Experimental Condensed Matter/AMO Physics

Part of Condensed matter/AMO physics

Solid-state 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. Levy uses 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 (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.

Soft Condensed Matter Physics

Goldburg and Wu are heavily engaged in the study of fluid turbulence in two dimensions. This is the area that has been dominated by theory and by computer simulations over many years. As a result of innovative techniques that were developed in Goldburg’s and Wu’s laboratories it has become possible in the last few years to study these phenomena experimentally. Current investigations focus on possible applications of the fluctuation-dissipation theorem to strongly driven systems (Goldburg) and to flow intermittency in a strongly stratified fluid and in a polymer solution (Wu). Wu also has an active biophysics program that focuses on transport in synapses and other topics.

Atomic, Molecular, and Optical Physics

Johnsen, in collaboration with M. Golde of our chemistry department, studies low-energy atomic collisions, in particular dissociative electron-ion recombination. Currently the main emphasis is on quantifying the yields of molecular fragments in radiating states. These physical processes are important for understanding chemical compositions in planetary atmospheres and in astrophysical environments.

Nanoscience

In 2004, the university administration invested in an initiative which has evolved into the Peterson Institute of NanoScience and Engineering (PINSE). A section of the Benedum Hall Engineering Center has been renovated into a clean room for a nanofabrication and characterization facility, which will be available to faculty across Departments of the Schools of Arts and Sciences and of Engineering. PINSE is a joint effort between the two schools, and is being directed by Prof. Hrvoje Petek from Physics and Astronomy and Prof. Hong-Koo Kim from Electrical Engineering. The primary focus of the Clean Room facility in the initial stage will be to establish state-of-the-art facilities for nanofabrication. As the funds become available and the user base grows, PINSE will also acquire equipment and capabilities for nanocharacterization. The major equipment that has been purchased includes a Raith e-beam lithography machine, JEOL transmission electron microscope, and Seiko dual-beam fast ion-beam lithography tool.







Within the Department of Physics and Astronomy, Levy and Petek are actively involved in nanoscience research that is strongly connected to PINSE. Levy’s research on quantum computing requires the fabrication of <10 nm Ge quantum dot arrays on Si substrates, which will form single qubits for optical manipulation of single spins. Petek is using nanolithography capabilities to generate metallic plasmonic nanostructures by patterning Si substrates. He and his group have developed a hybrid technique combining electron microscopy with femtosecond laser excitation, which is capable of imaging of plasmonic excitations in metallic nanostructures with <50 attosecond phase and 50 nm spatial resolution.