Quantum Information Processing And Its Application

Quantum information processing employs quantum mechanics to express and manipulate information, and it appeals much more powerful than the classic information processing. Recently, this field has drawn increasing attention. In this thesis, we mainly investigate two quantum information processing schemes: free evolution model and the one-way quantum computer, both of which do not involve quantum logic network.In the free evolution model, the time dependent external control (except for single qubit measurements) is not needed, which ensures the whole computation process can be implemented while isolated from environment. Moreover, for those systems where the interaction between qubits is difficult to modulate, this scheme provides a relative easier alternative. Meanwhile, this scheme is less flexible than the traditional approach with quantum gates. One needs to design a different system including the structure of the system, the Hamiltonian and the initial state for each different computation task.The one-way quantum computer, in the other hand, is universal. When the initial state, a two dimensional cluster state, has been prepared, all left work is to perform a series of single qubit measurements upon chosen qubits. This scheme consists no quantum input, output and quantum register, even unitary gates from some universal sets are not necessary. However, by utilizing quantum entangled states as its kernel physical resource, it does realize all required functions of the genuine quantum computer.In Chapter 2 we show how to implement several important quantum informationprocessing tasks--quantum state transfer, quantum state cloning and the generationof quantum entangled states, within the free evolution model. We describe that perfect state transfer can be carried out in spin networks which has the mirror inversion symmetry. Later, we demonstrate that star like spin network is capable of implementing optimal 1 → M Phase Covariant Cloning (PCC), also it can also be used to generate arbitrary W states. Further, we proposed a "repeat-until-success" scheme which provides a persistent approach to arbitrary symmetric states without any modulated control.Since the Graph state plays an crucial role in one-way quantum computer, we in-...