A.-B.A. Mohamed

Pairwise quantum correlations of a three-qubit XY chain with phase decoherence

Quantum correlations, including entanglement and discord with its geometric measure in a three-qubit Heisenberg XY chain, with phase decoherence, are investigated when a nonuniform magnetic field is applied. When the qubits are initially in an unentangled state, the nearest neighbor pairwise correlations are destroyed by phase decoherence, but stationary correlations appear for next-to-neighbor qubits. With an inhomogeneous magnetic field, the stationary correlations appear for nearest neighbor qubits and they disappear for next-to-nearest neighbor qubits. But when the qubits are initially in an entangled state, an inhomogeneous magnetic field can enhance the stationary correlations of next-to-neighbor qubits, but it cannot do so for nearest neighbor qubits. The decoherence effect on stationary correlations is much stronger for next-to-nearest neighbor qubits than it is for nearest neighbor qubits. Finally, a uniform magnetic field can affect the correlations when the qubits are initially in an entangled state, but it cannot affect them when the qubits are initially in an unentangled state.

Entropies and entanglement for decoherence without energy relaxation in a two-level atom

In this paper, we investigate the temporal evolution of various measures of degree of entanglement and total correlation of a single-mode light field interacting with a two-level atom. The phase-damped cavity is taken into account. The effects of phase damping on a temporal of partial entropies for the atom and the field, total entropy, the entropy difference and the sum of negative eigenvalues of the partially transposed density matrix as a quantitative entanglement measure for the master equation in the dressed-state approximation are taken into account.

Entropy and entanglement in the Jaynes–Cummings model with effects of cavity damping

The temporal evolution of entanglement for a single-mode field interacting with a two-level atom via intensity-dependent coupling in the off-resonant case has been studied, where the leakage of photon through the cavity is taken into account. The effects of cavity damping on the coherence properties of the atom and the field are studied. The amount of entanglement is compared with the total correlations. It is found that the atom–field system is inhibited from going into a pure state in the off-resonant case.

Quasi-Probability Distribution Functions for a Single Trapped Ion Interacting with a Mixed Laser Field

We give a fully analytical description of the dynamics of the quasi-probability distribution (Q-PD) functions for any model describing a single two-level qubit interacting with a field. The Wigner function at time (t = 0) and Q function for a pure state as an initial field state are studied. But, in this paper, the temporal behavior of the Q-PD functions for a coherent superposition state (SS) and a statistical mixture of coherent states (SM) for the interaction between a single ion and laser field are investigated. It is found that, the temporal behavior of the Q-PD functions is in very good agreement with its counterpart for the entanglement. If the curve of the entanglement between the trapped ion (specially for the second red sideband) and laser field are known, we can expect the shape of the Q-PD functions.

Stationary discord and non-local correlations via qubit damping

By using quantum discord (QD), measurement induced non-locality (MIN) and negativity (QE), quantum correlation and entanglement are investigated for two qubits in two different cases for the initial two qubit Werner states, taking into account the influence of qubit damping. It is shown that there is no asymptotic decay for MIN while asymptotic decay exists for QD and QE. Quantum correlations cannot be strengthened by introducing the damping. The appearance time of stationary correlations gets shorter with the increase in the damping parameter. Finally, a uniform damping qubit can affect the stationary correlations when the qubits are initially in an entangled state.

Effects of cavity damping on the entanglement for a three-level atomic system

Based on the master equation for the density matrix, the dynamics of the entanglement of the three-level atom interacting with single-mode field in a finite-Q cavity are studied. It was found that the cavity damping leads to growing entropy and a strong degradation of the entanglement, therefore the coherence loss and entanglement is very sensitive to any change in the cavity damping parameter.

Influence of phase damping on the entanglement for the damped JC model in the pure and mixed states

In this article, we investigate the effects of phase damping on the temporal evolution of different entanglement measurements and the amount of entanglement for the damped Jaynes-Cummings model. The master equation is solved for any initial state in the two-level atom. Superpositions of two coherent states (π/2 or π out of phase) and their statistical mixture state are taken as initial states when a phase-damped cavity is taken into account.

Geometric phase in cavity QED containing a nonlinear optical medium and a quantum well

The geometric phase (GP) in cavity QED filled with a nonlinear medium and containing a quantum well is analyzed. We observe collapses and revivals. The optical nonlinearity leads to high frequency oscillations of the GP. The GP is very sensitive not only to the dissipation rates but also to the amplitude of the laser pump.

Geometric Measure of Nonlocality and Quantum Discord of Two Charge Qubits with Phase Decoherence and Dipole-Dipole Interaction

The effects of both phase decoherence and dipole-dipole interaction on quantum correlations of superconducting (SC) charge qubits, placed in a single-mode SC-cavity, are investigated. When the initial qubit-states are unentangled, measurement-induced nonlocality (MIN), geometric quantum discord (GQD) and quantum entanglement (QE) have different evolutions. They remain at stationary nonzero values with phase decoherence. These stationary correlations clearly appear with the photon number of Fock state. The quantum correlations can be enhanced by dipole-dipole interaction that can weaken the phase decoherence effect. When the initial states of charge qubits are entangled, the appearance of the stationary correlations can be accelerated by the photon number. The correlations can be also increased by the dipole-dipole interaction. These increases can be weaken by the photon number. The photon number also leads to sudden death and sudden birth for QE while MIN periodically reaches its maximum values, but GQD decays continuously with respect to time until it tends to be zero. When the states of the qubits have no entanglement nor entanglement sudden death, MIN and GQD keep nonzero values. The steady-state of correlations is calculated. It is found that these correlations depend on the initial states, the photon number and the dipole-dipole interaction.

Influence of the phase damping for two-qubits system in the dispersive reservoir

An analytical solution of the master equation for two qubits-field system in the dispersive reservoir are investigated, the qubits are initially in werner states. Under the influence of the damping we investigate the quantum correlation in a two-qubit based on measurement-induced disturbance (MID). We compare MID and entanglement measured by negativity and illustrate their different characteristics. We find the effect of damping on MID is weaker than negativity. Negativity will experience a sudden transition but this will not happen for MID.