Physicists freeze motion of light for a minute

Aug 06, 2013

Physicists in Darmstadt have been able to stop something that has the greatest possible speed and that never really stops. We're talking about light. Already a decade ago, physicists stopped it very for a short moment. In previous years, this extended towards stop times of a few seconds for simple light pulses in extremely cold gases and special crystals. But now the researchers at Darmstadt extended the possible duration and applications for freezing the motion of light considerably. The physicists, headed by Thomas Halfmann at the Institute of Applied Physics of the Technische Universität Darmstadt, stopped light for about one minute. They were also able to save images that were transferred by the light pulse into the crystal for a minute – a million times longer than previously possible.

The researchers achieved the record by cleverly combining various known methods of their field. The result will have practical significance in future data processing systems that operate using light.

To stop the light, the used a glass-like crystal that contains a low concentration of ions – electrically charged atoms – of the element praseodymium. The also includes two laser beams. One is part of the unit, while the other is to be stopped. The first , called the "control beam", changes the of the crystal: the ions then change the to a high degree. The second beam, the one to be stopped, now comes into contact with this new medium of crystal and laser light and is slowed down within it. When the physicists switch off the control beam at the same moment that the other beam is within the crystal, the decelerated beam comes to a stop.

More precisely, the light turns into a kind of wave trapped in the . This can be explained in greatly simplified form as follows. The praseodymium ions are orbited by electrons. These behave similarly to a chain of magnets: if you put one into motion, the movement – mediated by magnetic forces – propagates in the chain like a wave. Since physicists call the magnetism of electrons "spin", a "spin wave" forms in the same manner when freezing the laser beam. This is a reflection of the laser's light wave. In this way, the Darmstadt researchers were able to store images, such as a striped pattern, made of within the crystal. The information can be read out again by turning the control laser beam on again.

The fact that only very short storage times were possible until now is because perturbing environments interfered with the spin wave, similar to how moving ships mix up waves in a lake. The information about the stored light wave is thus gradually lost. The perturbations can be alleviated by applying magnetic fields and high-frequency pulses. In our example, these fields reduce the number of boats on the lake, as it were.

How well this works depends strongly on the parameters of the driving optical fields, magnetic fields and the high-frequency pulses. There are very many variations, and the optimal setting can hardly be calculated because of the complexity. Therefore, the Darmstadt researchers used computer algorithms that quickly and entirely automatically find the best solutions during the experiment. One of the algorithms is based on natural evolution, which produces organisms that are adapted as well as possible to the environment. Using the algorithms, the researchers were able to optimize the , the magnetic field and the high-frequency pulses in such a manner that the spin waves survived nearly as long as is possible in the crystal.

Based on this success, Halfmann's team now intends to explore techniques that can store light significantly longer – perhaps for a week – and to achieve a higher bandwidth and data transfer rate for efficient information storage by stopped light.

Explore further: Nuclear spins control current in plastic LED: Step toward quantum computing, spintronic memory, better displays

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User comments : 7

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panorama
5 / 5 (3) Aug 06, 2013
This is really cool.
Tektrix
not rated yet Aug 06, 2013
Very cool, indeed! Spin-wave data processing, here we come!!
vacuum-mechanics
1 / 5 (8) Aug 06, 2013
More precisely, the light turns into a kind of wave trapped in the crystal lattice. This can be explained in greatly simplified form as follows. The praseodymium ions are orbited by electrons. These behave similarly to a chain of magnets: if you put one into motion, the movement – mediated by magnetic forces – propagates in the chain like a wave. Since physicists call the magnetism of electrons "spin", a "spin wave" forms in the same manner when freezing the laser beam. This is a reflection of the laser's light wave…..

What we do not know is why and how electron spin could create magnetic field which propagates in the chain like a wave. Understanding the mechanism behind (as below) would help the research….
http://www.vacuum...21〈=en
Q-Star
3 / 5 (9) Aug 06, 2013
What we do not know is why,,,,,


That is a question for preachers and philosophers, not scientists.

,,,,,, and how electron spin could create magnetic field which propagates in the chain like a wave.


Sure we (meaning science at the present stay) know who. We even know how well enough to do the things talked about in this article.

Understanding the mechanism behind (as below) would help the research….
http://www.vacuum-mechanics gobbledygook blah.


I think the researchers here are doing quite well without your help.
DarkHorse66
5 / 5 (3) Aug 07, 2013
@Q-Star
The only thing tha vac-mech ever seems capable of contributing to any thread is repeat spruiking/advertising of that link to his very own site. But you've been around long enough on this site and already know that, so I'm unlikely to be telling you anything new. My only message is:
DON'T FEED THE TROLLS! (especially that one, it's a waste of perfectly good bytes -and your precious time) ;)
I'd rather read your other, constructive contributions. SOME of us actually enjoy learning stuff. :)
Best Regards, DH66
gmurphy
not rated yet Aug 07, 2013
Pretty awesome that they used genetic algorithms to optimise the experimental configuration too
Gmr
1 / 5 (2) Aug 07, 2013
This is a better article than the previous "freezing light" article about the same technology: explanatory and credible in its analysis, not too breathless but still enthusiastic. Five!