We describe an experimental study of spin-projection noise in a high sensitivity alkali-metal magnetometer. We demonstrate a four-fold improvement in the measurement bandwidth of the magnetometer using continuous quantum non-demolition (QND) measurements. Operating in the scalar mode with a measurement volume of 2 cm^3 we achieve magnetic field sensitivity of 22 fT/Hz^(1/2) and a bandwidth of 1.9 kHz with a spin polarization of only 1%. Our experimental arrangement is naturally back-action evading and can be used to realize sub-fT sensitivity with a highly polarized spin-squeezed atomic vapor.
@article{arxiv.0907.2241,
title = {High Bandwidth Atomic Magnetometery with Continuous Quantum Non-demolition Measurements},
author = {V. Shah and G. Vasilakis and M. V. Romalis},
journal= {arXiv preprint arXiv:0907.2241},
year = {2010}
}