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Optical Computer Made From Frozen Light
neutron_p writes "Scientists at Harvard University have shown how ultra-cold atoms can be used to freeze and control light to form the "core" - or central processing unit - of an optical computer. Optical computers would transport information ten times faster than traditional electronic devices, smashing the intrinsic speed limit of silicon technology. This new research could be a major breakthrough in the quest to create super-fast computers that use light instead of electrons to process information. Professor Lene Hau is one of the world's foremost authorities on "slow light". Her research group became famous for slowing down light, which normally travels at 186,000 miles per second, to less than the speed of a bicycle."
Where do I get one of these? No, I want it now
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Most of the positive fanatics write lots of papers; those who think it's not going anywhere (like me) don't. There are sound physical reasons to be skeptical, in my mind:
1) Wavelengths are too big: 1 micron is now a large number, and optics doesn't work much smaller than this.
2) There are no good nonlinearities. Anyone can make a linear OR gate optically, but to function as an effective digital technology you need nonlinearity and level restoration. This is missing in pure optical systems, except at very high power levels. The high power levels imply low density. There are some optical gates which process data in "femtoseconds," but ask them how long it takes to get to the next gate. Maybe someday someone will invent a great, low power, fast, optically nonlinear material. Don't invest in it yet.
3) The serious workers are now mostly working in combined electronic/optical modes. The speeds here are limited by the gate speeds of the electronics, just like normal computers. You have to then ask if optics is a good (cost effective, space efficient, low power...) replacement for wire. Ultimately, the answer is probably yes, but there's an awful lot of work to do before that's true (for the distances of a few centimeters in high density computers, that is).
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became famous for slowing down light, which normally travels at 186,000 miles per second, to less than the speed of a bicycle.
ah yes, the Speed of a Bicycle (SoaB) metric for slow light.
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The best thing about frozen light is that you can put it in your freezer, so that when there's a blackout, it will thaw and then you'll have light.
Obviously it's not simply a temperature thing, since most of space is absolute zero, and I can see stars and suns and stuff. So it's not freezing light as in freezing water.
So how exactly do you stop photons from moving? How does this affect relativity (e=mc^2)? How does this affect our perception of the universe - ie; if the light from the star that we think is 10,000 light years away is only moving 20mph or so, it could really be millions of light years away?
Does like, time slow down? My heads spinning. Freeze sounds like the wrong word.
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It's not the same.
The c in E=mc^2 (or E^2 = M^2c^4 + p^2c^2) refers to an intrinsic property of spacetime. Bose Einstein Condensates and so on don't really alter that. One way to think about it is to stop with the 'slowing down light thing', and instead conceive it as the BEC swallowing up photons for a while, storing the information, and then reconstructing a new photon which is exactly identical at the end. This is pretty much the same, because in QM, you can't really track anything exactly, and you definitely can't distinguish between objects with the same properties.
From Wikipedia: 'In a sense, any light travelling through a medium other than a vacuum travels below c as a result of refraction. However, certain materials have an exceptionally high refractive index: in particular, the optical density of a Bose-Einstein condensate can be very high. In 1999, a team of scientists led by Lene Hau were able to slow the speed of a light beam to about 17 metres per second, and, in 2001, they were able to momentarily stop a beam.' Slowing light down is nothing new, it happens every time light travels through a medium other than the vacuum of space. Atmosphere, glass window, diamond, etc. It just so happens that we can now create in a laboratory these BEC's, a so-called "superfluid" which is basically a substance cooled to the point where nearly every atom collapses to the lowest quantum state (like, close to absolute zero). This gives it some interesting properties, like zero viscosity and an extremely high optical density. Hope that helps.
1) Wavelengths are too big: 1 micron is now a large number, and optics doesn't work much smaller than this.
This poster is correct. Since I have a Ph.D. in the field and the parent obviously knows something about optics, I might as well respond to the parent's critics.
IR photons are BIG. Forcing light to bend around corners is difficult. A waveguide must have a very high index of refraction if it is to be used to bend light within a reasonable radius. To the extent a Bose-Einstein Condensate helps this problem is encouraging if you don't mind cooling your computer to 2 millikelvin.
The speed of these optical computers always seems to come down to limitations of the silicon processors that work in conjunction with the light.
It's just a Bose-Einstein Condensate. These projects take time. While we are enamored with this BEC project, some poor grad student is working on carbon doping. Higher doping might improve the world of electronics far more than another optical computer claim.
I visited Hau's website and did, though, enjoy her papers. I just don't think the press release accurately portrays the low engineering potential of this work.