Study Of The Excitation Spectroscopy Of Atoms In A Strongly Coupled Cavity QED System By Ns Laser Pulses

The interaction between atoms and electromagnetic fields is a ubiquitous physical process in the physical world.Cavity quantum electrodynamics(cavity-QED)studies this interaction in the simplest way that atoms and resonant cavities are coupled.Since discovered by Purcell in 1946,the spontaneous emission rate of atoms in a cavity can be affected by the surrounding environment.Cavity quantum electrodynamics has rapidly developed and become one of the important ways to realize quantum information processing.Strongly coupled cavity-QED systems can also generate a variety of quantum resources,such as deterministic single-photon sources and two-photon sources,which are of vital importance in quantum information processing.The generation of deterministic single-photon sources has been achieved in neutral atoms,molecules,ions,quantum dots and various centers.However,quantum computing and quantum networks place heavy demands on the single-photon sources.The photons emitted must be indistinguishable and have high production efficiency.Strongly coupled cavity QED systems have obvious advantages in generating such single-photon sources over free-space coupled systems.In addition,the cavity-QED system can also be used to construct entangled photon states,such as W states and Greenberger-Horne-Zeilinger(GHZ)states.On the other hand,with the maturity of cold atom manipulation technology,people can capture single and multiple atoms using magneto-optical traps and optical dipole traps to transfer the atoms into an optical cavity efficiently.In strongly coupled cavity-QED systems,not only single-photon sources or two-photon sources can be generated,but also the characteristics of collective excitation and collective radiation of multiple atoms can be explored,which is one of the important topics in the research of strongly coupled systems.This thesis mainly completes two specific works:(1)An electro-optic intensity modulator is used to chop the continuous light waves into light pulses with the repetition frequency of 4 MHz and the pulse width of 5 ns.The chopped light pulses are injected into the distributed feedback(DFB)laser by a transmission-type injection locking method.In the experiment,by measuring the injection-locked range,we can find an injection-locked point with a large frequency difference of 31.5GHz.The temperature-controlled etalon is used to filter the laser pulses.The ON/OFF ratio of pulses filtered by the etalon is significantly improved and much better than the case without the etalon.(2)In strongly coupled cavity-QED system with multi atoms,strong pulses with the width of 5 ns is used to directly excite the atoms along the direction perpendicular to the cavity axis.Photons radiated into the cavity by the excited atoms are measured to obtain the excitation spectrum.We found that the excitation of the atoms is suppressed when the frequency of the light field is resonant to the transition of cesium atoms,however the excitation reaches maxima when the with frequency detuning is a certain value.We have established a theoretical model to describe the interaction between a three-level atom and the light.By solving the Schrodinger equation of the dressed atom,the nanosecond-pulse excited spectrum can be explained by the interference of different excitation paths of the strongly coupled cavity-QED system.