Operating four singlet-triplet qubits in a two-dimensional array of GaAs dots

Building small-scale spin-based quantum processors requires the ability to perform simultaneous, fast measurements in single- and two-dimensional qubit arrays, as well as overcome challenges like gate crosstalk, tuning in large parameter spaces, and pulse calibration. Here we present the simultaneous coherent manipulation and readout of a two-by-two singlet-triplet qubit array in GaAs, with a large multielectron dot coupler at the center. Using four independent charge-sensors read out via a frequency-multiplexed RF-reflectometry setup, we show coherent exchange oscillations, concurrently monitor the Overhauser field at the four sites of the array, and interlace different pulse operations. Finally, we establish a coherent exchange coupling between one qubit and the central multi-electron dot coupler, suggesting its use as a mechanism to provide on-demand connectivity within the array.