# Magneto-Optical Traps for Cold Atomic Gravimetry: Research Status and Development Trends
## 1 Introduction
When \(k_{\mathrm{eff}}\,g-2\pi\alpha=0\), changing the pulse interval T, all cosine curves will intersect at a point. The value of gravitational acceleration can be calculated using the chirp rate \(\alpha\) at that point [10]. Quantum projection noise (QPN) is one of the main sources of noise in atomic interferometric gravimetric experiments. QPN is determined by the number of atoms N involved in the interference, and it is proportional to \(1/\sqrt{N}\). The accuracy and sensitivity of the CAG measurement increases with the number of atoms involved in the interference [11]. The cooling and confinement of the atoms during this process is particularly important and directly affects the subsequent interference results in the vacuum cavity. However, there are few papers devoted to the structural characteristics and trends of magneto-optical traps. Atoms move very fast at room temperature, and their low density does not make them easy to manipulate. The lower the temperature, the slower the atoms move. The temperature of the atomic cluster should be reduced to the order of \(\mu\)k for interference to occur. At such a low temperature, there will be more atoms trapped. The cooling and trapping of the atoms is usually achieved by magneto-optical traps. In 1865, the British physicist [PERSON] proved that photons can act mechanically [12]. With the invention of lasers, the idea of the manipulation of atoms by means of lasers was born. The concept of atomic traps was first introduced in 1978 by [PERSON] et al. [13] at the Institute of Spectroscopy of the USSR Academy of Sciences. They used the scattering and dipole forces of the laser to control the motion of atoms in the optical field. When a cluster of atoms is irradiated with a large detuned laser standing wave field, the atoms are pushed by dipole forces to the lowest potential energy wave vents and nodes, forming atom traps. However, since only one-dimensional standing waves were analyzed and the number of trapped atoms was small, a potential trap was needed  
Figure 1: Schematic diagram of the working principle of the pulsed Raman atomic interferometer in the gravitational field. to hold the atoms at a stable equilibrium point in space. This was followed in 1979 by [PERSON]'s proposal to construct an atomic trap using the combination of the dipole and scattering forces [14]. Atoms are causally trapped near the center of the intersection of the two laser beams by using two large detuned Gaussian laser beams propagating in opposite directions. However, this idea has not been realized experimentally. With further research on MOTs, in 1983, [PERSON] and [PERSON] et al. proposed a scheme to overcome the heating effect of atoms by allowing the trapped and cooled laser beams to work in a time-sharing manner to confine them, but it was also not realized experimentally [15]. Summarizing the problems encountered in trapping cold atoms, [PERSON] et al. [16] proved the Earnshaw theorem for optical radiation in 1983, showing that the scattering force alone cannot trap an atom at an equilibrium point in free space, leading to the conclusion that the gradient force or dipole force is essential for any successful optical trapping. Inspired by this theorem, in 1984, [PERSON] [17] proposed to alternate the direction of the two laser beams and use the alternating electric field instead of the electrostatic field to form a stable atom trap using only pure scattering forces, and he successfully trapped oil particles in the experiment, breaking the limits of [PERSON]'s theorem for optical radiation. In 1986, a single-beam Gaussian laser was first used to realize a laser dipole force trap in sodium atomic vapor by [PERSON]. They first cooled the atoms into optical molasses, then irradiated the optical molasses with a Gaussian beam. A dipole force trap was buried in an optical molasses with a temperature of about 240 \(\upmu\)k and a diameter of about 1 cm. They finally achieved the trapping of atoms in a wide range of laser power and frequency detuning [18].