Large-angle adjustable coherent atomic beam splitter by Bragg scattering

Using a monochromatic (single-axial-velocity) and slow (250 m/s) beam of metastable helium atoms, we realize up to eighth-order Bragg scattering and obtain a splitting angle of 6 mrad at low laser power (3 mW). This corresponds to a truly macroscopic separation of 12 mm on the detector. For fifth-order scattering, we have observed several oscillations of the splitting ratio when varying the laser power ( Pendellosung oscillations ). The large splitting angle, the adjustable splitting ratio, and the cleanness of the split beams, with 200- mu m rms width each, make the beam splitter ideal for a large-enclosed-area atom interferomete

Ultracold metastable helium: Ramsey fringes and atom interferometry

We report on interference studies in the internal and external degrees of freedom of metastable triplet helium atoms trapped near quantum degeneracy in a 1:5 μm optical dipole trap. Applying a single π/2 rf pulse we demonstrate that 50% of the atoms initially in the m = +1 state can be transferred to the magnetic field insensitive m = 0 state. Two π/2 pulses with varying time delay allow a Ramseytype measurement of the Zeeman shift for a high precision measurement of the 2 3S1-2 1S0 transition frequency. We show that this method also allows strong suppression of mean-field effects on the measurement of the Zeeman shift, which is necessary to reach the accuracy goal of 0.1 kHz on the absolute transition frequencies. Theoretically the feasibility of using metastable triplet helium atoms in the m = 0 state for atom interferometry is studied demonstrating favorable conditions, compared to the alkali atoms that are used traditionally, for a non-QED determination of the fine structure constant