Researchers say they have slowed light to a dead stop, stored it and then released it as if it were an ordinary material particle.

January 19, 2001 12:27 PM

Researchers say they have slowed light to a dead stop, stored it and then released it as if it were an ordinary material particle. Cool, huh?
posted by tiaka (21 comments total)

I agree with what Rebecca said yesterday about this -- the ramifications of this are likely to reach far beyond anything we can imagine right now.
posted by jjg at 12:33 PM on January 19, 2001

It's a disruptive technology. We don't know what comes next, we just know that everything changes. If this works, networks become 1000 times faster, first at the core, and then moving out toward the edges. Quantum cryptography becomes practical and usable. Every "it's coming" service for the net (VOD, live interaction, etc.) that hasn't come becomes instantly trivial.
posted by faisal at 1:33 PM on January 19, 2001

Does it mean new pipes? Did all these towns waste time laying fiberoptics?

I am a layman. Use small words.

posted by capt.crackpipe at 2:34 PM on January 19, 2001

It goes well beyond fast computers, too -- once we start stopping light, it won't be long before crazy things like time travel become viable (Don't forget we're talking about "particles that can exist in many places or states at once"). jjg and Rebecca must be right; when you consider the fact that nobody can see the really big innovations coming (personal computers, the internet), it makes me wonder just how trivial those services faisal mentioned will seem 50 years from now.

posted by Eamon at 2:53 PM on January 19, 2001

This seems soooooo much bigger than "consumer products".
posted by internook at 3:43 PM on January 19, 2001

Bigger than 'consumer products' it may be but in the past we've generally seen comsumerism is a large part of what drives technological innovation.

Correct me if I'm wrong.
posted by machine at 3:50 PM on January 19, 2001

Yeah, I know the ramifications are way bigger, just that consumer products are where we get to enjoy the new technology. :)
posted by aaron at 4:14 PM on January 19, 2001

Dangit! Why can't we just settle on a nice set of laws and stick with it!?

Hell, I'd be perfectly happy with Newtonian physics, myself. It was working fine, but then people had to come along and screw with it...
posted by whatnotever at 4:26 PM on January 19, 2001

I'm thinking this will enhance sex technology like light years ahead.
posted by tiaka at 4:26 PM on January 19, 2001

Someone used the word swanky. Heh.
posted by swank6 at 5:32 PM on January 19, 2001

Well, the coolest thing about quantum physics is that you can theoretically do some strange things, like fiddle with the quantum state of an atom light years away, without touching it. Now I admit that my knowledge of quantum physics is very basic, and I hope someone will come along and correct all my mistakes, but what I guess I'm trying to say is this: any physics that lets you mess with atoms from across the universe can't help but "enhance sex technology."
posted by Eamon at 7:12 PM on January 19, 2001

One prediction, though: If they do find a way to do quantum cryptography out of this, someone else will find a way to break it.

(warning: long explanation ahead)
It's not clear that this can be done, even in theory. Breaking ordinary public-key cryptography amounts to being able to find the two prime factors of a very large number (as in hundreds of digits). As a practical matter, if you have a sufficiently large number of bits (like 512 bit or 1024 bit), it will take an astronomically long amount of time to break the code using normal Turing machines (such as the computers we use now). In theory, however, you can go through all of the possible prime factors and eventually find the solution. The problem is that if one adds one bit to the key, it takes twice as long to break the key. If it takes n computations to break a 512-bit key, it will take n^2 computations to break a 1024-bit key (on average).

With quantum cryptography, things are different. Every communication involves a perfectly random one-time key. There is no way to break this, even in theory. (Here's what this means: convert a message into ones and zeros. Then take a randomly generated sequence of ones and zeros of the same length, which only you and the recipient know, and add it to the message. Send the message publicly to the recipient. She then subtracts the sequence from the coded message to get the plaintext binary message.) Given that the publicly transmitted message has no discernable order to it (due to the addition of a randomly generated sequence), nobody can break the code given the message.

But what if someone intercepts the randomly generated sequence when you send it to the recipient? The bits sent are in the form of polarized photons, and when they are intercepted, they are irrevocably changed -- this is an intrinsic quality of quantum mechanics. The recipient will always be able to figure out that the one-time key has been tampered with.

But please note:
1) it is still theoretically possible to disrupt communications that are coded in such a method, even though the disruptor can't read the message;
2) once quantum computing is a mature technology, your old pgp keys are useless, and old messages that you sent using public-key cryptography can be broken. The number of operations increases much more slowly than n^#ofbitsinyourkey: you can't just increase your key size to buy yourself a few more years of privacy.



posted by UrineSoakedRube at 10:02 PM on January 19, 2001

Does it mean new pipes? Did all these towns waste time laying fiberoptics?

I am a layman. Use small words.

I'll try, but it's probably a good idea to get one's hands on a copy of this article in order to understand what is actually involved in quantum cryptography.

In order to successfully send a one-time quantum crypto key, you have to be able to send polarized photons over long enough distances without their polarizations being affected by thermal noise. In an experiment, Bennett and Brassard (a couple of Bell Labs folk) managed to send a message over a handful of miles (I forget how many, but it was less than 50). The longer you go, the fewer photons will remain unaffected by noise.

