Test of the isotopic and velocity selectivity of a lithium atom interferometer by magnetic dephasing

– A magnetic field gradient applied to an atom interferometer induces a M -dependent phase shift which results in a series of decays and revivals of the fringe visibility. Using our lithium atom interferometer based on Bragg laser diffraction, we have measured the fringe visibility as a function of the applied gradient. We have thus tested the isotopic selectivity of the interferometer, the velocity selective character of Bragg diffraction for different diffraction orders as well as the effect of optical pumping of the incoming atoms. All these observations are qualitatively understood but a quantitative analysis requires a complete model of the interferometer. If an inhomogeneous magnetic field is applied on a matter wave interferometer, the phase of the interference pattern is modified, provided that the matter wave has a non-zero magnetic moment. This type of situation was first considered [1, 2] as a test of the sign reversal of a spin 1/2 wave function by a 2π rotation. This effect was predicted since the foundation of quantum mechanics but considered for a long time as not observable. The first successful experimental test was made by H. Rauch and co-workers [3] in 1975 with their perfect crystal neutron interferometer and this work has been followed by several other experiments reviewed in the book of Rauch and Werner [4]. Similar experiments can be done by applying a magnetic field gradient on an atom interferometer: the fringe patterns corresponding to the various Zeeman sub-levels experience different phase-shifts and, when the gradient increases, the fringe visibility exhibits a series of minima and recurrences, as first observed by D. Pritchard and co-workers [5,6] and by Siu Au Lee and co-workers [7]. In this letter, we use our lithium atom interferometer to show that the dependence of the fringe visibility with the applied gradient gives a direct test of the selective character of our interferometer with respect to the atom velocity, to its isotopic (∗) E-mail:[email protected]