5 research outputs found
Cross-calibration of atomic pressure sensors and deviation from quantum diffractive collision universality for light particles
The total room-temperature, velocity-averaged cross section for atom-atom and
atom-molecule collisions is well approximated by a universal function depending
only on the magnitude of the leading order dispersion coefficient, . This
feature of the total cross section together with the universal function for the
energy distribution transferred by glancing angle collisions ()
can be used to empirically determine the total collision cross section and
realize a self-calibrating, vacuum pressure standard. This was previously
validated for Rb+N and Rb+Rb collisions. However, the post-collision energy
distribution is expected to deviate from in the limit of small
and small reduced mass. Here we observe this deviation experimentally by
performing a direct cross-species loss rate comparison between Rb+H and
Li+H and using the \textit{ab initio} value of . We find a velocity averaged total collision cross
section ratio, . Based on an
\textit{ab initio} computation of m/s, we deduce m/s,
in agreement with a Rb+H \textit{ab initio} value of .By contrast, fitting the Rb+H loss rate as a
function of trap depth to the universal function we find
m/s. Finally, this work demonstrates how to perform a cross-calibration of
sensor atoms to extend and enhance the cold atom based pressure sensor.Comment: 14 pages, 9 figure
Development of a cold atom pressure standard
In this thesis, we report the realization of the world's first cold atom based pressure standard
for the high- and ultra-high vacuum (UHV) regimes, < 10⁻⁶ Pa (1 Pa=1N/m²).
This standard is a fundamentally new approach to vacuum metrology as it is based on a
universal law governing quantum diffractive collisions between particles. We show that
a measurement of trap loss rate versus trap depth provides the velocity averaged total
collision cross-section, , - the only parameter required to quantify the pressure
of background particles given a measurement of the collision rate with a sensor atom.
This new quantum measurement standard is fully empirical, based on unchanging and
fundamental atomic constants, and does not rely on computations of total collision
cross-sections based on theoretical interaction potentials. We demonstrate, using a sensor
ensemble of ⁸⁷Rb atoms, that this new quantum pressure standard can be applied
to gases of both atomic species (He, Ar, and Xe) and molecular species (N₂, CO₂, and
H₂), surpassing the scope of existing orifice flow pressure standards. The accuracy of
this new standard was also verified by comparing it with an N₂ calibrated ionization
gauge traced back to an orifice flow standard. They agree within 0.5%. A complete
uncertainty analysis of this cold atom pressure standard is provided here. Moreover,
using this standard, we are able to observe and quantify the performance limits of two
industry-standard ionization gauges. Using this universal law, we can precisely measure
the total collision cross-section for the collision system of interest. As an
example, we show a precision measurement of for collisions between Rb and Ar.
The experimentally determined value of agrees with the theoretical computation
result within 1.0 %. Next, we demonstrate the use of a magneto-optical trap (MOT) as
a transfer pressure standard to extend the operational range of the cold atom pressure
standard by a factor of 100, from P < 10⁻⁷ Pa to include pressures up to P < 10⁻⁵ Pa.
Finally, a proposal for using a MOT as a primary pressure standard is presented.Science, Faculty ofPhysics and Astronomy, Department ofGraduat