Fast, High-Fidelity Conditional-Phase Gate Exploiting Leakage Interference in Weakly Anharmonic Superconducting...

Area of Science:

• Quantum Computing
• Superconducting Circuits
• Quantum Information Science

Background:

• Conditional-phase (CZ) gates are essential for quantum computation.
• Transmon qubits are a leading platform for superconducting quantum computers.
• Achieving fast and high-fidelity gates is crucial for scalable quantum computing.

Purpose of the Study:

• To present a novel 40 nanosecond CZ gate for transmon qubits.
• To demonstrate high fidelity and suppressed leakage using a specific pulse sequence.
• To investigate the factors limiting gate performance.

Main Methods:

• Implementation of a bipolar flux pulse to control transmon qubit interactions.
• Utilizing destructive interference within the pulse to suppress leakage errors.
• Employing a built-in echo mechanism to enhance gate fidelity.
• Conducting numerical simulations to validate experimental results.

Main Results:

• A 40 nanosecond CZ gate was experimentally realized.
• Achieved gate fidelity of 99.1% with leakage suppressed to 0.1%.
• The pulse demonstrated robustness against long-timescale flux control distortions.
• Simulations identified high-frequency dephasing and short-timescale distortions as key limitations.

Conclusions:

• The developed CZ gate approaches the speed limit imposed by exchange coupling.
• The pulse design effectively suppresses leakage and enhances fidelity.
• The findings provide insights into optimizing gate operations in transmon qubits.
• This work contributes to the development of more powerful superconducting quantum computers.