Quantum computing promises to revolutionize everything from drug discovery to cryptography, but one of the biggest hurdles has been scaling up qubits, the quantum bits that power these machines, without losing accuracy.<\/p>\n
Silicon spin qubits<\/a>, which encode information in the spin of electrons<\/a> trapped in silicon, are especially attractive because they\u2019re compatible with the same semiconductor technologies used to make today\u2019s computer chips. Yet they\u2019ve had a nagging weakness: when several qubits are operated in parallel, accuracy tends to drop.<\/p>\n Researchers from the RIKEN Center for Emergent Matter Science and their colleagues may have solved a portion of the puzzle. The research was published in Nature Physics and showed that it was possible to control many silicon spin qubits at once, which is an important step forward to building large-scale quantum computers using silicon technology.<\/p>\n When many qubits are driven at once, the microwave control signals may cause what is known as the \u201cAC Stark shift\u201d that changes the qubits\u2019 energy levels and therefore distorts the qubits\u2019 quantum state and reduces the level of accuracy.<\/p>\n Scientists Use AI to Cut Quantum Computing Errors by 100\u00d7<\/a><\/p>\n The researchers identified this effect as the main reason for their problem and therefore came up with a smart way to fix it. They did not calibrate every possible pair of qubits, which would be extremely difficult, but rather used pairwise phase calibration to correct for the undesirable phase changes.<\/p>\n As Yi-Hsien Wu, first author, explained:<\/p>\n \u201cRather 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.\u201d<\/p>\n With optimized device design and carefully tuned microwave pulses, the researchers achieved single-qubit gate<\/a> fidelities above 99.99%, with the best approaching 99.999%. Even more impressively, fidelities stayed above 99.99% when they operated up to three qubits simultaneously. Running all five qubits in parallel, fidelities remained around 99.9%, close to the threshold needed for fault-tolerant quantum computing.<\/p>\n The other degradation is due to drive-induced decoherence resulting from the increased microwave power needed to operate simultaneously. While this effect wasn\u2019t eliminated, the team believes further device improvements could reduce it.<\/p>\n New quantum computing architecture will enable high-fidelity communication<\/a><\/p>\n \u201cThis 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,\u201d said Leon Camenzind, co-first author and supervisor of the experiments.<\/p>\n By proving that shared microwave control lines can deliver reliable parallel operation, the study strengthens the case for silicon spin qubits as a practical path to large-scale quantum computers.<\/p>\n \u201cOur long-term goal is to build a fault-tolerant quantum computer based on silicon spin qubits, and reliable parallel control is an essential step toward that goal,\u201d added<\/a> Seigo Tarucha, project manager under JST\u2019s Moonshot Goal 6.<\/p>\n Silicon spin qubits (electron-sized building blocks) can meet this requirement. The ability to control all qubits at once and with near-perfect precision is as important as having more qubits. This shows how silicon spin qubits can achieve what is needed for the future of quantum computing.<\/p>\n Journal Reference:<\/p>\n