Research On Electromagnetically Induced Grating Based On Coupled Quantum Dot System

In recent years,semiconductor quantum dots have attracted the attention of researchers because of their rich physical properties and great development potential.Compared with ordinary atoms,semiconductor quantum dots(QDS)are characterized by good local size,level spacing,high nonlinear optical sensitivity and great design flexibility.Because of their outstanding inherent advantages,semiconductor quantum dots have become the focus of research in quantum optics and quantum information science,and have been widely used in photoelectric device design and preparation.On the other hand,because of its special structure,grating has many important applications in industrial production,such as optical splitter,optical storage and optical coupling.Because of these important uses of grating,the preparation and application of electromagnetically induced grating in the field of quantum optics have been studied deeply.On the basis of electromagnetically induced transparency,when coherent standing wave field is used instead of traveling wave field to act on medium,the polarization response of medium shows the characteristic of spatial periodicity,and there are periodic amplitude and phase modulation,which will lead to the diffraction effect of weak probe beam after passing through medium.In this paper,the optical transmission characteristics and electromagnetically induced grating phenomena of coupled quantum dot system are studied.We first study the optical Kerr nonlinearity of quantum dot molecular system and its diffraction effect on weak probe light by combining coherent standing wave field and quantum dot tunneling.Secondly,optical paritytime symmetry(PT symmetry)and parity-time antisymmetry(PT antisymmetry)are studied in quantum dot molecular system,and optical PT symmetry and PT antisymmetry are used to realize asymmetric transmission of light.The specific research contents are as follows:(1)We propose a scheme to fabricate phase gratings in a quantum dot molecule formed by coupling two quantum dots.When inter-point tunneling exists between quantum dots,the third-order optical nonlinearity is significantly enhanced due to the tunneling induced quantum coherence,in which the third-order dispersion effect is significant,accompanied by nearly disappearing linear and nonlinear absorption.Driven by the coherent standing wave field,the medium presents high transmittance and strong phase modulation,which makes the weak probe light diffracted through the medium.The results show that the diffraction intensity can be effectively adjusted by changing the weak driving intensity,the detuning of the driving field,the tunneling coupling intensity and the interaction length.Our scheme focuses on weak standing wave drive and weak tunneling strength,which provides a simple and practical method to obtain phase gratings and may have potential applications in quantum optics and quantum information processing devices in solid-state systems.(2)In order to further improve the diffraction efficiency and control the diffraction direction,we study the optical PT antisymmetry and its effect on the probe light diffraction in coupled quantum dot system.Combined with the spatial modulation of the standing wave drive field and the detuning,the coupled quantum dot system presents an optical PT antisymmetry,that is,the absorption of the medium presents a spatial symmetry,while the dispersion presents an antisymmetry.Under the condition of optical PT antisymmetric,the diffraction image after medium diffraction presents asymmetric characteristics,that is,the intensity of light field is concentrated in the positive or negative direction,which greatly improves the diffraction efficiency.Moreover,by modulating the physical parameters,the diffraction direction can be changed effectively so that the probe beam diffracts to different diffraction order.Our scheme provides a theoretical basis for the interaction between light and matter in the quantum dot system and the optical transmission characteristics as well as the quantum information processing in the solid state system,which has important applications for the development of semiconductor solid materials and new photonic devices.(3)We propose an efficient and controllable scheme of asymmetric diffraction gratings based on optical PT symmetry in multi-quantum dot molecular systems.In this scheme,the spatial dependence of absorption and dispersion of the medium can be changed by combining the standing wave driving field and particle number spatial modulation.Under the condition of proper physical parameters,the system exhibits significant PT symmetry,namely dispersion symmetry and absorption antisymmetry,which is the key to realize asymmetric diffraction gratings.It is observed that the positive and negative directions of diffraction can be adjusted by changing the sign of the modulation amplitude of the standing wave field or by changing the sign of the detuning of the probe field and the driving field.With the increase of the interaction length,the energy of the probe field shifts to the higher order diffraction direction.This enables highly efficient diffraction gratings with adjustable orientation.This scheme provides a feasible scheme for effectively controlling the diffraction direction and greatly improving the diffraction efficiency,and provides a possibility for applications in quantum information processing and realizing large angle optical beam splitter.