Ionic, Atomic and Molecular Physics

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

The MIT group will build a novel atom interferometer with which to measure the fine structure constant at the ppb level. This will be used to measure h/m, which will be combined with the group's recent atomic mass measurements to determine the molar Planck constant. This can be combined with other recent measurements to yield a measurement of the fine structure constant. The new interferometer uses Bose-Einstein condensates in a contrast interferometer - one in which the contrast of the fringes rather than their position oscillates when the phase being measured increases. This interferometer, a prototype of which was recently demonstrated, contains the following three major advances, any one of which would have substantially improved previous h/m experiments. Since the atoms are all in the same state, first-order AC Stark shifts are eliminated, the interferometer is insensitive to vibration, and an accurate phase measurement can be made in a single "shot" of the interferometer. The interferometer has the additional feature that the phase increases quadratically with the order of the beamsplitters. This will be exploited to make measurements to 1ppb in a single shot. The "next generation interferometer" will feature magnetic shielding and high optical quality viewports to reduce other systematic errors such as inhomogeneous magnetic fields and optical wavefront distortions.