  The physical nature of the currently observed dark energy in the universe is
completely unclear, and many different theoretical models co-exist.
Nevertheless, if dark energy is produced by vacuum fluctuations then there is a
chance to probe some of its properties by simple laboratory tests based on
Josephson junctions. These electronic devices can be used to perform `vacuum
fluctuation spectroscopy', by directly measuring a noise spectrum induced by
vacuum fluctuations. One would expect to see a cutoff near 1.7 THz in the
measured power spectrum, provided the new physics underlying dark energy
couples to electric charge. The effect exploited by the Josephson junction is a
subtile nonlinear mixing effect and has nothing to do with the Casimir effect
or other effects based on van der Waals forces. A Josephson experiment of the
suggested type will now be built, and we should know the result within the next
3 years.
