Novel Integrated Photonic Devices For Quantum Information Processor

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.