Optical Effects In An Artificial Hybrid Nanocrystal Complex

Due to the rapid advance of nanotechnology, a kind of artificial complex superstructure that we call it an artificial nanocrystal complex has been exploited. Each hybrid molecule in this kind of superstructure can be combined by two or more different nanoparticles. These nanoparticles may be semiCond- uctor quantum dot(SQD), metal nanoparticle, nanowire, magnetic compound,gene,ect. Because one hybrid molecule makes up of different components, such superstructure usually owes the essential physical properties of all the components. On the other hand, the essential physical properties of each components can be modulated by neighbouring components, then lots of new physical properties can be found. So such superstructure will be worthful in an further application.Optical effect such as slow light and Kerr nonlinearity have many potential application ,such as quantum information processing, light switch, and so on. Because that,it has attracted great attention in those fields. Kerr optical effect belongs to three-order nonlinear optical effect. The Kerr coefficient is direct proportion to the real part of three-order susceptibility. In the common case, the Kerr coefficient is very small. The result of many past theroetical and experimental researches shows that a large Kerr coefficient in a weak light will be obtained by the way of the coherent light control. Slow light means the speed of the light will be slow down. With the rapid progess of optical communication and optical computation, the control of light speed becomes more and more important. Electromagnetically Induced Transparency (EIT) and Coherent Population Oscillation (CPO) etc. are some amongs the usual ways to the generation of the slow light effect. In this thesis, we study the slow light effect in an artificial hybrid nanocrystal complex system. In this thesis, we also discuss one kind of optical effect: Phonon Induced Transparency (PIT), which is a similar to EIT. PIT owns some same optical properties of EIT, such as light passing through medium without absorption and slow light. The coupling between the phonon and the exciton is the physical mechanism of the generation of PIT. Without the phonon effect, the transparency will be dissappear. It is a very diffcult problem that the phonon surrounding leads to decoherence of the quantum computation. In this thesis, we discuss the phonon surrounding and the detuning will influence spin-orbit driven coherent oscillation in the quantum dot. Our theoretical result would shed light on how to efficiently suppress decoherence and distanglement.To summarize, some related theoretical investigation on slow light, Kerr nonlinearity and phonon induced transparency in an artificial hybrid nanocrystal complex are provided in this thesis and we have also studied phonon effect on the realization of quantum computation in quantum dot. Some results are listed as follows:(2) The research background, the fundamental conception and the method have been introduced, and the recent research achievement on slow light,nonlinear optics and quantum computation have been summarized as well.(2) Kerr nonlinearity in a hybrid nanocrystal complex is studied. We choose the hybrid molecule composed of quantum dot and metal particle as investigated object. By the generalized optical Bloch equations, the expression of the nonlinear susce- ptibility in a hybrid complex has been derived. We use GaAs / AlGaAs quantum dots and Au metal particles as example to find out how the Kerr nonlinearity changes. The results show that when the interparticle distance between quantum dot and metal particle is smaller, the nonlinear optical effect will be enhanced. Another important result is that the increasing quantum of Kerr coefficient is more than that of nonlinear absorption in some light frequencies. The result will be meanful in the furrther theoretical or experimental research. We also can obtain a different nonlinear optical response by altering the Rabi frequency of the control light, the frequency of the control or the proble light and the electric field polarization direction.(3) Slow light effect in a hybrid complex has been studied. The expression of linear optical susceptibility has been derived using the generalized optical Bloch equation too. Because of quantum coherent oscillation, slow light can be produced in a quantum dot system that has been treated as two-level energy system. When the coulomb interaction between metal particle and quantum dot is stronger, the group velocity index of signal light in hybrid complex are larger. At the same time, we also furtherly consider the factual case of the modern artificial technology: the distance between two nanoparticles cannot be constanted. The corresponding theoretical investi- gation has been carried throughed. The results show that the generation of slow light effect will not be influenced with a smaller half width of the distribution in Gaussian distribution or Lorenz distribution.(4) Phonon Induced Transparency in a hybrid complex is investigated. Because of the interaction between phonon and exciton, electromagnetically induced transparency can be generated in quantum dot system. We choose the hybrid molecule composed of Ag metal particle and quantum dot to find out how the phonon-induced transparency and slow light effect change. The results show that when the interparticle distance between metal particle and quantum dot is shorter, the group velocity index can be larger or smaller for choosing different electric field polarization of external light.(5) The effect of detunig and phonon surrounding on coherent oscillation in a single quantum dot has been studied. The results show that the detuning will break the symmetry of system and the population inversion in long- time limit will be not zero any longer. We also study the size of the quantum dot, the intensity of the magnetic field and spin-orbit constant coupling will be influence the population oscillation in the quantum dot. From the data, we know that the stronger magnetic field intensity, the smaller spin-orbit coupled coefficient, the larger size of quantum dot all can make the coherence time of population osicllation longer.In the last chapter, the main contents and conclusion of my dissertation have been summarized.