Comparison of two multiplexed portable cold atom vacuum standards

We compare the vacuum measured by two portable cold atom vacuum standards (pCAVS) developed at NIST. Each pCAVS converts the loss rate of atoms from a magnetic trap to a vacuum pressure using ab initio calculations of the quantum atom-molecule collision cross-section. Our pCAVS devices share the same laser system and atom number measurements are interlaced to allow both pCAVS to measure pressure concurrently. The two pCAVS together detected a leak on the order of 10⁻⁶ Pa L/s. After fixing the leak, the pCAVS measured a pressure of about 20 nPa with approximately 2% uncertainty. The two pCAVS agree within their uncertainties, even when swapping some of their component parts. The operation of the pCAVS was found to contaminate the vacuum slightly, leading to a pressure increase of approximately 1 nPa under normal operating conditions. With improved thermal management, we expect that the vacuum contamination can be decreased sufficiently to allow primary pressure measurements in the extreme-high-vacuum range (<10⁻¹⁰ Pa). The pCAVS promises to deliver accurate measurements of vacuum below 10⁻⁶ Pa a while suffering significantly less from systematics that plague Bayard-Alpert ionization gauges.