An iterative polygonal micromagnet design for spin-photon coupling on silicon

Research to realize full electrical spin manipulation and spin-photon coupling on silicon using micromagnets has been prevalent. To realize spin-photon coupling, micromagnets should be placed parallel to the double quantum dot connection direction. However, the parallelly placed micromagnet will also generate detrimental magnetic field gradients, which results in substantial dephasing of the qubit [Yoneda et al., Nat. Nanotechnol. 13, 102-106 (2018); Struck et al., npj Quantum Inf. 6(1), 40 (2020); Takeda et al., Nat. Nanotechnol. 16, 965-969 (2021)]. Here, we develop a scheme of an iterative polygonal micromagnet, which maximizes the qubit Rabi oscillation quality factor [Takeda et al., Sci. Adv. 2, e1600694 (2016)] Q, while allowing strong spin-photon coupling. To find the optimal structure of the micromagnet in the iterative process, the appropriate objective function R (proportional to 1/Q) is selected as the evaluation standard of micromagnet performance. The simulation results by the RADIA package show that the Q value of the polygonal micromagnet is 15% better than that of the rectangular micromagnet at most and up to approximately 30% in subsequent simulation using the OOMMF tool.