  We report the demonstration of a magnetometer with noise-floor reduction
below the shot-noise level. This magnetometer, based on a nonlinear
magneto-optical rotation effect, is enhanced by the injection of a squeezed
vacuum state into its input. The noise spectrum shows squeezed noise reduction
of about 2 dB spanning from close to 100 Hz to several megahertz. We also
report on the observation of two different regimes of operation of such a
magnetometer: one in which the detection noise is limited by the quantum noise
of the light probe only, and one in which we see additional noise originating
from laser noise which is rotated into the vacuum polarization.
