Magneto-optical trap

 I had the most amazing experience yesterday: I visited a lab that does magneto-optical trapping! MOT for short. That little red glow in there? That is a pool of rubidium atoms at 200 micro-kelvin!

Here's what it looks like on their camera:

The glowing egg in the middle! This is a super impressive MOT because it is a beautifully contained blob. Their early ones had streaks coming out. The atoms glow because they are laser-cooled, which means they absorb laser light directionally (which selectively slows them down - I can explain) and then they re-emit the light in all directions. SO COOL. They call it "the coldest spot in Bristol" when talking to funders :) For those of you new to this kind of thing: Warmth is the motion of atoms/molecules. Zero Kelvin is "absolute zero," the lowest limit for temperature, where all motion stops. It is unattainable due to quantum mechanics but 200 micro-kelvin is pretty close.

Here's the heart of the thing with the laser off and the room lights on. That tall part in the center is where the atoms get trapped. You have to turn the laser off if you want to stick your head in there and look around because it is a THIRTY WATT laser. (It's supposed to be a 48 watt laser but it's not working right; they're getting a new one.) This power of laser will instantly cook your cornea/retina, chop off your finger, etc. They showed me a hole that they accidentally burned through the wall.

The whole place is a gorgeous intricate web of laser paths, arranged to do various things like create optical "egg cartons" that hold atoms in a lattice of electromagnetic "cups." The discs are mirrors and the little cubes are beam splitters.

MOT is significant because it gets atoms cold enough for other sensitive experiments and applications such as quantum gases, atomic clocks, quantum computing, optical tweezers, and precision measurement. At normal temperatures, the atoms involved in any process are a chaotic mix of speeds, which makes any measurement you do with them kind of blurry; very cold atoms hold very still, can be better controlled, and more precisely sense whatever is going on around them. My main project while I'm here in Bristol is to create a new undergrad quantum course that has MOT as a destination, because it is exciting and relevant to current tech development. Whee!