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HARVARD GAZETTE ARCHIVES The Big Chill: Doyle's 'ultracold' trap unveils secrets of matter in the universe By Alvin Powell
Using ultracold temperatures, helium gas, and magnets, physics professor John Doyle has built a trap. He’s after the tiny particles that make up the world, the universe, and even ourselves: neutrons, atoms, and molecules. Doyle traps the particles and then studies them, looking for what they can tell him about the most basic rules of nature. Specifically, Doyle is looking for evidence of discrepancies in the theory known as the Standard Model, the major theory of how the basic particles of nature interact. The Model, Doyle said, was constructed using certain assumptions about how particles behave. As measurements of those particles become more and more precise, scientists like Doyle are better able to test those assumptions. From their work comes a better understanding of how the universe operates. Doyle is one of the world’s foremost experts in trapping cold particles. He has devised a method that is useful in trapping atoms and molecules of almost every kind, according to Physics Department Chairman David Nelson, Mallinckrodt Professor of Physics and professor of applied physics. That method, which slows down the particles, Nelson said, will allow researchers around the world to better study atoms and molecules that previously had to be studied as they zoomed by at speeds 20 times faster. "He developed a technique to cool atoms into an ultracold state which applies not to a few selected atoms, but which is applicable to almost the entire periodic table," Nelson said. "There’s a whole world out there he’s opened up that many people – including himself – will be moving in to explore." Doyle was promoted in July to professor of physics from John L. Loeb Associate Professor of Physics, a post he held since 1997. Doyle came to Harvard as an assistant physics professor in 1993 from the Massachusetts Institute of Technology, where he was a postdoctoral associate. He received a bachelor’s degree in electrical engineering in 1985 and a doctorate in condensed matter and atomic physics in 1991, both from the Massachusetts Institute of Technology. Inspirational Uncle Doyle grew up in Chicago, within an easy drive of his uncle, a Michigan farmer whose tinkering with electronics was driven by an active curiosity about the world around him. His uncle helped fire Doyle’s imagination. On one visit, he brought a sample of strontium 90 and a Geiger counter to illustrate radioactivity to the boy. "My uncle gave me radioactive materials and a Geiger counter when I was 10 years old," Doyle said. "I grew up in Chicago until the fourth grade and we visited him regularly." Doyle’s parents were also supportive of his budding interest in science, providing science books and chemistry sets. Despite his interest in science, Doyle’s move into physics was a gradual one. Doyle received his bachelor’s degree from M.I.T. in electrical engineering. After he graduated, he decided to go to graduate school to study physics, though he admits the problems facing electrical engineers and chemists also intrigued him. What tipped the balance in favor of physics, he said, was the new progress made in the mid-1980s in cooling and trapping atoms. "The trapping of atomic hydrogen and evaporative cooling, the possibility of doing that looked particularly interesting to me," Doyle said. Doyle’s trap uses temperatures below 1 degree Kelvin – or colder than minus 457 degrees Fahrenheit – to slow the particles. Even at those temperatures, the particles are still moving too fast to trap, so he pumps in helium gas. Collisions with the helium atoms slow the particles further, to the point where they can finally be snared by the trap’s magnetic fields. The trap itself is an array of magnets arranged so they all repel the target particles with equal force, effectively holding the particles at a point in space. Once trapped, Doyle studies the particles, looking for evidence that would either back up or violate current theories of how the particles behave. He hopes to eventually look for evidence of something called "time reversal violation," a term that describes how the universe came to be dominated by matter.The laws of physics, Doyle said, mostly do not prefer matter over antimatter, so physicists are looking for reasons why there’s so much more matter in the universe.Doyle is also studying neutrons, one of the particles in the atomic nucleus. When taken out of the nucleus, the neutrally charged neutron decays within about 10 minutes into a positively charged proton. By studying that decay, Doyle is hoping to learn about the "weak force," one of the four basic forces of nature. Looking ahead, Doyle said he’s interested in trying to observe neutrinos, one of the smallest sub-atomic particles and one of the hardest to detect. Neutrinos emitted from the sun, Doyle said, pass right through our bodies when they hit us, with no ill effect. To observe neutrinos, he said, observatories are built in a location where other particles would be screened out, such as the bottom of an abandoned mine. "There is a constant flux of neutrinos flowing through our bodies from the sun," Doyle said. "One has to think very carefully about how to build [a neutrino observatory] that would detect the neutrinos from the sun with high efficiency." Nelson described Doyle as "extremely outgoing and charismatic," and said he’s a popular instructor. "He’s not only an outstanding researcher, he’s one of the best teachers we have in the department," Nelson said. Doyle said he enjoys teaching all levels of students. His main goal, he said, is making the subject as clear as possible. "I try to put my mind into the mind of someone who’s seeing it for the first time," Doyle said.
Copyright 1999 President and Fellows of Harvard College |
