effects. One can also carry out a similar experiment using a beam of electrons, which have their own wave properties. Here, too, the result is a pattern of alternating bands. Moreover, it is possible to reduce the intensity of the source of the light, or of the electron beam, so that at any moment only one photon or electron is in flight. Given time, though, the same pattern will form. It would also form using a beam of slow, and ultracold atoms.
There are several advantages to constructing an interferometer based on slowly moving atoms. For example, such an instrument can be a very sensitive inertial sensor. Chu and Kasevich already have built an interferometer that uses slow atoms and that measures the acceleration of gravity with an accuracy of at least three parts in 108. Moreover, Chu expects to achieve a further improvement of a thousandfold. The result could be an atomic standard for gravity measurements that has greatly increased precision. In turn, that could influence the highly practical matter of searching for oil. Changes in the local gravity sometimes point out oil-bearing formations to geologists, and improvements in such gravity measurements might aid the mapping of such deposits.
Ultracold atoms can also assist in opening up other fundamental topics in quantum mechanics. At sufficiently low temperatures, such atoms should undergo a phenomenon called Bose condensation. This is not the condensation that occurs when a gas freezes into a solid. Rather, it is a quantum effect whereby all the atoms would take on the same ground state. Analogs exist in a laser or in superfluid helium, where many of the particles—photons or helium atoms—are considered to be in the same quantum state. Because ultracold atoms take on wave properties akin to those of photons and electrons, they should also undergo Bose condensation. The difference is that the ultracold atoms will form a dilute Bose gas, a new state of matter that has never before been observed or studied.
The direct manipulation of atoms and other elementary particles, with the scanning tunneling microscope, with lasers, and by using electric and magnetic fields, thus opens a host of prospects. These include fundamental tests of basic features in physical theories, new states of matter, studies of chemical reactions at the atomic level, new instruments for the precise measurement of time and of gravity fields, and even a new approach in searching for oil. Moreover, some of the basic laser techniques used in slowing and cooling atoms are also finding