Harvard’s Gerald Gabrielse — who kicked off this year’s “Frontiers in Physics” session, which traditionally closes the IPF — has earned his fair share of professional kudos from the physics community for his groundbreaking research at CERN in Switzerland, coming up with nifty new ways of trapping single particles to study them up close and personal.
For instance, back in 2002, his team made science news headlines when they published two papers in Physical Review Letters providing the first glimpses inside an antihydrogen atom. More recently, he’s used similar methods to make the most precise measurements to date of the electron’s “magnetic moment” — a finding that AIP’s Physics News Update dubbed its scientific breakthrough of the year in 2006.
Antimatter, as all good Star Trek fans know, provides the fuel that propels the Starship Enterprise through space, but in the hear and now, creating antimatter and figuring out how to store it in a container without it annihilating itself in the process has proven to be a sticky wicket. Particle accelerators have been producing tiny amounts of antimatter since the 1980s, even making antihydrogen atoms in the 1990s, but those bits raced through detecting instruments far too quickly to make useful measurements.
Gabrielse’s team used something called a “nested Penning trap,” which uses electric and magnetic fields to trap charged particles. It was invented by Hans Georg Dehmelt, who shared the 1989 Nobel Prize in Physics for the accomplishment. Gabrielse’s version consists of a long series of gold-plated electrodes cooled to about 4 degrees above absolute zero (that is cold, y’all!), placed in a very strong magnetic field. Here is a schematic of a basic Penning trap:
When an antiproton enters the trap, it gets captured in the lower part, and as they vibrate and collide with the cold electrons stored inside the trap, they lose most of their energy, ending up suspended in the center of the trap at those ultra-cold temperatures. Meanwhile, positrons are collected in the top part of the trap. At some point they are allowed to interact with the antiprotons to form antiatoms (antihydrogen). The problem is, they annihilate immediately. To get them to hang around a bit longer, Gabrielse added another element: a magnetic trap to capture the cold antihydrogen atoms once they’ve formed and “store” them long enough to make useful measurements.
Since then, Gabrielse’s research has focused on using the new ideas and methods he’s been developing over the past two decades to make more accurate measurements of the electron’s magnetic moment, or “g.” Just like the Earth behaves as if it has a magnet at its core (in that case, almost aligned with the axis of the Earth’s rotation), so, too, does the tiny electron, although in its case, the internal magnet seems to point in the same direction as the particle’s “spin.” The finer we can measure that magnetic moment, the better we can probe the quantum nature of electrons and further our understanding of quantum electrodynamics (QED).
The apparatus Gabrielse’s team built to make their measurement has been described repeatedly as a kind of “single-electron quantum cyclotron.” Here’s AIP’s Phil Schewe describing how it works:
“[They] create a macroscopic artificial atom consisting of a single electron executing an endless looping trajectory within a trap made of charged electrodes… supplemented by coils producing a magnetic field. The combined electric and magnetic forces keep the electron in its circular ‘cyclotron’ orbit. In addition to this planar motion, the electron wobbles up and down in the vertical direction, the direction of the magnetic field..”
It took them 20 years (and 6.5 doctoral theses), but Gabrielse and his cohorts improved the measurement of “g” by a factor of 6 over prior measurements dating back to 1986 (performed by Dehmelt, inventor of the Penning trap). They’ve measured it to an uncertainty of a mere 0.76 parts per trillion, and Gabrielse says they should be ready to announce an even more precise measurement by the end of this year. The number? It’s 137.035 999 710.
As a lighter note after his involved mathematical discussion, Gabrielse showed a doctored photo of a wall at the University of Washington (which also has an ongoing project to measure “g’), in which the value of “g” (as known in 1986) was chiseled — an homage to QED maven Richard Feynman, who once joked that every theorist should put “137″ on the office wall. Gabrielse crossed out the latter part of the value and replaced it with his new value, scrawled in black ink, like graffiti.
Among other things, the better measurements could give us that much more information of the internal structure of the tiny electron, enabling us to discover if, like the proton (made of quarks), it, too, is made of smaller components. “Measurements of the Earth’s magnetism gives us a glimpse into the inner structure of our planet,” Gabrielse explained in a February 1, 2007 article in Physics World (subscription required). “We have obtained a similar magnetic glimpse into another place we cannot travel to or see: a single electron.” On a practical basis, his techniques have led to several practical spinoffs, including a patented solenoid design being used for nuclear magnetic resonance, magnetic resonance imaging, and ion cyclotron resonance.
But the most significant implications, from a fundamental physics standpoint, is that this more precise measurement of the electron’s magnetic moment also allows us to more accurately test/determine the fine structure constant (known to cosmologists as alpha), that number that determines the strength of the electromagnetic force in our universe. Just pop the new value for “g” into existing QED equations, and voila! You’ve got a more refined value for alpha, with an uncertainty of just 0.7 parts per billion. That’s a good 10 times better than available via any other method.
Apart from the scientific importance and recognition of his work, Gabrielse has had the dubious honor of seeing his research reflected in broad popular culture. Bestselling novelist Dan Brown (The Da Vinci Code) set his sequel, Angels in Demons, partly at CERN, and built the plot around the production of antimatter and its potential as a powerful weapon. Quipped Gabrielse of the novel’s premise: “What The Da Vinci Code did for the Catholic chuch, Angels and Demons has done for my research.”
And he scored a first for quantum physics when one of his recent research papers provided fodder for a spoof exchange between actor/comedian Jim Carrey and late-night talk show host Conan O’Brien. The clip has been downloaded over 140,000 times from YouTube since the show aired earlier this year. (It’s a classic! You can find it here.) Gabrielse joked that this pretty much made him “the poster child for obscurity in physics,” but it didn’t seem like he minded too much. If only we lived in a world where more viewers were aware of his name as immediately recognize Carrey and O’Brien. We can dare to dream.