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Miguel Orszag

Publications and source records attributed to Miguel Orszag.

29 records · Page 2Linked to original sources
arXiv2014

Selftrapping triggered by losses in cavity QED

In a coupled cavity QED network model, we study the transition from a localized super fluid like state to a delocalized Mott insulator like state, triggered by losses. Without cavity losses, the transition never takes place. Further, if one measures the quantum correlations between the polaritons via the negativity, we find a critical cavity damping constant, above which the negativity displays a single peak in the same time region where the transition takes place. Additionally, we identify two regions in the parameter space, where below the critical damping, oscillations of the initial localized state are observed along with a multipeaked negativity, while above the critical value, the oscillations die out and the transition is witnessed by a neat single peaked negativity.

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arXiv2014

Quantum Correlations in Cavity QED Networks

We present a Review of the dynamical features such as generation, propagation, distribution, sudden transition and freezing of the various quantum correlation measures, as Concurrence, Entanglement of Formation, Quantum Discord, as well their geometrical measure counterparts within the models of Cavity Quantum Electrodynamics Networks. Dissipation and thermal effects are discussed both in the generation of quantum correlations as well as their effect on the sudden changes and freezing of the classical and quantum correlations in a cavity quantum electrodynamical network. For certain initial conditions, double transitions in the Bures geometrical discord are found. One of these transitions tends to disappear at a critical temperature

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arXiv2014

Thermal effects on the sudden changes and freezing of correlations between remote atoms in cavity QED network

We investigate the thermal effects on the sudden changes and freezing of the quantum and classical correlations of remote qubits in a cavity quantum electrodynamics (CQED) network with losses. We find that the detrimental effect of the thermal reservoirs on the system can be compensated via an efficient coupling of the fiber connecting the two cavities of the system. Furthermore, for certain initial conditions, we find a double sudden transitions in the dynamics of Bures geometrical quantum discord. The second transition tends to disappear at a critical temperature, hence freezing the discord. Finally, we discuss some ideas of the experimental realization of the present proposal.

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arXiv2014

Harnessing synthetic gauge fields for maximally entangled state generation

We study the generation of entanglement between two species of neutral cold atoms living on an optical ring lattice, where each group of particles can be described by a $d$-dimensional Hilbert space (qu$d$it). Synthetic magnetic fields are exploited to create an entangled state between the pair of qu$d$its. Maximally entangled eigenstates are found for well defined values of the Aharonov-Bohm phase, which are zero energy eigenstates of both the kinetic and interacting parts of the Bose-Hubbard Hamiltonian, making them quite exceptional and robust against certain non-perturbative fluctuations of the Hamiltonian. We propose a protocol to reach the maximally entangled state (MES) by starting from an initially prepared ground state. Also, an indirect method to detect the MES by measuring the current of the particles is proposed.

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arXiv2014

Determination of the maximum Global Quantum Discord via measurements of excitations in a cavity QED network

Multipartite Quantum Correlations is one of the most relevant indicator of the quantumness of a system in many body systems. This remarkable feature is in general difficult to characterize and the known definitions are hard to measure. Besides the efforts dedicated to solve this problem, the question of which is the best approach remains open. In this work, we study the Global Quantum Discord, GQD, as a bipartite and multipartite measure. We also check the limits of this definitions and present an experimental scheme to determine the maximum of the GQD via the measurements of the system's excitations, during the time evolution of the present system.

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arXiv2013

Geometric quantum discord with Bures distance: the qubit case

The minimal Bures distance of a quantum state of a bipartite system AB to the set of classical states for subsystem A defines a geometric measure of quantum discord. When A is a qubit, we show that this geometric quantum discord is given in terms of the eigenvalues of a (2 n_B) x (2 n_B) hermitian matrix, n_B being the Hilbert space dimension of the other subsystem B. As a first application, we calculate the geometric discord for the output state of the DQC1 algorithm. We find that it takes its highest value when the unitary matrix from which the algorithm computes the trace has its eigenvalues uniformly distributed on the unit circle modulo a symmetry with respect to the origin. As a second application, we derive an explicit formula for the geometric discord of two-qubit states with maximally mixed marginals and compare it with other measures of quantum correlations. We also determine the closest classical states to such two-qubit states.

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arXiv2013

Geometric quantum discord with Bures distance

We define a new measure of quantum correlations in bipartite quantum systems given by the Bures distance of the system state to the set of classical states with respect to one subsystem, that is, to the states with zero quantum discord. Our measure is a geometrical version of the quantum discord. As the latter it quantifies the degree of non-classicality in the system. For pure states it is identical to the geometric measure of entanglement. We show that for mixed states it coincides with the optimal success probability of an ambiguous quantum state discrimination task. Moreover, the closest zero-discord states to a given state are obtained in terms of the corresponding optimal measurements.

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arXiv2012

Thermally generated long-lived quantum correlations for two atoms trapped in fiber-coupled cavities

A theoretical model for driving a two qubit system to a stable long-lived entanglement is discussed. The entire system is represented by two atoms, initially in ground states and disentangled, each one coupled to a separate cavity with the cavities connected by a fiber. The cavities and fiber exchange energy with their individual thermal environments. Under these conditions, we apply the theory of microscopic master equation developed for the dynamics of the open quantum system. Deriving the density operator of the two-qubit system we found that stable long-lived quantum correlations are generated in the presence of thermal excitation of the environments. To the best of our knowledge, there is no a similar effect observed in a quantum open system described by a generalized microscopic master equation in the approximation of the cavity quantum electrodynamics (CQED).

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arXiv2005

Instability and entanglement of the ground state of the Dicke model

Using tools of quantum information theory we show that the ground state of the Dicke model exhibits an infinite sequence of instabilities (quantum-phase-like transitions). These transitions are characterized by abrupt changes of the bi-partite entanglement between atoms at critical values $κ_j$ of the atom-field coupling parameter $κ$ and are accompanied by discontinuities of the first derivative of the energy of the ground state. We show that in a weak-coupling limit ($κ_1\leq κ\leq κ_2$) the Coffman-Kundu-Wootters (CKW) inequalities are saturated which proves that for these values of the coupling no intrinsic multipartite entanglement (neither among the atoms nor between the atoms and the field) is generated by the atom-field interaction. We analyze also the atom-field entanglement and we show that in the strong-coupling limit the field is entangled with the atoms so that the von Neumann entropy of the atomic sample (that serves as a measure of the atom-field entanglement) takes the value $S_A={1/2}\ln (N+1)$. The entangling interaction with atoms leads to a highly sub-Poissonian photon statistics of the field mode.

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