  Superconducting nanowires undergoing quantum phase-slips have potential for
impact in electronic devices, with a high-accuracy quantum current standard
among a possible toolbox of novel components. A key element of developing such
technologies is to understand the requirements for, and control the production
of, superconducting nanowires that undergo coherent quantum phase-slips. We
present three fabrication technologies, based on using electron-beam
lithography or neon focussed ion-beam lithography, for defining narrow
superconducting nanowires, and have used these to create nanowires in niobium
nitride with widths in the range of 20-250 nm. We present characterisation of
the nanowires using DC electrical transport at temperatures down to 300 mK. We
demonstrate that a range of different behaviours may be obtained in different
nanowires, including bulk-like superconducting properties with critical-current
features, the observation of phase-slip centres and the observation of zero
conductance below a critical voltage, characteristic of coherent quantum
phase-slips. We observe critical voltages up to 5 mV, an order of magnitude
larger than other reports to date. The different prominence of quantum
phase-slip effects in the various nanowires may be understood as arising from
the differing importance of quantum fluctuations. Control of the nanowire
properties will pave the way for routine fabrication of coherent quantum
phase-slip nanowire devices for technology applications.
