RIKEN-led team keeps silicon spin qubit gates above 99.9% with all five qubits driven at once

RIKEN

Researchers from RIKEN, National Taiwan University, ETH Zurich and TU Delft drove all five qubits of a silicon spin array through one shared microwave line. Gate fidelity stayed at or above 99.9% in simultaneous operation, a level the article says meets the minimum for 2D surface-code error correction. The results cover single-qubit gates only, and the work was published in Nature Physics.

• Parallel driving used to pull fidelity down from above 99.9% to about 99.5%; the team traced most of the loss to microwave-induced phase shifts.
• They compensate by measuring the phase buildup between each pair of qubits, which takes N(N-1) calibration measurements.
• A single qubit driven alone reached 99.993% to 99.998%; with five driven together, the lowest qubit reached at least 99.90%.
• Idle silicon spins lose their phase far faster (T2* about 10 microseconds) than driven ones (about 100 microseconds), so simultaneous gates matter for error correction.
• No simultaneous two-qubit gate fidelities or full error-correction runs are reported; the faster gates with integrated nanomagnets are projections.