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[YOUR NAME HERE] thought you might be interested in this story from the University of Rochester.
MEDIA CONTACT: Tom Rickey, (585) 275-7954, or Marc Feldman, (585) 275-3799
October 18, 1994
Engineers Observe "Heartbeat" of Superconductors
Engineers have observed for the first time the movement of
the smallest packet of magnetic charge possible in a
superconductor, a find that makes it possible to measure the
"heartbeat" of a new type of ultrafast superconducting
University of Rochester engineers will report their
observation of a single flux quantum (SFQ) pulse at the Applied
Superconductivity Conference in Boston October 18.
"A single flux quantum pulse is something we've all known is
there, but no one until now has observed it directly because it's
so fast and the signal is so faint," says Thomas Hsiang,
professor of electrical engineering. "It's very exciting." His
team was able to pluck out single SFQ pulses from the 50 billion
that flow through a circuit during the blink of an eye.
SFQ pulses are at the heart of a new type of ultrafast
electronics that engineers around the country are creating. The
signals move so fast, in fact, that engineers have a difficult
time finding ways to test the new circuitry. But detecting and
tracing these bundles of magnetism is key for engineers trying to
build complex superconducting circuits.
"How can you test a circuit if it's faster than any
equipment you can buy?" asks Professor Marc Feldman. "All you
know is that either it works, or it doesn't. Now we have a non-
invasive way to check for SFQ signals."
Feldman is head of a Rochester team that is using SFQs as
the "information bit" in a new kind of logic circuit where
engineers shuttle about tiny bundles of magnetism to perform
computations. Even though the circuitry is based on single pulses
of magnetism, up to now no one has been able to observe them
The work is part of a five-year Rochester effort to build a
large digital filter using superconducting circuitry. Engineers
hope to build thousands of logic elements and put them together
to show that this new kind of logic can work up to 100 times
faster than today's fastest semiconductor circuits. This project
and a similar effort underway at the State University of New York
at Stony Brook are funded by the Department of Defense through
the University Research Initiative (URI) program. Researchers at
several companies and national laboratories are building SFQ
circuits as well.
"You can think of a single flux quantum pulse as a
fundamental particle that cannot be broken down into anything
smaller," says Feldman. "It's like the atom: We've all known that
atoms were there, but it's only been recently that we've been
able to observe them directly, with a scanning tunneling
microscope." While inert single flux quanta have been observed
before, none has ever been seen "on the fly," says Feldman.
To observe the SFQ pulses, scientists had to develop a
system to detect very faint signals very quickly. Hsiang and his
graduate students used an ultrafast laser to trigger an
electrical pulse that was converted by superconducting circuitry
into an SFQ pulse. Then they used an optoelectronic crystal as a
sort of "listening device" to detect slight changes as the pulse
traveled down a micro transmission line, and they used another
laser beam to detect changes in the crystal. All this was done
inside a cryogenic system at a temperature of just 1.8 degrees
above absolute 0.
"It's like shaking a rope at one end and then trying to
detect the pulse at the other," says Feldman. "But SFQ pulses are
much more rapid and much weaker."
When a flux quantum moves, it causes a very tiny change in
voltage. It is this tiny voltage pulse -- one millivolt lasting
just two picoseconds (one picosecond is one-millionth of one-
millionth of one second) -- that engineers saw. Hsiang says that
while he and others have detected faster electrical signals, no
one has ever been able to observe such a weak short-lived signal.
"An added significance is that this could be the beginning
of a new concept of optoelectronics, where we can combine both
optics and superconducting electronics into a single ultrafast
system," says Hsiang.
Working on the SFQ pulse detection project, besides Feldman
and Hsiang, are faculty member Roman Sobolewski and graduate
students Marc Currie, Chia-Chi Wang, and Douglas Jacobs-Perkins,
all in the Department of Electrical Engineering. Much of the work
was done in the University's new Center for Optoelectronics and
Imaging and the Laboratory for Laser Energetics.
About the University of Rochester
The University of Rochester (www.rochester.edu) is one of the nation's leading private universities. Located in Rochester, N.Y., the University gives students exceptional opportunities for interdisciplinary study and close collaboration with faculty through its unique cluster-based curriculum. Its College of Arts, Sciences, and Engineering is complemented by the Eastman School of Music, Simon School of Business, Warner School of Education, Laboratory for Laser Energetics, Schools of Medicine and Nursing, and the Memorial Art Gallery.