Generation Of Entangled States In Circuit QED System

Quantum information science is an interdisciplinary of quantum mechanics and modern information,it has a wide range of applications in quantum computation and quantum communication.Quantum entanglement is a central part of quantum information,it provides important resources for the realization of quantum communication and quantum computation effectively.So far,scientists have been able to prepare and manipulate many quantum entanglement states in a variety of physical systems.The circuit quantum electrodynamics(QED)system,which is a macroscopic solid state quantum system,has great potential in the preparation and manipulation of quantum entangled states.Compared with the microscopic quantum systems(cavity QED system,ion trap system,etc.),circuit QED system has good scalability and operability.Thus,it is one of the most likely physical systems to realize quantum computer and quantum communication.Based on circuit QED,we put forward three schemes to prepare N-qubit W states in separated resonators by one step in this paper.The main contents are as follows:In the first chapter,we mainly introduce the relevant theories of quantum entanglement and circuit QED system.Firstly,we introduce the background knowledge of quantum entanglement,including the definition of quantum entanglement,the characteristics and properties of several kinds of entanglement and the related application of entanglement states in the quantum information.Then,we sketch the circuit QED system.And,we introduce the classifications and physical principles of superconducting(SC)qubits and circuit cavities.In the second chapter,we mainly study a scheme for the preparation of N-qubit W state via resonance interaction.In this scheme,we do not need to apply any classical driving pulses during the whole operation process.Because the interaction between the SC qubits and the resonators is resonant and the strong coupling between the SC qubits and the resonators can be readily achieved,the evolution time is very short.Besides,the evolution time does not increase along with the increase of the number of the SC qubits.The results of the numerical simulation show that:the dissipation caused by the resonators is quite small and we can obtain a high fidelity.In the third chapter,we mainly research a scheme for the preparation of N-qubit W state via non-resonant interaction.The scheme also do not need to apply any classical driving pulse.The results of the nunerical simulation indicate that:there exist a reasonable detuning range to generate the W state with high fidelity after considering all the decoherence factors;our scheme is suited to generate high fidelity W state of small number of SC qubits.In the fourth chapter,we mainly study a scheme for the preparation of N-qubit W state by adiabatic evolution.Based on the adiabatic passage,the scheme does not need to control the Rabi frequency of classical field and the interaction time precisely during the whole operation.Moreover,the dissipation from the resonators and the energy relaxation can be omitted approximately.Finally,we mak:e a summary about the whole study and put forward a prospect.