A quantum device comprises first conductive members and second conductive members confining carriers in the z direction and having two dimensional electron gas on the xy plane. Third conductive members generating an electric field having an effect on the first conductive members. An insulating member easily passing a tunnel current between the first conductive members and the second conductive members. Another insulating member hardly passing a tunnel current between the first conductive members and the third conductive members. An electric field generated by a potential applied to the third conductive members has an effect on the sub-band of the first conductive members.