Characterization of a scalable donor based singlet-triplet qubit architecture*

We present a donor based quadruple quantum dot device, capable of hosting two singlet-triplet qubits fabricated by scanning tunnelling microscope lithography, with just two leads per qubit. The design is geometrically compact with each pair of dots independently controlled via one gate and one reservoir that both supplies electrons for the dots and measures the singlet-triplet state of the given qubit via dispersive sensing. We verify the locations of the four phosphorus donor dots via an electrostatic model of the device. We study one of the observed singlet-triplet states with a tunnel coupling of 39GHz and a S₀ to T_– decay of 2ms at zero detuning. We measure a 5GHz electrostatic interaction between two pairs of dots separated by 70nm. The results outline a low gate density pathway to a scalable 1D building block of atomic precision donors with dispersive readout.