Atomic-signal-based zero field finding technique for unshielded   laser-pumped atomic magnetometer
  We described a novel technique that can find the zero-field for unshielded laser-pumped atomic magnetometer using atomic signal itself. By comparing light density of pump beam after atomic vapor cell, it is decided which direction to move the compensation magnetic field and whether to increase or decrease the converging step length. The zero-field is found in less than 18s and the step length after converging is smaller than 10nT, 10nT and 40nT for x, y and z axes, respectively, limited by 50Hz noise in the lab environment. 
Haifeng Dong, Hongbo Lin, Xinbin Tang
physics.atom-ph quant-ph