Quantum computing at sub-zero temps
Computers would use quantum physics to create processing power
Daily Camera, April 16, 2005
Ray Simmonds fiddled with what looked like a ray gun of the sort preferred by the villains of cartoon fiction. It hung from a knot of pipes and wires along the ceiling, aimed into a grave-deep hole in the floor of his lab.
Fortunately for the planet, its role is not to vaporize, but to quantize.
The contraption, in Simmonds` National Institute of Standards and Technology laboratory, is a cryogenic refrigerator. It uses liquid helium to cool three ¼-inch sapphire-aluminum integrated circuits to temperatures a fraction of a degree above absolute zero.
"An ice cream cone would look like the sun if you were inside there," Simmonds said.
In such cold, his team`s experimental quantum superconducters kick into gear. They could eventually provide a way to do quantum computing on a relatively huge scale: The aluminum semiconductors Simmonds` team uses are about the width of a human hair.
Contrast that with the individual beryllium ions a different NIST team uses for their experimental quantum computer. They manipulate the quantum states with laser pulses in custom-made gold ion traps.
Simmonds, 34, seems at first glance more suited to pulling espresso shots than pushing buttons on a signal generator. He cut his finger opening up the ray-gun refrigerator and patched it with Scotch tape and a paper towel.
But he, two post-doctoral researchers and a graduate student are among hundreds of researchers worldwide seeking to create a working quantum computer.
The National Security Agency`s Advanced Research Development Activity has called it "one of the most active research areas of modern science."
By harnessing the peculiar properties of electrons described by the laws of quantum physics, scientists could theoretically create computers with enormous processing power. A quantum computer could crack problems in fields such as code breaking that render today`s best supercomputers no more effective than an abacus. That potential has piqued the interest of intelligence officials.
The key to quantum computing lies in the subatomic world`s ability to be two things at once.
Data stored as bits in a traditional binary computer is limited to strings of ones and zeroes. Data stored as quantum bits could be a one, a zero, or - and here`s where things get weird - both, in what`s called quantum superposition. Superposition is what gives quantum computing its zing.
Superposition doesn`t happen in the world that Einstein`s relativity describes, or we`d all be both at work and on the beach in Tahiti. To go quantum, things need to be really small or really cold.
Getting small means manipulating atoms with lasers to make their electrons dance and store information. Getting cold means achieving superconductivity, a state in which materials lose electrical resistance and captured electrons start to heed electromagnetic commands.
"This is a 1-D atom," Simmonds said. "Current oscillates back and forth in this little structure, whereas an atom is in three dimensions," with electrons rotating around the nucleus.
The team showed that it could use microwave alternating-current oscillations to control and measure each quantum bit as well as get the two quantum bits to communicate.
The work, published recently in the journal Science, is a collaboration with a University of California, Santa Barbara team lead by John Martinis, a former NIST physicist. He launched NIST`s superconducting quantum computing effort.
While a major step, there are still big challenges.
Kevin Osborn, a postdoctoral physicist working with Simmonds on the project, said they can only maintain a given quantum arrangement for a millionth of a second - little time to do much computing. But if they can lengthen that and improve their still-rudimentary control of the quantized electrons, the advantages could be immense, Osborn said.
"These are superconducting electronics," he said.
That means they could be mass-produced with the same photolithograpy that imprints the semiconductors powering home computers, cell phones and musical greeting cards.
David Wineland, the Boulder NIST scientist leading a 15-person quantum-computing effort based on beryllium ions, has done groundbreaking work in the atom-based approach. His team`s uses experimental quantum computers are up to three quantum bits.
"There are advantages and disadvantages with both superconductors and atoms," Wineland said. "I think they`re all, at this point, worth pushing."
James Olthoff, division chief for NIST`s Quantum Electrical Metrology Division in Gaithersburg, Md., agreed.
"Right now there are many roads and nobody knows which one will lead to success," he said.
© 2008 Todd Neff