High-resolution magnetometry with a spinor Bose-Einstein condensate

We demonstrate a precise magnetic microscope based on direct imaging of the Larmor precession of a Rb-87 spinor Bose-Einstein condensate. This magnetometer attains a field sensitivity of 8.3 pT/Hz(1/2) over a measurement area of 120 mu m(2), an improvement over the low-frequency field sensitivity of modern SQUID magnetometers. The achieved phase sensitivity is close to the atom shot-noise limit, estimated as 0.15 pT/Hz(1/2) for a unity duty cycle measurement, suggesting the possibilities of spatially resolved spin-squeezed magnetometry. This magnetometer marks a significant application of degenerate atomic gases to metrology.