Quantum logic with spin qubits crossing the surface code threshold.

Area of Science:

• Quantum Computing
• Semiconductor Physics

Background:

• High-fidelity quantum bit (qubit) control is essential for reliable quantum algorithms and fault tolerance.
• Achieving two-qubit gate fidelities above 99% is a major goal for semiconductor spin qubits, crucial for scalable quantum processors.
• The surface code, a leading quantum error correction code, requires error rates below approximately 1% for fault tolerance.

Purpose of the Study:

• To demonstrate a spin-based quantum processor in silicon with exceptionally high single- and two-qubit gate fidelities.
• To assess the performance of these high-fidelity gates, including crosstalk and idling errors.
• To execute a complex quantum algorithm, the variational quantum eigensolver, using the developed high-fidelity gate set.

Main Methods:

• Fabrication and operation of a spin-based quantum processor in silicon.
• Utilization of gate-set tomography to precisely measure single- and two-qubit gate fidelities.
• Implementation of the variational quantum eigensolver algorithm for molecular ground-state energy calculations.

Main Results:

• Achieved single- and two-qubit gate fidelities exceeding 99.5%.
• Maintained average single-qubit gate fidelities above 99% even when accounting for crosstalk and idling errors.
• Successfully executed the variational quantum eigensolver algorithm, demonstrating the practical application of the high-fidelity gates.

Conclusions:

• The developed silicon quantum processor surpasses the critical 99% two-qubit gate fidelity threshold, a key milestone for fault tolerance.
• Semiconductor spin qubits are now strongly positioned for advancements in fault-tolerant quantum computing.
• These high-fidelity gates are promising for applications in the current era of noisy intermediate-scale quantum devices.