13 research outputs found
Ground-state entanglement of spin-1 bosons undergoing superexchange interactions in optical superlattices
We discuss a model with ultra-cold atoms confined in optical superlattices.
In particular, we study the ground-state properties of two spin-1 bosons
trapped in a double-well potential. Depending on the external magnetic field
and biquadratic interactions different phases of magnetic order are realized.
Applying von Neumann entropy and number of relevant orbitals, we quantify the
bipartite entanglement between particles. Changing the values of the parameters
determining superlattices, we can switch the system between differently
entangled states
Witnesses of Quantum Chaos and Nonlinear Kerr-Like Oscillator Model
Here, we present a brief insight into some current methods allowing for the detection of quantum chaos phenomena. In particular, we show examples of proposals of the parameters which could be applied as indicators of quantum-chaotic behavior and already were presented in the literature. We concentrate here on the quantum fidelity and the fidelity-like functions, defined for the wave functions describing system’s evolution. The definition of the fidelity-like parameter also involves the operator of the mean number of photons/phonons. Discussing such parameter, we show here how it is possible to take into account in the discussion of quantum-chaotic systems simultaneously the behavior of the divergence of wave functions and the energy of the system represented by the mean number of photons/phonons. Next, we discuss entropy-type parameter which can also be a good candidate for the indicators of quantum chaos’ phenomena. We show the ability of all considered here parameters to be witnesses of quantum-chaotic behavior for the systems of the quantum nonlinear Kerr-like oscillator—the classical counterpart of such system can exhibit chaotic evolution in its canonical form
Sudden vanishing and reappearance of nonclassical effects: General occurrence of finite-time decays and periodic vanishings of nonclassicality and entanglement witnesses
Analyses of phenomena exhibiting finite-time decay of quantum entanglement
have recently attracted considerable attention. Such decay is often referred to
as sudden vanishing (or sudden death) of entanglement, which can be followed by
its sudden reappearance (or sudden rebirth). We analyze various finite-time
decays (for dissipative systems) and analogous periodic vanishings (for unitary
systems) of nonclassical correlations as described by violations of classical
inequalities and the corresponding nonclassicality witnesses (or quantumness
witnesses), which are not necessarily entanglement witnesses. We show that
these sudden vanishings are universal phenomena and can be observed: (i) not
only for two- or multi-mode but also for single-mode nonclassical fields, (ii)
not solely for dissipative systems, and (iii) at evolution times which are
usually different from those of sudden vanishings and reappearances of quantum
entanglement.Comment: 10 pages, 3 figure
Symmetry restoring and ancilla-driven entanglement for ultra-cold spin-1 atoms in a three-site ring
Mixedness, Coherence and Entanglement in a Family of Three-Qubit States
We consider a family of states describing three-qubit systems. We derived formulas showing the relations between linear entropy and measures of coherence such as degree of coherence, first- and second-order correlation functions. We show that qubit–qubit states are strongly entangled when linear entropy reaches some range of values. For such states, we derived the conditions determining boundary values of linear entropy parametrized by measures of coherence
Electromagnetically induced transparency for a double Fano-profile system
A Λ-like
model of atomic levels involving two auto-ionizing states is considered. The levels are
irradiated by two external electromagnetic fields, a strong driving and a weak probing
ones. The analytical formula for medium susceptibility shows an additional
electromagnetically induced transparency window caused by the second auto-ionizing level.
Characteristics of both transparency windows are analyzed depending on parameters of
auto-ionizing levels and the external driving field. Manipulation of these characteristics
seems to be very effective because of their large sensitivity with respect to the
parameters involved in the problem. This manipulation becomes even more feasible when
considered model is implemented in so-called laser-induced continuum structure
Sudden vanishing and reappearance of nonclassical effects, Phys. Rev. A 83
Analyses of phenomena exhibiting finite-time decay of quantum entanglement have recently attracted considerable attention. Such decay is often referred to as sudden vanishing (or sudden death) of entanglement, which can be followed by its sudden reappearance (or sudden rebirth). We analyze various finite-time decays (for dissipative systems) and analogous periodic vanishings (for unitary systems) of nonclassical correlations as described by violations of classical inequalities and the corresponding nonclassicality witnesses (or quantumness witnesses), which are not necessarily entanglement witnesses. We show that these sudden vanishings are universal phenomena and can be observed: (i) not only for two-or multimode but also for single-mode nonclassical fields, (ii) not solely for dissipative systems, and (iii) at evolution times which are usually different from those of sudden vanishings and reappearances of quantum entanglement
Quantum Steering in Two- and Three-Mode ??-Symmetric Systems
We consider two PT-symmetric models, consisting of two or three single-mode cavities. In both models, the cavities are coupled to each other by linear interactions, forming a linear chain. Additionally, the first and last of such cavities interact with an environment. Since the models are PT-symmetric, they are described by non-Hermitian Hamiltonians that, for a specific range of system parameters, possess real eigenvalues. We show that in the models considered in the article, the steering generation process strongly depends on the coupling strengths and rates of the gains/losses in energy. Moreover, we find the values of parameters describing the system for which the steering appears