Dmitry A. Pushin

Coherent control of neutrons via Bragg diffraction forms the foundation of perfect crystal neutron interferometry, facilitating both fundamental tests of quantum mechanics and applications in quantum information science. In cavity geometries, perfect crystals enable neutron confinement and have been employed in precision measurements of spin-orbit interactions and for neutron electric dipole moment (nEDM) searches. However, in these conventional configurations, neutrons undergo a single pass through the crystal geometry, placing a physical constraint on both crystal and in-flight interaction times and measurement sensitivity. In this work, we introduce a neutron loop cavity that coherently recirculates neutrons through repeated Bragg reflections between perfect silicon crystal blades. This structure is predicted to achieve a neutron unitary survival probability of ∼ 64 % for 10 000 Bragg reflections, corresponding to confinement times on the order of seconds. We propose a Schwinger interaction measurement that achieves a π spin rotation in 800 Bragg reflections, representing more than a tenfold improvement in sensitivity over recent measurements. Further applications include nEDM searches targeting the 10 − 27 e cm scale, as well as experimental tests of neutron parity violation, the neutron lifetime, and the quantum Zeno effect with neutrons.

A recent proposal suggested that neutron orbital angular momentum (OAM) states could be detected via spin-polarized absorption in polarized He 3 , with predicted cross-section variations linked to the neutron’s OAM. We experimentally tested this hypothesis using spin-polarized neutron beams with OAM = − 2 to 2, generated by fork-dislocation phase gratings and transmitted through a polarized He 3 cell. Within statistical precision, no OAM-dependent change in the absorption cross section was observed. This null result places stringent constraints on polarized He 3 -based OAM detection schemes. The absence of an effect in the given regime is traced to the proposal’s disregard of the spatial character of neutron OAM: Unlike spin, OAM arises from the transverse phase structure of the wavefunction and couples only through spatial gradients and overlap. The transverse extent of neutron OAM modes expands rapidly, producing a doughnut-shaped intensity profile with negligible overlap with on-axis He 3 nuclei, while off-axis capture samples only a locally uniform phase and reduces the interaction to the known spin dependence. These results establish the limits of absorptive nuclear methods for probing neutron OAM and emphasize the necessity of spatially resolved interactions in any viable detection scheme.

The theory of dynamical diffraction (DD) in perfect crystals is the backbone of high-precision neutron and x-ray diffraction experiments, enabling accurate determination of crystal-structure factors and the realization of perfect-crystal interferometers. In practice, however, real crystals exhibit deformations and imperfections, including surface roughness, defects, temperature gradients, angled crystal faces, and curvature, that degrade interferometer performance and are difficult to model using conventional DD theory, particularly in complex geometries. To address these challenges, a quantum information (QI) model for DD has been under development, with demonstrated experimental agreement both for ideal crystals and in the presence of some imperfections such as surface roughness and defects. Here, we present a unified quantum walk model that is now suitable for reproducing a broad range of established DD effects. We demonstrate this by incorporating several diverse internal crystal effects influencing DD intensity distributions, including linear temperature gradients, the DD Talbot effect, and angled or miscut crystals. These results establish the QI model as a comprehensive and flexible framework for experimental analysis, as well as for the design of next-generation perfect-crystal neutron interferometers and neutron optical components, such as condensing monochromators.

The experimental realization of neutron orbital angular momentum (OAM) states and neutron Airy beams has opened new avenues for structured neutron science in both materials characterization and fundamental physics. These additional degrees of freedom in scattering experiments enable the exploration of selection rules for neutrons, the analysis of scattering properties in topological materials, and the generation of auto-focusing neutron beams. In the effort to enhance the amount of spatial and angular-momentum information retrievable from a single measurement, and to overcome current phase-grating efficiency limits, here we demonstrate multimode structured neutron beams that enable simultaneous access to multiple, well-defined OAM modes, and to hybrid combinations of OAM and Airy states. This multimodal approach, analogous to wavelength- or OAM-multiplexing in optics, facilitates the efficient investigation of material scattering properties and nuclear interactions with a neutron source composed of a discretized OAM spectrum.

