Physicists in Australia have slowed a speeding laser pulse and captured it in a crystal, a feat that could be instrumental in creating quantum computers.
The scientists slowed the laser light pulse from 300,000 kilometers per second to just several hundred meters per second, allowing them to capture the pulse for about a second.
The accomplishment marks a new world record, but the scientists are more thrilled that they were able to store and recall light, an important step toward quantum computing.
"What we've done here is create a quantum memory," said Dr. Matthew Sellars of the Laser Physics Centre at the Australian National University in Canberra, Australia.
Slowing down light allows scientists to map information onto it. The information is then transferred from the light to the crystal, Sellars said. Then when the scientists release the light, the information is transferred back onto the beam.
"Digital information can be expressed with pulses of light," Sellars said. "If we can store the light pulses for a very long time, we have a memory that operates on a quantum scale."
To slow down the light, the researchers used a silicate crystal doped with a rare-earth element called praseodymium. Laser light pulses fired at the crystal are normally absorbed and don't pass through, Sellars said. But when a secondary laser was directed at the crystal, it became transparent, allowing light from the first laser to move through.
To store the light, the secondary laser was switched off, so the original light pulse was trapped. The secondary laser was directed onto the crystal once again to release the pulse.
Scientists can map information onto light beams using photons, which, like all elementary particles, have "spin." Spin gives them a natural orientation, similar to a compass needle. The spin can be oriented up or down, representing a one or zero. Flipping from up to down has the same effect as switching a tiny transistor on or off.
In the spooky world of quantum mechanics, particles like photons behave in mind-bending fashion, and can actually be oriented up and down simultaneously, until they are observed or measured. This arrangement is known as quantum superposition, and results in a unit of information known as a qubit (quantum bit), instead of the traditional bit.
The processing power of a quantum system -- and it is formidable -- is a direct result of the superposition state. Since the qubit can represent several values at once, a quantum system is exponentially more efficient than its classical counterparts. Just 40 qubits would equal the power of today's supercomputers.
"We're at the borderline from going from a few qubits to many more," said Raymond LaFlamme, director of the Institute for Quantum Computing at the University of Waterloo in Ontario, Canada. "But from a conceptual point of view, we're learning a new force of nature."
Quantum computers will exploit quantum mechanics to perform complex mathematical operations -- like cracking the most complex codes cryptography can dream up -- at blistering speed.
"The process of decryption and modifying information security will be a large application," said LaFlamme. "Entities such as the National Security Agency are very interested in building a quantum machine."
While acknowledging that quantum technology is still in its infancy, LaFlamme described the success of ANU's quantum memory experiment as "a milestone," and envisions steady progress in the future.
"The 19th century was the Industrial Age," he said. "The 20th century was hailed as the Information Age. I believe the 21st century will be the Quantum Age." source