Electron cycling in quantum confines.From Long Beach, Calif., at a meeting of the American Physical Society The American Physical Society was founded in 1899 and is the world's second largest organization of physicists. The Society publishes more than a dozen science journals, including the world renowned Physical Review and Physical Review Letters, and organizes more than twenty science Like a race car forced to stay within certain lanes of a speedway, a lone electron in a circular path should whirl along exclusively in specific allowed orbits, the rules of quantum mechanics quantum mechanics: see quantum theory. quantum mechanics Branch of mathematical physics that deals with atomic and subatomic systems. It is concerned with phenomena that are so small-scale that they cannot be described in classical terms, and it is say. In a Harvard University Harvard University, mainly at Cambridge, Mass., including Harvard College, the oldest American college. Harvard College Harvard College, originally for men, was founded in 1636 with a grant from the General Court of the Massachusetts Bay Colony. laboratory, physicists have devised an extraordinarily small, low-energy cyclotron cyclotron: see particle accelerator. cyclotron Particle accelerator that accelerates charged atomic or subatomic particles in a constant magnetic field. in which a single orbiting electron vividly demonstrates that predicted quantum behavior. Moreover, this artificial atom The term Artificial atom is commonly used to describe objects that have bound, discrete electronic states, as is the case with naturally occurring atoms. Semiconductor quantum dots are the most common example of artificial atoms. without a nucleus, as Gerald Gabrielse Gerald Gabrielse is an American physicist and the George Vasmer Leverett Professor of Physics at Harvard University. In 2007, he was elected a member of the National Academy of Sciences. and his colleagues refer to their diminutive apparatus, promises to make possible the most precise measurements yet of certain fundamental constants. "We think we can measure the strength of the bar magnet in the electron, called its magnetic moment, 10 times better than ever before," Gabrielse predicts. He and his colleagues use carefully controlled magnetic and electric fields to make the electron do laps in a vacuum within a small metal can at the heart of the apparatus. The can, about a centimeter across, is cooled to as low as 70 millikelvins--less than a 50th of the previous record chill for a trap containing a lone fundamental particle fun·da·men·tal particle n. See elementary particle. . At that temperature, the electron zips around for hours at a time in its lowest energy state, Gabrielse says. This so-called ground state is the orbital equivalent of the inner lane on the racetrack. If the device warms a little, the cavity walls emit a few microwave photons. When the frequency, or energy, of the photons is just right, they can bump the electron temporarily to a higher energy state. The excited electron traces a circular path with a larger radius. To nail down the magnetic moment, the Harvard group aims to measure accurately the photon frequency that most effectively boosts the electron from the ground state to the next-wider orbit, Gabrielse says. The team can identify that frequency by transmitting microwaves into the cavity and noting which frequency induces the most leaps to the higher level. |
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