Quantum Phase Slips and Transport in Ultrathin Superconducting Wires

We present a microscopic study of the quantum fluctuations of the superconducting order parameter in thin homogeneous superconducting wires at all temperatures below $T_c$. The rate of quantum phase-slip processes determines the resistance $R\left(T\right)$ of the wire, which is observable in very thin wires, even at low temperatures. Furthermore, we predict a new low-temperature metallic phase below a critical wire thickness in the 10-nm range, in which quantum phase slips proliferate.