  Electrical resistance usually originates from lattice imperfections. However,
even a perfect lattice has a fundamental resistance limit, given by the
Landauer conductance caused by a finite number of propagating electron modes.
This resistance, shown by Sharvin to appear at the contacts of electronic
devices, sets the ultimate conductance limit of non-interacting electrons.
Recent years have seen growing evidence of hydrodynamic electronic phenomena,
prompting recent theories to ask whether an electronic fluid can radically
break the fundamental Landauer-Sharvin limit. Here, we use single-electron
transistor imaging of electronic flow in high-mobility graphene Corbino disk
devices to answer this question. First, by imaging ballistic flows at
liquid-helium temperatures, we observe a Landauer-Sharvin resistance that does
not appear at the contacts but is instead distributed throughout the bulk. This
underpins the phase-space origin of this resistance - as emerging from spatial
gradients in the number of conduction modes. At elevated temperatures, by
identifying and accounting for electron-phonon scattering, we reveal the
details of the purely hydrodynamic flow. Strikingly, we find that electron
hydrodynamics eliminates the bulk Landuer-Sharvin resistance. Finally, by
imaging spiraling magneto-hydrodynamic Corbino flows, we reveal the key
emergent length scale predicted by hydrodynamic theories - the Gurzhi length.
These observations demonstrate that electronic fluids can dramatically
transcend the fundamental limitations of ballistic electrons, with important
implications for fundamental science and future technologies
