Scientists
at the National Institute
of Standards and Technology, Massachusetts Institute
of Technology and the University of Michigan have taken
a significant step toward the development of a quantum computer.
In a paper to be published in Nature magazine on
June 13, 2002, the authors propose a design for a quantum
computer based on a large number of interconnected ion traps
using techniques already demonstrated on a smaller scale.
A quantum
computer makes use of the properties of quantum systems
rather than transistors for performing calculations or storing
information. A computer transistor can be only in one of
two states (on or off) at one time, representing either
a 1 or a 0. Atoms or molecules in a quantum computer can
be manipulated to be in several different states simultaneously,
meaning they can process exponentially more information
than a traditional computer. Quantum computers could factor
very large numbers, perform cryptography, and aid science
in big projects such as modeling the world's weather.
NIST
has been a leader in the development of electro-magnetic
traps where ions can be stored, observed and manipulated.
Previous research papers have suggested that a quantum computer
could be developed by manipulating a large number of ions
in a single trap. "However, manipulating a large number
of ions in a single trap presents immense technical difficulties,
and scaling arguments suggest that this scheme is limited
to computations on tens of ions," the NIST/MIT/University
of Michigan team reports.
To build
a large-scale quantum computer, the team suggests instead
an architecture consisting of a large number of small, interconnected
ion traps. By changing the operating voltages in these traps
they can confine a few ions in each trap or
shuttle them from trap to trap. "In any particular
trap, we can manipulate a few ions using the methods already
demonstrated, while the connections between traps allow
communication between sets of ions," they write. This
shuttling scheme allows them to create both memory and logical
processing regions.
A first
step towards the development of such a computer has been
taken at NIST's Boulder, Colo., laboratories where a pair
of interconnected ion traps has been constructed; they are
separated by 1.2 mm. Efficient transport of ions between
the two traps has been demonstrated. The sample two-ion
trap device maintains stable electronic states indicating
that the method is a practical system for building a quantum
computer.
"We
have presented a realistic architecture for quantum computation
that is scalable to large numbers of qubits (quantum bits).
In contrast to other proposals, all local quantum state
manipulations necessary for our scheme have already been
experimentally tested in small quantum registers, and scaling
up to large ion-trap quantum computers appears straightforward,"
they conclude.
Authors
of the article are David Kielpinski of the Massachusetts
Institute of Technology, Christopher Monroe of the University
of Michigan, and David J. Wineland of the National Institute
of Standards and Technology. Copies of their paper can be
obtained from Sarabeth Harris, NIST, 325 Broadway, Boulder,
Colo., 80305; (303) 497-3237, sarabeth@boulder.nist.gov.
[A second
paper to be published in the journal Quantum Information
and Computation will report experimental results. A
preprint of this paper can be found at http://xxx.lanl.gov/
or by contacting NIST at the above address.]