Atom interferometer

An Atom interferometer is an interferometer based on exploiting the wave character of atoms.

Overview

Interferometry inherently depends on the wave nature of the object. As pointed out by de Broglie in his PhD-thesis, particles, including atoms, can behave like waves (the so called Wave-particle duality, according to the general framework of quantum mechanics). More and more high precision experiments now deploy atom interferometers due to their short de Broglie wavelength. Some experiments are now even deploying molecules to obtain even shorter de Broglie wavelengths and to search for the limits of quantum mechanics. In many experiments with atoms, the roles of matter and light are reversed compared to the laser based interferometers, i.e., the beam splitter and mirrors are lasers while the source emits rather matter waves (the atoms).

Interferometer types

Contrary to light, atoms are subject to gravity. In some apparatus, the atoms are ejected upwards and the interferometry takes place while the atoms are in flight, sometimes they are measured while falling in free flight. Yet other experiments do not negate gravitational effects by free acceleration, but use additional forces to compensate for gravity. While these guided systems in principle can provide arbitrary amounts of measurement time, their quantum coherence is still under discussion. Recent theoretical studies indicate however, that coherence is indeed preserved in the guided systems, but this has yet to be experimentally confirmed.

The early atom interferometers deployed slits or wires for the beam splitters and mirrors. Later systems, especially the guided ones, used light forces for splitting and reflecting ofthe matter wave.

Examples

History

The separation of matter wave packets from complete atoms was first observed by Esterman and Stern in 1930, when a Na beam was diffracted of a surface on NaCl. [I. Estermann & Otto Stern, "Zeits. F. Physik" 61, 95 (1930).] The first modern atom interferometer reported was a Young double slit experiment with metastable helium atoms and a microfabricated double slit by Carnal and Mlynek [O. Carnal & J. Mlynek, "Phys. Rev. Lett." 66, 2689 (1991).] in 1991, and an interferometer using three microfabricated diffraction gratings and Na atoms in the group around Pritchard at MIT. [D.W. Keith, C.R. Ekstrom, Q.A. Turchette & D.E. Pritchard, "Phys. Rev. Lett." 66, 2693 (1991).] Shortly afterwards, an optical version of Ramsey spectrometer typically used in atomic clocks was recognized also as an atom interferometer at the PTB in Braunschweig, Germany. [F. Riehle, Th. Kisters, A. Witte, J. Helmcke & Ch. J. Bordé, "Phys. Rev. Lett." 67, 177 (1991).] The largest physical separation between the partial wave packets of atoms was achieved using laser cooling techniques and stimulated Raman processes by S. Chu and coworkers in Stanford. [M. Kasevich & S. Chu, "Phys. Rev. Lett." 67, 181 (1991).]

References

ee also

*Electron interferometer
*C. S. Adams, M. Sigel & J. Mlynek, "Atom Optics", "Phys. Rep." 240, 143 (1994). Overview of the atom-light interaction
*P. R. Berman [Editor] , "Atom Interferometry". Academic Press (1997). Detailed overview of atom interferometers at that time (good introductions and theory).
* [http://www.physics.berkeley.edu/research/packard/Competition/Gyros/LaserRingGyro/Steadman/StedmanReview1997.pdf Stedman Review of the Sagnac Effect]