Number 35 (Story #1), May 22, 1991 by Phillip F. Schewe and Ben Stein ATOM INTERFEROMETRY has been demonstrated by scientists at MIT and at Konstanz University in Germany. Interferometry is a phenomenon in which a wave (light waves from a laser, for example) is split and made to interfere with itself, resulting in a characteristic pattern of constructive and destructive interference. Previously, electrons and neutrons---which according to quantum mechanics have wavelike properties---have been subjected to interferometry. Now this process has been extended to atoms. At MIT (David E. Pritchard, 617-253-6812) a highly collimated beam of sodium atoms with a de Broglie wavelength (the wavelength of sodium "matter waves") of 16 nm passes through three sets of diffraction gratings, the first two to establish an interference pattern and the third to sample the pattern. In the German experiment (O. Carnal and J. Mlynek) a beam of atomic helium with a de Broglie wavelength of from 0.56 to 1.03 angstroms passes through a system of slits, creating an interference pattern at a detection plane 64 cm away. Atom interferometry will permit certain new studies of quantum mechanics and may be useful in testing general relativity. (Both groups report in Physical Review Letters, 27 May 1991.)