SPEAKER – Dr Tuomo Tanttu, UNSW Sydney:
Many single-electron spin qubits employ magnetic fields at the order of 1 Tesla or above to enable quantum state readout via spin-dependent-tunnelling to an electron reservoir. This requires demanding microwave engineering for coherent spin resonance control and significant on-chip real estate, both of which limit the prospects for large scale multi-qubit systems. Alternatively, single-triplet (ST) readout enables high-fidelity spin-state measurement in much lower magnetic field . Here, we enable low-field characterization of metal-oxide-silicon (MOS) quantum dot qubits by combining coherent single-spin control with high-fidelity, single-shot, Pauli-spin-blockade-based S-T readout. We discover that the qubits decohere faster at low magnetic fields with TRabi2 = 18.6 us and T = 1.4 us at 150 mT . Their coherence is limited by spin flips of residual 29Si nuclei in the isotopically enriched 28Si host material, which occur more frequently at lower fields. Our finding indicates new trade-offs on frequency-stabilizing spin-qubits and highlights the importance of isotopic enrichment of device substrates for the realization of a scalable silicon-based quantum processor.
 M. Fogarty et al., Nature Commun. 9 (2018).
 R. Zhao et al., arXiv:1812.08347 (2018).