A five-qubit silicon spin array maintained gate fidelities above 99.99% while operating up to three qubits simultaneously, according to a study published in Nature Physics. The result targets a central obstacle to scaling silicon-based quantum computers: accuracy can decline when multiple qubits are controlled at the same time.
The researchers used a shared microwave control line to operate the array and identified microwave-drive-induced a.c.-Stark shifts as the dominant source of fidelity loss during parallel operation. The effect changes a qubit’s effective energy levels and shifts the phase of its quantum state, making control less precise, the study’s abstract reports.
Their mitigation method uses pairwise phase calibrations rather than a separate calibration for every possible combination of qubits. With tailored control pulses, individual-qubit fidelities exceeded 99.99%, with some approaching 99.999%. Parallel operation of all five qubits produced fidelities of at least 99.9%, while the researchers attributed the remaining degradation to drive-induced decoherence caused by the higher microwave power required.
The work matters because silicon spin qubits can be fabricated using established semiconductor manufacturing technologies, but the achievement remains a laboratory demonstration rather than an operational quantum computer. The study used a five-qubit device fabricated in an isotopically purified silicon/silicon-germanium quantum well.
Phys.org’s report, which was provided by RIKEN, describes the same Nature Physics study and quotes researcher Leon Camenzind calling reliable parallel control an important step toward scaling silicon processors. It is not independent confirmation of the result. The researchers said further device-design improvements could help address the decoherence observed during five-qubit operation.