Events for March 20, 2026

Abstract: Entangled photons possess nonclassical correlations that can be harnessed for imaging. In contrast to conventional optical imaging, quantum imaging based on coincidence detection of entangled photons demonstrated super-resolution beyond the classical diffraction limit. We will present both experimental imaging results and the underlying theoretical framework that explains these advantages. Because photons originate from atoms and molecules, our work also examines atomic physics at the interface between classical and quantum formalisms. We show that the Bloch equation, traditionally regarded as a classical equation of motion, can be reformulated to yield the quantum von Neumann and Schrödinger equations. This correspondence reveals a classical origin for the standard quantum spin equations and clarifies the relationship between the two descriptions. We have further developed a theory that models the multistage Stern–Gerlach experiment envisioned by Heisenberg and Einstein and conducted by Frische and Segre, with improved accuracy compared to existing treatments. More recently, we performed quantum measurements of atomic beam splitting under extremely low magnetic field gradients. Conventional Stern–Gerlach experiments rely on strong gradients to spatially resolve the split beams. In contrast, we use optical spectroscopy to resolve spatially overlapping atomic distributions that would otherwise appear inseparable, thereby enabling low-field quantum measurements. While conventional theoretical models agree with experiments at high magnetic fields, they exhibit noticeable discrepancies as the magnetic field gradient approaches zero. Our theory remains consistent with experimental observations across the entire field range. A key outcome of this work is an estimate of the electron spin collapse time, expressed in dimensionless units of Larmor precession cycles. For the three-stage Stern–Gerlach configuration, our validation constitutes a retrospective agreement with historical data. In the single-stage configuration, the test is prospective. The theoretical framework was fixed before the low-field experimental data were acquired, ensuring that no post hoc adjustments to the theory were introduced. Speaker(s): Lihong, Boulder, Colorado, United States