Timekeeping and accelerometry with robust light pulse atom interferometers

Abstract

Light pulse atom interferometry (LPAI) is a powerful technique for precision measurements of inertial forces and time. Laboratory LPAI systems currently achieve state-ofthe- art acceleration sensitivity and establish the international atomic time standard. However, the realization of practical LPAI in dynamic environments (e.g., rapidly accelerating or rotating platforms) has been limited in part by atom optics-the analogues to optical beamsplitters and mirrors. Atom optics in traditional LPAIs are composed of resonant laser pulses that are susceptible to variations in optical detuning and intensity expected in sensors designed for dynamic environments. This thesis investigates atom optics that use frequency- and intensity-modulated laser pulses to suppress sensitivity to these inhomogeneities. For atomic timekeeping applications, a Ramsey LPAI sequence based on stimulated Raman transitions and frequency-swept adiabatic rapid passage (ARP) was developed. Raman ARP drives coherent transfer in an effective two-level atomic system by sweeping the Raman detuning through the two-photon resonance. In experiments with ¹³³Cs atoms, Raman ARP reduced the sensitivity of Ramsey sequences to differential AC Stark shifts by about two orders of magnitude, relative to standard Raman transitions. Raman ARP also preserved fringe contrast despite substantial intensity inhomogeneity. The fractional frequency uncertainty of the ARP Ramsey sequence was limited by second-order Zeeman shifts to ~3.5 x 10-¹² after about 2500 s of averaging. For accelerometry applications, Raman ARP provided efficient, large momentum transfer (LMT) atom optics in an acceleration-sensitive LPAI. These atom optics produced momentum splittings of up to 30 photon recoil momenta between interfering wavepackets-the largest to date for Raman atom optics. This splitting, in principle, enables up to a factor-of-15 improvement in sensitivity over the nominal interferometer. By forgoing cooling methods that reduce atom number, this LMT method reduces the measurement uncertainty due to atom shot-noise and enables large area atom interferometry at higher data-rates. These features could prove useful for fielded inertial sensors based on atom interferometry.