A BEC magnetometer

Physicists at the University of Heidelberg have used a highly elongated Bose–Einstein condensate as a sensitive probe of the magnetic field emanating from a nearby sample. Where the field is weaker, more atoms within the BEC pile up in the trap, which hovers just a few microns from the surface under study. The density of atoms in the BEC can thus be converted into a map of the field at the sample surface. The sensitivity of this process is given by the energy scale of the BEC’s transverse confinement and is limited largely by atomic shot noise, the noise arising from fluctuations in the number of atoms at a specific location in the trap. Thus far, nanotesla field sensitivity and 3-µm spatial resolution have been achieved with the device. Some methods (such as with scanning Hall probe microscopes) can attain finer spatial resolution, and other methods (such as with superconducting quantum interference devices, or SQUIDs) can attain greater magnetic sensitivity, but the Heidelberg device has a region of sensitivity–resolution space all to itself. (S. Wildermuth et al., Appl. Phys. Lett. 88 , 264103, 2006 http://dx.doi.org/10.1063/1.2216932 .)