Demonstration of high-fidelity entangled logical qubits using transmons

Area of Science:

• Quantum Computing
• Quantum Information Science
• Error Correction

Background:

• Quantum error correction (QEC) is essential for fault-tolerant quantum computation.
• Existing QEC codes have limitations in detecting logical errors.
• Dynamical decoupling (DD) is a technique to mitigate errors in quantum systems.

Purpose of the Study:

• To propose and implement a novel method to suppress logical errors in quantum computers.
• To enhance the performance of quantum error correction codes by integrating dynamical decoupling.
• To achieve high-fidelity entangled logical qubits beyond breakeven fidelities.

Main Methods:

• Leveraging normalizer elements of QEC codes as DD pulses, termed normalizer dynamical decoupling (NDD).
• Developing a hybrid QEC-NDD strategy capable of handling arbitrary weight errors.
• Implementing an error-detecting version of the strategy on IBM transmon devices using the [[4, 2, 2]] code.

Main Results:

• The hybrid QEC-NDD strategy significantly outperforms standalone QEC or DD.
• A method for detecting logical errors, primarily due to crosstalk, affecting encoded Bell states was demonstrated.
• Experimentally achieved high-fidelity entangled logical qubits with fidelities exceeding unprotected qubits.

Conclusions:

• The proposed NDD strategy offers a powerful approach to drastically suppress logical errors in quantum computers.
• This hybrid method enables the creation of high-fidelity entangled logical qubits, a crucial step towards fault-tolerant quantum computation.
• The experimental results validate the effectiveness of NDD in improving quantum computational performance.