Semiconductor spins are one of the few qubit realizations that remain a serious candidate for the implementation of large-scale quantum circuits. Excellent scalability is often argued for spin qubits defined by lithography and controlled via electrical signals, based on the success of conventional semiconductor integrated circuits. However, the wiring and interconnect requirements for quantum circuits are completely different from those for classical circuits, as individual direct current, pulsed and in some cases microwave control signals need to be routed from external sources to every qubit. This is further complicated by the requirement that these spin qubits currently operate at temperatures below 100 mK. Here, we review several strategies that are considered to address this crucial challenge in scaling quantum circuits based on electron spin qubits. Key assets of spin qubits include the potential to operate at 1 to 4 K, the high density of quantum dots or donors combined with possibilities to space them apart as needed, the extremely long-spin coherence times, and the rich options for integration with classical electronics based on the same technology.
Vandersypen, L. M. K., Bluhm, H., Clarke, J. S., Dzurak, A. S., Ishihara, R., Morello, A., Reilly, D. J., Schreiber, L. R., & Veldhorst, M. (2017). Interfacing spin qubits in quantum dots and donors—hot, dense, and coherent. NPJ Quantum Information, 3(1), 34. https://doi.org/10.1038/s41534-017-0038-y