Mesoscopic physics in vapor-phase atomic systems: Collision-shift gradients and the 0-0 hyperfine transition

Abstract

Vapor-phase atomic clocks and atomic magnetometers are achieving levels of stability and measurement precision today that would have been considered unrealistic in the not too distant past. To make further progress, researchers will need a more detailed understanding of vapor-phase atomic physics, in particular, the manner in which mesoscopic variations of atomic perturbations map onto the observed resonant phenomena: length scales larger than that of homogeneous quantum dynamics, where atoms within some localized region of the vapor all experience the same optical and microwave fields and collisional perturbations; but smaller than that of the vapor as a whole, where the atomic system is described in terms of (for example) vapor pressure, heat content, and optical depth. In this paper, we discuss the issue of mesoscopic physics as it manifests itself in vapor-phase collision-shift gradients affecting the 0-0 hyperfine transition of $^{87}\mathrm{Rb}$. We show that these gradients not only produce increased line broadening but lead to lineshape asymmetry and an increased sensitivity of the observed resonance to power-broadening. We develop a statistical theory describing the experimental results, and through that theory we show that mesoscopic atomic physics encompasses a broader class of phenomena than that described by the circumscribed term ``inhomogeneous broadening.''