February 2012
Contact: Professor Katerina Gillen; kgillen@calpoly.edu
Physics Professor and Students are Hunting, Trapping Atoms
SAN LUIS OBISPO — Physics Professor Katharina Gillen and her students have built the university’s first Magneto Optical Atom Trap, boldly going where Cal Poly physics students have never gone before: on a quest to trap, freeze, slow and study atoms.
Professor Gillen and student Travis Frazer stand in front of Cal Poly's MOT -
Magneto Optical Trap for atoms. Next to the computeron the shelf at right is a toy
MOT the mother of one of Gillen's students made and embroidered for the professor.
Gillen, who specializes in atomic physics, received a three-year $200,000 National Science Foundation grant to fund final assembly of the trap, called a MOT in physics circles. The NSF grant is also funding a series of trapped atom experiments Gillen and her team of graduate and undergraduate students can now run on the MOT.
MOTs use lasers and magnetic fields to attract atoms — which normally travel several hundred miles per hour at room temperature — and collect them in a vacuum chamber.
Once the room-temperature atoms are released into its vacuum chamber, the MOT cools them down to one three-thousandth of a degree above absolute zero (a freezing -459.67 degrees Fahrenheit). Absolute zero is the temperature at which all physical motion stops completely, Gillen said. One three-thousandth of a degree above absolute zero is cold enough to slow the atoms’ speed down to about half a mile per hour, which makes them much easier to study.
Gillen’s MOT lab team currently includes undergraduate students Travis Frazer, Danielle May, Sara Monahan, Jennifer Rushing, and Jason Schray, as well as engineering graduate students Bert Copsey and David Roberts, who started their work in the group as undergraduates.
Gillen and her students have spent the past five summers in her lab, piecing together lasers, optical equipment, mirrors, circuitry, magnetic fields, a glass vacuum tube and other mechanical pieces that make a working MOT. They also connected the MOT to a computer that operates the trap and documents what’s happening inside it. “The students did the work. I told them what to do, and they put it together,” Gillen said.
The heart of the MOT. The vacuum chamber is the
cylinder at left with the blue light.
Their biggest challenge was to set the MOT’s lasers stable to within one-in-one-hundred-millionth of the precise frequency needed for trapping atoms.
Initially, they found that the system responsible for fine-tuning the MOT’s lasers to the precise frequency wasn’t working right. “It was the electronic component of the laser stabilization system. We were using an established circuit diagram with a design flaw — and the students figured out the flaw and fixed it,” Gillen said.
In summer 2011, Gillen and her students fired up the MOT for the first time — only to discover that it still wasn’t working right. The final culprit was an optical component responsible for setting the polarization of the MOT’s laser (one of the important properties of laser light when it comes to attracting atoms), which was not doing its job correctly. The team switched out the faulty optic, ran the MOT again, and it worked.
“The successful running of the MOT last summer marked a major milestone for the project,” Gillen said.
The resulting piece of high-tech equipment looks like a table set with an extremely elaborate version of the board game Mousetrap: laser emitters here, laser-bouncing mirrors there, metal tubing, and at its heart a glass chamber that looks a lot like a jar of jam.
The glass chamber is the vacuum tube — also made, vacuum-sealed and tested by Gillen and her students in her lab. It’s where atoms are channeled by the MOT’s lasers and magnets, then trapped, cooled and studied.
Gillen and her students presented their MOT work to the College of Science and Mathematics during fall quarter. The professor says their next step is to run an experiment that will send chilled atoms into a pure light trap formed behind a pinhole smaller than a strand of human hair. They will then document the properties of the light traps formed in the resulting patterns of shadow and light.
There are roughly 200 cold atom physics research groups around the globe and many are doing similar experiments, Gillen said. The results may have applications in the developing field of quantum computing.
Even if the students in Gillen’s Cal Poly MOT team don’t discover the key to cold neutral atom quantum computing in the next few months, they’re gaining a wide variety of science career skills along the way.
“They learn how to work with lasers, about laser safety, how to align the mirrors and work with the optics and optics equipment. They also learn how to create an interface between the equipment and the computer, and learn to program the computer to calculate light patterns. They learn to set up the lasers to channel the atoms to the center of the vacuum chamber; they learn to tune the lasers so they are ready to trap atoms,” Gillen said.
“These guys are doing things I learned about as a graduate student,” she stressed.
Frazer, a third-year physics major on Gillen’s MOT crew, agreed. “Lasers are cool. The theory behind lasers is cool. You have to be imaginative when designing the path of a laser in the MOT and how they’re all going to bounce around.”
His experience with the MOT and its optics setup will help him achieve his career goal: working in a laser optics research group.
He’s already ahead of his classmates in terms of working with high-tech equipment. “I was in a quantum physics lab during fall quarter and one day the oscilloscope wasn’t working. They were going to call in a tech and I said, ‘Wait, I know how to fix that.’ And I did.”