Rydberg Molecule Created For the First Time

krou writes "The BBC is reporting that the Rydberg molecule has been formed from two atoms of rubidium. Proven in theory, this is the first time it's been created, reinforcing the fundamental quantum theories of Enrico Fermi. Chris Greene, the theoretical physicist who first predicted that the Rydberg molecules could exist, said: 'The Rydberg electron resembles a sheepdog that keeps its flock together by roaming speedily to the outermost periphery of the flock, and nudging back towards the centre any member that might begin to drift away.' It's a sheepdog with a very short life-span, however; the longest lived molecule only lasted 18 microseconds. Vera Bendkowsky, who led the research, explained how they created the molecule: 'The nuclei of the atoms have to be at the correct distance from each other for the electron fields to find each other and interact. We use an ultracold cloud of rubidium — as you cool it, the atoms in the gas move closer together. We excite the atoms to the Rydberg stage with a laser. If we have a gas at the critical density, with two atoms at the correct distance that are able to form the molecule, and we excite one to the Rydberg state, then we can form a molecule.'"

Comments

Basic facts about Rb_2

[modrzej]

I've done a little research using Scholar (Phys. Rev. Lett. 85, 2458 - 2461 (2000)) and it seems that basic facts about Rydberg molecules are: 1) These are molecules made of two atoms of the same kind, enormously separated (minima of potential curves for example at about 1500 atomic units); 2) Because of extremly shallow minima of energy curve in witch they exist, they are unstable, so must be ultra cold; 3) This Rb_2 molecule despite being homonuclear, displays large dipole moment, which is unusual but predicted by theory. The experiment with rubidium described here proves that approximate quantum theory (I bet that existence of this molecule was predicted using Born-Oppenheimer approximation) is capable of describing effects subtle as this one (existence of Rb_2 Rydberg molecule is subtle one). I'm not an expert in relativistic effects, but it seems to me that this example of extremely distant separation of atoms in molecule could call for relativistic treatment: one Rb atom doesn't know of the other at once, because the information about the movement of the other can't travel faster than light. This effect may be big because of separation of these two atoms.

Re:What are the implications of this discovery?

[radtea]

I RTFA, but can someone more well-versed in Physics explain what sort of implications this has?

Not my field, but this is my sense of what's going on:

1) Rydberg atoms have one electron in a very high state of excitation, and look like Bohr-model atoms, as the highly-excited single outer electron is so far from the rest of the atom that the combination of the inner electrons and the nuclear charge look like a point-charge, so the outer electron experiences a 1/r potential. This makes Rydberg atoms theoretically tractable with simple Bohr theory, which is always fun to play with.

2) Rydberg molecules are make from a Rydberg atom and a normal (unexcited) atom. My guess is that the normal atom is actually inside the "orbit" of the Rydberg atom's outer electron, so it will be slightly polarized by the core field, and the resulting dipole will interact with the electron to produce the bound state. Sounds like a job for linear response theory.

3) In general, testing systems under such extreme conditions allows us to measure precisely various properties of matter, like the fine structure constant or the electric charge or whatever. I don't know if anything like that will come out of this, but extreme systems often allow for precise tests of esoteric phenomena.

4) Yes, this does validate quantum theory. No, it probably doesn't have much in they way of practical application, but then again, it doesn't have to.