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

We present two applications of the use, in Stern-Gerlach interferometry with metastable hydrogen atoms, of comoving magnetic fields, i.e. fields travelling at atomic velocites, which could allow us to reach the slow-atom domain. In the first application, atoms interact with a single extended zone of comoving B-field. A velocity coherent filtering effect is demonstrated and characterized. In the second one, atoms interact with a double zone of comoving B-field. This Ramsey's type configuration takes advantage of the fact that the sensitivity of the apparatus with respect to velocity changes is significantly enhanced.