They are the building blocks of what may one day become an enormously powerful quantum computer capable of solving in seconds problems that take today's fastest machines years to crack, U.S. physicists said on Wednesday.
"You can do the equivalent of multiple classical calculations at the same time in the quantum world," said Trey Porto, a researcher with the U.S. Commerce Department's National Institute of Standards and Technology or NIST, whose work appears in the journal Nature.
Porto and colleagues have coaxed pairs of super-cold rubidium atoms to repeatedly swap positions, a feat that could make them useful for storing and processing data in quantum computers.
In today's computers, the smallest unit of storage is a binary digit or bit, which can only have two values--zero or one. These form the basis of information storage in digital computing. When combined into groups of eight on a typical PC, these bits become bytes.
"In the quantum world, instead of just the possibilities of zeros and ones, you have a range of possibilities," Porto said in a telephone interview.
Quantum bits, or qubits, can also oscillate between the zero and one positions, like a half-flipped light switch. This flexibility could allow for many calculations to be carried out simultaneously, Porto said.
Porto's team isolated pairs of atoms in a lattice of light formed by six laser beams all fixed on one point, suspending the atoms in a uniform pattern. "There is no container. It is levitated by the laser beams."
They trapped these pairs in wells or dips formed by ripples in the light. When forced together in tight spaces, the atom pairs began to oscillate between zero and one, passing in and out of a state of entanglement.
Porto describes it in terms of two magic coins spinning in the air. "While they are spinning, these coins are correlated so that if one is heads up, the other is always heads down," he said.
So far, all the pairs are dancing the same tango. To be useful in a quantum computer, he and his team will need to figure out how to get different pairs to dance and spin independent of the neighboring atom pairs.
"We're just demonstrating the most fundamental, basic unit of what you would need," he said.