A new BEC magnetometer represents the first application for Bose-Einstein
condensates (BECs) outside the realm of atomic physics.
Physicists at the University of Heidelberg have used a
one-dimensional BEC as a sensitive probe of the magnetic fields
emanating from a nearby
sample. The field sensitivity achieved thereby is at the level of
magnetic fields of nanotesla strength (equivalent to an energy scale
of about 10-14 electronvolt) with a spatial resolution of only 3 microns.
Some methods (such as scanning hall probe microscopes) can attain
finer spatial resolution and some methods (such as superconducting
quantum interference devices -- SQUIDs) can attain higher magnetic
sensitivity, but for its range, the Heidelberg device has a region
of the sensitivity-vs-resolution space all to itself.
and his colleagues are pioneers in advancing the young science of
integrated atom optics (see PNU 516),
which seeks to guide atoms around microchips and exploit them for
future practical applications much as electronics manipulates electrons
in integrated circuits and photonics uses photons in optoelectronic structures.
To see how the BEC measures the electromagnetic potential above a
surface, consider that potential to be a landscape covered with peaks
and valleys. If now you flood the whole landscape with water you
would create an equi-potential flat surface at the top. To plumb the
submerged topography you could measure the total amount of the water
beneath the surface at any point. This is what the Heidelberg
Across the sample, where the potential is deep
(that is, where the fields are particularly strong) more atoms in
the BEC pile up. Thus the density of atoms in the BEC (which can be
measured by seeing how much light from a probe laser is absorbed at
points along the length of the BEC -- see figure at
Physics News Graphics)
can be converted into a map of
the fields at the sample surface.
According to Schmiedmayer
(firstname.lastname@example.org), the sensitivity of this process is
already so great that the measurement is limited to some extent by
"atomic shot noise," the atom equivalent of shot noise, the noise
encountered in measuring faint currents because of fluctuations in
the number of electrons arriving at a point a circuit or in
measuring light levels in a fiber because of fluctuations in the
number of arriving photons.
In the BEC case, the field measurements
will be more robust against such atom shot noise if more atoms can
be loaded into the BEC, which resides in a tiny atom trap mere
microns from the surface under study, while simultaneously keeping
the chemical potential constant.
The sensor's nanotesla field sensitivity
and micron spatial resolution should make it useful for discovering
new solid state and surface physics phenomena.
Wildermuth et al.,
Applied Physics Letters, published online 27 June 2006
Contact Jörg Schmiedmayer, University of Heidelberg, email@example.com
Jörg Schmiedmayer's lab