This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Silicon spin qubits are a promising platform for building scalable quantum computers as they are compatible with the semiconductor manufacturing technologies used to produce today's computer chips. However, they have an important weakness: silicon spin qubits typically lose accuracy when several qubits are under parallel control.
To be useful, quantum computers will need to operate many qubits simultaneously without compromising the accuracy of their operations. Now, in a study published in Nature Physics, researchers from the RIKEN Center for Emergent Matter Science and collaborators have addressed this challenge by achieving high-fidelity control of multiple silicon spin qubits operating in parallel. Using a five-qubit silicon array controlled through a single shared microwave line, they identified a key source of errors during the simultaneous operation of qubits and developed a way to mitigate its effects.
According to Leon Camenzind, a research scientist at RIKEN and co-first author who supervised the experiments, "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." Quantum computers process information using quantum bits, or qubits, which 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. Precisely controlling these spins is essential for carrying out quantum operations.
However, applying microwave control signals to multiple qubits at once can introduce errors that reduce computational accuracy. The researchers began their work by finding that the major source of this degradation is a phenomenon known as the AC Stark shift, which is induced by the microwave control signals. This effect changes the effective energy levels of a qubit, shifting the phase of its quantum state and making its operation less precise.
When several qubits are driven simultaneously, these shifts can interfere with the intended control of each qubit. To address this problem, the team developed a scalable mitigation protocol based on phase calibrations. "Rather than requiring an entirely separate calibration procedure for every possible combination of qubits, our method uses calibrations between pairs of qubits to compensate for the unwanted phase shifts," explains Yi-Hsien Wu, the first author who carried out the experiments as part of his Ph.D. research.
Using an optimized device design and carefully calibrated microwave control pulses, the team achieved single-qubit gate fidelities well above 99.99% on each of the five qubits when operated individually, with the best approaching 99.999%. Fidelity measures how accurately a quantum operation is performed. Importantly, by using the protocol, they were able to achieve fidelities above 99.99% when up to three qubits were operated simultaneously.
Extract — continue reading at the source.
