A five-qubit silicon device maintained highly accurate single-qubit operations while several qubits ran simultaneously. Pairwise calibration corrected unwanted phase shifts caused by microwave signals traveling through a shared control line. Three qubits exceeded 99.99% gate fidelity in parallel, while all-five operation achieved approximately 99.9%. A quantum processor can perform beautifully when its qubits take turns, then stumble when several work together. That problem threatens efforts to build useful machines, which must coordinate many operations before fragile quantum information fades. A five-qubit silicon experiment now shows how to preserve much of that accuracy during simultaneous control. Researchers at the RIKEN Center for Emergent Matter Science and collaborating institutions traced a major source of interference to the microwave signals controlling the qubits. They then developed a calibration method that compensates for unwanted changes in quantum phase. Their results, published in Nature Physics, support a simpler wiring approach for larger silicon quantum processors. False-coloured scanning electron micrograph of a cofabricated device identical to the one used in this experiment (scale bar, 100 nm). An array of five quantum dots …