Quantum phase-slip processes in superconducting nanowires of suitably small
cross-section have been proposed as the basis for a new current standard, based on physics
dual to that for the Josephson voltage standard. The practical realisation of such devices
presents several challenges. We consider the requirements which need to be met in constructing
a nanowire quantum-phase-slip device and in particular the need to maximise R, the normalstate
resistance of a length of nanowire equal to the superconducting coherence length. Titanium
and niobium–silicon are promising materials for the nanowires
