Light frozen for 1.5 seconds

[dragon]

Very cool, no pun intended.

Forget about ziplock bags. A cloud of ultracold atoms can store a beam of yellow light for 1.5 seconds. That timescale isn’t impressive for frozen peas, but it’s enough time for light to circle the Earth 10 times under normal conditions, researchers led by Lene Hau of Harvard University report.

This ability to store light may lead to more efficient ways to communicate, as well as new ways to explore quantum mechanical properties such as entanglement.

The new study is “a beautiful demonstration,” says Irina Novikova, a physicist at the College of William & Mary in Williamsburg, Va. Before this result, she says, light storage was measured in milliseconds. “Here, it’s fractional seconds. It’s a really dramatic time.”

Researchers knew that the information carried in light pulses could be transferred to clouds of ultracold atoms, called Bose-Einstein condensates. In this technique, a laser called a control laser prepares the atomic cloud for an incoming light beam. As the photons fly in, they leave an imprint in a subset of the atoms. This imprint, stored in a quantum property known as spin, contains all the relevant information needed to reconstitute the light beam. But the imprint is fragile and deteriorates in milliseconds. The light’s information is lost as other atoms in the cloud interfere with the imprint.

Hau and colleagues overcame this problem by sequestering the matter imprint from the rest of the atoms in the cloud. The team shone a pulse of laser light — which looks like the yellow light from street lamps, Hau says — into a small cloud of sodium atoms. A three-microsecond pulse produced a stretch of light about a kilometer long, but as the pulse entered the atom cloud, it began to compress. Like an accordion closing, the light folded up and crammed itself into a space just 0.02 millimeters long. The spin states of the sodium atoms in the light’s path were changed, forming the matter imprint. By turning off the control laser, the researchers were able to freeze the matter imprint.

Next, the researchers strengthened the magnetic field applied to the atom cloud to protect the imprint from interfering atoms. At a certain magnetic field, Hau says, interactions between the imprint and the rest of the atoms start to become repulsive, and the imprint separates from the cloud like a drop of oil in water. “This matter imprint digs a little hole for itself in the condensate,” Hau says. “It can snugly sit there for long periods of time.”

After waiting 1.5 seconds, the team revived the light beam. First, the researchers coaxed the matter imprint to the outside of the cloud by changing the magnetic field, and then they turned the control laser back on. The light beam that emerged from the atom cloud was weaker than the light beam that went in but similar in other regards, such as frequency and polarization, Hau says. Improving the stability of the magnetic field will likely lead to longer storage times, she adds.

This new method is a vast improvement over earlier methods, the researchers report in their paper, published December 4 in Physical Review Letters. The fidelity of the reconstructed light beam is 100 times better than earlier attempts, Hau says.

Transferring information between light and atoms could one day lead to better communication networks. Light-storage devices could also enable quantum communication, says quantum physicist Ortwin Hess of the University of Surrey in Guildford, England, who calls the new study “elegant and impressive.”

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[Morilore]

"Light frozen for 1.5 seconds" = really long relaxation times by manipulating magnetic properties of Bose-Einstein condensates to prevent nonradiative energy transfer.
Did I get that right? Someone know more about this subject than me?

[Solauren]

The fact you can freeze light alone is, in itself, very cool.

The possible applications for this are beyond me, but I'm sure they'll be revolutionary.

[salm]

Could you build some sort of cloaking device with this? If you build a suit that emmits this light capturing stuff and creates an "Aura" of it around the wearer wouldn´t it prevent a spectator to see the wearer for 1.5 seconds? So if the wearer is moving the spectator would allways see the wearer where he was 1.5 seconds ago.

[Sarevok]

Can this phenomenon be harnessed to store information ? A sort light based storage medium if you will.

[starslayer]

Could you build some sort of cloaking device with this? If you build a suit that emits this light capturing stuff and creates an "Aura" of it around the wearer wouldn´t it prevent a spectator to see the wearer for 1.5 seconds? So if the wearer is moving the spectator would always see the wearer where he was 1.5 seconds ago.

No. First, you'd see a black pocket where the suit was if you get this to work, and second, a Bose-Einstein condensate has a temperature near absolute zero, and you can't make one that's any warmer. So any one foolish enough to try building such a suit wouldn't be able to make it cold enough, nor could they prevent the condensate from interacting with something warmer than it (e.g., everything in the outside environment), thus reverting it to a normal state.

Can this phenomenon be harnessed to store information ? A sort light based storage medium if you will.

Not economically compared to other storage media, and it's tough to maintain (the condensate must be kept extremely cold, as described above, and the light containing pocket must be isolated from the rest of it).

[Andrew_Fireborn]

If any practical use comes of this, I'd venture it would be from a better insight into the nature of light, rather than the act itself.

Still an awesome feat of Science!

[Themightytom]

Can this phenomenon be harnessed to store information ? A sort light based storage medium if you will.

I suppose it could be kind of nice if you want to transport sensitive information, like a code key, once the original light is released the device is empty, cluing the authors in that someone has viewed it. Then you change the code knowing the information has been compromised. I feel like its overly elaborate.

if the entertainment industry ever made an economically feasible model it might kind of such since we could only watch our movie once.

what about astronomy? It would be like a "Pause" Button for the visible light from millenia ago we are either missing out on because the suns in the way or that we lack the advancement to fully analyze>

[starslayer]

I suppose it could be kind of nice if you want to transport sensitive information, like a code key, once the original light is released the device is empty, cluing the authors in that someone has viewed it. Then you change the code knowing the information has been compromised. I feel like its overly elaborate.

if the entertainment industry ever made an economically feasible model it might kind of such since we could only watch our movie once.

what about astronomy? It would be like a "Pause" Button for the visible light from millenia ago we are either missing out on because the suns in the way or that we lack the advancement to fully analyze>

No, no, and no. It's too difficult to maintain a BEC for very long (read: it's almost impossible). This is because the atoms must be maintained in the exact same ground state, which they tend to drift out of simply by interacting with their fellows after about a second or so. You can take measures to extend the coherence time, but we still can't do so for very long. While this is cool, it's not actually useful for much of anything.

Oh, and the astronomy? If the Sun's in the way, it's in the goddamned way. We can't get any light from behind it because it's fucking opaque. And if we "lack the advancement to fully analyze it," we just store the data on a computer until we can, which is what we do with all our data. I'm going through 10 year old data right now.

[Gil Hamilton]

Keep in mind what a Bose-Einstein Condensate is. Depending on the spin of a particular particle, it can either obey Fermi-Dirac statistics (sum of the spins in the particle is n*1/2 where n is an odd integer) or Bose-Einstein statistics (the total spin is an integer). In Fermi-Dirac statistics, no two particles may have the same state. In Bose-Einstein statistics, you can have multiple particles in the same state. What a Bose-Einstein condensate is is a lump of particles with such low energy that they all occupy the same ground state, all the waveforms of the particles overlap, and you get cool quantum effect on a larger than normal scale. This is not easy to achieve and was predicted well before physicists actually managed to make one (not easy as in the guys who did it got the Nobel Prize). While this leads to a phenomenon that is in scientific terms "totally awesome", it's hard to keep it that way because adding any sort of energy to it will most likely not make it a BE condensate anymore. This makes it hard to come up with practical uses for such a beast.