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Fermions and quantum computing

  1. Apr 9, 2005 #1
    Dear Folks:

    This is another example of convergence, which I' m always on the look out for. This may not be your interest, but please send it to any chemist you know.


    Erich J. Knight
    Shenandoah Gardens
    E-mail: shengar@aol.com
    (540) 289-9750

    Forwarded Message:
    Subj: [nanotech] fyi: fermions and quantum computing
    Date: 4/7/2005 4:50:08 PM Eastern Daylight Time
    From: lifestation2004@yahoo.co.uk
    Reply-to: nanotech@yahoogroups.com
    To: nanotech@yahoogroups.com
    Sent from the Internet (Details)

    Feat of experimental acrobatics leads to first synthesis of ultracold molecules

    University of Chicago 04.04.2005

    Feat of experimental acrobatics leads to first synthesis of ultracold
    Achievement could benefit fields of superchemistry, quantum computing

    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

    The experiments--conducted 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 2004.

    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.

    Cornell, Ketterle 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.

    "Atoms themselves 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
    Fahrenheit)--in solids.

    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," Chin said.

    Approximately two 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 the atoms.

    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.

    "Since 2003, 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," Chin said.

    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 computations.

    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.

    More information: www.uchicago.edu"

  2. jcsd
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