An Atomic Magnetometer with Spin-Projection Noise Proportional to **Supported by the National Natural Science Foundation of China under Grant Nos 51675034 and 61273067, and the Natural Science Foundation of Beijing Municipality under Grant No 7172123.

Abstract

There is a common sense view for atomic magnetometers that their spin-projection-noises (SPNs) are inversely proportional to , where T2 is the transverse relaxation time. We analyze the current atomic magnetometer types and give a counter-example of this common sense, which is the all-optical spin precession modulated three-axis atomic magnetometer proposed by our group in 2015. Unlike the other atomic magnetometers, the SPN of this kind of atomic magnetometers is proportional to due to the fact that the scale factor between Px and B can be unrelated to the transverse relaxation time T2. We demonstrate this irrelevance experimentally and analyze the SPN theoretically. Using short-pulse ultra-high power laser to fully polarize the atoms, the phenomenon that SPN decreases with T2 may also be demonstrated experimentally and a new tool for researching SPN in atomic magnetometers may be realized.