High-Fidelity Detection on $^{171} \mathrm{Yb}^+$ Qubit via $^2D_{3/2}$ Shelving

High-fidelity detection of quantum states is indispensable for implementing quantum error correction, a prerequisite for fault-tolerant quantum computation. For promising trapped ion qubits, however, the detection fidelity is inherently limited by state leakage. Here, we propose an efficient approach to enhance the fidelity of detecting $^{171} \mathrm{Yb}^+$ qubits through $^2D_{3/2}$ state shelving techniques. Leveraging selective shelving and state-dependent fluorescence, we mitigate the impact of state leakage and experimentally realize a fidelity of 99.88(2)%, while over 99.99% fidelity is predicted by utilizing state-of-the-art hardwares. Meanwhile, we demonstrate the feasibility of mid-circuit measurements, a crucial step for recent implementations of quantum error correction, by mapping the hyperfine qubit to metastable levels. Our research provides an essential component for realizing fault-tolerant quantum information processing with trapped-ion systems in the near future.