Dynamic Sensitivity Of Quantum Rabi Model With Quantum Criticality

Quantum phase transition is a physical phenomenon that occurs in quantum systems.Different from temperature-driven thermal phase transitions,the main physical reason for the quantum phase transition is the change of system parameters and quantum fluctuation.Normally,a system undergoing a quantum phase transition needs to satisfy the thermodynamic limit,i.e.,the components of the system need to converge to infinity.However,recent research has revealed that quantum phase transitions also exist in some finite component systems,including the quantum Rabi model.The quantum Rabi model is one of the simplest and most important models for describing the interaction between light and matter,and it consists of a single qubit(two-level atom)interacting with a single-mode bosonic field.In the infinite-frequency limit,where the frequency of the atom is much larger than the frequency of the bosonic field,the ground state of the quantum Rabi model experiences a quantum phase transition from the normal phase to the superradiance phase,and the critical position is determined by the frequencies of the cavity field and the atom in the system.Based on the fact that the quantum phase transition occurring in the ground state of the quantum Rabi model depends on the cavity frequency,in this thesis,we introduce an auxiliary atom coupled to the cavity field in the quantum Rabi model and modulate the frequency of the cavity field to change the critical position such that it can trigger the quantum critical state of the system.We find that the quantum decoherence of the auxiliary atoms exhibits hypersensitivity around the critical position,and hence it can characterize the dynamic sensitivity of quantum criticality in the quantum Rabi model.This thesis consists of four chapters.In the first chapter,we introduce the background,motivation and conclusions of the research for this thesis.In the second chapter,we outline some of the theoretical foundations required in this thesis.In the third chapter,we present our main research work which focus on the dynamic sensitivity of the quantum criticality in the quantum Rabi model.In the fourth chapter,we summarise the research in this thesis and clarify the application potential of our work,as well as the difficulties and challenges in its experimental realization.We also present some perspects on the furture development of this field.