Now, I have no idea how the store-light-then-release-it experiment linked to will change this. The quantum channel mentioned in the cite above is a light-tight box, but I don't know if ordinary fiber-optics lines can be used for this purpose. Possibly the rubidium experiment can be used to make line amplifier boxes which will keep the signal from degrading into pure noise, but I don't see how this can be done without changing the polarization properties of the photons themselves.

In short, I have no idea, but I doubt the stop light experiment will have any application to quantum cryptography.
posted by UrineSoakedRube at 10:34 PM on January 19, 2001

Well, sure it will have application to quantum cryptography. You send the polarized light into the box, stop the light, give the box to FedEx, and send it as far as you want. Recipient releases the light. Voila, no more distance limit.

Of course the size or the temperature requirements of the apparatus may prevent such a trick at present.
posted by kindall at 8:46 AM on January 20, 2001

Isn't this the same thing someone wrote about a month or two back, and it turned out that, no, they hadn't broken the speed of light after all?
posted by baylink at 7:10 PM on January 20, 2001

baylink:

I don't think so. Are you talking about the scientists who shot light into a room of cesium and when the first light particle hit the "left side" (I don't remember what side :-) of the room, it instantaneously left from the right side, in effect jumping it in time thingy?

If that's the thing you're thinking of, this one's different because the light particles can be trapped in a bottle (probably a pretty big one at this point) then released at any other time any other place. (That has the necessary lasers and other equipment, of course. :-)

Has anyone found more articles on this anywhere? Perhaps some with more detail of what exactly's going on?

The article doesn't really argue the point that they've stopped time much more than "Scientists stopped time. They're scientist, and they did it." There's no real evidence to me that time is actually being stopped as opposed to being destroyed and recreated.

The second beam of light they shoot into the gaseous mix could just be reformed into the same properties as the first ray, for instance. The don't really mention intensity except when they say the first one fades inside the bottle.
posted by cCranium at 6:29 AM on January 21, 2001

cCranium>Has anyone found more articles on this anywhere? Perhaps some with more detail of what exactly's going on?

The NYT article notes that the details will first be given in a paper in Nature.

kindall>Well, sure it will have application to quantum cryptography. You send the polarized light into the box, stop the light, give the box to FedEx, and send it as far as you want. Recipient releases the light. Voila, no more distance limit

Just in case someone thinks you're serious, no, this can't be done in practice. (See below).

cCranium>The second beam of light they shoot into the gaseous mix could just be reformed into the same properties as the first ray, for instance. The don't really mention intensity except when they say the first one fades inside the bottle.

This is where the article is less than clear -- it just says that the light ray can be reformed with "the same properties" without specifically stating that polarization is one of them. Unless this is the case, this can't be used for quantum cryptography as it is currently conceived.

Incidentally, the "breaking the speed of light" experiment that was mentioned is something different. That experiment was an exercise in the group velocity of a light packet exceeding c (the speed of light in vacuum), even though the phase velocity still did not exceed c. Einstein didn't say that nothing could exceed the speed of light, just that matter and information could not be sent faster than c.

cCranium>If that's the thing you're thinking of, this one's different because the light particles can be trapped in a bottle (probably a pretty big one at this point) then released at any other time any other place. (That has the necessary lasers and other equipment, of course. :-)

Again, I don't believe you can release the light at "any other time and place", even if you do have the necessary equipment. Given enough time, the spins of the Rb atoms that record the light's properties will relax and the information will be lost. Also, when you say a "pretty big [bottle]", that's an understatement. Remember, these atoms are cooled to a very low temperature, so you'd have to have some way to transport it while insulating it at that temperature. And that still wouldn't save the information indefinitely.
posted by UrineSoakedRube at 12:38 PM on January 21, 2001

Yeah, but remember... most of the advanced in the last 50 years were first described in Science Fiction stories.

They'll overcome those limitations. Didn't y'all always wonder what those little disks in the tricorders *were*? :-)
posted by baylink at 12:30 PM on January 23, 2001

baylink>Yeah, but remember... most of the advanced in the last 50 years were first described in Science Fiction stories.

They'll overcome those limitations. Didn't y'all always wonder what those little disks in the tricorders *were*? :-)

By those limitations, I assume you mean the time limit of the Rb gas in retaining the information of the first light wave.

Clearly, we have to wait for the Nature article to say any more about this particular experiment. But some limitations won't be overcome because they'll be worked around. Will people find a way to break quantum cryptography? I doubt it, because there are likely easier ways to find out what the messages being sent are. Also, it is considered impossible by current understandings of quantum mechanics, and I'll bet on quantum mechanics holding up for my lifetime. Will people store light waves indefinitely in supercooled Rb gas? Why bother? There are simpler ways to store information, and shipping a bottle of supercooled Rb gas defeats much of the purpose of sending information via light waves.

Remember when High-Tc superconductors were invented and people said that it was only a matter of time before we have superconducting energy cables, ridding ourselves of transmission losses? Those cables still haven't come, but the prediction misses the point: innovations in energy production (fuel cells, flywheel batteries, solar, wind) will have a much greater impact on the power industry than superconducting energy cables would, even if there was a cost-efficient way to use them.

Will this experiment change everything? Don't be too sure.
posted by UrineSoakedRube at 12:15 PM on January 24, 2001

hey geeks, the rest of us are at the TOP of the page...

; )
posted by Avogadro at 12:24 PM on January 24, 2001