Optimal repetitive readout of single solid-state spins determined by Fisher information.

Quantum systems, including superconducting circuits, trapped ions, quantum dots, solid-state defects, etc., have achieved considerable advancements in readout fidelity. However, the widely used threshold method disregards the importance of temporal characteristics of the signal during continuous measurements, leading to information loss. Here, we applied Fisher information to quantify the potential enhancement by using the temporal information. We proposed an optimal data processing method and derived the condition for equality to the error constrained by Fisher information. Applying this method to the single-shot readout of a [Formula: see text] nuclear spin of nitrogen-vacancy center marks a 33.8 ± 1.2% error reduction compared to the threshold method, improving the fidelity to 99.649(5)%. The versatility of our method is further demonstrated through the single-shot readout of charge states. This work illustrates the advantage of using photon arrival time for improving readout fidelity without upgrading experimental hardware. The method of using Fisher information to analyze readout fidelity also holds promise for broad applicability to other systems.