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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."
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.
Um.. you are wrong, so I'll correct you. "Glow in the dark" stuff glows because a chemical reaction is happening, and generating light. This is something completely different. These guys actually brought light to a hault, so that a pulse of light stopped in the crystal
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helps to explain how they're achieving this with a graphic representation. Still a little technical for me, but it kinda makes sense.
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how can this possibly relate to quantum computing?
From http://www.sciam.com/2001/0701issue/0701hau.html
"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."
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.
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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
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Since this is not a spontaneous process, the wavelength of the emitted photon can be identical to that of the original photon without violating conservation of energy. In fact, all the characteristics of the photon--wavelength, polarization, phase, etc.-- are stored in the crystal and can be recovered, so that the emitted photon is identical to the original.
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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.
/. 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.
Perhaps some of the enlightened
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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It has been done, but not with anything in the "gas" state as is commonly understood. The light-freezing trick was done, IIRC, with a Bose-Einstein condensate. This much-ballyhooed creation is made from a bit of ultracold sodium gas, but it isn't in the same physical state as a gas any more than superfluid helium is.
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When the 'material' is beamed with the second laser, it makes the material 'liquid'-like to light, allowing the light to travel through. As the second laser is reduced in energy, the 'material' becomes more and more viscous until it totally absorbs the energy of the light that is in it (becoming 'solid' to light). It stores the light's energy AND it's wave pattern.
Cool idea.
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You can read this story here: http://www.scifi.com/scifiction/classics/classics_ archive/shaw/shaw1.html