The cold atom vacuum standard at NIST: measuring ultra high vacuum and beyond

The cold atom vacuum standard (CAVS) is an accurate sensor for vacuum pressure in the ultra-high vacuum regime and beyond. By measuring the loss rate of ultra-cold atoms from a conservative magnetic trap, the CAVS infers the pressure of the surrounding vacuum from the scattering cross sections for gas atoms or molecules with a cold, trapped sensor atom. Because these scattering cross sections can be calculated a priori, the CAVS doubles as a primary standard, as it is a sensor that requires no direct calibration. In this talk, I will introduce the operating principle, describe the various CAVSs that have been constructed, discuss some of the progress to date, and speculate on future studies. NIST has constructed three different CAVS devices with different sizes, technical capabilities, and sensor atom species. In 2023, we reported the first comparison of two CAVSs – a laboratory-sized version based on ⁸⁷Rb and a portable version based on ⁷Li – to a traditional vacuum metrology apparatus, an orifice flow standard. This initial experiment showed agreement between all three, with the CAVS measurement having roughly 2 % total relative uncertainty. We have recently completed a comparison between three different CAVSs – a laboratory-sized version that can use either ⁷Li or ⁸⁷Rb and a portable version that uses ⁷Li – and the orifice flow standard. We anticipate our new comparison will have total relative uncertainties of the CAVS measurements of < 1 %, potentially exposing previously unreported systematic effects.