Resul Eryigit

Correlation and nonlocality measures as indicators of quantum phase transitions in several critical systems

Abstract We have investigated the quantum phase transitions in the ground states of several critical systems, including transverse field Ising and XY models as well as XY with multiple spin interactions, XXZ and the collective system Lipkin–Meshkov–Glick models, by using different quantumness measures, such as entanglement of formation, quantum discord, as well as its classical counterpart, measurement-induced disturbance and the Clauser–Horne–Shimony–Holt–Bell function. Measurement-induced disturbance is found to detect the first and second order phase transitions present in these critical systems, while, surprisingly, it is found to fail to signal the infinite-order phase transition present in the XXZ model. Remarkably, the Clauser–Horne–Shimony–Holt–Bell function is found to detect all the phase transitions, even when quantum and classical correlations are zero for the relevant ground state.

Factors affecting international tourism flows to Turkey: a gravity model approach.

A gravity-based modelling effort is undertaken to analyse the factors affecting the numbers of international tourists visiting Turkey from the top 11 originating countries for 1995–2005. It is found that an eight-factor model (GDP per capita, tourism climate index, population of the originating country, tourism price index, distance, earthquake, neighbouring country, September 11 terrorist attacks) can explain most of the data. The usual negative distance effect and the tourism climate index are found to be the most important indicators of the magnitude of tourism flows. An unexpected finding, however, is the relative insignificance of the Iraq War dummy.

Quantum Correlations in non-Markovian Environments

We have studied the analytical Markovian and non-Markovian dynamics of quantum correlations, such as entanglement, quantum discord and Bell nonlocalities for three noisy qubits. Quantum correlation as measured by quantum discord is found to be immune to death contrary to entanglement and Bell nonlocality for initial GHZ- or W-type mixed states.

Quantum correlations between identical and unidentical atoms in a dissipative environment

We have studied the dynamics of quantum correlations such as entanglement, Bell nonlocality and quantum discord between identical and unidentical atoms interacting with a single-mode cavity field and subject to cavity decay. The effect of single-atom detuning, cavity decay rate and initial preparation of the atoms on the corresponding correlation measures have been investigated. It is found that even under strong dissipation, time evolution can create high quantum discord while entanglement and Bell nonlocality stay zero for an initially separable state. Quantum discord increases while entanglement decreases in a certain time period under dissipation for the initial state that both atoms are in the excited state if the qubits are identical. For some types of initial states, cavity decay is shown to drive the system to a stationary state with high entanglement and quantum discord.

Ab initio volume-dependent elastic and lattice dynamical properties of chalcopyrite CuAlSe2

We have performed an ab initio study of the volume dependence of elastic and lattice dynamical properties of chalcopyrite semiconductor CuAlSe2. The calculations have been carried out within the local density functional approximation using norm-conserving pseudopotentials and a plane-wave basis. Born effective charge tensors, dielectric permittivity tensors, the phonon frequencies at the Brillouin zone centre and their Gruneisen parameters are calculated using density functional perturbation theory. We compare the Gruneisen parameters of the calculated quantities with those of zinc-blende type materials and find similar trends. Calculated elastic stiffness constants show pseudocubic behaviour.

Dynamics of entanglement and Bell non-locality for two stochastic qubits with dipole?dipole interaction

We have studied the analytical dynamics of Bell non-locality as measured by the CHSH inequality and entanglement as measured by concurrence for two noisy qubits that have the dipole–dipole interaction. The non-local entanglement created by the dipole–dipole interaction is found to be protected from sudden death for certain initial states.

Dissipative dynamics of quantum correlations in the strong-coupling regime

The dynamics of entanglement and quantum discord between two identical qubits strongly interacting with a common single mode leaky cavity field have been investigated beyond the rotating wave approximation (RWA) by using recently derived Lindblad type quantum optical master equation [F. Beaudoin, J.M. Gambetta, A. Blais, Phys. Rev. A {\bf 84}, 043832 (2011)] that can describe the losses of the cavity field in a strong atom-field coupling regime. Contrary to previous investigations of the same model in the dissipative regime by using the standard Lindblad quantum optical master equation in a strong-coupling regime, the atom-field steady states are found to be cavity decay rate independent and have a very simple structure determined solely by the overlap of initial atomic state with the subradiant state which is valid for all coupling regimes. Non-RWA dynamics are found to have remarkable effects on the steady state quantum discord and entanglement that cannot be achieved under RWA conditions, for instance, they can induce steady state entanglement even for the initial states that have no overlap with the subradiant state. Moreover, the non-RWA dynamics are found to reverse the initial state dependence of steady state entanglement and quantum discord contrary to the RWA case.

First-principles calculations on vibrational and dielectric properties of chalcopyrite CuGaS2

We have performed a first-principles study of structural, dynamical and dielectric properties of chalcopyrite semiconductor CuGaS2. The calculations have been carried out within the local density functional approximation using norm-conserving pseudopotentials and a plane-wave basis. Born effective charge tensors, dielectric permittivity tensors, the phonon frequencies at the Brillouin zone centre and mode oscillator strengths are calculated using density functional perturbation theory. The calculated properties help resolve the source of some of the discrepancies in the experimental literature.

Creation of quantum correlations between two atoms in a dissipative environment from an initial vacuum state

Abstract We have investigated the effect of counter-rotating terms on the dynamics of entanglement and quantum discord between two identical atoms interacting with a lossy single mode cavity field for a system initially in a vacuum state. The counter-rotating terms are found to lead to steady states in the long-time limit which can have high quantum discord, but have no entanglement. The effect of cavity decay rate on this steady-state quantum discord has been also investigated, surprisingly, the increase in cavity decay rate is found to enhance the steady-state quantum discord.

Classical memoryless noise-induced maximally discordant mixed separable steady states

Abstract We have investigated the dynamics of quantum discord and entanglement for two qubits subject to independent global transverse and/or longitudinal memoryless noisy classical fields. Global transverse and/or longitudinal random fields are found to drive the system to maximally discordant mixed separable steady states for suitable initial conditions. Moreover, two independent noises in the system are found to enhance both the steady state randomness and quantum discord in the absence of entanglement for some initial states.