Accumulation gate for quantum device

A quantum device comprising:

• a substrate comprising:
• a layered structure forming a quantum well layer at or below an interface of the substrate, and
• a doped region connected to the layered structure for exchanging charge carriers with the quantum well layer;
• and
• a patterned layer of electrically conductive material forming a set of gates at or above the interface of the substrate,
• wherein the set of gates comprises at least one accumulation gate comprising:
• an accumulation pad configured to accumulate there below a two-dimensional charge carrier gas (2DCCG) in an active region of the quantum well layer connected to the doped region depending on an electric field generated below the accumulation pad,
• a connection pad configured to connect a first electrode to the accumulation gate for setting an accumulation gate voltage to the accumulation pad determining the generated electric field, and
• an electric pathway between the accumulation pad and the connection pad, wherein at least part of the electric pathway is narrowed to form a nanoscale constriction for cutting off the active region of the quantum well layer below and confining the 2DCCG, below the accumulation pad, to the cut off active region;
• wherein the accumulation pad, up to the nanoscale constriction, has a surface area of at least one tenth square micrometer.