Determination of the ⁸⁷Rb atomic number density in thin rubidium vapors

In recent years, the research in the fields of quantum computing, quantum communication and quantum precision measurement has set off the "second quantum revolution" and become an international hotspot. Background cold atomic vapor density is an important parameter in the vacuum systems. At present, the methods of measuring atomic vapor density include absorption line method and fluorescence method. However, for the negative exponential relation between the atomic vapor density and the measurement results of the existing methods, it is impossible to accurately measure the lowdensity atomic vapor. Therefore, based on the principle of magneto-optical Effect and coherence detection, we propose a method to measure the atomic vapor density of rarefied alkali metals. Taking 87Rb atom as an example, under different temperature and pressure conditions, the final measured atomic vapor density range is 1.47 x 10¹²∼5.66 × 10¹³ m^-3. The accuracy of this method is about 3∼4 orders of magnitude higher than the existing method. The method effectively solves the measurement problem of low-density atomic vapor.