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Scientists propose design for large-scale quantum computer

Scientists at MIT, the National Institute of Standards and Technology and the University of Michigan have taken a significant step toward developing a quantum computer.

In a paper published in Nature on June 13, 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. The authors are David Kielpinski, a postdoctoral fellow in MIT's Research Laboratory of Electronics, Christopher Monroe of the University of Michigan and David J. Wineland of NIST.

A quantum computer makes use of the properties of quantum systems rather than transistors for performing calculations or storing information. A transistor can only be 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 help with big projects such as modeling the world's weather.

The National Institute of Standards and Technology (NIST) has developed electromagnetic 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 research team reported.

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," the paper's authors wrote. 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 laboratories in Boulder, Colo., where a pair of interconnected ion traps has been constructed. Researchers have demonstrated efficient transport of ions between the two traps separated by 1.2 mm. 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," the researchers concluded.

A version of this article appeared in MIT Tech Talk on July 17, 2002.

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