【作者】 邹长铃；

【导师】 韩正甫； 郭光灿；

【作者基本信息】 中国科学技术大学 ， 光学， 2013， 博士

【摘要】 在传统的电子集成芯片领域,纳米加工技术、量子隧穿效应、功耗和散热等方面制约着基于电子芯片的信息技术的进一步发展。量子信息科学应运而生,基于量子态的叠加原理、量子不可克隆原理和量子精密测量、有望实现高效的量子计算、高速而安全的量子信息传输,并能够突破经典噪声和不确定性原理的限制实现更加精确的测量。经过近三十的努力,量子信息在很多物理体系中取得了卓有成效的进展,包括电子和空穴自旋、核自旋、光子、机械振子、超导约瑟芬结、原子和离子阱。其中,光子具有多重自由度、室温环境下的退相干小、信息传输速率高以及技术成熟等多方面的优势,因此人们已经在基于光子的量子态的量子信息处理方面取得了众多突破性的进展。然而,传统光学元件尺寸较大并且光路受到环境温度、气流和振动的影响非常大,限制了光子量子信息处理的进一步扩展。在集成光学芯片上,固态介质组成的光学元件和光路性能稳定、能耗更小可扩展性强,因而是光子量子信息处理的必然发展趋势。本论文致力于研究集成光学芯片上的量子信息处理。一方面,研究各种集成光学元件的基本性质,与实验结合设计各种新的器件,并开发新的材料和物理体系来提高器件的性能,从而实现对量子态的制备和操控。另外一方面,光的传播可以类比量子态的演化,因而赋予集成芯片的光学研究新的内涵和物理,可以利用集成光学芯片模拟量子模型或者基于量子力学原理设计新颖的集成光学元件。本论文具体的研究内容包括以下几个方面：1.集成光学芯片器件基本性质集成光学芯片上最基本的组成部分是光子的载体,即波导和微谐振腔。波导可以传输光子,连接不同的集成器件；谐振腔可以局域光子,增强光子与物质的相互作用,基于两者可以实现各种不同功能的光学器件。我们研究小组深入研究了各种波导结构和回音壁模式微谐振腔的基本性质。结合过去几年我们小组的实验进展,本论文详细介绍了回音壁模式光学微腔的基本性质、实际的材料和制备方法。本人在理论上研究了回音壁模式的耦合模式理论,研究了其与近场波导的平行和垂直耦合,对实验中的回音壁模式的高效激发和收集提供理论支持。为了避免在低温腔内进行实验时对微腔近场操控的限制,本人还研究了非对称的回音壁模式微腔的方向性发射。首次给出高Q单向性发射的回音壁模式的基本原理,并基于此设计和优化了实用的方向性发射微腔。另外还首次给出远场激发回音壁模式微腔的自洽理论,为自由空间耦合高Q回音壁模式微腔提供理论指导。2.集成芯片上光子与二能级体系相互作用二能级原子是最简单的量子体系,利用光子与其作用,可以实现单光子光源、原子媒介的光子光子相互作用以及光子媒介的原子原子相互作用,从而用于量子纠缠、量子态的制备和存储等应用。我们小组致力于实现固态量子点和微腔的强耦合实验,希望基于此构造固态量子信息处理器。因此,本人开展了这个方面的理论研究。在波导和回音壁模式微腔附近,由于局部的电磁场模式密度的改变会造成原子自发辐射速率的改变。基于此,我们提出利用纳米光纤和表面等离子体的复合结构,实现高效的单光子源。实验上已经观测到了回音壁模式腔对量子点荧光寿命的调制效应。我们提出了各种改进的实验方案来帮助解决在单个量子点和回音壁模式微腔的强耦合实验中遇到的一些困难。例如,通过用混杂有量子点的聚合物包裹微腔表面,可以实现更加高效和稳定的强耦合。3.光与机械相互作用本人将机械振子这样一个新的元素引入到集成光学芯片上,从而实现更多实用的光学器件和量子信息处理。光机械作用的一个特点就是任意波长的光子携带的动量都可以转移到机械体系上,光与机械相互作用无需频率共振。本人的研究包括两个方面：(1)用经典的光力控制机械振子的运动从而实现对光路的调制。在集成芯片上,微纳结构的质量和弹性系数非常小而更容易变形,利用波导和微腔对光的束缚,可以在输入光能量很小的情况下调节机械振子的状态。利用这种光机械相互作用使得光与光间接地相互作用,可以实现相位和能量的调制器,具有全光特性和低功耗的优势。(2)利用简谐振子的量子态实现量子信息处理,包括量子纠缠和光子频率转换等。我们首次提出了一种室温下实现光机械量子纠缠的实验体系。该体系由一个高机械品质因子(Qm)的机械谐振子和高光学品质因子(Qo)的微盘腔组成,均由Si3N4材料制备,与其它光学集成器件兼容。在这个体系中,如果固定其他参数不变,纠缠只与温度和机械Qm的比值有关,也就是说Qm越高,量子纠缠就能在越高的温度下存在。机械体系其独有的性质有望在集成光学芯片量子信息处理中发挥重要的作用。4.集成光学量子模拟利用集成光学芯片,可以构造特定的结构来模拟和类比其他物理体系,实现对某些量子物理问题的模拟研究。本人利用集成光学芯片模拟了量子开放体系,并研究了系统与环境相互作用的马尔科夫、非马尔科夫动力学过程。通过直接观测电磁场的能量分布和演化,可以直观的理解系统与环境相互作用的内在物理机制。在集成光学芯片上,可以非常方便的控制环境的尺寸以及系统与环境的相互作用强度,从而研究其中各个细节。值得一提的是,我们还证明了通过对系统施加周期性的调制可以改变系统的演化,加快或者减慢系统能量的耗散速率。类似于自旋体系的动力学解耦,我们的研究为集成光学芯片提供了一种新的方法来控制光学耗散。更重要的是,这种光学与量子的模拟或者类比为我们研究基本物理过程和现象提供了新的视角。5.量子力学启发的新器件设计通过量子力学与集成光学芯片的模拟类比,本人借鉴量子力学中的一些有趣的现象和原理来设计新的集成光学器件。(1)基于绝热量子态演化模型的激发方式,首次提出介质波导模式与表面等离子体模式的高效转化。在实验上这一激发方式已经被证实。在此基础上进一步提出了新颖的利用表面等离子体模式的高效集成偏振器件：起偏器和偏振分束器,可以实现光学芯片上的偏振量子态的操控。(2)基于连续体中的局域态模型实现一种全新的金刚石光学芯片,突破了传统的芯片上器件只能在低折射率基底上制备高折射率微纳光学结构的限制,提供了一个新的集成光学实验平台,有望用于光子与金刚石内的NV色心的强相互作用以及基于此的量子信息处理和量子网络。更多还原

【Abstract】 Since great progresses have been achieved in both science and technology recent-ly, efficient and quick information acquisition, processing and transmission are urgently required. However, further development of the traditional electronic chips is limited, be-cause further reducing the size of various electronic components will lead to inevitable quantum effect and the heating problem. Thus, the electronic circuits are facing the chal-lenges of fabrication, power consumption and heat dissipation. As the times require, the quantum information science arises:quantum no-cloning theorem guarantees the safety of quantum information communication; utilizing the superposition principle of quantum states, quantum algorithm is efficient for the information processing; quantum metrology can break the limitations of classical noise and quantum uncertainty princi-ple, thus very small quantities can be measured accurately. During the last thirty years, great efforts have been dedicated to the quantum information processing in various sys-tems, such as electron and hole spins, nuclear spins, photons, mechanical oscillators, superconducting qubits, atoms and ions. Among them, photons have many advantages, including:they possesses multiple degrees of freedom to encode quantum information, which is potential for higher signal processing