The Study On The Entanglement Degree In Two-qubit Quantum Heisenberg Models

Quantum entanglement is one of the most basic characteristics of quantum mechanics. In 1935, Einstein noticed the intriguing characteristic , when he proposed EPR. At the sametime, Schrodinger singled out "quantum entanglement ". Quantum entanglement showsthe quantum characteristic that local realism cannot explain. Experiments have tested that entanglement violates the Bell inequalities, which firms people s confidence to the basic theory of quantum mechanics. On the other hand , quantum entanglement has begun to be viewed as a potentially useful resource , and be used in quantum communication and information processing . Quantum teleportation , quantum cryptographic and quantum computation make use of quantum entanglement. It plays a vital role in quantum mechanics and quantum information , so quantification of entanglement is very important.In this paper, firstly we get entanglement degree and critical temperature T_c (whenentanglement degree is zero) in two-qubit quantum Heisenberg models H_XX,H_XXX ,H_XXZ and H_XYZ .Then we get entanglement degree and critical temperature T_c of these modelswhen their Hamiltonians are added BS₁^z , BS₂^z and BS^z separately. We discuss theinfluence of B on entanglement degree and critical temperature . We find that the uniform magnetic field B can induce entanglement in some models that exit no entanglement before, and can reduce or extend the range of entanglement degree of some models. So we can offer the proof of obtaining any entanglement degree and convenient outside controlling conditions. This is just the meaning of the paper.