Universal quantum gate set approaching fault-tolerant thresholds with superconducting qubits.

Area of Science:

• Quantum Computing
• Superconducting Qubits
• Quantum Information Science

Background:

• Superconducting qubits are a leading platform for quantum computation.
• Developing high-fidelity quantum gates is essential for building scalable quantum computers.
• Characterizing gate performance accurately is critical for identifying and mitigating errors.

Purpose of the Study:

• To characterize a universal set of all-microwave gates for two superconducting transmon qubits.
• To assess the fidelity of single-qubit and two-qubit gates using quantum process tomography.
• To introduce an efficient representation for quantum gate characterization.

Main Methods:

• Utilized quantum process tomography (QPT) to fully characterize gate operations.
• Implemented microwave control pulses for gate operations on transmon qubits.
• Calculated gate fidelities, including Clifford group generators and single- and two-qubit rotations.

Main Results:

• Achieved gate fidelities exceeding 95% (98%) without (with) state preparation and measurement error subtraction.
• Demonstrated high fidelity for single-qubit rotations (π/4, π/8) and a two-qubit controlled-NOT gate.
• Introduced a visually informative Pauli basis representation for quantum process maps.

Conclusions:

• The high-fidelity gate set is a key component for scalable superconducting qubit architectures.
• This work advances the limits of quantum gate characterization accuracy.
• The developed gate set is suitable for implementing quantum error correction schemes.