Quantum limit of optical magnetometry in the presence of ac Stark shifts -art. no. 013808

We analyze systematic (classical) and fundamental (quantum) limitations of the sensitivity of optical magnetometers resulting from ac Stark shifts. We show that in contrast to absorption-based techniques, the signal reduction associated with classical broadening can be compensated in magnetometers b ased on phase measurements using electromagnetically induced transparency ( EIT). However due to ac Stark-associated quantum noise the signal-to-noise ratio of FIT-based magnetometers attains a maximum value at a certain laser intensity. This value is independent on the quantum statistics of the ligh t and defines a standard quantum limit of sensitivity. We demonstrate that an EIT-based optical magnetometer in Faraday configuration is the best cand idate to achieve the highest sensitivity of magnetic-field detection and gi ve a detailed analysis of such a device.