Light Stopped, Held And Re-emitted By A Crystal

nherc writes: "An article in Nature talks about an incredible new crystal that can actual stop and hold light to be later emitted. It's mentioned light has previously been "slowed" by super cooled gases, but this certainly blows that away. They mention this could be a major step towards quantum computing."

Re:Magical Crystal = Glow In The Dark Stuff?

how can this possibly relate to quantum computing?

From http://www.sciam.com/2001/0701issue/0701hau.html [sciam.com]

"Another application for slow and stopped light could be quantum computers, in which the usual definite 1's and 0's are replaced with quantum superpositions of 1's and 0's called qubits. Such computers, if they can be built, would be able to solve certain problems that would take an ordinary computer an enormously long time. Two broad categories of qubits exist: those that stay in one place and interact with one another readily (such as quantum states of atoms) and those that travel rapidly from place to place (photons) but are difficult to make interact in the ways needed in a quantum computer. The slow-light system, by transforming flying photons into stationary dark state patterns and back, provides a robust way to convert between these types of qubits, a process that could be essential for building large-scale quantum computers. We can imagine imprinting two pulses in the same atom cloud, allowing the atoms to interact, and then reading out the result by generating new output light pulses."

Re:Magical Crystal = Glow In The Dark Stuff?

But, this sounds like it actually holds the photons and releases them later. Or at least that's what the submission infers.

Based on the article, it appears more like the complete energy from the photons is absorbed by the atoms. The photons can then be emitted later by changing the intensity of the laser that is causing the atoms to hold onto it. I don't see this as really trapping light. It looks more to me like the energy from the "holding laser" plus the energy from the photons manages to push the electrons to a higher valence level and leave them there, even when the incoming photon supply is turned off. Then I would suspect that lowering the intensity of the holding laser would allow the electrons to drop to a less excited state and thus release the energy in the form of photons. It really sounds just like a fluorescent light except that you now have control over when the photons are actually generated by the excited atoms.

Feel free to correct me vigorously. I haven't thought about this kind of stuff in earnest for more than 15 years.

whats next

optical ram that is a crystal matrix that actually holds the image and energy?

constant speed of light

E=0?

No, really, I know light speed changes. c is just for light in a vacuum... This is really neat stuff, and I hope this becomes a leap forward in understanding quantum mechanics.

Light speed doesn't change

Only average lightspeed changes. The speed of light (photons - same speed as all massless particles) is always c (about 300kk in m/s). However, the light can be delayed. When a photon hits an atom, it usually transfers its energy to an electron, which jumps to a higher orbital. The electron then nearly instantly drops down to its old orbital and gives off the energy in the form of (guess what) a photon. A constant rate of interception and expulsion by atoms can cause the average speed of the light to be slowed, but the photon is always moving at c. The crystal/laser combination mentioned in the article just keeps the energy from the light a LOT longer than the picoseconds it spends in electrons normally

The Previously Mentioned Method

Fucntioned by super cooling a special gas in a chamber, and then shining a specialized laser (yeah, I don't know the specifics) through the gas, opening a pathway through it.

Light was then shined through this pathway, then the laser was cut, "trapping" the light in the gas. What actually happened was that this left an "imprint" in the cooled gas, and when the laser was beamed through the gas again, the imprint of light activated and the beam of light continued.

There was a serious issue with degradation though. The longer the light was trapped in the gas, the poorer the quality the beam of light was when it was reanimated.

Seems like this new method has improved immensely upon that weakness.

The Crystal of Earendil?

Is this basically what the crystal Galadriel gives to Frodo does? Stores light, until it's needed in his "darkest hour?" If it is, it means that those damn elves are still decades ahead of us in technology! We must find them, take their tech, and destroy them!

Colin Winters
...who thinks Galadriel is hot...

War with the Elves? Suicide!

Vietnam aside, I really don't like the chances of any army against one with significantly superior technology - and the US army is heavily trained to rely on the superiority of its tech.

Futhermore, the peaceniks would have a field day with this - I doubt the Elf War would be very popular on the home front. It would take a really strong president to overcome this...

Vote Sauron in 2004!
(This post was a paid message from the Committe to Elect Sauron, a not-for-profit organization dedicated to America's future as the stronghold of the Dark Lord.)

The reason it's old news

is that they've not only stopped light, but made it go backwards, reversing time, so this 'discovery' got projected into the future, where we're reading about it now as if it were new, altho it's been done some time ago.

Re:Which version of the Pentium

AMD has a quantum CPU almost ready for production. Unfortunately, their trials show that when your cooling fan fails the probability wave collapses and your cat dies.

Light goes at c

A lot of people have been saying that light only goes at c in a vacuum. This isn't quite right.

