RIKEN Scientists Achieve Simultaneous High-Fidelity Control of Five Silicon Spin Qubits
RIKEN researchers have simultaneously controlled five silicon spin qubits at approximately 99.9% fidelity, overcoming a key error source that had blocked the scaling of silicon quantum processors.
Researchers at the RIKEN Center for Emergent Matter Science and their collaborators have reported a significant advance in silicon quantum computing, publishing their findings in Nature Physics. The team operated five silicon spin qubits simultaneously over a shared microwave control line, with each individual qubit achieving single-qubit gate fidelity well above 99.99% — the highest approaching 99.999%. When up to three qubits were active at the same time, fidelity remained above 99.99%. With all five qubits controlled at once, accuracy held at approximately 99.9%, approaching the levels needed for practical fault-tolerant quantum computing.
The central problem the team tackled was the AC Stark shift: microwave control signals alter a qubit's effective energy levels, introducing unwanted phase shifts that reduce accuracy when multiple qubits are operated together. To counteract this, the researchers devised a pairwise calibration method — rather than mapping every possible combination of qubits, calibrations performed between pairs are used to compensate for the unwanted shifts, making the approach practical for larger systems.
Co-first author Leon Camenzind of RIKEN said the results show "high-fidelity control can be maintained even when several qubits are operated at the same time." First author Yi-Hsien Wu, who carried out the experiments as part of his PhD research, noted that the pairwise strategy avoids a separate calibration procedure for every qubit combination.
Some residual error remained, traced to drive-induced decoherence from the higher microwave power needed for parallel operation — a limitation the team says improved device design could help address. Silicon spin qubits are compatible with established semiconductor manufacturing, making them a promising platform for scaling up quantum processors.
