Fig. 1: Charge stability diagram of a single P donor (L) and a 1P–2P molecule (R_α − R_β).

a Overview STM micrograph of the device during STM lithography. Bright regions are exposed silicon which are subsequently dosed with phosphine to form conductive leads to the central qubit region (dotted white rectangle). b The central device region before dosing, with three sites (L, R_α, R_β) circled. c The same area following phosphine dosing and imaging. Here additional STM imaging of the surface in the fast (horizontal) scan direction has resulted in the tip un-intentionally creating additional dangling bonds along a scan line (position marked by the red arrow). In the final dosed image surface features containing phosphorus are marked whilst all unmarked bright spots are single dangling bonds incapable of incorporating P atoms. d Measured charge stability diagram of the device, showing I_SET as a function of V_L and V_R (V_C = 750 mV, V_B = 300 mV). Discontinuities represent charge state transitions on the three sites (blue-L, green-R_α or pink-R_β dashed lines). Inter-site charge transitions between R_α and R_β are highlighted in yellow. White numbering gives the electron occupation numbers [L, R_α, R_β]. Spin readout of Zeeman doublet states is only possible within the purple shaded areas. The operating point for the spin control experiments is given by the triangular red marker.