Top: a schematic illustration of the device consisting of in-plane gates (red), a SET charge sensor (yellow) and an antenna (light-grey wire). By applying an alternating current I ac through the antenna, an alternating magnetic field B ac is produced, enabling magnetic control. Bottom: an artistic impression of the three phosphorus atoms (blue, green and red) incorporated into the silicon crystal. The attracted electron wave function is depicted in yellow. The three nuclear spins and the electron spin define the four-qubit quantum processor.
