Ultracold metastable helium: Ramsey fringes and atom interferometry

摘要

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 mu m optical dipole trap. Applying a single pi/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 pi/2 pulses with varying time delay allow a Ramsey-type measurement of the Zeeman shift for a high precision measurement of the 2(3) S-1-2 S-1(0) 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.