the entanglement at zero-temperature is studied in a two-qubit xz spin-1/2 chain model in anexternal magnetic field which is applied in the z direction. we have obtained an analytical relation forthe effect of the external magnetic field on the concurrence. it is shown that the ground state of thesystem depends on the strength of exchange coupling. we have shown that the analytical relation oft...

We examine the behavior of the spectral function for the T μ μ operator in QCD in the two regimes where it is possible to make analytical progress; weak coupling, and close to a second order QCD phase transition. We determine the behavior of the bulk viscosity in each regime. We discuss the problem of analytic continuation of the (lattice) Euclidean correlation function to determine the spectra...

We discuss the holographic derivation of the magnetic susceptibility of the quark condensate. It is found that the susceptibility emerges upon the account of the ChernSimons term in the holographic action. We demonstrate that Vainshtein’s relation is not exact in the hard wall dual model but is fulfilled with high accuracy. Some comments concerning the spectral density of the Dirac operator are...

Randomly correlated ensembles of two quantum systems are investigated, including average entanglement entropies and probability distributions of Schmidt-decomposition coefficients. Maximal correlation is guaranteed in the limit as one system becomes infinite-dimensional. The reduced density operator distributions are compared with distributions induced via the Bures and Hilbert-Schmidt metrics....

In the realm of quantum theory a state of a physical system is most generally expressed by its density operator ˆ̺. Knowledge of this operator gives complete information of the quantum state. Schemes have been proposed in a number of fields in quantum physics to determine ˆ̺ from measurements either explicitely [1,2,3,4,5,6,7] or indirectly via quasiprobability distributions [8,9,10,11] for mixed...

The charge-current density and two-photon operators consistent with a single-particle semi-relativistic Hamiltonian are derived within a suitable functional derivative formalism which preserves gauge invariance. An application to electron scattering is presented and results are compared with a fully relativistic case and the non-relativistic cases corrected through fourth order in M−1.

The problem of expanding a density operator p in forms that simplify the evaluation of important classes of quantum-mechanical expectation values is studied. The weight function P(n) of the P representation, the Wigner distribution W(o), and the function (n ~ p ~o), where ~n) is a coherent state, are discussed from a unified point of view. Each of these quasiprobability distributions is examine...

Statistical mechanics relies on the complete though probabilistic description of a system in terms of all the microscopic variables. Its object is to derive therefrom static and dynamic properties involving some reduced set of variables. The elimination of the irrelevant variables is guided by the maximum entropy criterion, which produces the probability law carrying the least amount of informa...