The Transfer Of Arbitrary Two Qubit Pure State In The Spin Chains

In the nineteen sixties, Feynman had proposed the idea of quantum computer. However, until the past twenty years, the superiority of quantum information and communication is well known and many researchers throw themselves to the field. When the papers concerning this field are emerging, quantum information becomes one of the most active subjects. The biggest difference of quantum and classical communication is that quantum medium can make communication progress absolutely safe that classical method cannot possess. It is because classical communication can be easily wiretapped, so classical information must be encoded. Even so, it also has the risk of crack. However, quantum communication can transfer information safely on the basis of entanglement property that only quantum system possesses. Once the progress is wiretapped, it is easy to be realized and the information will be transferred again to make sure the communication safe. Photons are usually the medium for quantum communication. Now quantum communication has great development and can be achieved hundred kilometers away. It is believed that it will not take a long time to make it into reality. Compared with classical computation, the greatest superiority of quantum computation is parallelism. It is determined by the nature of quantum mechanics. Quantum algorithm can solve some problems that the classical computer is powerless.In quantum computation, the short communication is significantly important. Spin chain channel proposed by S. Bose became the focal point. It has several advantages. First of all, spin chain channel can avoid information conversion between the solid system of quantum computer and the medium, which photon cannot possess. Secondly, it is not necessary to manipulate the intermediate qubits of spin chain, so it is easy to operate. This paper studies the transfer of arbitrary two qubit pure state in the spin chain channels and analyzes the relevant influences from the spin environment, asynchronous measurements and imperfect initialization. Since it is not satisfactory by directly extending Bose's transfer scheme, we suggest to apply an improved scheme by using two pairs of inhomogenous spin chain and auxiliary one which form dual-rail channel. The results show that the improved scheme can achieve perfect transfer and greater success probability in a longer distance. Moreover, the dual-rail spin chains channel is immune to the influence of spin environment. We also find that success probability is not seriously affected by asynchronous measurements, as long as the difference of measurement time on two auxiliary spin chains is small enough. The general expression of success probability is given in the influence of imperfect initialization in the improved dual-rail channel when transfer is perfect.There are four chapters in this thesis. In chapter 1, we systematically introduce some quantum algorithm and the model of quantum computation. In chapter 2, the transfer of quantum state is briefly introduces. In chapter 3, we introduce some protocols in spin chain channel. In chapter 4, we make a summary on the transfer of arbitrary two qubit pure state. The conclusions and prospects are given in chapter 5.