Two applications of alkali-metal atoms in pressure standards

We describe recent developments on two means to use alkali-metal atoms to measure pressure. The first operates in the ultra-high-vacuum regime with pressures below 10^-6 Pa and uses the rate of atom loss from a trapped sample of ultracold, microkelvin lithium or rubidium atoms due to collisions with residual, typically room-temperature atoms and molecules in the vacuum. Specifically, we modeled the small, percent size imperfections in measuring pressure due to glancing collisions that do not impart sufficient kinetic energy to the ultracold atoms for them to leave their shallow magnetic trap. This research was done by researchers at NIST. The second pressure sensor operates in low and medium vacuum of order 100 Pa. This sensor uses the decay of laser-induced spatially periodic population gratings in trace amounts of rubidium atoms to infer diffusion coefficients and therefore pressure. Populating gratings decay due to collisions between rubidium atoms and the background gasses that lead to large changes in momenta. Here, we analyzed systematic uncertainties in the experimental setup and showed quantitative agreement with a theoretical determination of diffusion coefficients for a select set of non-reactive gasses. This research was performed in collaboration with researchers at York University, Canada.