-- 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
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 molecules.
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
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, Department of Defense, Petroleum
Research Fund, and the Sloan Foundation.
Boston University's Physics Department, part of its
College and Graduate School of Arts and Sciences,
provides research opportunities in areas such as nanoscience,
experimental high-energy physics and astrophysics,
molecular biophysics, theoretical condensed-matter
physics, and polymer physics. Research in the Department
of Aerospace and Mechanical Engineering includes robotics,
MEMS, and nanotechnology.
Boston University, with an
enrollment of more than 29,000 in its 17 schools and
colleges, is the fourth largest independent university
in the United States.