相干原子介质内的光操控及量子关联光场

发布时间：2018-10-18 10:12

【摘要】：电磁感应透明(EIT)是由于量子干涉所导致的一种原子相干效应,可有效抑制光场的共振吸收,同时增强介质的色散和非线性效应。近年来,EIT介质已经被成功作为信息存储单元应用于量子网络。随着光量子通信的蓬勃发展,人们对相干原子介质提出更全面的要求,比如操控光信号的传输以及制备非经典光场。前者能有效补偿传输过程的光子损耗并作为通信过程中的光量子器件;后者可直接将量子关联光场的频段拓展至原子吸收线,实现量子信道与量子节点之间高效率的信息交互,并且产生的光场具有线宽窄、相干长度长等优点。利用原子系综产生关联光场的过程因为无需光学谐振腔,容易实现多个空间模式的同时放大,从而获得高维度的量子关联,为并行量子计算、量子密集编码、提高量子成像质量等提供了技术保障。另外,本文以铯原子的D1线跃迁能级为研究对象,其对应的光源为895 nm,与InAs量子点激子发射的波段相匹配,为原子和固态系统之间的相干界面搭建了桥梁。全文围绕着这样的思路,首先介绍了EIT、电磁感应吸收光栅、无反转放大、双EIT和四波混频的基本概念、产生机制并回顾国内外在相关方向的研究进展及应用。在此基础上开展了对原子系综内光子晶体、EIT光放大、连续变量量子关联光场的实验与理论研究。1)研究了基于EIT的光子晶体对光场传输特性的操控。利用驻波场耦合三能级的EIT介质,构造出折射率在空间周期排列的一维光子晶体结构,从而获得对入射光束高效率的布拉格反射信号,并完全阻止其在共振频率处的传输,实现了一种动态可控的近似光子频率带隙。理论上采用传输矩阵的方法,融合了EIT介质的量子干涉效应与折射率周期调制的光子晶体特性,对探针场的透射和反射进行数值模拟,得到与实验现象的较好吻合,证实了原子介质内部存在光子晶体结构。2)研究了Tripod型Dual EIT透明窗口处的高增益相干光放大。在三能级∧型EIT基础上额外引入一束信号光,作用于第三个基态与激发态之间的跃迁。扫描探针光频率,其透射谱线中会出现两个EIT窗口,它们的频率相近时存在相互耦合,增强基态之间的原子相干性。在利用Dual EIT抑制光场吸收的同时,借助基于自旋交换碰撞的布居数转移机制来增加第三个基态上的原子数,进一步提高信号光的泵浦速率,实现透明窗口内的相干光放大。理论计算得到的增益谱与实验结果也符合较好。3)对四波混频产生EPR纠缠态光场的理论分析。由双∧型三能级光与原子耦合体系的哈密顿量出发,提出将原子算符等效为光场算符与泵浦场和原子参数的乘积。对量子化光场做二阶微扰近似并提取四波混频的相位匹配项,得到描述放大过程的有效哈密顿量：利用原子的三阶非线性效应,将两个泵浦光光子的能量转换为一对斯托克斯和反斯托克斯光子。由EPR纠缠判据分析了两光场正交分量之间的不可分性,讨论了泵浦失谐、超精细分裂能级间隔、相互作用长度、泵浦功率以及自发辐射噪声对纠缠的影响,为实验获得最大纠缠提供了充分的理论依据。4)研究了铯原子D1线高维度量子关联光束的实验制备。将TEM01的厄米高斯横模注入四波混频的光放大器,获得了一对TEM01高阶模式的量子关联光束。对它们的空间子模式进行提取,分析光场子模式之间的强度噪声关联特性,获得同时具备时域和空间域的2.5 dB的高维度量子关联光束,提高了光场加载信息的能力。其中创新性的工作如下：Ⅰ.理论上从光子晶体的角度去分析探针光在电磁感应吸收光栅内的传输,验证了系统内部光子晶体结构与EIT的有机结合。Ⅱ.借助Dual EIT的能级配置首次在实验上获得对EIT的相干光放大。利用光学厚介质内自旋交换碰撞引起的布居数转移机制来提高信号光泵浦能态的布居数,从而在较低的泵浦功率下即可获得很高的增益。Ⅲ.结合二阶微扰近似的理论与四波混频过程的相位匹配条件,首次给出双∧型光-原子耦合体系的有效哈密顿量来类比非简并光学参量放大过程。对比铷和铯两种原子介质,提出限制纠缠度的最主要因素在于基态超精细分裂的大小。Ⅳ.利用TEM01的高阶厄米高斯横模作为四波混频放大过程的种子光,首次在实验上获得铯原子吸收线附近的高维度量子关联光束。
[Abstract]:Electromagnetic induction transparent (EIT) is a kind of atomic coherence effect caused by quantum interference, which can effectively restrain the absorption of light field and enhance the dispersion and non-linear effect of the medium. In recent years, EIT media have been successfully applied to quantum networks as information storage units. With the vigorous development of D2D communication, more comprehensive requirements for coherent atomic media, such as the transmission of optical signals and the preparation of non-classical optical fields, are proposed. the former can effectively compensate the photon loss of the transmission process and act as the light-emitting device in the communication process; the latter can directly extend the frequency band of the quantum-related optical field to the atomic absorption line, realize the high-efficiency information interaction between the quantum channel and the quantum node, and the generated optical field has a line function, and has the advantages of long chain length and the like. The process of generating an associated optical field by using an atomic ensemble is provided with the technical guarantee for parallel quantum computation, quantum dense coding, improved quantum imaging quality and the like by simultaneously amplifying a plurality of spatial modes without the need of an optical resonant cavity. In addition, using the D1 line transition energy level of caesium atom as the research object, the corresponding light source is 895 nm, matching with the wave band emitted by InAs quantum dot exciton, and a bridge is built for the coherent interface between the atom and the solid state system. In this paper, the basic concepts of EIT, electromagnetic induction absorption grating, non-inversion amplification, double EIT and four-wave mixing are introduced, and the research progress and application of EIT, electromagnetic induction absorption grating, non-inversion amplification, double EIT and four-wave mixing are introduced. In this paper, the experiment and theoretical research of photonic crystal, EIT optical amplification and continuous variable quantum correlation optical field in atomic ensemble are carried out. The control of the optical field transmission characteristics of photonic crystal based on EIT is studied. using a standing wave field to couple a three-level EIT medium, a one-dimensional photonic crystal structure with a refractive index arranged in a space cycle is constructed, so that the Bragg reflection signal with high efficiency for the incident light beam is obtained, and the transmission of the Bragg reflection signal at the resonance frequency is completely prevented, a dynamic controllable approximate photon frequency band gap is realized. By adopting the method of transmitting matrix theoretically, the quantum interference effect of EIT medium and the photonic crystal characteristics of refractive index period modulation are fused, and the transmission and reflection of the probe field are simulated numerically to obtain good agreement with the experimental phenomenon, The photonic crystal structure inside the atomic medium is confirmed. 