— A research team that in 2003 created an exotic new
form of matter has now shown for the first time how
to arrange that matter into complex molecules.
by Cheng Chin, now at the University of Chicago, and
his colleagues under the leadership of Rudolf Grimm
at Innsbruck University in Austria-may lead to a better
scientific understanding of superconductivity and
advance a growing new field called superchemistry.
In the long term, they may also provide a strategy
that could aid the development of quantum computers.
"In this field,
it's hard to predict what's going to happen, because
none of this was possible before 2003," said
Chin, an Assistant Professor in Physics. Chin, Grimm
and five colleagues will report their findings in
a future issue of journal Physical Review Letters.
The new form of matter
that the Innsbruck University team produced in 2003
is called a Fermion superfluid, which exists only
at temperatures hundreds of degrees below zero. Superfluids
exhibit characteristics distinctively different from
the solids, liquids and gases that dominate everyday
life. Most notably, superfluids can flow ceaselessly
without any energy loss whatsoever. Science magazine
named this work one of the top 10 breakthroughs of
In creating the Fermion
superfluid, the team extended the work that earned
the Nobel Prize in Physics for Eric Cornell, Wolfgang
Ketterle and Carl Wieman in 2001. Those scientists
had succeeded in creating the first Bose-Einstein
condensate. Building on the work of Satyendra Nath
Bose, Albert Einstein predicted in the 1920s that
a special state of matter would form when a group
of atoms collapsed into their lowest energy state.
In this state now named for them, all of the atoms
behave as if they are all one giant atom.
and Wieman created their Bose-Einstein condensate
out of bosons, one of the two major categories of
subatomic particles. Bosons carry force, while the
other category of particles, fermions, comprise matter.
Chin and the Innsbruck team showed in 2003 that, with
some difficulty, fermions-in this case, lithium atoms-also
can be coaxed into a Bose-Einstein condensate.
cannot become condensed. They are not bosons,"
Chin said. "But once they are paired they become
bosons, and you can go to this superfluid state."
The laws of quantum
mechanics forbid fermions from condensing. Chin and
his colleagues used a technique called Feshbach resonance
to bind two atoms into a simple molecule that behaves
like a boson. The process is carried out in a magnetic
field and resembles the type of electron pairing that
causes superconductivity-the unimpeded flow of electricity
at temperatures near absolute zero (minus 459.6 degrees
This type of electron
pairing is called Cooper pairing. Cooper pairings
are the long-distance marriages of the subatomic world,
where electrons are bonded at distances far greater
than usual. "We have discovered a handle to adjust
the interactions between atoms and between molecules,
which allows us to synthesize complex quantum objects,"
years ago, the Innsbruck scientists found a deep and
unexpected connection between Bose-Einstein condensates
and the bonding of Cooper pairs. They learned that
they could use a pair of atoms to
simulate the electrons of a Cooper pair. And more
importantly, they could control the interactions of
In their latest achievement,
Chin and his colleagues have learned how to use Feshbach
resonance as the control that binds the simple molecules
made of cesium atoms into even larger clusters at
temperatures near absolute zero.
the controlled synthesis of simple molecules made
of two atoms has opened up new frontiers in the field
of ultracold quantum gases," said Rudolf Grimm,
a professor of experimental physics at Innsbruck University
and a co-author of the Letters article. Their present
work now shows that ultracold simple molecules can
be merged to form more complex objects consisting
of four atoms, he said.
An important feature
of this synthesis process is its tenability, Chin
said. "In a magnetic field you can experimentally
adjust it to any value, so we can control the process."
The synthesis of ultracold
molecules is so new, it is difficult to predict potential
applications, Chin said. But it puts a new field called
superchemistry on a firm experimental footing. In
superchemistry, scientists are able to precisely control
the pairings and interactions of the atoms and molecules
in Bose-Einstein condensates.
"We are physicists,
but now our field's starting to overlap with chemistry,"
As ultracold molecules
are synthesized into complex quantum objects, phenomena
hidden at the subatomic scale will now become visible
almost to the naked eye. "These objects may open
up completely new possibilities to study the rich
quantum physics of few-body objects, including chemical
reactions in the quantum world," Grimm said.
Control of quantum
objects may ultimately lead to the realization of
a quantum computer, Chin said. Although possibly still
decades from fruition, a quantum computer would work
much faster than today's computers. The idea would
be to use atoms in ultracold gas as bits, the basic
units of information storage on a computer, with Feshbach
resonance controlling their interactions to perform
Chin now is setting
up his laboratory at the University of Chicago and
plans to continue studying quantum manipulation and
computation based on cold atoms and molecules in collaboration
with Grimm's Innsbruck team.
"Based on the
speed of progress in this field, I think there probably
will be more surprises," Chin said.