  Recent advances in nanofluidics have allowed exploration of ion transport
down to molecular scale confinement, yet artificial porins are still far from
reaching the advanced functionalities of biological ion machinery. Achieving
single ion transport that is tuneable by an external gate -- the ionic analogue
of electronic Coulomb blockade (CB) -- would open new avenues in this quest.
However, an understanding of ionic CB beyond the electronic analogy is still
lacking. Here we show that the many-body dynamics of ions in a charged
nanochannel result in a quantised and strongly nonlinear ionic transport, in
full agreement with molecular simulations. We find that ionic CB occurs when,
upon sufficient confinement, oppositely charged ions form 'Bjerrum pairs', and
the conduction proceeds through a mechanism reminiscent of Onsager's Wien
effect. Our findings open the way to novel nanofluidic functionalities, such as
an ionic-CB-based ion pump inspired by its electronic counterpart.
