The fundamental concept of quantum coherence plays a central role in quantum physics, cutting across disciplines of quantum optics, atomic and condensed matter physics. Quantum coherence represents a universal property of the quantum s- tems that applies both to light and matter thereby tying together materials and p- nomena. Moreover, the optical coherence can be transferred to the medium through the light-matter interactions. Since the early days of quantum mechanics there has been a desire to control dynamics of quantum systems. The generation and c- trol of quantum coherence in matter by optical means, in particular, represents a viable way to achieve this longstanding goal and semiconductor nanostructures are the most promising candidates for controllable quantum systems. Optical generation and control of coherent light-matter states in semiconductor quantum nanostructures is precisely the scope of the present book. Recently, there has been a great deal of interest in the subject of quantum coh- ence. We are currently witnessing parallel growth of activities in different physical systems that are all built around the central concept of manipulation of quantum coherence. The burgeoning activities in solid-state systems, and semiconductors in particular, have been strongly driven by the unprecedented control of coherence that previously has been demonstrated in quantum optics of atoms and molecules, and is now taking advantage of the remarkable advances in semiconductor fabrication technologies. A recent impetus to exploit the coherent quantum phenomena comes from the emergence of the quantum information paradigm.

Understanding the coherent dynamics of electron spins in quantum dots (QDs) is important for potential applications in solid-state, spin-based electronics and quantum information processing. Here, results are presented focusing on optical initialization, manipulation, and readout of spin coherence in various semiconductor nanostructures. Layered semiconductor nanocrystals are fabricated containing a spherical "quantum shell" in which electrons and holes are confined. As in a planar quantum well, the quantized energy levels and g-factors are found to depend on the shell thickness. Taking this idea a step further, nanocrystals with a concentric, tunnel-coupled core and shell are investigated. Based on the energy and g-factor dependences in these structures, spins can be selectively initialized into, and read out from, states in the core and shell. In contrast to these two ensemble measurements, we next turn to measurements of single electron spins in single QDs. First, we demonstrate the detection of a single electron spin in a QD using a nondestructive, continuously averaged magneto-optical Kerr rotation (KR) measurement. This continuous single QD KR technique is then extended into the time domain using pulsed pump and probe lasers, allowing the observation of the coherent evolution of an electron spin state with nanosecond temporal resolution. By sweeping the delay between the pump and probe, the dynamics of the spin in the QD are mapped out in time, providing a direct measurement of the electron g-factor and spin lifetime. Finally, this time-resolved single spin measurement is used to observe ultrafast coherent manipulation of the spin in the QD using an off-resonant optical pulse. Via the optical Stark effect, this optical pulse coherently rotates the spin state through angles up to pi radians, on picosecond timescales.

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 report progress in calculations of spin coherence and spin transport properties in nanoscale geometries, including calculations of g-factors in quantum dots, exchange interactions in Si/Ge quantum dots, tuning of spin coherence times for electron spin, tuning of dipolar magnetic fields for nuclear spin, spontaneous spin polarization generation and new designs for spin-based teleportation and spin transistors. Our new proposal for electron-spin based teleportation is mediated by single photons and does not require correlated photon detection (Bell detection). We find that electric transport in nonmagnetic semiconductors is unstable to the formation of spin polarized packets at room temperature. We also predict that orbital angular momentum quenching in quantum dots will drive g factors closer to 2 than previously expected. These calculations may be of use in semiconductor spintronic devices or quantum computation.

In recent years, the physics community has experienced a revival of interest in spin effects in solid state systems. On one hand, the solid state systems, particularly, semiconductors and semiconductor nanosystems, allow us to perform benchtop studies of quantum and relativistic phenomena. On the other hand, this interest is supported by the prospects of realizing spin-based electronics, where the electron or nuclear spins may play a role of quantum or classical information carriers. This book looks in detail at the physics of interacting systems of electron and nuclear spins in semiconductors, with particular emphasis on low-dimensional structures. These two spin systems naturally appear in practically all widespread semiconductor compounds. The hyperfine interaction of the charge carriers and nuclear spins is particularly prominent in nanosystems due to the localization of the charge carriers, and gives rise to spin exchange between these two systems and a whole range of beautiful and complex physics of manybody and nonlinear systems. As a result, understanding of the intertwined spin systems of electrons and nuclei is crucial for in-depth studying and controlling the spin phenomena in semiconductors. The book addresses a number of the most prominent effects taking place in semiconductor nanosystems including hyperfine interaction, nuclear magnetic resonance, dynamical nuclear polarization, spin-Faraday and spin-Kerr effects, processes of electron spin decoherence and relaxation, effects of electron spin precession mode-locking and frequency focussing, as well as fluctuations of electron and nuclear spins.

The past few decades of research and development in solid-state semicon ductor physics and electronics have witnessed a rapid growth in the drive to exploit quantum mechanics in the design and function of semiconductor devices. This has been fueled for instance by the remarkable advances in our ability to fabricate nanostructures such as quantum wells, quantum wires and quantum dots. Despite this contemporary focus on semiconductor "quantum devices," a principal quantum mechanical aspect of the electron - its spin has it accounts for an added quan largely been ignored (except in as much as tum mechanical degeneracy). In recent years, however, a new paradigm of electronics based on the spin degree of freedom of the electron has begun to emerge. This field of semiconductor "spintronics" (spin transport electron ics or spin-based electronics) places electron spin rather than charge at the very center of interest. The underlying basis for this new electronics is the intimate connection between the charge and spin degrees of freedom of the electron via the Pauli principle. A crucial implication of this relationship is that spin effects can often be accessed through the orbital properties of the electron in the solid state. Examples for this are optical measurements of the spin state based on the Faraday effect and spin-dependent transport measure ments such as giant magneto-resistance (GMR). In this manner, information can be encoded in not only the electron's charge but also in its spin state, i. e.