A marginally less cranky physics post than the previous: the big story in my area of physics this week is probably the Harvard experiment involving the storage and transport of light pulses. Like the ILC announcement, this has been written up in the Times, and you can also read the Harvard press release or the much more informative PhysicsWeb report.
The basic idea here is an extension of the "stored light" trick that Lene Hau's group at Harvard did a few years ago. They illuminate a sample of atoms with two different laser beams, which leads to the absorption of one of the two. They then switch the other beam off, wait a little while, and turn it back on, and the absorbed light is regenerated.
The new wrinkle here is that the atom sample they used is a Bose-Einstein Condensate split into two parts, and the initial absorption causes some atoms from one of the condensates to start moving. They switch the second laser off for long enough for the moving atoms to make it from one condensate to the other, and then turn it back on, and recover the original pulse from the neighborhood of the second condensate.
It's a clever experiment, but I think I'll need to read the actual paper to figure out what the fuss is about. I mean, it's cool and all, but I'm not quite sure what the point is. But then, I've never really understood the point of the "slow" and "stopped" light stuff in the first place...
The "stopped" light thing is particularly puzzling to me. The light has basically been absorbed. Granted, it's been used to put the atoms into a long-lived superposition state, rather than a typical short-lived excited state, but it's still essentially absorption, and not a big shock to anyone who's heard of the dressed state picture. The fact that the recovered pulse is still coherent with the original absorbed pulse is kind of neat, but that's stimulated emission for you.
I'm not really clear on what this new experiment adds to the picture. Specifically, I don't understand the role of the second condensate-- I get that the absorption causes some of the atoms in the first BEC to start moving, and separate themselves from the others, but I don't see what's gained by having those atoms enter a second condensate before turning the laser back on. The pulse recovery ought to work exactly the same way with spatially separated atomic wavefunctions as with a single excited BEC, so it can't be that the second condensate is needed for the recovery to work. It would be really cool if the second condensate amplified the signal in some way, so you got more light out, but there are some tiny little issues with conservation of energy there, so that can't be it.
I dunno. I'll have to get the paper from Nature, and see if I can figure out why this is so exciting. In my copious free time...
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"Stopped light" is (I believe) a misleading terms designed for sound-bites on TV and for raising money. The analogy is to "quantum teleportation" (which intentionally evokes Star Trek and the like), "squeezed light" (which wrongly relates to common-sense experience with pressure), and... well, I'm sure that we can come up with many such examples.
The Harvard research is excellent, and matter waves with BEC are likely the basis of important future technologies, once we peel away the hard-sell verbiage.
Integrated electrooptics has been, for several years, a fast-growing segment of the VC (Venture Capital) world, growing even right after the Dotcom Crash. The more purely optical, the more advantages for certain applications. The combination of ultra-cold, optics, BEC, and the like is very important.
I recall (imperfectly) that when Franklin was asked:
"What good is Electricity?" [the latter word being the title of his book, as well as its subject] he reportedly answered:
"What good is a newborn baby?"
the stored light is more like transfering an oscillation from the EM field to a dipole (that hopefully doesn't spontaneously emit too much), and then back out. EIT and fast/slow light are neat and have QM interference explanations, but you can also understand it all with coupled oscillators, and can see similar effects in two inductively coupled RLC circuits. The BEC part is just to get a dense, non-Doppler broadened ball of atoms to date. This is why it can be done in solids at room temperature! If someone says they have a neat quantum effect in a solid at room temperature, well hold on to your wallet! Of course the fact that the atoms are stable and make a solid is QM, everything is, but oftentimes simpler explanations are available!
As far as I can tell, the significance of the second BEC is this:
It's not actually a second BEC. It's a spatially separated part of the same BEC. See, the emission of the information in the light is not from the atoms which absorbed the light alone, but from the system of them *and* the substrate of ground-state BEC atoms. Otherwise the information in the light is lost.
The fact that the experiment worked with a completely different set of ground-state BEC atoms shows that the separated BECs have truly identical ground states, and therefore are one BEC.
I think.
If the second condensate is coherent with the first, thats a new twist. Other than some interference experiments of Ketterle and the beautiful 4 wave mixing experiments of Bill Phillips, much of BEC work is proving that Reif and other Stat Mech books are right, or providing a cold dense source of atoms. Course dem fellas is just gettin started, lots of good stuff to come!
I think the reason for the interest in general is that there are some nice big-dollar industrial and commercial applications for the various techniques. Specifically, I think they are regarded as a potential avenue to more efficiently and economically blend optical computing with more conventional silicon/electronics techniques. I think it removes one of the many bottlenecks in that process.
If true, these types of experiments are a small step on the road to better performing processor chips. And if that's true, then someone stands to make a pile of money off it when Intel, AMD, or IBM get involved.
(Caveat: VLSI and silicon optics are as much my field of engineering as string theory is your field of physics....)