  It has long been realized that even a perfectly clean electronic system
harbors a Landauer-Sharvin resistance, inversely proportional to the number of
its conduction channels. This resistance is usually associated with voltage
drops on the system's contacts to an external circuit. Recent theories have
shown that hydrodynamic effects can reduce this resistance, raising the
question of the lower bound of resistance of hydrodynamic electrons. Here we
show that by a proper choice of device geometry, it is possible to spread the
Landauer-Sharvin resistance throughout the bulk of the system, allowing its
complete elimination by electron hydrodynamics. We trace the effect to the
dynamics of electrons flowing in channels that terminate within the sample. For
ballistic systems this termination leads to back-reflection of the electrons
and creates resistance. Hydrodynamically, the scattering of these electrons off
other electrons allows them to transfer to transmitted channels and avoid the
resistance. Counter-intuitively, we find that in contrast to the ohmic regime,
for hydrodynamic electrons the resistance of a device with a given width can
decrease with its length, suggesting that a long enough device may have an
arbitrarily small total resistance.
