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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."
Um. Yes, It stores energy, then releases it later. But, this sounds like it actually holds the photons and releases them later. Or at least that's what the submission infers.
The article seems a bit sketchy and makes a connection that I don't think is 100% valid, how can this possibly relate to quantum computing? This has nothing to do with electron spin. It has alot to do with trapping photons, then later releasing them by exciting the atoms.
My guess is that the fundamental difference is the wavelength of the light emitted when it is released is the same as the wavelength of the light that was stored in the crystal.
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Well, no. It's hard to tell from the lack of detail in the Nature article, but from it's description, it sounds like this material can be made to absorb light, and somehow another laser is later used to extract it. (Same wavelength and phase?) It's not like there are photons standing still somewhere.
The article does not say that they actually stopped the light beam, which is impossible on the grounds of relativity theory.
The trick is that they can give an idefinite halt to the photon reemission.
As light beam passes through any material the photons get absorbed by atoms they hit on their way. In normal circumstances the atoms immeditely reemit the photons in order to get back to previous, lower energy state.
The success of the experiment is that it demonstrates the technology to give an indefinite delay to forementioned reemission.
Or, at least, that's what textbooks on quantom mechanics I've got say :D
The second laser performs as an energy pump. A photon of the correct configuration could raise an electron to a new energy state. A second laser, emitting photons of another configuration, could raise the new energy state to a higher level. It might be the means used to keep the electron from falling immediately to the base energy level. If all of this sounds like the process is somewhat more complex than the simple description in the article, that is correct. If the developers have succeeded in stopping, then restarting light after a measurable time delay, even a very short one, they have made progress. Getting atoms and electrons to stabilize in desired states at room temperature is not a simple lab exercise, and achieving it is a major accomplishment.
I'm not sure that quantum computing couldn't somehow benefit from this technology. Typically, you would need the emission (or not) of a photon to represent/detect a quantum state. At some point the system has to resolve and interface to us. I believe that medium is a photon, or series of photons.
The truth is, I'm guessing here, but how else do you build a human interface to a quantum system?
Knowledge is like ignorance.. too much can be just as bad as not enough.