A coherent electric analogue of the Stern-Gerlach experiment

A coherent electric analogue of the Stern-Gerlach experiment has been performed with helium atoms in Rydberg states. The atoms, travelling in pulsed supersonic beams, were prepared in superpositions of Rydberg states with different static electric dipole polarisabilities using pulses of microwave radiation. State-dependent forces were then exerted on them, transverse to their direction of propagation, using inhomogeneous electric fields. These fields were generated between a pair of electrodes in a wedge configuration. The forces applied resulted in the coherent evolution of each atomic wavepacket into a superposition of spatially separated momentum states. The classical paths of least action associated with these momentum states evolved over time up to a separation of ∼2 nm. The coherent evolution of the atoms, and hence the superposition of atomic wavepackets in this ‘half-loop’ electric Rydberg-atom interferometer, was monitored by measuring the internal Rydberg state populations at the end of each measurement cycle. The experimental data are in good quantitative agreement with the results of semiclassical calculations of the phase evolution of the atomic superposition states which account for contributions from Stark shifts, the momentum differences between the classical paths of least action through the apparatus, and the spatial separation of the atomic wavepackets.