High-Fidelity Controlled-Phase Gate for Binomial Codes via Geometric Phase Engineering

Area of Science:

• Quantum Computing
• Quantum Information Science
• Quantum Error Correction

Background:

• High-fidelity two-logical-qubit gates are critical for fault-tolerant quantum computation using bosonic codes.
• Existing experimental fidelities for these gates have historically been below 90%.

Purpose of the Study:

• To propose and experimentally demonstrate a novel geometric phase engineering approach for controlled-phase gates.
• To achieve fast and high-fidelity logical operations for binomially encoded logical qubits.

Main Methods:

• Utilizing geometric phase engineering for controlled-phase gates on binomially encoded logical qubits.
• Leveraging the structural simplicity of geometric drives to reduce optimization dimensionality.
• Incorporating system nonlinearities for enhanced gate performance.

Main Results:

• Experimentally demonstrated a process fidelity of 97.4±0.8% for a controlled-Z gate between two lowest-order binomial codes (with postselection).
• Achieved 94.9±0.7% fidelity without postselection, surpassing previous two-logical-qubit gate fidelities in bosonic codes.
• Showcased fast and high-fidelity logical operations.

Conclusions:

• Geometric phase engineering offers an effective and experimentally feasible pathway to high-fidelity logical operations in bosonic quantum processors.
• This method addresses the challenge of achieving high fidelities necessary for fault-tolerant quantum computation.