Ionic, Atomic and Molecular Physics

麻省理工学院的团队将建造一种新型的原子干涉仪，用来测量ppb级的精细结构常数。这将被用来测量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，得到精细结构常数的测量结果。新的干涉仪在对比度干涉仪中使用玻色-爱因斯坦凝聚体--当被测量的相位增加时，条纹的对比度而不是它们的位置发生振荡。这台干涉仪的原型最近被演示出来，它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漂移，干涉仪对振动不敏感，干涉仪一枪即可进行准确的相位测量。该干涉仪还具有相位随分束器阶数二次增加的特点。这将被利用来在一次拍摄中测量到1 ppb。“下一代干涉仪”将配备磁屏蔽和高光学质量的视窗，以减少其他系统误差，如不均匀磁场和光学波前失真。

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.