Abstract
We present enabling experimental tools and atom interferometer implementations in a vertical “fountain” geometry with ytterbium Bose–Einstein condensates. To meet the unique challenge of the heavy, non-magnetic atom, we apply a shaped optical potential to balance against gravity following evaporative cooling and demonstrate a double Mach–Zehnder interferometer suitable for applications such as gravity gradient measurements. Furthermore, we also investigate the use of a pulsed optical potential to act as a matter wave lens in the vertical direction during expansion of the Bose–Einstein condensate. This method is shown to be even more effective than the aforementioned shaped optical potential. The application of this method results in a reduction of velocity spread (or equivalently an increase in source brightness) of more than a factor of five, which we demonstrate using a two-pulse momentum-space Ramsey interferometer. The vertical geometry implementation of our diffraction beams ensures that the atomic center of mass maintains overlap with the pulsed atom optical elements, thus allowing extension of atom interferometer times beyond what is possible in a horizontal geometry. Our results thus provide useful tools for enhancing the precision of atom interferometry with ultracold ytterbium atoms.
Highlights
BEC Source and Atom OpticsEach of the experiments reported in this work begins with a trapping and cooling sequence for the production of a ytterbium (174 Yb) Bose–Einstein condensate consisting of 105 atoms [11]
Pulsed optical lattices are crucial tools for high precision atom interferometry (AI), with applications ranging from tests of fundamental physics to force sensing [1,2,3,4,5]
Terrestrial pulsedlattice atom interferometers have relied on a vertical geometry of diffraction beams in order to fully realize the inherent power of the method, as the loss of spatial overlap with the pulsed lattice from atoms falling due to gravity is suppressed in this configuration
Summary
Each of the experiments reported in this work begins with a trapping and cooling sequence for the production of a ytterbium (174 Yb) Bose–Einstein condensate consisting of 105 atoms [11]. Following cooling in the MOT, atoms are transferred into a crossed optical dipole trap (ODT) for evaporative cooling towards BEC. A consequence of this general characteristic of optically trapped Yb is that the expansion of the BEC after release is mostly along the vertical, as most of the initial chemical potential is converted to kinetic energy in this direction [13,14], a quantity we measure to be k B × (42 ± 5) nK through absorption imaging after long expansion times. The quantity δ is always less than 2π × 1 MHz and varied with sub-Hz precision using direct digital synthesis radio-frequency sources that drive the lattice AOMs. We note that the measured kinetic energy in the vertical direction corresponds to a velocity spread of ∆v ' 0.5vrec , where vrec = hk g /m is the recoil velocity with k g = 2π/λ g and m is the mass of a Yb atom.
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