Bootstrapping quantum universality: cross-species calibration of a cold atom pressure sensor

The atomic sensor is poised to become the first primary UHV pressure standard.  The sensor ensemble loss rate is the density of background particles times the loss rate coefficient<σ_lossv>. Until recently, it was thought that <σ_lossv>could only be determined from knowledge of the interatomic potentials or from calibration with a known pressure.  However, its universal dependence on trap depth allows an experimental determination of the characteristic ”quantum diffractive energy” (U_d) and thus <σ_lossv>for any background species.  This self-calibrating feature opens up the possibility of measuring gases for which the calculation and calibration techniques are not feasible.

Here we directly compare the self-calibrating method for ⁸⁷Rb-H₂ collisions with calculations of the ⁶Li+H₂ cross section.  The ⁸⁷Rb-H₂ trap loss rate was used to determine the H₂ background pressure and, subsequently, to determine the <σ_totv>coefficient for ⁶Li-H₂ collisions in a dual species magnetic trap. This cross-calibration is necessary because U_d for ⁶Li-H₂ collisions is large, limiting the precision to which <σ_totv>can be determined via loss rate dependence . We compare our results to ab-initio calculations performed at NIST [PRA 99, 042704 (2019)], providing further evidence of the applicability of the self-calibrating technique.