Temporal Atom Optics with a Gravitational Cavity

In thc optical rcgimc, multiplc hcanm interference is a pcrpular method to drastically cnhiincc the resolution of i i n intcrfcrnmctcr. Wc rcport hcrc on the rcalixition of ii multiple bem intcrfcrometcr with niiittcr W;IVCS. An atom is cohcrcntly split into morc than two aloniic wavcpackcts hy optical pumping into a vclocity dcpcndcnt inultilcvcl dark superposition state. The monienta o f two ad.jacent paths diffcr by two photon niomcnta. Whcn the atom is spatially recombined, wc ohscrvc an intcrfercncc signal that shows ;in Airy-function likc pattern characteristic for multiplc hcani interference. This method offers thc prospect o f achieving a very high resolution, since the enclosed arca is larger than that of the corresponding conventional two-beam intcrfcrometcr. For our experimcnt, we usc a cesium atomic beam and two counterpropagating optical hcams in a e-0polarization configuration tuncd to the 6Sln(F=4)-6Pln(F=4) transition of the cesium DI -line. In a first laser pulse, ccsium atonis are optically pumped into a dark superposition of thc five even magnetic ground state sublevels (mr; = -4, -2, .... 4). The momenta of the atoms in these sublevels are 0,2hk, ... ,8hk relative to the momentum of the mF = -4 sublevel (Fig. I ) . The paths spatially separate for a time T, after which a second laser pulse splits each of the five paths further into five. A third pulse at time T after the second pulse closes all partial interferometers. To read out the interferometer, we detect the fluorescence emitted during the final pulse. Typical interferometer signals for T = 5 ps are shown in Fig. 2 as a function of the phase of the final pulse. With no additional phase, the atoms are already in a dark state at this time and no fluorescence is emitted. When the phase is varied, fluorescence can be observed since the atom is not dark any more for the light field. The experimental width of the dip presently is 0.32.2~. which is broader than the theoretical value of 0.18.2~. but clearly narrower than the value 0 . 5 2 ~ observed in a two-beam interferometer. With the use of colder atoms and magnetic shielding a fringe width close to the theoretical value should be possible. For much longer interaction times we expect a washing out of the fringes caused by a recoil phase shift that increases quadratically with the path number. When the total interaction time 2T is an integer multiple of the two-photon recoil energy, a revival of the original fringe pattem OCCUIS.