speed and information transmission rate; the decoherence of photon at room temperature is very weak, thus information can be transmitted with high fidelity; there is a very long history of study on optics and the op-tical technology has been very mature. Therefore, many breakthroughs on the quantum information processing have been achieved by photons, such as quantum computation, quantum simulation and quantum teleportation.However, there are also constraints on the photon-based quantum information pro-cessing in traditional space optical circuits. For example, the them are large and occupy considerable space, and the distance between optical devices is very sensitive to the environment temperature, airflow and vibrations. Therefore, for further scalable quan-tum information processing, all the optical components need to be integrated on chip. The photonic integrated circuits (PICs) with compact optical devices can greatly save the material, spaces and less power consumption. In addition, the PIC made of solid material are more stable, enable further scalable quantum information processing.This thesis is devoted to the study of PIC and quantum information processing based on it. On the one hand, the basic properties of optical waveguides and resonators are studied, and a variety of devices for PICs are designed. New materials and structures are also introduced to PIC to improve the optical performance and functionality. On the other hand, I explored the analogues between the quantum physics and optics in PIC, proposed the schemes to simulate quantum mechanics by PIC, and borrowed ideas from quantum mechanics to design novel integrated optical devices.There are several topics studied in this thesis, including:1. The basic properties of the integrated optical devicesIn the PIC, the basic components are waveguide and resonant cavity. Waveguide can guide photons and connect different devices; resonant cavity can trap photon and enhance the light-matter interaction. A variety of optical devices with different func-tionalities are constructed by waveguides and resonant cavities. Our group is dedicating to study the basic properties of waveguide and resonator structures. We have studied the fundaments of whispering gallery (WG) microresonators, including the optical proper-ties of WG modes, the practical fabrication of WGM microcavities and their applica-tions. In addition, the near field waveguide coupled to WG modes are studied theoreti-cally, both parallel and perpendicular configures investigated. To avoid the limitation of near-field coupler, we also studied the free space excitation and collection of asymmet-ric resonant cavities. Our theoretical studies provide a guideline for the experimental studies on the high-Q WG modes.2Interaction between photon and two level systemsThe two-level atom is the simplest quantum system, and it can interact with photon-s. The photon-atom interaction, atomic-mediated photon-photon interaction and photon-mediated atom-atom interaction can be applied for generating single photon source, preparing and storing quantum states and quantum entanglements. Our group focused on the strong coupling between solid-state quantum dots and microcavities. Therefore, we have studied the photon-atom interaction in theory. The spontaneous emission rate of two-level system will be changed when putting two-level system in the vicinity of waveguide or WG microresonators. Based on this, we proposed a hybrid structure com-posed of nanofiber and metal substrate for efficient single photon source. We have also demonstrated the modulation of the fluorescence of quantum dots near WG microres-onator experimentally. In addition, we presented experimental schemes to improve the behavior of experiment systems or solve the problems encountered in experiment. For example, with a polymer coated microcavity, efficient and stable strong coupling can be achieved. 