Theory of spin qubits and the path to scalability

Spin qubits have emerged as a leading platform for quantum information processing due to their long coherence times, small footprint, and compatibility with the existing semiconductor industry. We first provide an introduction to the different qubit implementations currently being investigated, including single electron-spin qubits, hole-spin qubits, donor qubits, and multispin encodings. We discuss how the confinement and strain present in semiconductor heterostructures produce addressable levels whose spin degree of freedom can be used to encode a qubit. A large emphasis is placed on reviewing the theoretical foundations and recent experimental demonstrations of proposed mechanisms for long-range coupling, including hybrid approaches based on circuit QED and Andreev qubits, as well as spin shuttling. Finally, we review a recent proposal for linking spin qubits using topological spin textures.