Single Quantum Dots

Special focus is given to the optical and electronic properties of single quantum dots due to their potential applications in devices operating with single electrons and/or single photons. This includes quantum dots in electric and magnetic fields, cavity-quantum electrodynamics, nonclassical light generation, and coherent optical control of excitons.

This book reviews recent advances in the field of semiconductor quantum dots via contributions from prominent researchers in the scientific community. Special focus is given to optical, quantum optical, and spin properties of single quantum dots.

This book highlights the most recent developments in quantum dot spin physics and the generation of deterministic superior non-classical light states with quantum dots. In particular, it addresses single quantum dot spin manipulation, spin-photon entanglement and the generation of single-photon and entangled photon pair states with nearly ideal properties. The role of semiconductor microcavities, nanophotonic interfaces as well as quantum photonic integrated circuits is emphasized. The latest theoretical and experimental studies of phonon-dressed light matter interaction, single-dot lasing and resonance fluorescence in QD cavity systems are also provided. The book is written by the leading experts in the field.

Special focus is given to the optical and electronic properties of single quantum dots due to their potential applications in devices operating with single electrons and/or single photons. This includes quantum dots in electric and magnetic fields, cavity-quantum electrodynamics, nonclassical light generation, and coherent optical control of excitons.

Quantum dots as nanomaterials have been extensively investigated in the past several decades from growth to characterization to applications. As the basis of future developments in the field, this book collects a series of state-of-the-art chapters on the current status of quantum dot devices and how these devices take advantage of quantum features. Written by 56 leading experts from 14 countries, the chapters cover numerous quantum dot applications, including lasers, LEDs, detectors, amplifiers, switches, transistors, and solar cells. Quantum Dot Devices is appropriate for researchers of all levels of experience with an interest in epitaxial and/or colloidal quantum dots. It provides the beginner with the necessary overview of this exciting field and those more experienced with a comprehensive reference source.

Semiconductor nanostructures are attracting a great deal of interest as the most promising device with which to implement quantum information processing and quantum computing. This book surveys the present status of nanofabrication techniques, near field spectroscopy and microscopy to assist the fabricated nanostructures. It will be essential reading for academic and industrial researchers in pure and applied physics, optics, semiconductors and microelectronics. The first up-to-date review articles on various aspects on quantum coherence, correlation and decoherence in semiconductor nanostructures

We present an overview of the theoretical background and experimental re sults in the rapidly developing field of semiconductor quantum dots - systems 8 6 of dimensions as small as 10- -10- m (quasi-zero-dimensional) that contain a small and controllable number (1-1000) of electrons. The electronic structure of quantum dots, including the energy quan tization of the single-particle states (due to spatial confinement) and the evolution of these (Fock-Darwin) states in an increasing external magnetic field, is described. The properties of many-electron systems confined in a dot are also studied. This includes the separation of the center-of-mass mo tion for the parabolic confining potential (and hence the insensitivity of the transitions under far infrared radiation to the Coulomb interactions and the number of particles - the generalized Kohn theorem) and the effects due to Coulomb interactions (formation of the incompressible magic states at high magnetic fields and their relation to composite jermions), and finally the spin-orbit interactions. In addition, the excitonic properties of quantum dots are discussed, including the energy levels and the spectral function of a single exciton, the relaxation of confined carriers, the metastable states and their effect on the photoluminescence spectrum, the interaction of an exciton with carriers, and exciton condensation. The theoretical part of this work, which is based largely on original re sults obtained by the authors, has been supplemented with descriptions of various methods of creating quantum-dot structures.

The outstanding research efforts in quantum information processing over the past two decades reflect the promise this field of physics provides for practical applications in information science as well as for new approaches towards a better understanding of fundamental questions in quantum mechanics. This thesis focuses on the photon as a principal resource to perform quantum information tasks and on schemes to imprint quantum bits onto its various degrees of freedom. Its weak coupling to the environment makes the photon an ideal carrier to securely transmit information by quantum cryptographic protocols. Moreover, efficient implementations of quantum computing using solely linear optics have been proven. Unfortunately, scalability is not easily achieved by a purely photonic approach since the generation of indistinguishable single photons from multiple emitters remains a difficult task. Thus, proposals for more complex quantum networks suggest an architecture with single photons as information carriers between atomic ensembles that act as storage and processing nodes. Computations including a limited number of qubits, however, may be performed by the linear optics scheme. The thesis starts with the generation and characterization of single-photon states, using a source based on a single optically pumped quantum dot. The capability of these states to implement a quantum algorithm using linear optics and single-photon interference is experimentally demonstrated for the first time. Error correction makes the interferometric setup robust against phase-noise. After successful realization of this proof-of-principle experiment, attention is drawn to the need of plug-and-play single-photon sources. Especially quantum key distribution, the most advanced quantum information technology to date which has even found its way into commercial devices, requires compact and low-cost non-classical light sources.Therefore, a single-photon source based on electrically pumped quantum dots is presented that exhibits unmatched spectral purity and single-photon statistics. Results towards the realization of quantum networks are presented in the following chapters, covering the generation of narrow-band single photons which can efficiently couple to atomic resonances. Photons with a spectral width of less than 3 MHz are created by ultra-bright cavity-enhanced spontaneous parametric down-conversion, and their quantum statistics is studied in detail. A setup for time-bin encoding is demonstrated, capable of imprinting quantum information onto these narrow-band single photons. This thesis concludes with slow-light experiments in atomic ensembles as a model system for atom-photon interaction on the single-photon level. The described experiments demonstrate striking features that make the single photon one of the most remarkable physical systems for the field of quantum information.