Preparation Of Entangled State Based On Faraday Rotation Mechanism And Characteristics Of Superconducting Artificial Atoms

Quantum entanglement is a very attractive feature of quantum mechanics. It plays a very important role in the measurement of quantum nonlocality and process-ing tasks in quantum information. Therefore, the preparation of different quantum entanglement in the quantum information has become an important topic. At the same time, the systems for preparing entangled states also have attracted much attention. The cavity quantum electrodynamics system is one of the important de-vice for the preparation of entangled state. The successful combination of Faraday rotation mechanism and the cavity quantum electrodynamics reduces the require-ment of cavity quality and the difficulty of experiment. In addition, there are many quantum information carriers, among which superconducting artificial atom has at-tracted a lot of attention, because of its good scalability. In recent years, the circuit quantum electrodynamics system has been put forward, in which, superconducting artificial atoms are installed in the transmission line resonator. Circuit quantum electrodynamics system is similar to cavity quantum electrodynamics system, due to superconducting artificial atoms in circuit quantum electrodynamics system play the same role as atoms in cavity quantum electrodynamics system. This structure is thought to be a kind of promising candidates to realize the quantum information processing.In this dissertation, we first introduce the basic knowledge related to quantum entanglement. Then we make a simply introduce about the cavity quantum elec-trodynamics system. And we use the Faraday rotation occurred in the photons’ process of input and output in the low quality cavity to realize the preparation of the atomic GHZ state. Then we make a simple introduction about the circuit quan-tum electrodynamics system which composed of superconducting artificial atoms and transmission line resonator. And by using the characteristics of superconduct-ing artificial atoms we can realize the preparation of the X-type entangled state. The main research content is as follows:(1) Based on Faraday rotation mechanism, we put forward a scheme to prepare GHZ state by using Faraday rotation which occurred in the process of photons input and output in low quality cavity. The cavity used in this scheme is low quality cavity, and the coupling between atoms and cavity is not strong, meanwhile, the quantum information is encoded in the low atomic energy level, so the scheme is insensitive to the cavity decay and the atomic spontaneous emission. In addition, our scheme doesn’t have to impose classical field on cavity and also needs not choose interaction time. This greatly reduces the experimental difficulty. Therefore, our scheme is simple and feasible under the current technology condition.(2) Based on superconducting artificial atomic properties, we put forward a scheme to prepare X-type four qubit entangled state by using the broken symme-tries of superconducting artificial atoms in the one dimensional transmission line resonator. In the scheme, △-type three-level artificial atoms are different from nat-ural atoms, because it can produce circulatory transition. Through choosing the appropriate interaction time and implementing simple operations, we can finish the preparation of entangled state. Because of the excited states of artificial atoms and the states of photons are adiabatically eliminated, this scheme is robust to artificial atomic spontaneous emission and attenuation of transmission resonator.These schemes can be implemented under existing experimental conditions, so they have important reference value for quantum information processing which based on Faraday rotation mechanism or the characteristics of the superconducting artificial atoms. And they can provide reliable theoretical basis for the implemen-tation of quantum communication and quantum computing.