2) The high-gain coherent light amplification at the transparent window of the Opod-type Dual EIT is studied. A beam of signal light is additionally introduced on the three-level EIT base, acting on the transition between the third ground state and the excited state. Two EIT windows appear in the transmission spectral lines of the scanning probe. Their frequencies are close to each other, and the atomic coherence between the ground states is enhanced. At the same time, using Dual EIT to suppress the absorption of optical field, by means of the spin-exchange collision-based transfer mechanism of the cloth residence, the valence of the third ground state is increased, the pumping speed of the signal light is further improved, and the coherent light amplification in the transparent window is realized. The gain spectra and experimental results obtained by theoretical calculation also accord with the experimental results. The theoretical analysis of the EPR entangled state light field is generated for the four-wave mixing. The product of atom operator equivalent to light field operator and pump field and atomic parameter is proposed based on the Hamiltonian of the two-phase three-level light and atom coupling system. A two-order perturbation approximation for the quantized optical field is made and the phase matching term of the four-wave mixing is extracted to obtain the effective Hamiltonian describing the amplification process: the energy of the two pumping light photons is converted into a pair of Stokes and anti-Stokes photons by using the third order nonlinear effect of the atom. The inseparability between orthogonal components of two optical fields is analyzed by EPR entanglement criterion, and the effects of pump detuning, ultra-fine splitting energy level interval, interaction length, pump power and spontaneous emission noise on entanglement are discussed. In this paper, we provide sufficient theoretical basis for the experiment to obtain the maximum entanglement. 4) The experimental preparation of the high-dimension quantum correlation beam with the cesium atom D1 line is studied. A pair of TEM01 high-order modes of quantum correlation beam are obtained by injecting the Em Gaussian transverse mode of TEM01 into the optical amplifier with four-wave mixing. The spatial sub-modes are extracted and the correlation characteristics of the intensity noise between the optical field sub-modes are analyzed to obtain the high-dimension quantum-associated light beams with the time-domain and the spatial domain of 2.5 dB, and the capacity of the optical field loading information is improved. The innovative work is as follows: I. In theory, the transmission of the probe light in the electromagnetic induction absorption grating is analyzed from the angle of the photonic crystal, and the organic combination of the photonic crystal structure inside the system and EIT is verified. II. The second EIT's energy level configuration was used for the first time to gain amplification of the coherent light for EIT. By using the cloth displacement mechanism caused by the spin-exchange collision in the optical thick medium, the cloth residence number of the signal light pump energy state can be improved, so that a high gain can be obtained under the lower pump power. III. Based on the theory of the second order perturbation approximation and the phase matching condition of the four-wave mixing process, the effective Hamiltonian of the two-mode optical-atomic coupling system is given for the first time to analogize the process of non-degenerate optical parametric amplification. The most important factor to limit the entanglement degree is the size of the ultra-fine splitting of the ground state. IV. A high-dimensional quantum correlation beam near the absorption line of caesium atom was obtained on the experiment for the first time by using the high order Ermi Gaussian transverse mode of TEM01 as the seed light of the four-wave mixing amplification process.
【学位授予单位】：山西大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O43

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