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Introduction to Atom Interferometry

Matter wave interferometers, in which de Broglie waves are coherently split and then recombined to produce interference fringes, have opened exciting new possibilities for precision and fundamental measurements with complex particles. The aim of our research program is to make qualitatively new and/or precise measurements in atomic physics, measure inertial effects, and perform fundamental experiments in quantum mechanics – all based on our ability to measure interactions that displace the de Broglie wave phase or change the quantum coherence of the beams. As an integral part of this program, we are continuing to develop new atomic optical components, such as nanoscale gratings and microfabricated atom interaction regions, as well as new atom optical techniques, such as time-dependent beamsplitters to produce longitudinal coherences and enhancement of the effective coherence length of atom beams by time-domain velocity selection.

Our atom/molecule interferometer realizes a Mach-Zehnder geometry using three nanofabricated transmission gratings, and generates a "white-fringe" (i.e. insensitive to momentum spread in the beam) interference pattern. Its most unique feature – unduplicated by any of the other atom interferometers demonstrated – is a spatial separation of the two interfering beam paths which permits the application of an interaction to only one of the two paths. (See Figure).
 
 


Caption: A schematic, not to scale, of our atom interferometer (thick lines are atom beams). The 0th and 1st diffracted orders from the first grating strike the middle grating where they are diffracted to form an interference pattern in the plane of the third grating. A thin septum is placed between the two arms of the interferometer. An optical interferometer (thin lines) measures the relative positions of the atom gratings.
 

Because a typical atom deBroglie wavelength (~ 1/6 of an Angstrom) is 30,000 times smaller than an optical wavelength, and because atoms have mass and internal structure, atom interferometers are remarkably sensitive devices.  Accelerations, rotations, electromagnetic fields, and interactions with other atoms change the phase and contrast of the atom fringes.  Consequently, atom interferometers make some of the world's best gyroscopes, gravity gradiometers, precision clocks, and measurement devices for atomic properties such as van der Walls forces and electric polarizability.

For a comprehensive review article covering many accomplishments in atom and molecular optics and interferometry at MIT, see: Optics and Interferometry with Atoms and Molecules

A more recent review article on Atom Optics identifies the theoretical background, enabling technologies, and current research objectives of atom-wave research.

Several writeups in popular press have featured our atom interferometer.