High-Fidelity, Low-Latency State Detection for 300 Trapped Ion Qubits

State detection plays a pivotal role in performing general quantum information processing tasks on trappedion computing platforms, which are now approaching a scale of 1000 qubits. However, there are few solutions capable of achieving high-fidelity low-latency readout for over 100 ions. To address this challenge, we proposed an Ion-Pixel-Mapping (IPM) algorithm that generated the most correlated pixels projected onto each ion, and derived the optimal thresholds for state discrimination. A lower-latency hardware system equipped with a Step-Pointer Detection Unit (SPDU) was also implemented for simultaneous readout. By constraining the readout latency to a few milliseconds, we achieved a fidelity greater than 99.7% on a platform with 300 Yb<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> qubits, thus paving the way for detecting large-scale ion qubit arrays.