Symmetry-Breaking Zeeman-Coherence Parametric Wave Mixing Magnetometry
  The nonlinear magneto-optical effect has significantly impacted modern society with prolific applications ranging from precision mapping of the Earth's magnetic field to bio-magnetic sensing. Pioneering works on collisional spin-exchange effects have led to ultra-high magnetic field detection sensitivities at the level of $fT/\sqrt{Hz}$ using a single linearly-polarized probe light field. Here we demonstrate a nonlinear Zeeman-coherence parametric wave-mixing optical-atomic magnetometer using room temperature rubidium vapor that results in more than a three-order-of-magnitude optical signal-to-noise ratio (SNR) enhancement for extremely weak magnetic field sensing. This unprecedented enhancement was achieved with nearly a two-order-of-magnitude reduction in laser power while preserving the sensitivity of the widely-used single-probe beam optical-atomic magnetometry method. This new method opens a myriad of applications ranging from bio-magnetic imaging to precision measurement of the magnetic properties of subatomic particles. 
Feng Zhou, Chengjie Zhu, E. W. Hagley, L. Deng
physics.optics physics.atom-ph