Researchers at the University of Pittsburgh have
developed a way to create semiconductor islands smaller
than 10 nanometers in scale, known as quantum dots.
The islands, made from germanium and placed on the
surface of silicon with two-nanometer precision,
are capable of confining single electrons.
"We believe this development moves us closer to
our goal of constructing a quantum computer," said
Jeremy Levy, Pitt professor of physics and astronomy
and director of the Pittsburgh-based Center for Oxide-Semiconductor
Materials for Quantum Computation. Levy and colleagues
reported on the advance in a paper published in October
2005 in the journal Applied Physics Letters.
computers do not yet exist, but it is known that
they can bypass all known encryption schemes used
today on the Internet. Quantum computers also are
capable of efficiently solving the most important
equation in quantum physics: the Schrödinger
equation, which describes the time-dependence of
quantum mechanical systems. Hence, if quantum computers
can be built, they likely will have as large an impact
on technology as the transistor.
have a property known as "spin," which
can take one of two directions--clockwise and counter-clockwise.
Because of their quantum-mechanical nature, electrons
can spin in both directions at once. That bizarre
property allows the spin to be used as a "quantum
bit" in a quantum computer. The ability to confine
individual electrons, as opposed to "puddles" of
electrons used in conventional computer technology,
is essential for the working of a quantum computer.
next step, said Levy, is to perform electronic
and optical measurements on these materials to
prove that there is indeed one electron on each
quantum dot and to probe the coupling between the
spins of neighbor electrons. "We can do that now because we
have this control over the spacing and the size," he
results achieved by Levy and colleagues are an
example of "essentially nano" research, which
involves manipulating properties at the smallest
scales--from one to 20 nanometers.
Pitt has invested heavily in nanoscale research,
beginning with the establishment of its Institute
for NanoScience and Engineering (INSE), and continuing
with the NanoScale Fabrication and Characterization
Facility, which contains core technology such as
electron-beam lithography, transmission electron
microscopes, and a state-of-the-art cleanroom environment.
The INSE is an integrated, multidisciplinary organization
that brings coherence to the University's research
efforts and resources in the fields of nanoscale
science and engineering. For more information, visit www.nano.pitt.edu .
Other researchers on the study were John T. Yates
Jr., R.K. Mellon Professor of Chemistry and Physics
at Pitt; former Pitt chemistry graduate student Olivier
Guise; Joachim Ahner of Pittsburgh-based Seagate
Technology; and Venugopalan Vaithyanathan and Darrell
G. Schlom of Pennsylvania State University.
This research was supported by the Defense Advanced
Research Projects Agency's Quantum Information Science
and Technology Program.