The manufacturing technology behind everyday computer chips could help build larger quantum computers. Silicon spin qubits offer that possibility, but the precision they achieve on their own can slip when several are controlled at once.
Researchers from the RIKEN Center for Emergent Matter Science and their collaborators have now demonstrated a way to preserve much of that precision during simultaneous operation. Working with five silicon qubits controlled through a single shared microwave line, they identified a major source of control errors and developed a calibration protocol to compensate for it. Their study was published in Nature Physics.
Quantum bits, or qubits, represent combinations of the conventional binary states 0 and 1. In silicon spin qubits, information is encoded in the spin of an electron trapped in a silicon substrate. Microwave signals manipulate those spins to carry out quantum operations. A useful quantum computer must perform many such operations simultaneously, making reliable parallel control essential.
The team’s optimized device design and carefully calibrated microwave pulses produced single-qubit gate fidelities well above 99.99% on each of the five qubits when tested individually, with the best approaching 99.999%. Fidelity measures how accurately a quantum operation is performed. With the new protocol, fidelities stayed above 99.99% when up to three qubits operated at the same time.
“This shows that high-fidelity control can be maintained even when several qubits are operated at the same time and represents an important step toward scaling up silicon-based quantum processors,” says Leon Camenzind, a RIKEN research scientist and co-first author who supervised the experiments.
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