Ionic, Atomic and Molecular Physics

麻省理工学院的小组将建立一个新的原子干涉仪，用它来测量ppb水平的精细结构常数。这将用于测量h/m，它将与该小组最近的原子质量测量相结合，以确定摩尔普朗克常数。这可以与其他最近的测量相结合，以产生精细结构常数的测量。新的干涉仪在对比干涉仪中使用玻色-爱因斯坦凝聚物——当被测量的相位增加时，条纹的对比度而不是它们的位置会振荡。这种干涉仪，其原型最近被展示，包含以下三个主要进展，其中任何一个都将大大改进以前的h/m实验。由于原子都处于相同的状态，消除了一阶交流斯塔克位移，干涉仪对振动不敏感，并且可以在干涉仪的单次“射击”中进行精确的相位测量。该干涉仪还具有相位随分束器的阶数呈二次增长的特性。这将用于在单次射击中进行1ppb的测量。“下一代干涉仪”将具有磁屏蔽和高光学质量的视口，以减少其他系统误差，如不均匀磁场和光波前畸变。

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.