Granularity Noise Limit in Atomic-Ensemble-Based Metrology

Quantum Physics [Submitted on 7 Apr 2026] Granularity Noise Limit in Atomic-Ensemble-Based Metrology Chen-Rong Liu, Chuang Li, Runxia Tao, Yixuan Wang, Mingti Zhou, Xinqing Wang, Ying Dong Conventional noise analysis in atomic-ensemble sensing assumes a continuous-medium approximation, thereby treating the atomic system as a deterministic dielectric. Here, we demonstrate that this assumption breaks down due to the discrete, particulate nature of the ensemble, giving rise to an intrinsic "atomic granularity noise" (AGN) that fundamentally competes with the optical measurement noise (OMN, typically photon shot noise). By introducing a discrete-atom statistical framework, we derive a unified noise-scaling law governed by a single dimensionless resource ratio, \mathcal{R} = \bar{N}_{\mathrm{ph}}/\bar{N}_{\mathrm{at}} at (the photon-to-atom flux ratio). This law predicts a continuous crossover from an OMN-limited regime to an AGN-limited regime. Crucially, our results reveal a counter-intuitive constraint for sensor optimization: increasing optical probe power -- standard practice to mitigate OMN -- can paradoxically degrade sensitivity by driving the system into the AGN-dominated regime. Furthermore, we identify a critical resource threshold, \mathcal{R}_{\mathrm{crit}}, beyond which quantum-enhanced metrology using non-classical light fails to improve sensitivity, as it becomes limited by the AGN. Comments: 3 figures Subjects: Quantum Physics (quant-ph); Atomic Physics (physics.atom-ph) Cite as: arXiv:2604.05420 [quant-ph]   (or arXiv:2604.05420v1 [quant-ph] for this version)   https://doi.org/10.48550/arXiv.2604.05420 Focus to learn more Submission history From: Chen-Rong Liu [view email] [v1] Tue, 7 Apr 2026 04:32:00 UTC (1,117 KB) Access Paper: HTML (experimental) view license Current browse context: quant-ph < prev   |   next > new | recent | 2026-04 Change to browse by: physics physics.atom-ph References & Citations INSPIRE HEP NASA ADS Google Scholar Semantic Scholar Export BibTeX Citation Bookmark Bibliographic Tools Bibliographic and Citation Tools Bibliographic Explorer Toggle Bibliographic Explorer (What is the Explorer?) Connected Papers Toggle Connected Papers (What is Connected Papers?) Litmaps Toggle Litmaps (What is Litmaps?) scite.ai Toggle scite Smart Citations (What are Smart Citations?) Code, Data, Media Demos Related Papers About arXivLabs Which authors of this paper are endorsers? | Disable MathJax (What is MathJax?)