Enabling Leakage Reduction via Fast and High-Fidelity Qutrit Readout

Quantum error correction (QEC) is essential for achieving fault-tolerant quantum computing. However, qubits—the fundamental building blocks of quantum systems—are often not pure two-level systems and can leak into higher energy states, complicating error detection and correction. If these leakage errors are not addressed, they can proliferate, undermining QEC protocols and leading to significant computational inaccuracies. To combat this, a multi-level qubit readout is vital for identifying and mitigating these errors and ensuring robust error correction. We introduce a high-fidelity three-level readout protocol that outperforms traditional discriminators by utilizing matched filters in conjunction with lightweight neural networks. This innovative approach allows for faster and more accurate leakage detection. Designed for real-time implementation on FPGAs, our protocol enhances both the detection and mitigation of leakage errors, thereby improving the reliability of QEC and advancing the progress toward fault-tolerant quantum computation.