Light goes always at c, period. When it goes through a solid, a better metaphor is that it has to slalom around the atoms in the solid. Of course due to QM it's really more like that Charles Addams cartoon with a ski track leading up to a tree, splitting around, and continuing on. At this point, classical approximations stop making sense, and you have to start talking about amplitudes. You can get the Feynman New Zealand videotapes here [amazon.com]. It's an excellent but basic and easily understandable introduction to quantum electrodynamics.

In any event, this doesn't seem to be the same mechanism (unless the amplitudes get stuck as if the photon were going in a loop). It appears to be a similar mechanism, as pointed out elsewhere, to glow-in-the-dark paint. Terribly exciting, but not foundation-shattering, unfortunately. It would be a lot of fun if it were.

Another minor wrinkle is that c is very slightly faster than the speed of light in a vacuum, because a vacuum isn't quite empty. Particles come into the vacuum and immediately annihilated each other all the time. You can theoretically get rid of these by putting a vacuum between two plates so close together that these virtual particles can't form.

At long last, no more Dark Crystal

At last, we can get some light into that thing. I was getting really tired of The Dark Crystal [imdb.com]
:-)

Is it just me...

...or does the picture at the start of the article make everyone else think of "Missile Command"?

TheFrood

This page . . .

helps to explain [aip.org] how they're achieving this with a graphic representation. Still a little technical for me, but it kinda makes sense.

Needs a better name...

"a crystal of yttrium silicate containing a few atoms of the element praseodymium"

They need a catchy marketing name... Something like DyLithium Crystals.

Re:Is this anything like "Slow glass"?

When I first read a story with "slow glass" in it, I thought "That might be cool." Then I thought about how much energy was somehow stored internally if I left a sheet lying in the desert in direct sunlight for ten years. Then I thought about what would happen if all that energy were discharged at once when the crystal structure (or whatever) was damaged by, say, the neighborhood brat throwing a brick through it. And decided that I wouldn't want any of that stuff in my house!

Power Industry?

Could this be used to create more efficient solar panels? The photons are converted directly into energy, "stored" in the atoms. Rather than re-release the photons as light, would it be possible to capture that energy and convert it into something more useful?

My understanding of optics is rather lacking... something is nagging at the back of my mind telling me that this wouldn't work...

Holographic Buffer

You guys don't get this, do you? It is not a "light capacitor" or a new twist on "glowies". What has been done here is to use subatomic particles to store information about coherent light signals.

Perhaps some of the enlightened /. geeks remember stirrings that show up from time to time in cyberspace regarding holographic 3D memory. The premise is that, using holographic media, it is theoretically possible to store massive (a terabye in 10 sq. cm) amounts of data in an extraordinarily small space without electron lag which is a problem in high-speed microelectronics.

In optoelectronic computing systems and quantum computing systems the ability to store photons and photon signals is tantamount to the realization of full scale optoectronic (and quantum-based) computing.

I digress. This is awesome and I am very enthusiastic. Once again, it doesn't stop light, bend time, slow light, warp space or anything else like it. And it doesn't glow in the dark. It's like a single-channel holographic buffer and it is absolutely wonderful!

Vortan out

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Quantum computing?

I actually don't see how this can be applied to quantum computing, yet.

This sounds almost exactly like an optical transistor, except that a transistor actually is an amplifier.

To make it more like a transistor, imagine a 2 part crystal; part A is continually primed to be discharged, laser like. Part B is the light capturing component. A 'gate' laser turns B on and off, an input laser is the signal, and the lazed output is the output.

Quantum computing and quantum mechanics deals with superposition and tunneling, to my understanding, so unless they can feed in 4 inputs, freeze the crystal, and then get one 'correct' output when they unfreeze it, I fail to see how this is quantum.

Given that I described a transistor, I can see this as being critical to an optical computer :)

Source = input
Gate = freezing laser
Drain = output

You can make an optical and gate this way:

Combine input A and B into one beam. If they are in phase (both true) their output signal amplitude doubles. If they are out of phase (one true, one false) their output amplitude is zero. Pass this combined signal through two crystals.

Pass a *second* 'clock' signal as well that happens to be out of phase and half the amplitude of a true signal. The first crystal fires true when the clock and input signal cancel to produce a '1'. The second crystal fires false when the clock and the input signal combine to produce a '-1'

MPAA ban light research.

The MPAA announced today that it has worked with the US government to ban light research under the Digital Millenium Copyright Act. A spokes person said "We are happy that we have nipped this little thing in the bud. Controlling light would allow people to create special viewing devices that could delay light at one end and allow people to watch previously 'recorded' films. We think that such a device could even be incorporated into a pair of glasses." They then went on to speculate that quantum computers could be built that were so fast, they could generate DVD decryption keys in fractions of a second, and that there were many other uses that pirates could come up with.