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The redefinition of the International System of Units (SI) promotes the transformation of the vacuum measurement system toward quantization, and the quantization of vacuum parameters is one of the most leading, prospective and subversive research directions in the field of international vacuum metrology, and the quantum vacuum measurement is based on the quantum effect of the microscopic particle system, and the use of optical means and the theory of quantum mechanics to realize the precision measurement of the vacuum parameters. We develop a lithium-cooled atom vacuum measurement apparatus, which mainly consists of a 7Li atom trap system and a continuous expansion vacuum system. In this work, an experimental study of ultrahigh vacuum measurement is carried out by manipulating 7Li atoms and utilizing the loss characteristics of lithium cold atoms in magneto-optical and magnetic traps, and the results show that for the four commonly used gas molecules in vacuum, namely N2, Ar, He, and H2, in the vacuum range of (3×10–8–4×10–5) Pa, the maximum measurement uncertainty is 7.6%–6.0% (k = 2) based on 7Li cold atoms, and the cold atom vacuum measurement results are in good agreement with those of the traditional ionization vacuum gauges, and their relative sensitivities are in good agreement with those of the ionization vacuum gauges, and the maximal deviation of the relative sensitivity factor is less than 8%, which verifies the accuracy and reliability of the cold-atom quantum vacuum measurements. The research results are of great significance in promoting the development of new cross-generation vacuum measurement technology and meeting the needs of space science exploration, ultra-precision measurement and high-end equipment manufacturing.
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Keywords:
- ultra-high vacuum measurement /
- cold atom /
- magneto-optical trap /
- magnetic trap
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图 1 7Li冷原子真空测量装置实物图
Figure 1. Photo of 7Li cooled atomic vacuum measurement device.
图 2 碰撞体系的损失率系数kloss与阱深U的关系曲线
Figure 2. Loss rate coefficient kloss versus trap depth U for the collision system.
图 3 7Li冷原子真空测量装置原理图
Figure 3. Schematic diagram of the 7Li cold atom measurement apparatus.
图 4 3D MOT真空腔体中7Li冷原子团拍摄照片
Figure 4. Photo of 7Li cold atom clusters in 3D MOT vacuum cavity.
图 5 7Li原子2S基态和2P激发态能级图
Figure 5. Energy level diagrams of 2S ground state and 2P excited state of 7Li atom.
图 6 磁光阱和磁阱中冷原子损失率测量控制时序
Figure 6. Timing sequence of the cold atom loss rate measurements in MOT and MT.
图 7 磁光阱和磁阱中冷原子损失率测量曲线
Figure 7. Measurement curves of the loss rate of cold atoms in MOT and MT.
图 8 损失率Γloss与冷原子测量真空度p的关系曲线
Figure 8. Curve of loss rate Γloss versus cold atom measurement vacuum pressure p.
图 9 分离规灵敏度因子与冷原子测量真空度的关系曲线
Figure 9. Curve of the sensitivity factor of the extractor gauge versus the vacuum pressure of the cold atom measurement.
表 1 ab initio第一性原理实验测量的损失率系数kloss和半经典理论计算值比对
Table 1. Comparison of the loss rate coefficient kloss measured by the ab initio first principle experiment and the calculated value of the semiclassical theory.
碰撞体系 第一性原理测量值
kloss /
(10–15·m3·s–1)半经典理论计算值
kloss /
(10–15·m3·s–1)7Li-N2 1.36 0.27 7Li-Ar 1.21 0.059 7Li-He 1.04 1.29 7Li-H2 1.56 2.12 
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表 2 冷原子校准的分离规相对N2的灵敏度因子
Table 2. Sensitivity factors of extractor gauge relative to N2 by cold atom calibration.
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表 3 冷原子真空测量不确定度汇总表
Table 3. Summary of cold atom vacuum measurement uncertainties.
不确定度来源 评定方法 不确定度分量 损失率不确定度$ {u_{\text{r}}}({\varGamma _{{\text{loss}}}}) $ A类 10–8 Pa 0.03%@N2; 0.02%@Ar 10–7 Pa 0.07%@N2;0.05%@Ar;0.05%@He;0.04%@H2 10–6 Pa 0.04%@N2; 0.1%@Ar; 0.02%@He;0.04%@H2 10–5 Pa 0.06%@N2;0.04%@Ar;0.07%@He;0.08%@H2 B类 0.6% 损失率不确定度$ {u_{\text{r}}}({\varGamma _{{\text{MT}}}}) $ A类 1.6%@N2; 1.7%@Ar; 1.5%@He; 1.5%@H2 B类 0.6% 损失率不确定度$ {u_{\text{r}}}({\varGamma _{{\text{MOT}}}}) $ A类 0.05%@N2; 0.07%@Ar; 0.09%@He; 0.06%@H2 B类 0.6% 损失率系数不确定度$ {u_{\text{r}}}({k_{{\text{tot}}}}) $ — 0.8%@N2; 0.3%@Ar; 2.4%@He; 1.9%@H2 玻尔兹曼常数不确定度$ {u_{\text{r}}}({k_{\text{B}}}) $ — 忽略不计 气体分子温度不确定度$ {u_{\text{r}}}(T) $ B类 0.3% 本底真空波动不确定度$ {u_{\text{r}}}(w) $ A类 10–8 Pa 2.5%@N2; 2.5%@Ar; 2.0%@He; 2.7%@H2 10–7 Pa 0.5%@N2; 0.7%@Ar; 0.6%@He; 0.8%@H2 10–6 Pa 0.07%@N2;0.07%@Ar;0.08%@He;0.1%@H2 10–5 Pa 忽略不计 合成标准不确定度 10–8 Pa 3.3%@N2; 3.2%@Ar; 3.6%@He;3.8%@H2 10–7 Pa 2.2%@N2; 2.2%@Ar; 3.1%@He;2.8%@H2 10–6 Pa 2.1%@N2; 2.0%@Ar; 3.0%@He;2.7%@H2 10–5 Pa 2.1%@N2; 2.0%@Ar;3.0%@He; 2.7%@H2
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