Axial localization enabled by quantum correlations

Abstract

Accurate axial localization is essential for identifying the object position along the optical axis, which directly impacts the resolution and fidelity of image reconstruction. However, conventional localization techniques rely on first-order intensity measurements and numerical propagation based on image sharpness metrics, making them susceptible to noise and diffraction-induced artifacts. Here, we propose a quantum correlation based axial localization method enabled by entangled photon pairs, where the axial position is encoded in the correlation peak width. In contrast to classical intensity-based approaches, the proposed method exploits second-order correlations and operates independently of the imaging modality and specimen. We analyze the evolution of the correlation peak width with defocus and show that it provides a direct and reliable indicator of the axial position. The proposed approach demonstrates enhanced noise robustness and avoids computationally intensive optimization procedures. This physics-driven framework enables robust axial localization in lensless, noninvasive, and photon-limited imaging scenarios and holds potential for advancing high-fidelity quantum imaging systems.