoncito, Argentina.

astro-ph↗

arXiv2007

Abrupt Changes in the Dynamics of Quantum Disentanglement

Entanglement evolution in high dimensional bipartite systems under dissipation is studied. Discontinuities for the time derivative of the lower bound of entanglement of formation is found depending on the initial conditions for entangled states. This abrupt changes along the evolution appears as precursors of entanglement sudden death.

quant-ph↗

arXiv2006

Entanglement properties in the Inhomogeneous Tavis-Cummings model

In this work we study the properties of the atomic entanglement in the eigenstates spectrum of the inhomogeneous Tavis-Cummings Model. The inhomogeneity is present in the coupling among the atoms with quantum electromagnetic field. We calculate analytical expressions for the concurrence and we found that this exhibits a strong dependence on the inhomogeneity.

quant-ph↗