Publication | Open Access
Universal control of a six-qubit quantum processor in silicon
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2022
Year
Quantum ScienceEngineeringQuantum ComputingPhysicsNatural SciencesQuantum FeedbackQuantum AlgorithmComputer EngineeringLarge Qubit CountFuture Quantum ComputersQuantum DevicesSix-qubit ProcessorQuantum EntanglementQuantum Error CorrectionUniversal ControlQuantum Characterization
Quantum computing at scale demands many reliably operated qubits, yet increasing qubit count often conflicts with high fidelity, and semiconductor quantum‑dot spins—though promising—have so far been demonstrated only with one to four qubits, each optimized for either single‑ or two‑qubit gates, initialization, or readout. The study aims to scale a silicon quantum processor to six qubits while maintaining high‑fidelity universal control, state preparation, and measurement. The authors built and operated a six‑qubit silicon processor, employing Hamiltonian engineering, high‑level circuit abstraction, efficient calibration, and measurement‑based initialization with real‑time feedback and quantum‑non‑demolition readout. The resulting device demonstrates that six qubits can be universally controlled with respectable fidelities, enabling more complex quantum protocols and marking a significant step toward large‑scale quantum computers.
Future quantum computers capable of solving relevant problems will require a large number of qubits that can be operated reliably. However, the requirements of having a large qubit count and operating with high-fidelity are typically conflicting. Spins in semiconductor quantum dots show long-term promise but demonstrations so far use between one and four qubits and typically optimize the fidelity of either single- or two-qubit operations, or initialization and readout. Here we increase the number of qubits and simultaneously achieve respectable fidelities for universal operation, state preparation and measurement. We design, fabricate and operate a six-qubit processor with a focus on careful Hamiltonian engineering, on a high level of abstraction to program the quantum circuits and on efficient background calibration, all of which are essential to achieve high fidelities on this extended system. State preparation combines initialization by measurement and real-time feedback with quantum-non-demolition measurements. These advances will allow for testing of increasingly meaningful quantum protocols and constitute a major stepping stone towards large-scale quantum computers.