Original URL: http://www.theregister.co.uk/2012/05/07/faster_than_light_quantum/

US gov boffins achieve speeds FASTER THAN LIGHT

'Loophole' found in Special Theory of Relativity

By Lewis Page

Posted in Science, 7th May 2012 13:04 GMT

Scientists working in a US government laboratory say they have managed to transmit a signal from point to point faster than the speed of light in a vacuum - in a development apparently violating the laws of physics.

According to a statement issued by the US National Institute of Standards and Technology (NIST):

According to Einstein's special theory of relativity, light traveling in a vacuum is the universal speed limit. No information can travel faster than light.

But there's kind of a loophole ...

Sadly this isn't the sort of loophole which seems likely to lead to hyperdrive starships or interstellar portal technology or anything like that. But it does, in effect, let information go faster than light. In a way.

This is achieved by taking an ordinary pulse of light and changing its shape so that the peak of the pulse moves quickly from the back towards the front. As the entire pulse is already travelling at very close to speed-of-light-inna-vacuum, the peak is now travelling faster than light.

Apparently so much was already old hat, but the processes used thus far produce a very noisy signal and the increase in apparent speed is not really very big. But now a new and potentially usable refinement known as "four wave mixing" has been developed. The NIST boffins describe their new process like this:

In four-wave mixing, researchers send 200-nanosecond-long "seed" pulses of laser light into a heated cell containing atomic rubidium vapor along with a separate "pump" beam at a different frequency from the seed pulses. The vapor amplifies the seed pulse and shifts its peak forward so that it becomes superluminal. At the same time, photons from the inserted beams interact with the vapor to generate a second pulse, called the "conjugate" because of its mathematical relationship to the seed. Its peak, too, can travel faster or slower depending on how the laser is tuned and the conditions inside the laser.

In the latest experiments, the NIST scientists say, they made a pulse-peak travel from point to point and it showed signatures "corresponding to" a situation where the peak covered the distance some 50 nanoseconds sooner than light travelling through vacuum would have done.

Actually using this method to transmit normal humdrum information faster than light would still violate the laws of physics. However it seems that it might be possible to use four-wave superluminal signals to transmit quantum information, made up of qubits whose value is not simply 0 or 1 but potentially any value from 0 to 1.

"By performing measurements of quantum discord between fast beams and reference beams, the group hopes to determine how useful this fast light could be for the transmission and processing of quantum information," the NIST announcement says.

Those with the boffinry puissance to understand the science (and the relevant subscription) can read all about it here, in the journal Physical Review Letters. ®