Research On Optical Properties And Applications Of Periodically Modulated Quantum System

In recent years,low-dimensional nanomaterials have been extensively explored due to their special physical properties and great potentiality.Semiconductor quantum dots,as a kind of 0-dimensional nanomaterials,have flexible energy level structure design and electrical and optical properties like that of a single atom,so they have attracted attention in the field of quantum science.At the same time,semiconductor quantum dots have advantages in scalability and compatibility with traditional semiconductor manufacturing processes,so they are widely used in quantum computing and optoelectronic device design.In addition,as a kind of beam with helical phase wavefront and annular light intensity distribution,the photon of vortex light carries orbital angular momentum.Because orbital angular momentum provides additional photon degrees of freedom,vortex optics are widely used in fields of communication and quantum science.At the same time,the annular light intensity distribution also provides an effective method to control the optical properties of the medium and is used in the field of quantum optics.On the other hand,electromagnetically induced grating is a periodic optical structure based on electromagnetically induced transparency.The electromagnetic induced grating uses the coherent standing-wave field to make the polarization response of the medium change periodically,so that the probe light is diffracted through the medium.This paper mainly studies the optical properties and applications of periodic quantum systems.First,we study the gain phase grating generated by quantum dot molecular system by using standing wave field and double tunneling effect between quantum dots;Secondly,the optical parity-time symmetry(PT symmetry)and parity-time anti-symmetry(PT anti-symmetry)in one-dimensional and two-dimensional lattices are studied in the cold atom system;Due to the unique spatial characteristics of vortex light and the orbital angular momentum carried by photons,the two-dimensional asymmetric diffraction grating is studied in the quantum dot molecule by using the optical characteristics control of vortex light on the medium and the tunneling effect between quantum dots.The specific research contents are as follows:(1)We propose a scheme to fabricate gain phase gratings in a double quantum dots molecules system.The scheme for gain-phase grating is proposed via double tunneling effect in the quantum dot molecules system with five-level structure,which is formed by two quantum dots due to inter-dot tunneling.Combining the stranding-wave control field with the double tunneling effect,the weak probe field could be diffracted to the high-order direction with the strong diffraction intensity.In the presence of double tunneling,the gain accompanied with the certain dispersion occurs,which is responsible for the preparation of the high-efficiency grating.It is found that the first-,second-,and other-order diffraction intensities are simultaneously higher than the central intensity and the diffraction intensities could be controlled by adjusting the parameters such as tunneling intensities,interaction length,probe detuning,relative phase and Rabi frequencies of external fields.The scheme we present can be utilized to develop a new photonic device for optical network and communication.(2)The optical PT-symmetric and PT-antisymmetric characteristics are simultaneously investigated in the four-level atoms trapped in one-dimensional and two-dimensional optical lattices.The atoms with Gaussian-distributed density are driven into the closed-loop configuration by a standing-wave field,two microwave fields and a probe field,where the relative phase of the external fields plays an essential role in changing the effective polarizability of such a system.It is found that the relative phase could lead to the switching from absorption to gain accompanied by the larger dispersion,and meanwhile induce the giant gain with the simultaneous presence of the positive and negative dispersion.With the aid of spatial atomic density and standing-wave modulation,both the optical PT symmetric and PTantisymmetric are achieved in one-dimensional and two-dimensional optical lattices,where the PT antisymmetric with the gain is presented.Furthermore,changing the other parameters such as Rabi frequencies and probe detuning have an impact on the realization of PT symmetry and PT anti-symmetry,which may have some important applications in quantum information processing.(3)An asymmetric two-dimensional phase grating is realized using vortex light modulation in an N-type double quantum dots molecules system.Based on the large detuning of the driving field,the system exhibits an optical Kerr effect,which provides for reduced absorption and enhanced dispersion,and the spatial modulation of the vortex light,the system exhibits a spatially dependent optical response.By adjusting the orbital angular momentum number,we find that the diffraction intensity and diffraction distribution of the system change,allowing the conversion between first and third quadrant diffraction.The diffraction efficiency in the higher-order direction can be greatly enhanced compared with the ordinary standing wave driven system.Of course,other parameters of the system,such as tunneling intensity,interaction length,and Rabi frequency,also affect the diffraction intensity and direction.The remarkable feature of the scheme is the generation of asymmetric gratings by combining the spatial modulation of vortex light and the optical Kerr effect,which not only provides theoretical help for asymmetric optical transmission properties but also opens new ideas for the design of optical devices.(4)We propose an alternative scheme for implementing a two-dimensional(2D)asymmetric grating with high diffraction intensity in a five-level quantum dots molecules system,which is induced by the interdot tunneling and is driven by a 2D standing-wave field and a vortex optical field.In the presence of the vortex beam,diffracting a weak probe beam into higher-order directions could be achieved,where the diffraction direction could be switched among different quadrants by simply adjusting the orbital angular momentum.Furthermore,other parameters such as tunneling strength,probe detuning,beam waist and Rabi frequencies have a certain impact on diffraction intensity and diffraction direction.The scheme we present has the striking feature for effectively controlling the diffraction direction and greatly improving the diffraction efficiency in 2D space,which is beneficial to the potential applications in quantum information processing and design of optical devices.