Number 226 (Story #1), May 15, 1995 by Phillip F. Schewe and Ben Stein MOLECULE INTERFEROMETRY , the splitting and recombining of molecule waves, has now been performed by David Pritchard and his colleagues at MIT, enabling new types of measurements on molecules. Like all forms of matter, a molecule can be thought of as a quantum wave spread out in space rather than as a particle having a definite location. But a molecule's wave nature is hard to detect because its relatively large mass gives it a high momentum even at low velocity. Equivalently, the molecule's "wavelength" is small, at least 10,000 times smaller than that of visible light. Fortunately new nanotechniques have permitted the building of an obstacle course for waves on a size scale that allows one to do for molecule waves what one normally does only for light waves, such as measuring an index of refraction. For example, with their interferometer (employing tiny nanofabricated gratings), the MIT researchers have conducted refraction measurements of diatomic sodium molecule waves passing through gas samples. The interferometer splits the molecule wave (wavelength 0.11 angstroms) into separate wavelets. Some of the molecule wave traverses a sample of neon gas and later recombines with another part of the wave to form an interference pattern which yields the index of refraction. The measurements suggest that the neon exerts a relatively large long-range force on the sodium molecule. (M.S. Chapman et al, 12 June 95 article in Physical Review Letters; Pritchard's work on atomic interferometry (Update 209) appeared in the 13 February 1995 Physical Review Letters.)