Freezing light with a laser, bose-einstein condensate explosions

In this month’s SciAm, there is an article called “Frozen Light” on pg 66, by Lene Vestergaard Hau. She says in it

illus. pg. 69 fg. 5

Furthermore, at fig. 6, same page, she says

We learn from the National Institute of Science and Technology staff writer Michael Baum, referring to Bose Einstein Condensate functions (known as “bossanovas”) of rubidium-85 chilled to 3 billionths of a degree above AZ, that

found here.

What would be the effects of halting the light pulse using Hau’s methods, then destroying the BEC using the methods shown above? What would happen to the light pulse whose information is contained in entirety in the BEC? The light pulse disappears when frozen, and the BEC disappears when it approaches AZ. Would the light pulse be lost to this world? Where did the photon(s) themselves go? The BEC would no longer be held in the quantum state necessary to retain the information of the light pulse, so the energy of the pulse is effectively lost. If no increase in temperature, gravity, electricity, or magnetism is measured during this explosion, would this mean that we have effectively thwarted Einstein, in that we have destroyed matter without forming it to energy? Is this a ‘practical’ application of the theoretical particles in space that randomly become and unbecome?


The particles that appear in space and then dissapear are a different concept. What happens when these occur is energy is borrowed to form a particle and an anti-particle. Then the two usually collide and return the energy. So no net energy is gained or lost. I would be wary of anything that says the energy or matter simply dissapears. Maybe the matter is spontaneosly turning into energy in response to the lack energy around it. I know that doesn’t sound very plausible, but it’s better than ‘it just dissapears’.

Homer, although I am not qualified to answer your posts, I do like them. They make me think.

:smiley: Thanks for the kind comments, Anth. While I may not know what 2 is or where it came from, I do enjoy putting it with another 2 and seeing if it makes 4.


Does any of the week-day crowd know this scientific riddle?


First some slight back ground ‘Frozen Light’ is not really a frozen photon stream, it is in fact the storage and retrieval of information encoded into the phase structure of a light wave, see here.
Altering the state of the storage material in particular its internal energy structure would destroy the oscillation in the electron cloud and thus the information encoded in this structure by the light wave would be lost.

The energy of the system as whole is preserved however, as the light wave transferred energy to the electron cloud where it is stored until a window into the material is re-established or, it is used up heating the material as its internal energy equilibrium changes.

Note: This is not my area of specialty, and this post and the referenced material have grossly simplified several parts of this process.

I’d put my money on some sort of photon-phonon conversion of light into kinetic energy, as mentioned in the post above. Good one, Tim.

Sorry for bumping this again, but I can’t believe none of our science heavyweights have weighed in on this conundrum.

What is a phonon? I couldn’t find anything that explained it very well, the best was who claimed it was a lattice of vibrational energy. They also mentioned that they are useful in superconductivity.


This is because photons have no rest mass; if they’re not moving they don’t have energy.

I addressed this in the thread Heisenberg’s Uncertainty Principle, Wrong??. Basically, the experimenters believe their detectors are just not detecting the “vanished” particles.

Britt answers this well enough, but let me add more detail. The BEC stores the state information and energy (and other conserved quantities) of the photons. Under very controlled circumstances, this information and energy can then be converted back into photons. By destroying the state information, you’ve made the process irreversible. All of the photon’s energy (and other conserved quantities) is still in the BEC. Probably transformed into heat.

A phonon is a quantum of sound. Within a crystal (which is any solid with a well-defined lattice of atoms), sound waves have quantized energy and momentum. The term phonon refers to this quantized wave. In amorphous solids (no regular lattice) and fluids (i.e. liquids, gases, plasmas, BEC’s) sound waves are not quantized and so there’re no phonons.

Thanks for the clarifications, Pleonast. If you keep answering my questions so clearly, you’re going to start getting ‘crazy man’ emails from me saying “Yeah, well what if we do x to y and then…” :eek: Heh heh just kidding. You hope.



My pleasure; I try my best. Many of my undergrad nights were spent explaining physics to my philosophy friends. Keep asking crazy questions; I regularly lurk in General Questions. Except when I’m traveling, which is often.

I think Britt and Pleonast answered the OP quite well, and I have nothing to add to their explanations.

