  We investigate the fine structure of magnetic fields in the atmosphere of the
quiet Sun. We use photospheric magnetic field measurements from {\sc
Sunrise}/IMaX with unprecedented spatial resolution to extrapolate the
photospheric magnetic field into higher layers of the solar atmosphere with the
help of potential and force-free extrapolation techniques. We find that most
magnetic loops which reach into the chromosphere or higher have one foot point
in relatively strong magnetic field regions in the photosphere. $91%$ of the
magnetic energy in the mid chromosphere (at a height of 1 Mm) is in field
lines, whose stronger foot point has a strength of more than 300 G, i.e. above
the equipartition field strength with convection. The loops reaching into the
chromosphere and corona are also found to be asymmetric in the sense that the
weaker foot point has a strength $B < 300$ G and is located in the
internetwork. Such loops are expected to be strongly dynamic and have short
lifetimes, as dictated by the properties of the internetwork fields.
