  The topic of quantum fluctuations in quasi-1D superconductors, also called
quantum phase slips (QPS), has attracted a significant attention. It has been
shown that the phenomenon is capable to suppress zero resistivity of
ultra-narrow superconducting nanowires at low temperatures T<<Tc and quench
persistent currents in tiny nanorings. It has been predicted that a
superconducting nanowire in the regime of QPS is dual to a Josephson junction.
In particular case of an extremely narrow superconducting nanowire embedded in
high-impedance environment the duality leads to an intuitively controversial
result: the superconductor enters an insulating state. Here we experimentally
demonstrate that the I-V characteristic of such a wire indeed shows Coulomb
blockade, which disappears with application of critical magnetic field and/or
above the critical temperature proving that the effect is related to
superconductivity. The system can be considered as the dynamic equivalent of a
chain of conventional Josephson junctions.