3. OptomechanicsThe mechanical oscillators are introduced to the PIC, enabling more practical opti-cal devices and quantum information processors. The characteristic of the optomechan-ical interaction is that the momentum of light at any wavelengths can be transferred to the mechanical system. Our study includes two aspects:(1) Controlling of the classi-cal movement of mechanical oscillator through light. In the integrated chip, the micro-and nanomechanical oscillators are soft and easy to distort. In addition, waveguide or cavity can increase local intensity of light and enhance the optomechanical interaction-s. Therefore, we used the light in the waveguide to control the position of a nearby nanostring oscillator, so as to tune the effective index of waveguide modes and mod-ulate the phase of transmitted light in waveguide.(2) Utilizing the quantum state of the harmonic oscillator for quantum information processing, including quantum entan-glement generation and photon frequency conversion. We proposed an experimental system for optomechanical entanglement at room temperature. The system consists of a nanostring oscillator with high mechanical quality factor (Qm) and a microdisk res-onator with ultrahigh optical quality factor (Qo). The system is fabricated by Si3N4, which is compatible to other silicon-based components. We demonstrated that in this system, the entanglement depends on the ratio of temperature to Qm. That means that quantum entanglement can exist at high temperature for ultrahigh Qm mechanical os-cillators. The unique properties of optomechanics are expected to play important roles in the PIC-based quantum information processing.4. Integrated photonic quantum simulatorWith photons, we can construct specific structures to simulate other physical mod-els, such as quantum models. We proposed to simulate the quantum open system by PIC. In this simulation of system-environment interaction, the quantum Markovian and non-Markovian dynamics processes are studied. By directly observing the energy dis-tribution of the electromagnetic field, the intrinsic physical mechanisms of system-environment interaction are understood. Taking advantages of the PIC that the sizes of environment and system and the interaction between them can be controlled precisely, the physics therein can be studied in detail. It is worth noting that, we also demonstrated the photonic dynamical decoupling through a sequence of modulations to the system, and we observed the accelerated and inhibited system energy dissipation. Our research thus provides a new method to control the optical dissipation of PIC. More important-ly, the photonic quantum simulation provides a different perspective to study the basic physical processes and phenomena. 5. Novel optical devices inspired by quantum mechanicsThere is intrinsic analogue between the Schrodinger equation and the Maxwell e-quation, therefore we can borrow interesting phenomena and principles from quantum mechanics to the design novel integrated optical devices.(1) The adiabatic mode con-verter. Based on the model of adiabatic evolution of quantum states, we proposed an efficient conversion between dielectric waveguide modes and surface plasmon mode. This converter has been demonstrated in our experiment. Furthermore, we proposed novel and efficient integrated devices, polarizer and polarization beam splitter, to ma-nipulate the polarization states of photons.(2) Novel photonic chip made by low re-fractive index material on a high refractive index substrate. Based on the bound state in the continuum model, we proposed a novel diamond optical chip, which broke the limitation of traditional optical chips that light can only be confined in high refractive index structures. This provides a new PIC platform, and is expected to be used for strong interaction between photon and NV centers in diamond.更多还原