January 8, 1997

Two University of Rochester researchers have won a one-year grant to work on a new kind of computer that may solve problems that are impossible for conventional computers to crack.

The $155,000 grant from the Army Research Office will fund research on quantum computing, an as-yet unrealized technology that relies on the schizophrenic nature of quantum mechanics. Researchers Marc Feldman and Mark Bocko, two members of Rochester's electrical engineering department who are experts in superconducting electronics, propose using superconductors to move quantum computers from theory to reality.

"Right now, we're at the point where we believe quantum computing can be done," Feldman says. "We're just trying to see how it can be done with current or near-future technology."

Quantum computers won't replace conventional computers, but they may fill a certain niche. For example, Peter Shor of the AT&T Bell Laboratories electrified the field two years ago by showing that quantum computers can outperform conventional ones in factoring large numbers -- a task with applications in encryption, a field that offers security in the burgeoning realm of electronic financial transactions. A large security-key number that would take the age of the universe to factor on a conventional computer would take a fraction of a second to factor on a quantum computer.

Rather than using binary bits labeled as "zero" and "one" to encode data, as in a conventional computer, quantum computing stores information in "qubits" -- bits that can represent both "zero" and "one" simultaneously. Bocko calls this phenomenon "the equivalent of an object being in two places at once."

"You can think of a binary bit like a coin," he says. "When you flip a coin, it always lands in either the 'heads' state or the 'tails' state. But if the coin were a qubit it could be in a state which is both 'heads' and 'tails' simultaneously."

When a quantum computer is put to work on a problem, it considers all possible answers by simultaneously arranging its qubits into every combination of "zeroes" and "ones." Since one sequence of qubits can represent many different numbers, a quantum computer would make far fewer computations than a conventional one in solving some problems. After the computer's work is done, a measurement of its qubits provides the answer.

Researchers in other laboratories have made microscopic qubits using single atoms that interact with laser beams. Feldman and Bocko's proposed qubit is a tiny superconducting ring. The two different directions of current within this ring represent the two states of the qubit.

Many scientists believe it's technologically impossible to build a quantum computer using millions of atomic qubits. Feldman and Bocko's plan to use integrated circuit manufacturing techniques to make superconducting qubit chips should solve that problem, but it will certainly create others. "For example," Feldman says, "a quantum computer is so fragile that computations have to be carried out in complete isolation at temperatures just thousandths of a degree above absolute zero."

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