The Interaction Between Light And Atom Inside A Micro-cavity

The interaction between light and atom is an important issue in quantum optics and atomic physics.Since several kinds of nonclassical light field were experimentally generated,much interest has been induced about the interaction between atoms and nonclassical states.The interaction between atom and squeezed light,which has been investigated extensively and especially is very important in quantum entanglement generation and quantum information processing,has been more attractive.To investigate the interaction between atom and nonclassical field,on the one hand,we want to explore the new features of the atom locating in a nonclassical environment,which is quite different from the interaction with the coherent light in some aspects,and this is also important to understand the fundamentals of the atom-field interaction.On the other hand,most generated nonclassical light are very weak,so their interaction with single atom can bring us a clear physical picture.Investigating atom-photon interaction at the single-atom and single-photon level is playing an important role in quantum entanglement,quantum decoherence,generation of single-photon resource and quantum information processing.One more motivation is probably more convincing:several groups in the world, including our group,has already realized the single atom manipulation,and our institute,state key laboratory of quantum optics and quantum optics devices,has strong experimental background of the generation, measurement and application of various nonclassical fields,therefore the theoretical works in this thesis are fundamentally based on the experiments or closely related to the experiments.Cavity Quantum Electrodynamics(Cavity QED) is the best way to demonstrate the interaction between atom and light field.As a special system that can experimentally observe the quantum behavior of single particle,Cavity QED is not only an important tool to explore the nonclassical properties in the quantum physical world,such as the Schr(o|¨)dinger cat state,quantum measurement,etc.,but also can play an important role in quantum computation,quantum state preparation and quantum communication.Yet,the effective control of single or few atoms is a precondition of realizing the above-mentioned process.With the development of the technologies,cold atoms with ultra-low temperature and single atom manipulation with micro-optical dipole trap have already been realized.From 1990s to the beginning of 21 century,the combination of high quality micro-cavity and atom cooling and trapping technology eventually provided a good experimental test of the Jaynes-Cummings model in the strong interaction regime at the single atom and single photon level.Our experimental group has already established a high quality micro-cavity system and a double Magnetic Optical Trap(double MOT) system for Cavity QED experiment,we have realized optical dipole trap of atoms and long-time control of single atom.We also have a group involving the generation of nonclassical light.We have obtained the sub-Poissonian light field near atomic line,and are trying to generate the squeezed vacuum state and the EPR state at exact transitions of Cs atom.All these experiments constitute the basis of investigating the interaction of single atom and field, especially nonclassical field,in the micro-cavity.It should be pointed out that,through the study of the interaction between the atom and the nonclassical field,we want to explore the new quantum phenomenon in this process and to understand more fundamentals.Meanwhile by using the real experimental parameters,we also want to predict or explain some experimental results.Basically,we started from the Hamiltonian of the atom-field interacting system(generally,the reservoir is considered),using the usual method of quantum optics(such as the Schr(o|¨)dinger Equation,Master Equation, Fokker-Planck Equation and Langevin Equation) and the initial condition, to discuss the system either by some theoretical deducing pocess or numerical simulations(Mathematica,Matlab and qotoolbox,etc.),and we obtained some significative results.The main works accomplished in this thesis are the following:1.We discussed the optimized parameter of optical dipole trap,such as the wavelength,the power and the waist of the trapping light for obtaining optical dipole traps with 1mK in depth,based on the existing experimental conditions.2.We proposed a scheme of generating bi-dimentional optical lattices formed by sub-half-wavelength traps by using several sets of laser evanescent standing waves propagating at the surface of a dielectric prism.The characteristics of the optical traps including their depths and the sizes are analyzed.It is shown that the micro-optical lattice with sub-half-wavelength size can be achieved by the interference of the selected evanescent waves.With a few Watts of the trapping laser beams in power,an optical lattice with a potential depth around 1 mK can be achieved.This provides a possible way of controlling single atom in a sub-micron range.3.Using the dressed atom theory about strong atom-field coupling,one can explain some experimental results well.Further considering the multilevels of the atom Cs,we obtained the magic wavelength of its D₂ line by calculating the influence of trapping light on the atomic fine-structure.This work provides a reliable method for analyzing the complicated energy level of the atom in the real experiments.4.We investigated the interaction of atoms and light field(including classical and nonclassical field) and the evolution of the properties of atom and field,including the inversion,decay,absorption and fluorescence spectrum of the atom,and the fluctuations and photon statistics of the light field.We focused on the entanglement and nonclassicality evolution of an atom in a squeezed vacuum—a typical nonclassical field,and compared it with that of the coherent state.It shows that the atom-field entanglement in squeezed vacuum is much stronger and stable than that of coherent state,whereas the nonclassicality of the light field depends on its initial status.This investigation is trying to find a new insight into the relation between entanglement and nonclassicality of light fields and the result shows that nonclassical field may provide helps for getting strong quantum entanglement,and the strong entanglement implies the better control of the atom and photon mutually in a nonclassical environment.5.By putting the atoms directly into a squeezed light generator—a degenerate optical parametric oscillator(DOPO),we investigated the photon statistics of the intracavity field and analyzed the influence of the optical bistability and the modified threshold of the systen.The result is that when there are many atoms in the cavity it shows strong sub-Poinssonian and weak anti-bunching effects,which may be used for the generation of Fock state with arbitrary photon numbers and when there is only one atom in the cavity,the system shows both strong sub-Poissonian and anti-bunching,as is expected.This feature is supposing for the generation of single photon source.6.We also discussed the influence of the cavity and light parameter of the Cavity QED system on the properties of the output field,such as the photon statistics and the power spectrum,etc.This discussion is helpful for our experiment of generating single-photon source with proper parameters,such as the cavity length,and the pumping power,etc.