Vacuum Pressure Measurement Of Cold Atoms In The Magneto-optical Trap And Magnetic Trap

Intensive research in area such as deep space exploration,gravitational wave de-tection,and quantum computing has placed higher demands on the accuracy of vacuum metrology.However,the routine vacuum metrology methods would destroy the back-ground vacuum gas composition during the measurement process,and there are calibra-tion loss and calibration drift in the reactive gas environment.Therefore,it is necessary to develop a high-precision,self-calibrating vacuum metrology method to measure and calibrate the vacuum pressure.Under the above demand,cold-atom vacuum standard of-fers a new vacuum metrology solution.Compared with traditional metrology methods,the cold-atom vacuum standard has advantages such as zero traceability chain,high mea-surement accuracy,non-destructive measurement,and is expected to further develop the ultimate vacuum pressure measurement.Based on universal physical properties and quan-tities,the method investigates atomic loss through the collision mechanism between cold atoms and background gas molecules,thus eliminating the need for repeated calibration of related equipment.This provides a new idea for the high-precision measurement of vacuum pressure and the reformulation of international standards for vacuum pressure.We construct an experimental setup for vacuum metrology of cold ⁷Li atoms,and separately investigate the establishment of a cold atom vacuum standard under different trap depth conditions.This topic is discussed in detail in the following works:1.An ultra-high vacuum system is built with an ultimate vacuum pressure of 1×10^-9Pa.The experimental system consists of a lithium source,a two-dimensional magneto-optical trap system,a three-dimensional magneto-optical trap system and a gas inlet.The first two are separated by a CF16 diode and the second two by a differential pumping tube,which ensure that the vacuum pressure of the three-dimensional magneto-optical trap sys-tem is not affected by the lithium vapor pressure when the lithium source is operating at high temperature,thus reducing the effect of vacuum pressure fluctuations on the mea-surement results.The connection of the three-dimensional magneto-optical trap system to the measured system is achieved by the gas inlet device.2.An atomic escape model is established to accurately calibrate the magneto-optical trap depth,and the results are used to accurately calibrate the loss rate coefficient,thus improving the accuracy of the vacuum metrology results.The loss rate coefficients are affected differently in different trap depth ranges.For cold ⁷Li atoms,the magnetic trap depths in the order of 1 m K can be considered as an ideal atomic collision carrier.In contrast,the magneto-optical trap depth in the order of 1 K has a non-negligible effect on the loss rate coefficient.Therefore,we accurately measure the magneto-optical trap depth using the kick and recapture method.The experimental results prove that the trap depth varies in the range of 0.14 K-0.34 K with an uncertainty of less than 3%under the current experimental conditions.3.The experimental procedure and results of vacuum pressure measurement based on the magneto-optical trap and magnetic trap are compared in detail,using N₂as the background gas environment,the results show that the pressure measurement results of the both agree with the real-time readings of the ionization gauge.Under the current con-ditions,the upper limit of vacuum pressure measurement based on the magneto-optical trap is 1.38×10^-5Pa,and 1.42×10^-6Pa based on the magnetic trap.However,the quadrupole magnetic trap is limited in the ultimate vacuum pressure calibration due to the Majorana spin-flip loss.In contrast,the magneto-optical trap does not have this limiting factor,that is,the the range of vacuum pressure measurement in a magneto-optical trap is wider.In addition,the the accuracy of the vacuum pressure measurement results based on the magneto-optical trap is slightly higher than that of the magnetic trap,and the cor-responding optional cycle is at least 5.5 times shorter than that of the magnetic trap under current conditions.After comparative analysis,the vacuum pressure measurement based on the magneto-optical trap has higher signal-to-noise ratio,shorter measurement cycle,wider measurement range,and less uncertainty.