Physicist Steven Chu may be on the verge of becoming the nation's top energy official, but physics clearly is never far from his mind. To wit: on the day of his Senate confirmation hearing this week to become President-elect Barack Obama's energy secretary, a paper Chu co-wrote was posted by one of his co-authors on the Web site

Chu, 60, is director of Lawrence Berkeley National Laboratory and a 1997 Nobel laureate in physics, but he's also an active researcher who publishes regularly.

The new paper, "Noise-Immune Conjugate Large-Area Atom Interferometers," describes a high-sensitivity atom interferometer setup, a device that can be used to measure fundamental physical constants and even provide tests of Albert Einstein's general relativity, the reigning theory of gravity.

But it's pretty dense stuff, so we asked Holger Müller, a physicist at the University of California, Berkeley, and one of the study's co-authors, to enlighten us. "You take an atom and make it go one way or the other," splitting it into two paths using laser light and later recombining those paths, Müller says. The atoms traveling along the paths act as matter waves.

"The waves oscillate a certain number of times between the points where the paths are split and recombined," he says. "If that number is the same for both, a maximum of one wave will merge with a maximum of the other, which makes for maximum amplitude of the wave after combining." Alternately, if the waves differ by half an oscillation, one wave's maximum will meet another's minimum, canceling each other out. By monitoring the output, the researchers can determine what influences are acting on the atoms, allowing them to make precision measurements of the effects of gravity or electromagnetism, for instance.

The interferometer described in the new paper encloses a much larger area and thus should be far more sensitive than past models in tests measuring gravity, Müller notes, making it especially well-suited to challenging Einstein.

Photo credit: Roy Kaltschmidt/Lawrence Berkeley National Laboratory