Coherent State Control of Non-Interacting Quantum Entanglement

We exploit a novel approximation scheme to obtain a new and compact formula for the parameters underlying coherent-state control of the evolution of a pair of entangled two-level systems. It is appropriate for long times and for relatively strong external quantum control via coherent state irradiation. We take account of both discrete-state and continuous-variable degrees of freedom. The formula predicts the relative heights of entanglement revivals and their timing and duration.Comment: Published in PRA, 10 pages, 7 figure

Sudden Death of Entanglement of Two Jaynes-Cummings Atoms

We investigate entanglement dynamics of two isolated atoms, each in its own Jaynes-Cummings cavity. We show analytically that initial entanglement has an interesting subsequent time evolution, including the so-called sudden death effect.Comment: 3 pages, 3 figure

Hubbard model In Square Lattices: A Mean-field Hartree-fock Approach

Cataloged from PDF version of article.This thesis is mainly an effort to reproduce the well-known results that HartreeFock approximation gives for the Hubbard Model in two dimensions. As the area of application magnetic phases in the finite-size square lattices was chosen. The reason of choosing this particular area is that in the sources we went through mean-field theory was used only for examining the magnetic phases for rectangular density of state not for the actual density of states of a square lattice. We used the mean-field Hartree-Fock approximation and obtained the phase diagrams for the paramagnetic, ferromagnetic, charge density wave (CDW) and spin density wave (SDW) phases. The antiferromagnetic phase was found to be a special kind of the SDW phase. The hamiltonians used for the ferromagnetic and paramagnetic cases were identical. However because of the non-diagonal correlations present in the system the CDW and SDW hamiltonian was different.Yönaç, MuhammedM.S

Sudden death of entanglement of two jaynes–cummings atoms

We investigate entanglement dynamics of two isolated atoms, each in its own Jaynes-Cummings cavity. We show analytically that initial entanglement has an interesting subsequent time evolution, including the so-called sudden death effect. PACS numbers: 03.65. Yz, 03.65.Ud Entanglement is a defining feature of quantum mechanics that makes fundamental distinctions between quantum and classical physics. As an unambiguous and quantifiable property of sufficiently simple multi-party quantum systems, entanglement has a definite time evolution that has recently begun to be studied in several contexts Entanglement in a quantum system may deteriorate due to interaction with background noise or with other systems usually called environments. Interest was originally concerned with the consequences for quantum measurement and the quantum-classical transition The purpose of this paper is to examine two interesting time-evolving quantum systems that have no route for mutual iteraction, but whose mutual entanglement nevertheless evolves in an unusual way. We have chosen the "double Jaynes-Cummings" model consisting of two two-level atoms. Each one is in a perfect one-mode nearresonant cavity and interacts with its initially unexcited cavity mode, but each is completely isolated from the other atom and cavity. By tracing over the cavity modes at time t we are left with a mixed state of atoms A and B similar to that treated previously by us The double Jaynes-Cummings Hamiltonian for our system may be written as, Clearly there will be no interaction between atom A and atom B or between cavity a and cavity b. The eigenstates of this Hamiltonian are products of the dressed states of the separate JC systems, which are well known In that connection we note that there are, in principle, six different concurrences that provide information about the overall entanglements that may arise. With an obvious notation we can denote these as Ba . Symmetry considerations can provide natural relations among these, which we will report elsewhere with the first index denoting the state of atom A and the second denoting the state of atom B (↑= excited state ↓=ground state), the initial state for the total system (1