The disclosure relates to a quantum device and method of fabricating the same. The device comprises one or more semiconductor-superconductor nanowires, each comprising a length of semiconductor material and a coating of superconductor material coated on the semiconductor material. The nanowires may be formed over a substrate. In a first aspect at least some of the nanowires are full-shell nanowires with superconductor material being coated around a full perimeter of the semiconductor material along some or all of the length of the wire, wherein the device is operable to induce at least one Majorana zero mode, MZM, in one or more active ones of the full-shell nanowires. In a second aspect at least some of the nanowires are arranged vertically relative to the plane of the substrate in the finished device.