July 28, 2011 — Purdue University researchers have created an ultrapure gallium arsenide (GaAs) semiconductor crystals that capture new states of matter, with potential applications in future high-speed quantum computing.
In the ultrapure semiconductor GaAs, electrons do not follow single-particle physics laws, and are governed by mutual interactions. This provides insights into fundamental physics, said Michael Manfra, the William F. and Patty J. Miller Associate Professor of Physics who leads the group at Purdue, noting that the exotic states are "beyond" standard solid-state physics models, and are non-existant in standard materials.
Manfra and his research team designed and built a high-mobility gallium-arsenide molecular beam epitaxy (MBE) system at Purdue’s Birck Nanotechnology Center. The MBE tool makes ultrapure semiconductor materials with atomic-layer precision, creating a perfectly aligned lattice of gallium and arsenic atoms that can capture electrons on a two-dimensional plane, preventing vertical motion and limiting planar movement.
When the electrons are captured in these "microscopic wells," they can interact only with each other," he said. Purity is important; impurities scatter electrons.
Once the desired material is fabricated, electrons must be cooled to extremely low temperatures. Gabor Csathy, an assistant professor of physics, cooled the material and electrons to 5millikelvin (close to absolute zero). Cooled electrons become "aware" of neighboring electrons, enabling "collective motion," explained Csathy.A magnetic field is applied, creating conditions that lead to the "correlated state."
The work, which is in very early stages, could eventually lead to viable quantum computing materials, Manfra added. As the electrons interact, they rearrange to acheive minimum energy level and eventually form new ground states, he said.
Csathy, who specializes in quantum transport in semiconductors, takes the electron measurements. Semiconductor quality is measured in electron mobility (centimeters squared per volt-second). The group achieved an electron mobility measurement of 22 million centimeters squared per volt-second, among the top in the world, he said.
Manfra and Csathy presented their work at Microsoft’s Station Q summer meeting on June 17 at the University of California at Santa Barbara (UC Santa Barbara). This meeting, sponsored by Microsoft Research, brings together leading researchers to discuss novel approaches to quantum computing. They also received a $700,000 grant from the Department of Energy based on their preliminary results.
In addition to Manfra and Csathy, the research team includes associate professors of physics Leonid Rokhinson and Yuli Lyanda-Geller; professor of physics Gabriele Giuliani; graduate students John Watson, Nodar Samkharadze, Nianpei Deng and Sumit Mondal; and research engineer Geoff Gardner.