Controllable Dynamics And Quantum Phase Transition In The Extended Cavity QED System

The theory of light-matter interaction and its application have always been the frontier researches of physics,materials,information and other disciplines.Therein-to,cavity quantum electrodynamics(cavity QED)studies the theory of the interaction between the qubits(atoms,molecules,artificial atoms,etc.)and the quantized elec-tromagnetic field in an optical cavity(or microwave cavity).In recent years,with the development of micro-nano technology,the cavity QED system can enter the strong coupling(atomic-field coupling rate is greater than the rate of decay of system),and even ultrastrong coupling(atomic-field coupling rate is close to the eigenfrequency of system)regimes.Thus many novel physical phenomena emerge in these regimes,such as vacuum Rabi splitting,coherent occupation conversion,quantum entangle-ment in the strong coupling regimes,and quantum phase transition(QPT),ground state degeneracy,quantum vacuum radiation in the ultrastrong coupling regimes and so on.Based on the above effects,the study of cavity QED not only has important research significance for the development of quantum mechanics,the understanding of basic physics problems,and the exploration of novel quantum multi-body effects,but can also promotes the development of new technologies such as the coheren-t manipulation of photon and atomic,quantum simulation,and quantum precision measurement.Although the investigation of cavity QED has become an important research topic in quantum physics and information science,there are still many problems to be solved,such as the realization of controllable dynamics in the ultrastrong coupling regime and the debate of ground-state superradiant QPT in the cavity QED system,etc..In view of the above problems,during my PhD study,we propose how to realize controllable dynamics and QPT in the extended cavity QED system by combining the anharmonicity of qubit and the optomechanical coupling.The main contents are as follows:1.By studying the influence of the weak anharmonicity of qubit on the dy-namics of cavity QED system,we propose a theoretical method for implementing the controllable dynamics in ultrastrong coupling regime.The results show that,in the extended cavity QED system considering the weak anharmonicity of qubit,the switchable dynamical evolution can be realized in the ultrastrong coupling regime,by changing the exchange symmetry of system's eigenstate with a short pulse.This pro-vides theoretical guidance for quantum information processing(e.g.,ultrafast quan-tum gate operation)in the ultrastrong coupling regime.2.We investigate the influence of the weak anharmonicity of qubits on the Superfluid-Mott-insulator phase transition in a coupled cavity QED system,and shows the ground-state phase diagrams under the mean-field approximation.The results show that the weak anharmonicity of qubits can enormously affect the distri-bution of Mott-insulator phase,and the single excitation Mott lobe disappears when the anharmonicity becomes zero.This can be used to guide the implementations of quantum simulations using the superconducting circuits.3.We introduce the optomechanical coupling into the cavity QED systems described by the Dicke and Rabi models,and study the superradiant QPT and phonon statistical characteristics in the extended systems.We find that the superradiant QPT and phonon blockade triggered by a single-photon can be realized in these systems.Moreover,this superradiant QPT will not be limited by the A~2term of normal cavity QED systems,which breaks through the limitations of no-go theorem in the traditional theory of superradiant QPT.This work inspires the development of single-photon detection and single-photon quantum devices.