Boston University's World's Fastest Moving Nanostructure
Nanomechanical device bridges classic and quantum physics
February 09, 2005
Nanotechnology leapt into the realm of quantum mechanics this past winter
when an antenna-like sliver of silicon one-tenth the width of a human hair
oscillated in a lab in a Boston University basement. With two sets of
protrusions, much like the teeth from a two-sided comb or the paddles from a
rowing shell, the antenna not only exhibits the first quantum nanomechanical
motion but is also the world's fastest moving nanostructure.
A team of Boston University physicists led by Assistant Professor Pritiraj
Mohanty developed the nanomechanical oscillator. Operating at gigahertz
speeds, the technology could help further miniaturize wireless communication
devices like cell phones, which exchange information at gigahertz
frequencies. But, more important to the researchers, the oscillator lies at
the cusp of classic physics, what people experience everyday, and quantum
physics, the behavior of the molecular world.
Comprised of 50 billion atoms, the antenna built by Mohanty's team is so far
the largest structure to display quantum mechanical movements.
"It's a truly macroscopic quantum system," says Alexei Gaidarzhy, the paper's
lead author and a graduate student in the BU College of Engineering's
Department of Aerospace and Mechanical Engineering. The device is also the
fastest of its kind, oscillating at 1.49 gigahertz, or 1.49 billion times a
second, breaking the previous record of 1.02 gigahertz achieved by a
nanomachine produced by another group.
According to Gaidarzhy, during the past several decades engineers have made
phenomenal advances in information technology by shrinking electronic
circuitry and devices to fit onto semiconductor chips. Shrinking electronic
or mechanical systems further, he says, will inevitably require new
paradigms involving quantum theory. For example, these mechanical/quantum
mechanical hybrids could be used for quantum computing.
Because Mohanty's nanomechanical oscillator is "large," the research team
was able to attach electrical wiring to its surface in order to monitor tiny
discrete quantum motion, behavior that exists in the realm of atoms and
At a certain frequency, the paddles begin to vibrate in concert, causing the
central beam to move at that same high frequency, but at an increased and
easily measured amplitude. Where each paddle moves only about a femtometer,
roughly the diameter of an atom's nucleus, the antenna moves over a distance
of one-tenth of a picometer, a tiny distance that still translates to a
100-fold increase in amplitude.
When fabricating and testing the nanomechanical device, the researchers
placed the entire apparatus, including the cryostat and monitoring devices,
in a state-of-the-art, copper-walled, copper-floored room. This set-up
shielded the experiment from unwanted vibration noise and electromagnetic
radiation that could generate from outside electrical devices, such as cell
phone signals, or even the movement of subway trains outside the building.
Even with these precautions, performing such novel experiments is tricky.
"When it's a new phenomenon, it's best not to be guided by expectations
based on conventional wisdom," says Gaidarzhy. "The philosophy here is to
let the data speak for itself."
The group carries out the experiments under extremely cold conditions, at a
temperature of 110 millikelvin, which is only a tenth of a degree above the
absolute zero. When cooled to such a low temperature, the nanomechanical
oscillator starts to jump between two discrete positions without occupying
the physical space in between, a telltale sign of quantum behavior.
In addition to Gaidarzhy, Mohanty's team consists of Guiti Zolfagharkhani, a
graduate student, and Robert L. Badzey, a post-doctoral fellow in BU's
Physics Department. Their paper appears in the January 28, 2005 issue of
Physical Review Letters. The research was supported by grants from the
National Science Foundation, U.S. Department of Defense, the American
Chemical Society's Petroleum Research Fund, and the Sloan Foundation.
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