June 12, 2002 (7)
Quantum computing with individual atoms
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Michigan Ion Trap |
ANN ARBOR---Researchers at the University of Michigan's
Center for Optical Coherent
and Ultrafast Science (FOCUS) and Department
of Physics have reported the first demonstration of laser-cooling
of individual trapped atoms of different species. This may be an important
step in the construction of a future "quantum computer," in
which quantum superpositions of inputs are processed simultaneously in
a single device. Trapped atoms offer one of the only realistic approaches
to precisely controlling the complex quantum systems underlying a quantum
computer.The demonstration is described in the April 2002
issue of Physical Review in an article, "Sympathetic Cooling of Trapped
Cd+ Isotopes," by Boris B. Blinov, Louis Deslauriers, Patricia Lee,
Martin J. Madsen, Russ Miller, and Christopher Monroe. Partially based
on these results, Monroe has proposed a new "Architecture for a Large-Scale
Ion-Trap Quantum Computer," with co-authors David Kielpinski (MIT)
and David Wineland (National Institute of Standards and Technology), in
the June 13 issue of the journal Nature.
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Scalable Ion Trap Computer |
Interest in quantum computing has mushroomed in
the last decade as its potential for efficiently solving difficult computing
tasks, like factoring large numbers and searching large databases, has
become evident. Encryption and its obverse, codebreaking, are just two
of the applications envisioned for quantum computing if and when it becomes
a practical technology. Quantum computation has captured the imagination
of the scientific community, recasting some of the most puzzling aspects
of quantum physicsonce pondered by Einstein, Schroedinger and others
in the context of advancing computer science. "Right now, there's
a lot of black magic involved in understanding what makes a quantum computer
tick and how to actually build one," Monroe said. "Many physicists
doubt we'll ever be able to do it, but I'm an optimist. We may not get
there for decades, but given enough time and resources - and failing unexpected
roadblocks like the failure of quantum mechanics - we should be able to
design and build a useable quantum computer. It's a risky business, but
the potential payoff is huge."
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Target Quantum bits entangled |
In their experiment, the Michigan researchers
used electric fields to confine a crystal of exactly two Cd+ atoms of
different isotopes. They were able to cool the single 112Cd+ atom to a
chilly 0.001 degree Celsius above absolute zero through direct laser cooling
of the neighboring 114Cd+ atom. Laser cooling of this "refrigerator
atom" removes unwanted motion in the atom crystal without affecting
the internal state of the other atom. This is an important step toward
scaling a trapped atom computer, where "qubits" of information
are stored in the quantum states within the individual atoms.
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The architecture proposed in the Nature article
describes a "quantum charge-coupled device" (QCCD) consisting
of a large number of interconnected atom traps. A combination of radiofrequency
(RF) and quasistatic electric fields can be used to change the operating
voltages of these traps, confining a few charged atoms in each trap or
shuttling them from trap to trap, and the traps can be combined to form
complex structures. The cooling of multiple species demonstrated at Michigan
is a key component of this broader proposal."This is a realistic architecture for quantum
computation that is scalable to large numbers of qubits," the authors conclude. "In contrast to other proposals, all quantum state manipulations
necessary for our scheme have already been experimentally tested with
small numbers of atoms, and the scaling up to large numbers of qubits
looks straightforward."
For more information, contact Christopher Monroe, (734) 615-9625, crmonroe@umich.edu.
To learn more about FOCUS, visit http://www.umich.edu/~focuspfc/.
Contact: Judy Steeh
Phone: (734) 647-3099
E-mail: jsteeh@umich.edu
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