Vacuum pressure measurement based on 6Li cold atoms in a magneto-optical trap

Ultra-high vacuum measurement and extremely high vacuum (UHV/XHV) measurement play an importantrole in high-tech fields such as deep space exploration, particle accelerators, and nanoscience; with thecontinuous extension of the lower limit of measurement, especially when it reaches the order of 10-10 Pa, higherrequirements are placed on the accuracy of the measurement. At present, in the field of UHV/XHVmeasurement, ionization gauges based on the principle of neutral gas ionization are commonly applied to thevacuum measurement. However, traditional ionization vacuum gauges during use can create electronicexcitation desorption effects, soft X-rays, and the effect of hot cathode outgassing, thereby affecting theaccuracy of measurement and limiting the lower limit of measurement. Compared with the traditionalmeasurement technology, this method uses the relationship between the loss rate and pressure caused by thecollision of cold atoms trapped in the trap depth with the background gas to calculate the gas density andinversely calculate the vacuum pressure. Based on the intrinsic quantum mechanical properties of cold atomcollisions, this method is expected to be developed into a new vacuum traceability standard. In this paper,based on the small-angle approximation and impulse approximation under the quantum scattering theory, theloss rate coefficient of the collision of 6Li cold atoms with background gas molecules is calculated. According tothe ideal gas equation, the pressure inversion formula is obtained. The collision loss rate is extracted byaccurately fitting the loss curve of the cold atom. In order to improve the accuracy of vacuum inversion andreduce the influence of quantum diffractive collision on loss rate measurement, the trap depth under theconditions of a certain cooling laser intensity, detuning, and magnetic field gradient is determined by thephotoassociation method. Finally, in a range of 1 x 10-8-5 x 10-6 Pa, the inverted pressure value is comparedwith the measured value of the ionization meter, proving that this method has good accuracy and reliability inthe inversion of vacuum pressure. At present, the main factor restricting the improvement of accuracy is theinfluence of the collision between the excited atoms in the magneto-optical trap and the background gas on theloss rate measurement. In the future, with the proportion of excited atoms and the excited state C6 coefficientto be precisely determined, the uncertainty of vacuum pressure measurement can be further reduced