Simultaneous operation of four singlet-triplet qubits in a two-dimensional array of GaAs quantum dots*

The operation of spin-based quantum processors requires the ability to perform simultaneous and fast measurements in qubit arrays, while overcoming challenges like mitigating crosstalk, tuning in large parameter spaces, and calibrating gate-voltage pulses.
We present the simultaneous coherent manipulation and readout of a two-by-two array of singlet-triplet qubits in GaAs in a geometry where all four qubits can in principle be coupled to a multielectron dot located at the center of the array. Using frequency-multiplexed radio-frequency reflectometry to read out four independent charge sensors, each capacitively coupled to one qubit, we monitor via simultaneous single-shot measurements the fluctuating Overhauser gradients within all four qubits and further induce simultaneous coherent exchange rotations within all qubits. Finally, we demonstrate coherent spin-exchange rotations between one qubit and the multielectron dot, suggesting its use as a coherent coupler that may provide on-demand “any-to-any” qubit-qubit connectivities within the array.