TY - JOUR T1 - Collisions of room-temperature helium with ultracold lithium and the van der Waals bound state of HeLi JF - Phys. Rev. A Y1 - 2020 A1 - Constantinos Makrides A1 - Daniel S Barker A1 - James A Fedchak A1 - Julia Scherschligt A1 - Stephen Eckel A1 - Eite Tiesinga AB -

We have computed the thermally averaged total, elastic rate coefficient for the collision of a room-temperature helium atom with an ultracold lithium atom. This rate coefficient has been computed as part of the characterization of a cold-atom vacuum sensor based on laser-cooled Li 6 or Li 7 atoms that will operate in the ultrahigh-vacuum (p< 10− 6 Pa) and extreme-high-vacuum (p< 10− 10 Pa) regimes. The analysis involves computing the X 2 Σ+ HeLi Born-Oppenheimer potential followed by the numerical solution of the relevant radial Schrödinger equation. The potential is computed using a single-reference-coupled-cluster electronic-structure method with basis sets of different completeness in order to characterize our uncertainty budget. We predict that the rate coefficient for a 300 K helium gas and a 1 μ K Li gas is 1.467 (13)× 10− 9 cm 3/s for He 4+ Li 6 and 1.471 (13)× 10− 9 cm 3/s for He 4+ Li 7, where the …

VL - 101 CP - 012702 U5 - https://doi.org/10.1103/PhysRevA.101.012702 ER - TY - JOUR T1 - Development of a new UHV/XHV pressure standard (cold atom vacuum standard) JF - Metrologia Y1 - 2017 A1 - Julia Scherschligt A1 - James A Fedchak A1 - Daniel S Barker A1 - Stephen Eckel A1 - Nikolai Klimov A1 - Constantinos Makrides A1 - Eite Tiesinga AB -

The National Institute of Standards and Technology has recently begun a program to develop a primary pressure standard that is based on ultra-cold atoms, covering a pressure range of 1 x 10-6 to 1 x 10-10 Pa and possibly lower. These pressures correspond to the entire ultra-high vacuum range and extend into the extreme-high vacuum. This cold-atom vacuum standard (CAVS) is both a primary standard and absolute sensor of vacuum. The CAVS is based on the loss of cold, sensor atoms (such as the alkali-metal lithium) from a magnetic trap due to collisions with the background gas (primarily H2) in the vacuum. The pressure is determined from a thermally-averaged collision cross section, which is a fundamental atomic property, and the measured loss rate. The CAVS is primary because it will use collision cross sections determined from ab initio calculations for the Li + H2 system. Primary traceability is transferred to other systems of interest using sensitivity coefficients.

VL - 54 UR - https://arxiv.org/abs/1801.10120 CP - 6 U5 - https://doi.org/10.1088/1681-7575/aa8a7b ER -