Physicists at UC Santa Barbara
have made an important advance in electrically controlling quantum states of
electrons, a step that could help in the development of quantum computing. The
work is published online today on the Science Express Web site.
 | | David Awschalom
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The researchers have demonstrated the ability to electrically manipulate, at
gigahertz rates, the quantum states of electrons trapped on individual defects
in diamond crystals. This could aid in the development of quantum computers
that could use electron spins to perform computations at unprecedented speed.
Using electromagnetic waveguides on diamond-based chips, the researchers were
able to generate magnetic fields large enough to change the quantum state of
an atomic-scale defect in less than one billionth of a second. The microwave
techniques used in the experiment are analogous to those that underlie magnetic
resonance imaging (MRI) technology.
The key achievement in the current work is that it gives a new perspective
on how such resonant manipulation can be performed. "We set out to see
if there is a practical limit to how fast we can manipulate these quantum states
in diamond," said lead author Greg Fuchs, a postdoctoral researcher at
UCSB. "Eventually, we reached the point where the standard assumptions
of magnetic resonance no longer hold, but to our surprise we found that we actually
gained an increase in operation speed by breaking the conventional assumptions."
While these results are unlikely to change MRI technology, they do offer hope
for the nascent field of quantum computing. In this field, individual quantum
states take on the role that transistors perform in classical computing.
"From an information technology standpoint, there is still a lot to learn
about controlling quantum systems," said David Awschalom, principal investigator
and professor of physics, electrical and computer engineering at UCSB. "Still,
it's exciting to stand back and realize that we can already electrically control
the quantum state of just a few atoms at gigahertz rates –– speeds
comparable to what you might find in your computer at home."
The work was performed at UCSB's Center for Spintronics and Quantum Computation,
directed by Awschalom. Co-authors on the paper include David. M. Toyli and F.
Joseph Heremans, both of UCSB. Slava V. Dobrovitski of Ames Laboratory and Iowa
State University contributed to the paper.
Posted November 19th, 2009
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