s-wave collisional frequency shift of a fermion clock
Eric L. Hazlett, Yi Zhang, Ronald W. Stites, Kurt Gibble, and Kenneth M. O’Hara
Accepted
We report an s-wave collisional frequency shift of an atomic clock based on fermions. In contrast to bosons, the fermion clock shift is insensitive to the population difference of the clock states, set by the first pulse area in Ramsey spectroscopy, q1. The fermion shift instead depends strongly on the second pulse area q2. It allows the shift to be canceled, nominally at q2 = p/2, but correlations perturb the null to slightly larger q2. The frequency shift is relevant for optical lattice clocks and increases with the spatial inhomogeneity of the clock excitation field, naturally larger at optical frequencies.