Scalable donor-based electron spin qubit unit in silicon

Donor-based spin qubit has gained attention, for its long coherence time and great scalability on processing. With the development of scanning tunneling microscope (STM) lithography and micro-nano fabrication, large-scale donor-based spin qubit devices are promising. However, manufacturing is not the only challenge. There are two critical issues including the tunability of the two-qubit coupling and the addressability of computing qubits. In this talk, we propose a scalable unit of donor-based electron spin qubits that incorporates an ancilla donor. In particular, we introduce an asymmetric structure that exhibits great compatibility between the tunability of two-qubit coupling and the addressability, with the aid of so-called 'superexchange' and hyperfine interaction. And the fidelity of single-qubit and two-qubit gates can exceed the fault-tolerant threshold. Moreover, the asymmetric scheme can resist the valley oscillation of the tunneling coupling, with a nanoscale placement accuracy of donors. Consequently, the proposed scheme is a promising prototype for the large-scale fault-tolerant spin-based quantum processor.