Chin Hee Pah

Exact solution of an Ising model with competing interactions on a Cayley tree

The exact solution of an Ising model with competing restricted interactions on the Cayley tree, and in the absence of an external field is presented. A critical curve is defined where it is possible to get phase transitions above it, and a single Gibbs state is obtained elsewhere.

Phase diagram of the three states Potts model with next nearest neighbour interactions on the Bethe lattice

Abstract We have found an exact phase diagram of the Potts model with competing nearest neighbor and next nearest neighbor interactions on the Bethe lattice of order two. The diagram consists of five phases: ferromagnetic, paramagnetic, modulated, antiphase and paramodulated, all meeting at the multicritical point ( T = 0 , p = 1 / 3 ) . We report on a new phase which we denote as paramodulated, found at low temperatures and characterized by zero average magnetization lying inside the modulated phase. Such a phase, inherent in the Potts model has no analogues in the Ising setting.

An ising model with three competing interactions on a Cayley tree

In this paper we consider an Ising model with three competing restricted interactions on the Cayley tree J2(J3). The translation invariant and periodic Gibbs measures for these models are investigated and the problem of the phase transition in these classes is solved.

Ising Model with Competing Interactions on Cayley Tree of Order 4: An Analytic Solution

We investigate an Ising model with two restricted competing interactions (nearest neighbors, and one-level neighbors) on the Cayley tree of order four. We derive a recurrent equation for the Cayley tree of order k. We found an analytic solution for the given interactions in the case of order 4. Our result of the critical curve shows the existence of the phase transition occurs in this model. We also give the calculation of the free energy from the description of Gibbs measure of the given Hamiltonian on Cayley tree of order four.

Periodic and Weakly Periodic Ground States for the λ-Model on Cayley Tree

In this paper we consider the λ-model on the Cayley tree of order two. We describe the periodic and weakly periodic ground states for the considered model.

Orthogonal preserving quadratic stochastic operators: Infinite dimensional case

In the present paper, we consider orthogonal preserving quadratic stochastic operators defined on infinite dimensional simplex. We provide a full descriptions of such kind of operators. Moreover, certain examples are given.

On Ground States of λ-Model on the Cayley Tree of order two

In the paper, we consider the λ-model with spin values {1, 2, 3} on the Cayley tree of order two. We describe ground states of the model.

Exact solution for an Ising model on the Cayley tree of order 5

We investigate an Ising model with two restricted competing interactions (nearest neighbors, and one-level neighbors) on the Cayley tree of order 5. The translation Gibbs measures is considered for this model. Our result of the critical curve shows that the phase transition occurs in this model, further it confirms a particular case of a conjecture.

On connected sub-tree of Cayley tree of order 2 with fixed nodes

We found an exact formulation for a finite sub-tree counting problem. Solution to two extremal cases are Catalan Triangle introduced by Shapiro and ballot Catalan triangles. The general solution could be expressed as linear combination of these Catalan triangles.

The effect of finite bandwidth squeezed light on entanglement creation in the Dicke model

We analyse the relation between local two-atom and total multi-atom entanglements in the Dicke system composed of a large number of atoms. We use concurrence as a measure of entanglement between two atoms in the multi-atom system, and the spin squeezing parameter as a measure of entanglement in the whole n-atom system. In addition, the influence of the squeezing phase and bandwidth on entanglement in the steady-state Dicke system is discussed. It is shown that the introduction of a squeezed field leads to a significant enhancement of entanglement between two atoms, and the entanglement increases with increasing degree of squeezing and bandwidth of the incident squeezed field. In the presence of a coherent field the entanglement exhibits a strong dependence on the relative phase between the squeezed and coherent fields, that can jump quite rapidly from unentangled to strongly entangled values when the phase changes from zero to π. We find that the jump of the degree of entanglement is due to a flip of the spin squeezing from one quadrature component of the atomic spin to the other component when the phase changes from zero to π. We also analyse the dependence of the entanglement on the number of atoms and find that, despite the reduction in the degree of entanglement between two atoms, a large entanglement is present in the whole n-atom system and the degree of entanglement increases as the number of atoms increases.