Optical Cavity QED In Solid-state System-Theory To Realization

Quantum computation studies the principle of coherent superposition and solves certain problems much faster than on a conventional classical computer. This matter of fact has triggered in the past years a lot of studies on the theoretical and practical aspects of quantum computing. Different physical systems, including nuclear magnetic resonance, linear optics, cold trapped ions, quantum dots, Josephson junctions in superconducting circuits, and cavity quantum electrodynamics (QED), have been proposed to implement quantum information. Among them, optical cavity QED where atoms are strongly coupled to quantized electromagnetic fields through dipole-interaction inside a high-Q cavity, offers an almost ideal system for the generation of entangled states and the implementation of quantum information processing.This thesis is mainly focused on both the theory and experiment of cavity-QED-based quantum information. The first part theoretically studies quantum information processing with optical cavity QED technique.Chapter 1 gives a brief introduction to basic quantum information science and cavity QED. We begin our introduction by giving some important concepts. To describe cavity QED, we first consider an atom-photon interaction, which is the standard Jaynes-Cummings model, and then discuss the strong and weak coupling regimes, and finally summarize the current physical systems for cavity QED research.Chapter 2 discusses the preparation and transmission of the atomic quantum states. As two typical examples, we first describe how to produce nontrivial Dicke states of N trapped neutral atoms in an optical cavity with a very high fidelity in the presence of cavity decay. Then we show that quantum teleportation of atomic inherent states can be performed with cavity QED.Chapter 3 focuses on the realization of quantum computation with optical cavity QED, which is the central task of quantum information science. To overcome the scalability difficulty of current FP-cavity-QED-based quantum computing, we propose a new quantum hardware model with whispering gallery modes (WGMs) on a silicon chip. The scheme has a high experimental feasibility under current laboratory technique, and can be used for large-scale quantum information processing. This series of theoretical work is also the primary motivation why we pursue WGM cavity QED research.Chapter 4 introduces single photon source, which is of great importance for quantum key distribution and linear optics quantum computation. Toward this goal, we propose two highly effective scheme to prepare microwave and optical single photon state.The second part largely investigates the cavity QED experiments in the past two years, which represents significant progress of this field in our group.Chapter 5 first introduces the basic theory and coupling mechanism of WGMs. WGM microresonators are a promising cavity due to the ability to obtain quality factors exceeding 100 million in micron-scale volumes. Then we discuss two kinds of WGM cavities, namely, microsphere and microdisk. To efficiently excite the WGMs, tapered optical fibers are used and studied. We obtain and control the under-, over- and critical-coupling of WGMs in both microspheres and microdisks.Chapter 6 details the most important experimental advance in our group. We cooperate with Wang Group at University of Oregon, and develop a simple but effective method to fabricate high-Q (20 million) nonaxisymmetric fused silica microspheres. The deformed microsphere microcavity provides highly directional emission of WGMs, and it essentially allows free-space effective coupling, which is significant in various cavity QED experiments at low temperature. Also, cooperating with Dr. Lan Yang at California Institute of Technology, we directly observe the lateral spatial distribution of WGMs with different azimuthal mode numbers, which agrees with the theory very well. The result is of importance in many applications ranging from cavity QED to biosensing since it directly affects the coupling strength of a local polarizability at the surface of the resonator to the WGMs.Chapter 7 is the latest work, which can be termed coupled cavity QED. We theoretically study a parallel optical configuration which includes N periodically coupled whispering-gallery-mode resonators. The model shows an obvious effect which has a direct analogy with the phenomenon of multiple electromagnetically induced transparency in quantum systems. If the coupled cavities system includes single or multi-dipoles, there will be more interesting phenomena. We cooperate with Professor Wong at Columbia University, and address this subject by study a coupled nanocavity system in which single PbS quantum dots interact with this system.