Primary Pressure Standard with Cold Atoms

We developed a method of using an ultra-cold ensemble of atoms confined in a trap as an atomic primary pressure standard. This primary standard uses a 3D MOT to trap $^{87}$ Rb and then transfers them into a quadrupole magnetic trap where atoms could collide with background gas atoms in a shallower trap, resulting in loss of the atoms. The measured loss rate is proportional to the density of the background gas particles and to a velocity-averaged collision cross-section. The advantages of this cold atom standard (CAS) are that it is based on immutable atomic properties, can be used to measure the pressure of any species - in contrast with existing pressure standards which only measures either Argon or Nitrogen, and it transduces loss rate into pressure. The CAS is currently being tested against a NIST-calibrated ionization gauge using both Argon and Nitrogen over the pressure range (10$^{-6}$ - 10$^{-9}$) Torr. The gauge factor for Argon is found to be 1.25 and the Nitrogen measurements have allowed the long-range Vanderwals coefficient for N$_{2}$ - Ar elastic collisions to be determined, which allows us for it to be used as a standard. We also studied the Majorana losses in this quadrupole magnetic trap and reduced its effect to improve the accuracy of the CAS.