Universal logic with encoded spin qubits in silicon.

Area of Science:

• Quantum computing
• Quantum information science
• Solid-state physics

Background:

• Quantum computation faces challenges due to errors from noise and imperfect control, hindering fault tolerance.
• Correlated errors, often caused by microwave control of qubits, are a significant obstacle for many qubit technologies.
• Existing methods require strict error characterization and correlation management for fault-tolerant quantum computation.

Purpose of the Study:

• To demonstrate an alternative approach to quantum computation using energy-degenerate encoded qubit states.
• To achieve universal quantum control by bypassing microwave-associated correlated error sources.
• To explore a pathway towards scalable fault tolerance in quantum computing.

Main Methods:

• Utilized energy-degenerate encoded qubit states controlled by nearest-neighbor contact interactions for partial spin swaps.
• Employed voltage pulses for calibrated sequences of partial swaps, enabling all-electrical control.
• Fabricated a six-qubit array using 28Si/SiGe quantum dots on a scalable platform.

Main Results:

• Achieved universal quantum control for two encoded qubits, bypassing microwave-related correlated errors.
• Quantified operational fidelity using interleaved randomized benchmarking: 96.3% ± 0.7% for encoded CNOT, 99.3% ± 0.5% for encoded SWAP.
• Demonstrated high quantum coherence and low crosstalk control through partial swap operations.

Conclusions:

• The developed all-electrical control method using partial swaps offers a robust pathway to fault-tolerant quantum computation.
• Enriched silicon's quantum coherence, combined with electrical control and error-insensitive encoding, addresses key challenges in quantum computing.
• This approach provides a strong foundation for achieving scalable fault tolerance and unlocking computational advantage.