Atomic interferometry was born recently, towards the end of the 1980s. Its development has been extremely fast, new techniques being pioneered independently and almost simultaneously in different laboratories all over the world. Nowadays, these techniques have reached a high level of sophistication, opening a wide area of fundamental and practical applications. In this paper the general architecture of interferometers in which matter waves are coherently manipulated is described. Various realizations of atom and molecule interferometers are reported, together with the major results obtained with each type of interferometer. Finally, new trends and perspectives are given. Whilst the techniques seem to be almost completely achieved, new developments are coming up, such as the use of new and non-ordinary sources. Forthcoming applications are numerous. They deal with the most fundamental aspects of quantum mechanics, with the metrology of fundamental constants, with the use of interferometers as very sensitive probes of external interactions and inertial effects, with atomic nanolithography, etc.

Delayed-choice experiments have been performed using an atomic Stern-Gerlach interferometer operating with a low-intensity beam of metastable hydrogen atoms. By use of a fast-commutable analyzer, it is possible to modify the operating mode of the interferometer while the atom has already entered the device. Various types of delayed-choice experiments have been carried out to check the standard interpretation of quantummechanics. Within the experimental accuracy, our results do not show any discrepancy between permanent and delayed-choice operating modes of the interferometer. ͓S1050-2947͑96͒00712-3͔

No abstract