ABSTRACT
This chapter provides a detailed analysis of nontrivial fluctuation effects in ultrathin superconducting wires. As the wire thickness decreases, the superconducting transition gets broader, exactly as it was detected, for example, in the experiments. A clear manifestation of a crucial role played by quantum fluctuations in superconducting nanowires was provided in the experiments by Tinkham et al. The chapter explores a microscopic theory of quantum phase slips in superconducting nanowires. Equilibrium voltage noise in such nanowires can be viewed as a direct consequence of the fluctuation-dissipation theorem: As soon as the current flow in our system becomes dissipative, equilibrium voltage fluctuations should inevitably be expected. Although discrete charge carriers are certainly present in superconducting nanowires, they form a superconducting condensate flowing along the wire without any scattering.
