Theory of Electrons in Solids

University Of California-San Diego, La Jolla CA

Investigators

Abstract

This award supports theoretical research in condensed matter physics. There is always a special fascination in the study of particles on the atomic scale where their motion is governed by quantum theory. In traditional condensed matter physics, the manifestation of the quantum properties is usually as a result of an enormous aggregate of elementary particles such as electrons or phonons. Driven by the steady miniaturization of the electronics components and by the advances in the techniques of making "microscopic" systems, i.e., approaching atomic size, a trend of research emerges where the quantum effects of a few electrons can govern the outcome of the dynamics of a system of size perceptible to humans or their machine surrogates, technically designated as "macroscopic." Such interplay of a nano-system, of size of a few billionths of a meter, of electrons with macroscopic objects forms the central theme of these studies, an exercise akin to the promise of Archimedes to move the earth from one firm spot. The aim of this project is theoretical contribution to construction of fundamental devices in quantum information processing and computation and in spin-enhanced optoelectronics. Research is planned on the theory of the basic physical processes involved in the realization of the quantum algorithms by means of laser manipulation of electrons and their spin degrees of freedom in semiconductor nanostructures. We have shown in theory that a laser beam can be made to produce an excitation which will rotate the spin of a single electron in a quantum dot or to switch on and off an interaction between two electrons in two dots. These quantum operations are the building blocks from which any quantum computation is possible given a sufficient set of these dots with electrons in them. In this research, (1) we seek means to enhance the on-demand interaction between two electrons by examining the effect of a nano-resonance cavity of light; (2) we design laser pulse shapes to accomplish the quantum operations, at the same time alleviating the undesired influence of other elements of the system and of the environment; (3) we theorize how to exhaustively quantify the dance of the two electrons set in motion by the laser in the presence of decoherence effects of the environment. A spin-off of the theory of quantum control of the interaction of two spins is the optical control of an ensemble of spins to create a magnet which could be switched on and off within ten picoseconds (ten trillionth of a second). We investigate the proximity of ferromagnets to a semiconductor heterostructure as means of generation of electron spin alignment and control. These lead to new functions of an electronic device dependent on the spin. The detailed study of the electron spin transport in the semiconductor next to the interface with the ferromagnets yields the basis of the spin device performance. The quantum operations are the basis of a universal, scalable quantum computer based on laser-operated semiconductor nanosystems. Our methods of spin polarization generation and control are the basic elements of spintronics. Both approaches are founded on the strengths of current technology and industry and yet they deviate substantially from current research fashion. They lead directly to proposals of tests of optical control of magnetism; applications to building prototype quantum computers; and designs of spintronics devices with low power demand. This research provides the basis for enabling collaborations to test and implement these ideas with groups of experimental physicists and engineers and benefits from the interaction. Foremost in our goal is the education of a new generation of quantum scientists and engineers. The taming of the nanoworld fires the imagination of the young at all education levels. The interdisciplinary nature of the research gives a broad education. A textbook is being written to disseminate the new emphasis of quantum theory in macro-micro interaction. Work is done through the UCSD California Institute for Telecommunication and Information Technology for contact with industry. %%% This award supports theoretical research in condensed matter physics. There is always a special fascination in the study of particles on the atomic scale where their motion is governed by quantum theory. In traditional condensed matter physics, the manifestation of the quantum properties is usually as a result of an enormous aggregate of elementary particles such as electrons or phonons. Driven by the steady miniaturization of the electronics components and by the advances in the techniques of making "microscopic" systems, i.e., approaching atomic size, a trend of research emerges where the quantum effects of a few electrons can govern the outcome of the dynamics of a system of size perceptible to humans or their machine surrogates, technically designated as "macroscopic." Such interplay of a nano-system, of size of a few billionths of a meter, of electrons with macroscopic objects forms the central theme of these studies, an exercise akin to the promise of Archimedes to move the earth from one firm spot. The aim of this project is theoretical contribution to construction of fundamental devices in quantum information processing and computation and in spin-enhanced optoelectronics (spintronics). The quantum operations are the basis of a universal, scalable quantum computer based on laser-operated semiconductor nanosystems. Our methods of spin polarization generation and control are the basic elements of spintronics. Both approaches are founded on the strengths of current technology and industry and yet they deviate substantially from current research fashion. They lead directly to proposals of tests of optical control of magnetism; applications to building prototype quantum computers; and designs of spintronics devices with low power demand. This research provides the basis for enabling collaborations to test and implement these ideas with groups of experimental physicists and engineers and benefits from the interaction. Foremost in our goal is the education of a new generation of quantum scientists and engineers. The taming of the nanoworld fires the imagination of the young at all education levels. The interdisciplinary nature of the research gives a broad education. A textbook is being written to disseminate the new emphasis of quantum theory in macro-micro interaction. Work is done through the UCSD California Institute for Telecommunication and Information Technology for contact with industry. ***