Entangledphotons possess nonclassical correlations that can be harnessed for imaging. Incontrast to conventional optical imaging, quantum imaging based on coincidencedetection of entangled photons demonstrated super-resolution beyond theclassical diffraction limit. We will present both experimental imaging resultsand the underlying theoretical framework that explains these advantages.Because photons originate from atoms and molecules, our work also examinesatomic physics at the interface between classical and quantum formalisms. Weshow that the Bloch equation, traditionally regarded as a classical equation ofmotion, can be reformulated to yield the quantum von Neumann and Schrödingerequations. This correspondence reveals a classical origin for the standardquantum spin equations and clarifies the relationship between the twodescriptions. Three unexpected experimental observations are presented. First,we model the multistage Stern–Gerlach experiment envisioned by Heisenberg andEinstein and conducted by Frische and Segre, with improved accuracy compared toexisting treatments. More recently, we performed quantum measurements of atomicbeam splitting under extremely low magnetic field gradients. ConventionalStern–Gerlach experiments rely on strong gradients to spatially resolve thesplit beams. In contrast, we use optical spectroscopy to resolve spatiallyoverlapping atomic distributions that would otherwise appear inseparable,thereby enabling low-field quantum measurements. While conventional theoreticalmodels agree with experiments at high magnetic fields, they exhibit noticeablediscrepancies as the magnetic field gradient approaches zero. Our theoryremains consistent with experimental observations across the entire fieldrange. A key outcome of this work is an estimate of the electron spin collapsetime, expressed in dimensionless units of Larmor precession cycles. Finally,inserting a null (zero magnetic field gradient) Stern–Gerlach stage before astandard stage yielded surprising effects as well.