In one embodiment the cover comprises one or more apertures formed through the cover, wherein the quantum computing circuit package comprises one or more wires arranged to pass through the one or more apertures respectively to connect to the (e.g. plurality of circuit elements of the) quantum computing circuit. As with the apertures through the holder, the apertures through the cover also help to provide routes for connecting wires to the quantum computing circuit, e.g. when the quantum computing circuit has off-chip control wiring, and particularly when the circuit elements of the quantum computing circuit are formed on both faces of the substrate. In this latter case, when apertures are provided through both the holder and the cover, this allows circuit elements on both faces of the substrate to be accessed and connected to easily.

The (e.g. surface of the) cover is preferably configured to be spaced from the circuit elements on the (e.g. face of the) substrate, so the cover does not contact the circuit elements formed on the substrate (e.g. when at least some of the circuit elements are arranged on the face of the substrate facing the cover). This helps to avoid short-circuiting the circuit elements of the quantum computing circuit (e.g. against the surface of the cover facing the substrate).

The cover may be any suitable and desired shape. In one embodiment the cover is substantially planar. In one embodiment the cover is substantially cuboid. Preferably the shape of the cover is complementary to the shape of the holder (and, e.g., the substrate), e.g. to enclose the substrate.