News Article
Physicists Tweak Quantum Force
Research
at the University of Florida has physicists tweak quantum force
reducing the barrier to tiny devices.
Cymbals don't clash of their own
accord, in our world anyway. But the quantum world is bizarrely
different. Two metal plates, placed almost infinitesimally close
together, spontaneously attract each other.
What seems like magic is known as the
Casimir force, and it has been well documented in experiments. The
cause goes to the heart of quantum physics: Seemingly empty space is
not actually empty but contains virtual particles associated with
fluctuating electromagnetic fields. These particles push the plates
from both the inside and the outside. However, only virtual particles
of shorter wavelengths, in the quantum world, particles exist
simultaneously as waves, can fit into the space between the plates,
so that the outward pressure is slightly smaller than the inward
pressure. As a result the plates are forced together.
Now, University of Florida physicists
have found they can reduce the Casimir force by altering the surface
of the plates. The discovery could prove useful as tiny micro electro
mechanical systems (MEMS) devices that are already used in a wide
array of consumer products, become so small they are affected by
quantum forces.
“We are not talking about an
immediate application,” says Ho Bun Chan, an assistant professor of
physics and the first author of a paper on the findings that appears
in the on line edition of the journal Physical Review Letters. “We
are talking about, if the devices continue to be smaller and smaller,
as the trend of miniaturisation occurs, then the quantum effects
could come into play.”
More specifically, the finding could
one day help reduce what MEMS engineers call “stiction”, when two
very small, very close objects tend to stick together.
Although stiction has many causes,
including, for example, the presence of water molecules that tend to
clump together, the Casimir force can contribute. Such quantum
effects could prove important as the separations between components
in tiny machinery shrink from micrometer, or millionths of a metre,
toward nanometre size, Chan said.
“A lot of people are thinking of ways
to reduce stiction, and this research opens up one possibility,” he
said.
Dutch physicist Hendrik Casimir first
predicted that two closely spaced metal plates would be mutually
attracted in 1948. It took several decades, but in 1996, physicist
Steve Lamoreaux, then at the University of Washington, performed the
first accurate measurement of the Casimir force using a torsional
pendulum, an instrument for measuring very weak forces.
Subsequently, in a paper published in
Science in 2001, Chan and other members of a Bell Labs team reported
tapping the Casimir force to move a tiny metal see saw. The
researchers suspended a metal sphere an extremely tiny but well
controlled distance above the see saw to “push” it up and down.
It was the first demonstration of the Casimir force affecting a
micromechanical device.
In the latest research, the physicists
radically altered the shape of the metal plates, corrugating them
into evenly spaced trenches so that they resembled a kind of three
dimensional comb. They then compared the Casimir forces generated by
these corrugated objects with those generated by standard plates, all
also against a metal sphere.
The result: “The force is smaller for
the corrugated object but not as small as we anticipated,” Chan
said, adding that if corrugating the metal reduced its total area by
half, the Casimir force was reduced by only 30 to 40 percent.
Chan said the experiment shows that it
is not possible to simply add the force on the constituent solid
parts of the plate, in this case, the tines, to arrive at the total
force. Rather, he said, “the force actually depends on the geometry
of the object.”
“Until now, no significant or non
trivial corrections to the Casimir force due to boundary conditions
have been observed experimentally,” wrote Lamoreaux, now at Yale
University, in a commentary accompanying publication of the paper.
Besides Chan, the other authors of the
paper are UF doctoral students Yiliang Bao and Jie Zou, and Bell Labs
scientists Raymond Cirelli, Fred Klemens, William Mansfield and
Chien-Shing Pai. The research was funded by the U.S. Department of
Energy.
accord, in our world anyway. But the quantum world is bizarrely
different. Two metal plates, placed almost infinitesimally close
together, spontaneously attract each other.
What seems like magic is known as the
Casimir force, and it has been well documented in experiments. The
cause goes to the heart of quantum physics: Seemingly empty space is
not actually empty but contains virtual particles associated with
fluctuating electromagnetic fields. These particles push the plates
from both the inside and the outside. However, only virtual particles
of shorter wavelengths, in the quantum world, particles exist
simultaneously as waves, can fit into the space between the plates,
so that the outward pressure is slightly smaller than the inward
pressure. As a result the plates are forced together.
Now, University of Florida physicists
have found they can reduce the Casimir force by altering the surface
of the plates. The discovery could prove useful as tiny micro electro
mechanical systems (MEMS) devices that are already used in a wide
array of consumer products, become so small they are affected by
quantum forces.
“We are not talking about an
immediate application,” says Ho Bun Chan, an assistant professor of
physics and the first author of a paper on the findings that appears
in the on line edition of the journal Physical Review Letters. “We
are talking about, if the devices continue to be smaller and smaller,
as the trend of miniaturisation occurs, then the quantum effects
could come into play.”
More specifically, the finding could
one day help reduce what MEMS engineers call “stiction”, when two
very small, very close objects tend to stick together.
Although stiction has many causes,
including, for example, the presence of water molecules that tend to
clump together, the Casimir force can contribute. Such quantum
effects could prove important as the separations between components
in tiny machinery shrink from micrometer, or millionths of a metre,
toward nanometre size, Chan said.
“A lot of people are thinking of ways
to reduce stiction, and this research opens up one possibility,” he
said.
Dutch physicist Hendrik Casimir first
predicted that two closely spaced metal plates would be mutually
attracted in 1948. It took several decades, but in 1996, physicist
Steve Lamoreaux, then at the University of Washington, performed the
first accurate measurement of the Casimir force using a torsional
pendulum, an instrument for measuring very weak forces.
Subsequently, in a paper published in
Science in 2001, Chan and other members of a Bell Labs team reported
tapping the Casimir force to move a tiny metal see saw. The
researchers suspended a metal sphere an extremely tiny but well
controlled distance above the see saw to “push” it up and down.
It was the first demonstration of the Casimir force affecting a
micromechanical device.
In the latest research, the physicists
radically altered the shape of the metal plates, corrugating them
into evenly spaced trenches so that they resembled a kind of three
dimensional comb. They then compared the Casimir forces generated by
these corrugated objects with those generated by standard plates, all
also against a metal sphere.
The result: “The force is smaller for
the corrugated object but not as small as we anticipated,” Chan
said, adding that if corrugating the metal reduced its total area by
half, the Casimir force was reduced by only 30 to 40 percent.
Chan said the experiment shows that it
is not possible to simply add the force on the constituent solid
parts of the plate, in this case, the tines, to arrive at the total
force. Rather, he said, “the force actually depends on the geometry
of the object.”
“Until now, no significant or non
trivial corrections to the Casimir force due to boundary conditions
have been observed experimentally,” wrote Lamoreaux, now at Yale
University, in a commentary accompanying publication of the paper.
Besides Chan, the other authors of the
paper are UF doctoral students Yiliang Bao and Jie Zou, and Bell Labs
scientists Raymond Cirelli, Fred Klemens, William Mansfield and
Chien-Shing Pai. The research was funded by the U.S. Department of
Energy.
