Nonlinear Effect And Coherent Manipulation In Electromagnetically Induced Coherent Atomic Media

The electromagnetically induced transparency effect in quantum coherent media can change the linear and nonlinear susceptibilities of the media,and the corresponding optical properties of the media can be also dramatically altered,which is presented as follows:firstly,the linear absorption of the media is reduced,but the dispersion of the media is enhanced;secondly,the coherent control for the transformation of quantum states between atom and photon becomes easy to be realized;thirdly,the nonlinear effect of atomic media is greatly enhanced.Because of these nonlinear optical properties,lots of quantum optical phenomena associated with electromagnetically induced transparency have attracted considerable attention and have been widely studied over the past few decades,including enhanced high order nonlinearities,lasing without inversion(LWI),optical bistability and multistability,multi-wave mixing,high-precision atom localization,low group-veloctity,and so on.The further research for such optical phenomena may be helpful not only to understand better the essence of quantum theory but also to further predict and discover the new potential applications.In this thesis for the Doctorate,we have mainly realized the manipulation of optical bistability and multistability in electromagnetically induced coherent media.Moreover,we have obtained the high-precision and high-resolution two-dimensional(2D)and three-dimensional(3D)atom localization via the controlled atomic-level population and the probe absorption measurement.The main contents are as follows:1)The optical bistability(OB)and multistability(OM)have been realized in a generic four-level Y-type atomic system driven coherently by a probe laser and a single elliptically polarized field(EPF)by means of a unidirectional ring cavity.Taking the dipole and rotating-wave approximation,the input-output relationship for the fields can be derived by using the density matrix equations.The results show that the bistable threshold and the area of the bistable hysteresis loop can be effectively modified by adjusting the relevant parameters of the system,such as the frequency detuning of the probe field,the intensity of the EPF,the atomic cooperation parameter,and so on.Moreover,we also discuss the influences of the relative phase between two components of the polarized electric field of the EPF with the presence of the spontaneously generated coherence(SGC)effect on the behaviors of OB and OM.These results provide theoretical guidance for the realization of all-optical switching by utilizing EPF in atomic systems.2)Two-dimensional(2D)atom localization in the sub-wavelength domain is investigated in a microwave-driven five-level hyper inverted-Y atomic system.Because of the spatially dependent atom-field interaction,the information about the position of the atom can be obtained directly by measuring the phase-sensitive absorption-gain spectra of the probe field,thus leading to atom localization.In the case of steady-state solution,the numerical results show that when two orthogonal standing-wave fields are applied to couple the same atomic energy-level transition,the atom can be localized at a particular position by properly adjusting the system parameters,and two-dimensional localization peaks with different structures,such as lattice-like,crater-like,and spike-like patterns,can be obtained.At the same time,the precision and spatial resolution of atom localization are greatly dependent on the frequency detuning of the probe field,the intensities of two control fields,and the relative phase of the driving fields.Moreover,the maximum probability of finding an atom at a particular position within one period of standing-wave fields can reach 100%by choosing appropriate system parameters.Thus,the high-precision and high-resolution 2D atom localization is indeed achieved.More interestingly,the high-precision and high-resolution 2D atom localization can be attributed to the joint quantum interference effect induced by the combination of two orthogonal standing-wave fields,the two control fields,and the microwave-driven field.It has potential applications in optical communications,the fabrication of novel optoelectronic devices,and atom nanolithography.3)We propose a scheme for the realization of high-precision and high-resolution three-dimensional(3D)atom localization based on far-field spatial interference effect in a generic double two-level atomic system.Using three orthogonal standing-wave fields coupling atomic energy-level transition,we achieve the phase-shift-dependent 3D atom localization via measuring the population of the excited states.The investigations show that the control for precision of 3D atom localization can be achieved by adjusting the frequency detuning of the probe field and the phase shifts associated with standing-wave fields.More importantly,we establish the connection between 3D atom localization and the far-field spatial interference via defining the visibility of the far-field spatial interference pattern.We find that the enhancement of the intensity of far-field spatial interference can lead to the improvement of 3D atom localization precision.Then,using the similar approach,the behaviors of 3D atom localization in a ladder-type three-level atom and a V-type three-level atom are investigated,respectively.Based on the own characteristics of atomic systems and the quantum interference effect,the conditional position distribution of the atom is not the same any longer in eight subspaces,and the detecting probability of an atom in some subspaces can be increased by adjusting the system parameters.It is worth pointing out that the maximum probability of detecting the atom within a cubic wavelength can be improved by a factor of eight.In addition,we have also discussed the influence of spontaneously generated coherence(SGC)effct on 3D atom localization.In conclusion,this thesis deepens our awareness and understanding of the characteristics of nonlinear optics in electromagnetically induced coherent media,and helps us to further realize the quantum coherent manipulation.These investigations may have some reference value for the developments of precision nonlinear spectroscopy,optoelectronics,quantum information as well as quantum coherent manipulation.