Study On The Quantum Communication Via A Two-qubit Heisenberg Spin Model

Quantum information science is a new subject,which is the combination of quantum mechanics and classical information theory.Based on the fundamental principles of quantum mechanics and the properties of quantum coherence,quantum information focuses on various quantum actions such as quantum information storage, quantum coding,quantum computation and quantum communication.By means of the quantum characteristics of microcosmic particles,quantum information can exhibit some distinct advantages in contrast to its classical counterpart.As we know, Heisenberg spin chain is one of the simplest spin chains in the condensed matter physics and it has good entanglement property,observability and maneuverability,so it is natural possible candidate as the carrier of qubit.In this thesis,we investigate theoretically the process of quantum teleportation(QT) and quantum dense coding (QDC)via a two-qubit Heisenberg spin model in detail.First of all,we investigate the influence of the Dzyaloshinski-Moriya(DM) interaction on the entanglement of the two-qubit Heisenberg XYZ spin model in the presence of the intrinsic decoherence.Then,the process of QT using the Heisenberg model as quantum channel is studied and the influence of the DM interaction on the average teleportation fidelity is analyzed.We find that when the channel is initially in the entangled state |ψ₂(0)〉=c|01〉+d|10〉,the average fidelity is always larger than 2/3.Moreover,under a certain condition,the average fidelity can be enhanced by adjusting the DM interaction,and the intrinsic decoherence leads to a suppression of the fluctuation of the average fidelity.Finally,by utilizing the two-qubit Heisenberg model as entanglement resource,we study the QDC process and discuss various factors affecting the optimal coding capacity.It is shown that the optimal coding capacity is always larger than one,implying that such QDC is superior to any classical communication.Futhermore,when the initial state of the system is |ψ₁(0)〉=2^1/2/2(|00〉+|11〉),the optimal coding capacity is equal to 2 no matter what the other parameters of the system are.