Frozen assets

US physicists believe ultra-cold atoms could hold key to optical computers.

US physicists who became famous for ‘freezing light’ now believe their work could hold the key to creating the memory and central processing unit for future optical computers.

New research by Lene Vestergaard Hau, professor of physics at HarvardUniversity, could provide a vital step in the race to create the next generation of computers that code information in light rather than in electronic signals.

This optical technology could allow data to be processed much faster than in current electronic devices, which are nearing their theoretical limit for miniaturisation and increased speed.

Hau’s group had previously used a cloud of ultra-cold sodium atoms to bring light, which normally travels at 186,000 miles/sec, to a standstill. She and former graduate student, Zachary Dutton, have now calculated that ultra-cold atoms in the form of Bose-Einstein condensates (BECs) can be used to perform controlled coherent processing with light.

After forming the atom cloud, Hau illuminated this with a precisely tuned laser beam, creating a new medium where the optical properties of light can be controlled. A pulse of light is then sent into the cloud, where it is slowed and at the same time spatially compressed by factors of tens of millions. The light pulse can move through the cloud with no absorption.

Inside the cloud, the light pulse creates a holograph-like imprint, which follows the slowed light as it continues through the atoms.

After it is slowed and compressed the light pulse can be stopped by turning off the illuminating laser beam. The imprint remains until the laser beam is once again sent in to illuminate the cloud, reviving the light pulse, which then commences its movement forward. ‘During the time the optical information is stored we could use the interaction between atoms in the cloud to controllably process the information,’ said Hau. ‘This represents a whole new regime for manipulating light.’

The research could allow the volume of data carried by fibre optic telecommunications cables to significantly increase. If a large number of information-carrying light pulses come to a node at one time, processing this volume of information is difficult. But Hau’s research could allow some pulses to be put in a holding pattern, allowing the node to cope.