Quantum Leap in Computing
by Leander Kahney

3:00 a.m. Mar. 23, 2000 PST
Federal researchers say they've created the most robust quantum computer ever, indicating that the concept is rapidly moving from theory to practice and could create the most powerful computing devices ever dreamed of.

If the trend of increasing performance continues, a quantum computer that triples today's fastest computers could be built in five years, according to physicist Raymond Laflamme, who helped build the world's first 7-qubit computer described in the most recent issue of Nature.

"Right now it's impossible to say if we can scale these technologies," said Laflamme, the project's lead researcher. "But if you asked me five years ago if we could build a 7-qubit computer in five years, I would have said it was impossible."

Quantum effects give sub-molecular computers great power. Still, quantum computers may never be general-purpose computing devices and are more likely to be targeted at massive number-crunching problems like encryption and decryption, searches of huge databases and simulations of quantum physical states.

While the theoretical foundations of quantum computing were set in the 1980s, scientists had been unable to build quantum computers until recently.

The first 3-qubit quantum computer was created just 18 months ago at the Department of Energyís Los Alamos National Laboratory in New Mexico. The lab's researchers describe in the Nature paper how they used a test tube of trans-crotonic acid and a powerful nuclear magnetic resonance spectrometer to create the 7-qubit (pronounced kew-bit), or quantum bit, quantum computer.

Physicist David Wineland of the National Institute for Standards and Technology, who is working on a competing quantum computing technology, said the work was important but ultimately the NMR technology will hit a roadblock.

"It's significant because it's the most complicated system people have been able to do something interesting on," he said. "But people in the field generally feel that the final quantum computer won't be an NMR computer."

Laflamme's quantum computer was created by manipulating the nuclei of seven molecules in a test tube of trans-crotonic acid, hence 7-qubit. Like a spinning magnet, the molecules' nuclei can be lined up with electromagnetic pulses from the nuclear NMR spectromotor, which is a specialized version of the imaging devices commonly used in hospitals.

"It's like trying to manipulate needles with bulldozers," Laflamme said.

The lining up of a nucleus parallels the encoding of information in conventional computers as binary ones or zeros. However, unlike a traditional bit, which is either on or off, the nuclei are subject to the very weird laws of quantum physics that allow them to simultaneously be in multiple states. In other words, they can be a one or a zero at the same time.

Wineland said that the NMR approach will run out of steam at 15 qubits because key interactive effects between the quantum particles start to disappear.

Wineland is working on one of several different approaches to quantum computing that utilizes trapped ions instead of fluid liquids.

Laflamme compared his research to the early days of computing, when computers weighed 30 tons and were built from thousands of vacuum tubes. Back then, computer scientists predicted that one day computers would weigh only 5 tons and be built from hundreds of tubes.

"What do we have today?" Laflamme asked. "Laptops and Palm Pilots."

"On my optimistic days I think we will have quantum computers in 20, 30, 40 years maybe," he said. "On my pessimistic days, I think quantum computing is crazy."