Solid–state Physics

Part of Experimental Condensed Matter/AMO Physics

Solid-state implementations of quantum computation: Quantum Information (QI) is an emerging field that has united efforts (both experimental and theoretical) from a wide variety of traditional areas in physics. For experimentalists the overarching goal in this field is to create, evolve and measure quantum states in a variety of physical systems; for theorists, a long-range goal is to understand the interrelationships between quantum mechanics, information, communication and computation. QI is interdisciplinary, drawing researchers from other disciplines such as computer science, chemistry and electrical engineering, but it remains deeply rooted in physics. Quantum computers may eventually find use in a variety of disciplines, both within and beyond physics, if for no other reason than their ability to efficiently solve the Schrödinger equation. Quantum computers themselves are far from being realized, but the goals for quantum computation are well-aligned with many other scientific goals that people have been pursuing for decades. Over the last fifteen years or so, researchers with prominence in magnetic resonance, quantum optics, AMO, semiconductor nanostructures, superconducting electronics, nanomechanics, and other areas have jump-shifted into QI. Quantum information processing is the inexorable consequence of increased control over any quantum-mechanical system. Our department has several faculty members working in the area of quantum information.



Over the last five years, Levy has served as director of the Center for Oxide-Semiconductor Materials for Quantum Computation (COSMQC). This center links research carried out at Pitt and a number of other institutions. The goal has been to develop quantum bits using the spin of electrons localized on Ge quantum dots. The research is strongly interdisciplinary and strongly connected with nanotechnology. Heberle’s work is also focused on quantum information research, using excitonic states in quantum dots to form qubits. Both Levy and Heberle use advanced femtosecond optical techniques to prepare, control, and analyze quantum states in semiconductors.



Petek and Snoke work in experimental areas closely related to quantum information; both are interested in creating and detecting highly coherent quantum states. Snoke is attempting to achieve Bose condensation of excitons in semiconductor quantum well structures. Petek has been using sub-10-fs laser pulses to create coherent phonons in silicon, and to create and measure localized plasmons in patterned silver nanostructures.



Theoretical research in quantum information is carried out by Gerjuoy, Levy, and Tabakin. Gerjuoy works on issues related to entanglement between two-level and d-level quantum systems, and has also written a definitive review of Shor’s algorithm. Tabakin has developed a comprehensive software package that allows researchers to simulate quantum algorithms within the density operator formalism. Levy has worked on methods for encoding quantum information in spin systems. Liu is interested in quantum phase transitions in cold atomic gases and in condensed matter systems.



Educational activities surrounding quantum information include a weekly seminar that has been organized in collaboration with R. Griffiths at CMU, a course offered by Griffiths at CMU on quantum computation, and quantum computing tutorials developed by C. Singh.



Ultrafast Processes in Solid-state Materials: We have assembled a strong team of experts in this area (Heberle, Petek, and Snoke) to tackle important fundamental problems in solid-state physics, such as non-equilibrium dynamics of charge carriers in metals and Bose-Einstein condensations in semiconductors. These phenomena are characterized by strong interactions between charge carriers and the underlying lattices. Investigations of quantum coherence are an important part of this research. To make such investigations feasible, several new techniques have been devised. For instance, Petek has developed a powerful (time-resolved) 2-photon photoemission spectroscopic technique to investigate fast relaxation processes in metals. The technique allows him to study the processes that induce decoherence between electron and hole pairs. Likewise, Snoke has developed ingenious means, such as controlled stress fields in one case and 2D quantum wells in the other, to confine laser-generated excitons. The hope is that, with a sufficiently high density of excitons, a long-lasting condensate may result. There are also many interesting ideas of advancing the technology of fast optics, such as using semiconductor nanostructures as fast optical switches (Snoke), and laser controlled atomic motions on surfaces (Petek).



Wide-bandgap semiconductors: This is a class of materials that have the potential of producing robust and highly efficient light sources, such as LEDs and lasers. In their semiconductor optics laboratory, Choyke and Devaty have focused in recent years on fabricating and studying porous SiC and GaN. Optical techniques are used to characterize bulk materials as well as the effects of various impurities and surface states. Novel device applications are also sought.