BUFFALO, N.Y. -- A novel device, developed by a team led by
University at Buffalo engineers, simply and conveniently traps,
detects and manipulates the single spin of an electron, overcoming
some major obstacles that have prevented progress toward
spintronics and spin-based quantum computing.
Published online this week in Physical Review Letters,
paper brings closer to reality electronic devices based on the
use of single spins and their promise of low-power/high-performance
"The task of manipulating the spin of single electrons is a
hugely daunting technological challenge that has the potential, if
overcome, to open up new paradigms of nanoelectronics," said
Jonathan P. Bird, Ph.D., professor of electrical engineering in the
UB School of Engineering and Applied Sciences and principal
investigator on the project. "In this paper, we demonstrate a novel
approach that allows us to easily trap, manipulate and detect
single-electron spins, in a scheme that has the potential to be
scaled up in the future into dense, integrated circuits."
While several groups have recently reported the trapping of a
single spin, they all have done so using quantum dots, nanoscale
semiconductors that can only demonstrate spin trapping in extremely
cold temperatures, below 1 degree Kelvin.
The cooling of devices or computers to that temperature is not
routinely achievable, Bird said, and it makes systems far more
sensitive to interference.
The UB group, by contrast, has trapped and detected spin at
temperatures of about 20 degrees Kelvin, a level that Bird says
should allow for the development of a viable technology, based on
In addition, the system they developed requires relatively few
logic gates, the components in semiconductors that control electron
flow, making scalability to complex integrated circuits very
The UB researchers achieved success through their innovative use
of quantum point contacts: narrow, nanoscale constrictions that
control the flow of electrical charge between two conducting
regions of a semiconductor.
"It was recently predicted that it should be possible to use
these constrictions to trap single spins," said Bird. "In this
paper, we provide evidence that such trapping can, indeed, be
achieved with quantum point contacts and that it may also be
The system they developed steers the electrical current in a
semiconductor by selectively applying voltage to metallic gates
that are fabricated on its surface.
These gates have a nanoscale gap between them, Bird explained,
and it is in this gap where the quantum point contact forms when
voltage is applied to them.
By varying the voltage applied to the gates, the width of this
constriction can be squeezed continuously, until it eventually
closes completely, he said.
"As we increase the charge on the gates, this begins to close
that gap," explained Bird, "allowing fewer and fewer electrons to
pass through until eventually they all stop going through. As we
squeeze off the channel, just before the gap closes completely, we
can detect the trapping of the last electron in the channel and its
The trapping of spin in that instant is detected as a change in
the electrical current flowing through the other half of the
device, he explained.
"One region of the device is sensitive to what happens in the
other region," he said.
Now that the UB researchers have trapped and detected single
spin, the next step is to work on trapping and detecting two or
more spins that can communicate with each other, a prerequisite for
spintronics and quantum computing.
Co-authors on the paper are Youngsoo Yoon, Ph.D., a UB doctoral
student in electrical engineering; L. Mourokh of Queens College and
the College of Staten Island of the City University of New York; T.
Morimoto, N. Aoki and Y. Ochiai of Chiba University in Japan; and
J. L. Reno of Sandia National Laboratories.
The research was funded by the U.S. Department of Energy. Bird,
who also has received funding from the UB Office of the Vice
President for Research, was recruited to UB with a faculty
recruitment grant from the New York State Office of Science,
Technology and Academic Outreach (NYSTAR).
The University at Buffalo is a premier research-intensive
public university, the largest and most comprehensive campus in the
State University of New York. UB's more than 28,000 students pursue
their academic interests through more than 300 undergraduate,
graduate and professional degree programs. Founded in 1846, the
University at Buffalo is a member of the Association of American