Nobody Expects Bose-Einstein Condensation

An interesting tidbit that occurred to me in thinking about the "unexpected uses of technology" panel (well, along with the "Total Eclipse of the Heart" thing): In a certain sense, my entire professional career is derived from unexpected uses of technology.

I'm not talking about the physics-with-the-dog thing, though that's pretty unexpected, but rather my research career. I work in atomic physics, specifically the subfield of laser-cooled atoms, and the most important paper I wrote involved Bose-Einstein condensates of rubidium. In fact, I got my start in the field as a skinny undergrad trying to do laser cooling of rubidium.

This turns out to be possible through a quirk of technological history. The original laser cooling experiments were mostly done with sodium, because you could get a dye laser to operate at the right wavelength to laser cool sodium atoms (about 589 nm, that yellow-orange color you get from certain kinds of street lights). In the late 80's, though, people figured out that rubidium was also a good candidate, with a laser cooling transition in the near-infrared, at 780 nm.

Rubidium turns out to have a number of really nice properties, leading Eric Cornell to jokingly dub it "God's Atom." What really made it take off, though, was that people figured out you could get the laser cooling wavelength for rubidium from diode lasers. And diode lasers are manufactured in mass quantities because they're used in CD players, laser printers, and other commercial electronic devices. So, rather than needing to spend a couple hundred thousand dollars to get a dye laser system up and running, you could get a working laser system for a couple of grand.

That puts the basic laser cooling apparatus within reach of smaller research institutions and undergraduate colleges, and now everybody and their brother has a rubidium MOT. Carl Wieman and Eric Cornell used a diode-based system to cool and trap rubidium, and then to make a Bose-Einstein condensate in 1995, winning themselves a Nobel Prize, and launching a whole new field of research.

And it's all possible because somebody figured out you can do science with the lasers in your CD player.

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Element: Sodium (Na) Atomic Number: 11 Mass: one stable isotope, 23 amu Laser cooling wavelength: 589 nm Doppler cooling limit: 240 μK Chemical classification: Alkali metal, column I of the periodic table. Like the majority of elements, it's a greyish metal at room temperature. Like the other…
Element: Rubidium (Rb) Atomic Number: 37 Mass: two "stable" isotopes, 85 and 87 amu (rubidium-87 is technically radioactive, but it's half-life is 48 billion years, so it might as well be stable for atomic physics purposes. Laser cooling wavelength: 780 nm Doppler cooling limit: 140 μK Chemical…
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Being able to tune diodes electronically and thermally, and with optical feedback had something to do with it, too, but I agree that without availability the other advantages aren't as important.

I remember, back in the early '90s, salespersons who were willing to sort through their stack of laser diodes and sell me the ones closest to 780, which made the tuning a lot easier, since you didn't have to cool the lasers as much.

"In fact, those who do expect it...I'll start again. Our Condensate consists of three people, Bose, Ein, and Stein...no, wait a minute..."

Diode lasers are great. We use a $10 one for position encoding at 4 K, where it actually operates much more efficiently than at room temperature.