  Detection and imaging of an electrically conductive object at a distance can
be achieved by inducing eddy currents in it and measuring the associated
magnetic field. We have detected low-conductivity objects with an optical
magnetometer based on room-temperature cesium atomic vapor and a
noise-canceling differential technique which increased the signal-to-noise
ratio (SNR) by more than three orders of magnitude. We detected small
containers with a few mL of salt-water with conductivity ranging from 4-24 S/m
with a good SNR. This demonstrates that our optical magnetometer should be
capable of detecting objects with conductivity < 1 S/m with a SNR > 1 and opens
up new avenues for using optical magnetometers to image low-conductivity
biological tissue including the human heart which would enable non-invasive
diagnostics of heart diseases.
