Atom Interferometers

Good to see progress in this field. Certainly will lead to much more precise measurements due to the small wavelength of their de Broglie waves.

Here is the article:

Interferometer for Lighter Atoms

A new atom interferometer works at less extreme temperatures and with lighter atoms than previous designs, opening up a new route to precision measurements of fundamental constants.

n atom interferometer uses laser pulses to first split apart a collection of atoms and then recombine them to reveal a wave-like interference pattern. Usually, this pattern is only visible when the atoms are cooled to a few millionths of a degree above absolute zero, but now a team of researchers working with lithium atoms has done it at somewhat higher temperatures. This lithium interferometer could be used to measure the fine structure constant—a key fundamental constant of electromagnetism—with a precision that could eventually be competitive with other techniques.

Many research groups around the world are developing atom interferometers to precisely measure gravity and inertia, as well as fundamental constants. The fine structure constant, for example, can be determined by precisely measuring the amount of kick, or recoil, that atoms receive when hit with a laser pulse inside an interferometer. These sorts of experiments typically use relatively heavy atoms, like cesium or rubidium, but a bigger kick—and therefore a bigger signal—could be had with lighter atoms. “We asked ourselves what is the lightest atom we could practically use,” says Holger Müller of the University of California, Berkeley. The answer was lithium, as it is both low in mass and controllable with existing laser technology.

To make a high-precision lithium interferometer, one would typically need to cool the atoms to below 1 microkelvin, so that their average thermal motion would be less than the kick in velocity they receive from laser pulses. To reach this low temperature, however, “hot” atoms would be removed, enough to weaken the interference signal. To keep more atoms, Müller’s team developed an interferometer that required less cooling.

The team’s setup traps around a million lithium atoms and cools them to 300 μK. For each interference run, they shut off the trap and expose the atoms to a sequence of four laser pulses. The first pulse gives an upward kick to a fraction of the atoms (call them “moving” atoms) while leaving the rest alone (“static” atoms). This “beam-splitting” pulse is followed by two pulses that act like mirrors, directing a portion of the moving atoms back down toward the static ones. The fourth pulse recombines the two groups, causing them to interfere. In principle, this interference should be visible as an oscillation in the number of moving atoms as one varies the time between laser pulses—which is equivalent to lengthening one arm of a traditional optical interferometer. However, two complications stand in the way of measuring this signal.

Article Continues Here