  We demonstrate a scalable device architecture that facilitates indirect
exchange between singlet-triplet spin qubits, mediated by an intermediate
quantum state. The device comprises five quantum dots, which can be
independently loaded and unloaded via tunneling to adjacent reservoirs,
avoiding charge latch-up common in linear dot arrays. In a step towards
realizing two-qubit entanglement based on indirect exchange, the architecture
permits precise control over tunnel rates between the singlet-triplet qubits
and the intermediate state. We show that by separating qubits by 1 um, the
residual capacitive coupling between them is reduced to 7 ueV.