Homer, I just want to compliment you on the intelligence and creativity that you displayed in trying to apply the knowledge from those articles to push the boundaries of what we know. It’s hard, as popular science articles can often give false impressions in their efforts to be both dramatic and understandable, but I’m impressed that you keep asking questions and looking at things in new ways.

This last sentence isn’t actually true. Phonons are quantized compressional waves, i.e. sound waves. Sound can of course travel in liquids (e.g. water) as well as solids. The interactions are just more complicated, so it’s not always useful to talk in terms of phonons. However, there are exceptions. For example, in superfluid helium (my current area of expertise), Landau derived an accurate representation of the non-superfluid part as a weakly interacting gas of phonons (and rotons, another type of excitation), which works really well, and is consistent with experimental measurements, including speed of sound measurements.

Just a minor nitpick.

Let me apologize in advance for the following techno-speak.

In my defense, I didn’t explicitly state that superfluids have no phonons (since BEC’s and superfluids are not quite the same thing, although many similarities exist). To be even more precise, the phonons of fluids have such short lifetimes as to be useless for modeling bulk properties.

I’m not especially familiar with superfluids (although I do know superconductivity), so I will trust your judgement. But the way I understand phonons, they require a lattice. Is it possible that the component of superfluid He being modeled with phonons has a lattice structure? Also, aren’t rotons a part of the superfluid component? I’m assuming they’re analogous to flux quanta in superconductors (basically, little rings of supercurrent).

Giraffe, I truly appreciate your praise. :slight_smile: While I’m near obsessed with physics, I can’t do the math (I simply cannot comprehend math above higher level algebra), so I get left out. I do love to theorize, however.

You guys have given great answers so far. I can’t begin to thank y’all enough (Chronos, you too, even though you haven’t posted here) for the patience and diligence you guys show in answering (what would probably seem to me if I were in your shoes) to be rather ignorant or presumptuous queries.

One quick question, however… how fast does change propogate through a superfluid? If a cooling system were to use a superfluid, would circulation be necessary? I wouldn’t think so; if heat (or whatever other variable) propogates through the entirety of the fluid quickly enough, and with little enough resistance, you’d expect to be able to cool one area of the fluid and that would maintain the required temperature level for the entirety of the fluid even if the fluid were being heated in another area. Hmmm… this is interesting… you’d only need to remove exactly the amount of heat introduced this way, because no additional heat would be introduced by turbulence, pressure, restriction, and the other normal ‘extraneous’ heat creators in a normal cooling system.

Too bad superfluids don’t work at room temperature yet. You’d never have your coolant pump go out again, there’d be no pump to go out!

I just thought of something… can you induce a vacuum state in non-fluids? Such as magnets, electricity, heat… or is vacuum behavior inherent only in ‘real’ matter? Well… I suppose the pos/neg forces of magnets and electricity could be likened to a vacuum/pressure state… but as for heat/cold… Well, I guess heat flows to cold, so… Except, doesn’t electricity flow ‘backwards’, from neg>pos? I guess vacuum/pressure is just a realization of a natural flow from more to less (of whatever variable) in a physical state. Order to chaos. Heck. I should be a physics major so I can quit relying on youse guyses for answers, that’d make it easier on all of us!


Vacuum questions:
A vacuum
I) The absence of matter (or more precisely the absence of particles with non-0 rest mass).
II) The lowest possible pressure, Given that with-in a system of unequal pressures the system will tend towards equalization of the pressure by redistributing the mass from the high pressure system to the low pressure system.

The second definition is a non-quantum definition and is in fact a non-quantum effect.

Electrical charge: Vacuum as in complete absence yes. Several particles have 0 electrical charge. A Collection of particles canexibit 0 overall charge.
Vacuum as in lowest possible electrical charge on a non-quantum level, 0 charge is probably the equivalent state you are looking for. Although the mecanism for maintaining this state is quite different, than in a true vacuum.
Magnetic fields: Almost certainly not. Field effects are quiet different from particle effects as they reflect the structure of space-time rather than objects within it. (OK so this is the way I interpret these effects, for completeness I will state there are other interpretations).
Heat: the complete absence yes 0 Kelvin. Objects in this state would exhibit similar properties for electromagnetic waves as a vacuum causes in matter.

I am afraid super-flluids are outside of my field so I will have to leave them for the others