  The smaller the system, typically - the higher is the impact of fluctuations.
In narrow superconducting wires sufficiently close to the critical temperature
Tc thermal fluctuations are responsible for the experimentally observable
finite resistance. Quite recently it became possible to fabricate sub-10 nm
superconducting structures, where the finite resistivity was reported within
the whole range of experimentally obtainable temperatures. The observation has
been associated with quantum fluctuations capable to quench zero resistivity in
superconducting nanowires even at temperatures T-->0. Here we demonstrate that
in tiny superconducting nanorings the same phenomenon is responsible for
suppression of another basic attribute of superconductivity - persistent
currents - dramatically affecting their magnitude, the period and the shape of
the current-phase relation. The effect is of fundamental importance
demonstrating the impact of quantum fluctuations on the ground state of a
macroscopically coherent system, and should be taken into consideration in
various nanoelectronic applications.
