  We study the coupling between a singlet-triplet qubit realized in a double
quantum dot to a topological qubit realized by spatially well-separated
Majorana bound states. We demonstrate that the singlet-triplet qubit can be
leveraged for readout of the topological qubit and for supplementing the gate
operations that cannot be performed by braiding of Majorana bound states.
Furthermore, we extend our setup to a network of singlet-triplet and
topological hybrid qubits that paves the way to scalable fault-tolerant quantum
computing.
