Studies On Optical Nonreciprocal Transmission And Quantum Fisher Information In Coupled Microcavities

Advanced techniques for quantum information processing like quantum coherent manipulation and quantum precision measurement are increasingly flourishing and will have a profound impact on the social and economic development.One of the key points is selecting a suitable physical system to explore various practical quantum information processing technologies convenient for manipulation and integration.Since the birth of quantum optics,cavity quantum electrodynamics(QED)systems have provided a good platform for studying interactions between quantized light fields and relevant materials,and recently become one of the most promising physical systems suitable for quantum information processing owing to significant progresses of manufacturing abilities and experimental techniques.Cavity QED systems can exhibit rich interactions,such as optomechanical interactions and dipole interactions by introducing various entities like mechanical oscillators and atoms/ions,and thereby is one hot topic of modern research.Hence,we carry out in this dissertation theoretical studies on quantum manipulations referring to nontrivial photon transmission and quantum metrology helping to improve measurement limits by considering a few typical cavity QED systems.To be more concrete,here we focus on nonreciprocal transmission of high isolation ratios based on nonlinear bistable transmission in two multi-mode optomechanical systems on one hand,while consider quantum Fisher information in an anisotropic Rabi model under the super-strong dipole-interaction mechanism on the other hand.First,we introduce the basic concepts and research background on cavity QED systems,optomechanical systems,optical bistable behaviors,optical non-reciprocity and quantum precision measurement in the dissertation.Next,we give the basic theories and mathematical knowledges on dynamic equations,steady-state solutions and stability judgment of optomechanical systems as well as classical and quantum Fisher information.Second,we study the nonreciprocal transport property of a four-mode optomechanical system in an asymmetric structure when a driving field is input to one side(either from the left or from the right).The system consists of three optical cavities coupled in series and a mechanical oscillator(the oscillator is in the first optical cavity),resulting in an asymmetric optomechanical nonlinearity.In the case of a strong input field,transmittivities in opposite directions exhibit staggered bistable behaviors when the impedance matching condition is broken.We find,in particular,that it is viable to realize a reversible higher isolation ratio in a wider ranges of input power or cavity detuning,by modulating relevant parameters such as optomechanical coupling strength,coupling strengths between optical modes,and mechanical oscillator frequency.This work can provide a flexible platform for realizing nonreciprocal transport even if two input fields come simultaneously from opposite sides,and may be extended to optical networks composed of more coupled cavities.Again,we extend the previous work by considering an alternative four-mode optomechanical system,symmetric in structure,to study the nonreciprocal transport when the driving field is input from one side(either from the left or from the right).The system consists of three optical cavities coupled in series and a mechanical oscillator inserted in the middle cavity,which can also result in an asymmetric optical-mechanical nonlinearity.We find once again that transmittivities in opposite directions could exhibit staggered bistable behaviors in the presence of a strong driving field,as a relatively simple impedance matching condition is broken.Compared with the previous work,this system allows to just suppress the bistable lower branch or just enhance its upper branch;control the transition of nonreciprocal transmission at equivalent positive and negative isolation ratios via parameters adjustment.Last,we study instead the quantum metrology in two-level systems interacting with single-mode bosons in the super-strong coupling region.Starting from an anisotropic Rabi model,we first derive the system ground state(not the vacuum state again)by considering the counter-rotating terms under a transformed rotating-wave approximation.We then calculate the corresponding quantum Fisher information(GFI)characterizing the upper limit of measurement precision.Our results show,in particular,a super-additivity of QFI,referring to the fact that the summation of QFIs for two subsystems is always larger than that of the global system.