Measuring and Computing Finite Pulse Corrections in a Recoil-Sensitive Strontium Atom Interferometer Operating on Single Photon Transitions*

Atom interferometers can be used for precision measurements of the fine structure constant by measuring the ‘recoil velocity’ of an atom — the change in an atom’s velocity when it absorbs a photon. Interferometer phase shift calculations are useful for designing recoil-sensitive interferometers and extracting the recoil velocity from measured phase shifts. These calculations are often performed in the limit of instantaneous atom-laser interactions, but real laser pulses have finite duration. Interferometer phase shifts can depend on pulse length, which can introduce systematic errors in high-precision measurements of the fine structure constant.

We present a new perturbative approach for computing finite pulse effects in atom interferometers and a new experimental platform for measuring the recoil velocity of an atom. The theory framework enables computations of pulse-length dependent corrections to the interferometer phase, and optimization of pulse deadtimes to maximize interferometer contrast. We also present measurements of finite pulse dependent phase shifts in a recoil-sensitive atom interferometer operating with single-photon transitions on the intercombination line of Sr. The interferometer operates with a ~3mK atom cloud, and the two arms of the interferometer are individually addressed via state-selective laser pulses leveraging the zeeman sublevels of the 3P1 manifold. We accumulate ~1 rad of recoil-dependent interferometer phase and observe finite pulse corrections at the 80 mrad level.  While this interferometer’s sensitivity to the recoil velocity of an atom is well below the sensitivity of the current state-of-the-art, it serves as a productive platform for characterizing finite pulse effects and it may represent the first observation of recoil-dependent phase shifts in a Strontium atom interferometer operating on single photon transitions.