Design Proposed for Large-Scale Quantum Computer

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 [at] boulder.nist.gov (sarabeth[at]boulder[dot]nist[dot]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.]