We report an entoptic phenomenon in which the classical two-lobed Boehm's brushes are transformed into a multilobed structure by projecting spin-orbit-coupled light onto the human retina. These structured beams, composed of nonseparable superpositions of circular polarization and orbital angular momentum, produce azimuthally modulated entoptic patterns through polarization-dependent scattering in the retina. Unlike Haidinger's brushes, which arise from dichroic absorption in the macula, the observed effect is driven by angular variations in scattering strength relative to the local polarization direction. In regions where scattering centers exhibit polarization orientations that converge toward a common point, their combined contributions reinforce one another, producing brighter and more sharply defined entoptic lobes whose number and orientation vary systematically with the topology of the spin-orbit stimulus. Psychophysical measurements across retinal eccentricities from 0.5^° to 4^° in eleven participants revealed that contrast detection thresholds decreased exponentially with eccentricity, consistent with polarization-sensitive scattering by isotropic structures in the nonfoveal retinal regions. From the psychophysical fits, the mean eccentricity at which the entoptic pattern reached a 50% threshold was [Formula: see text] with a 95% CI of [0.72, 1.34]^°, indicating that the spin-orbit-induced entoptic structure becomes perceptually robust at approximately 1^° retinal eccentricity and that perception improves with increasing retinal eccentricity. Together, these findings demonstrate that spin-orbit light modulates scattering-based visual phenomena in previously unrecognized ways, enabling approaches for probing retinal structure and visual processing using topological features of light.

Purpose: Psychophysical discrimination of structured light (SL) stimuli may be useful in screening for various macular disorders. The circularly-oriented macular pigment optical density (coMPOD), calculated from the discrimination performance of SL-induced entoptic phenomena, may reveal a novel functional biomarker of macular health. This study investigated the potential influence of eye dominance and testing order effects on SL-based stimulus perception, factors that potentially influence the sensitivity of screening tests based on SL technology. Methods: A psychophysical task was performed where various SL-based entoptic images with multiple azimuthal fringes rotating with a specific temporal frequency were projected onto the participants’ retinas ( n = 28). By occluding the central areas of entoptic images, the retinal eccentricity R _T of the perceivable area of the stimuli was measured. The scale parameter of the coMPOD profile ( α -value) was calculated for each participant using a spatiotemporal sensitivity model that takes into account the perceptual threshold measurements of SL stimuli with varying spatial densities and temporal frequencies. Results: The mean ± SD α -values for the dominant and non-dominant eyes were 0.11° ± 0.06° and 0.11° ± 0.05°, respectively. Similarly, the values for the first and second eyes were 0.11° ± 0.05° and 0.10° ± 0.05°, respectively. The Pearson correlation coefficient between eye dominance and testing order effects was r = 0.80 ( p < 0.01). The Bland–Altman plots for both factors indicated zero bias. Conclusions: The results indicated repeatable measurements for both eyes, implying minimal impact from eye dominance and testing order on SL-based stimulus perception. The results provide a foundation for future studies exploring the clinical utility of SL tools in eye health.

The entoptic phenomena of Haidinger’s and Boehm’s brushes provide a noninvasive window into the structural and functional organization of the human retina. These percepts arise from polarization-dependent interactions within distinct retinal layers: radial diattenuation by macular pigments in the fovea produces Haidinger’s brushes, whereas polarization-sensitive scattering in the non-foveal retina gives rise to Boehm’s brushes. Recent advances in structured light have introduced spin–orbit beams with spatially varying polarization fields that conform to the intrinsic symmetry of retinal polarization interactions, enabling systematic expansion and enhancement of these entoptic patterns. By aligning the optical field topology with retinal architecture, such beams generalize the formation of Haidinger’s and Boehm’s brushes to complex multi-lobed geometries and provide a path toward quantitative mapping of perceptual structure across eccentricity. This review outlines the optical and biological foundations of polarization perception, summarizes recent results demonstrating its enhancement through spin–orbit structured illumination, and describes psychophysical methods for characterizing stimulus geometry, contrast sensitivity, and retinal dependence. Finally, it highlights how these techniques establish a framework for functional retinal mapping and potential future diagnostic applications capable of detecting disruptions associated with central or non-foveal retinal disease.

The experimental realization of neutron orbital angular momentum (OAM) states and neutron Airy beams has opened new avenues for structured neutron science in both materials characterization and fundamental physics. These additional degrees of freedom in scattering experiments enable the exploration of selection rules for neutrons, the analysis of scattering properties in topological materials, and the generation of auto-focusing neutron beams. In the effort to enhance the amount of spatial and angular-momentum information retrievable from a single measurement, and to overcome current phase-grating efficiency limits, here we demonstrate multimode structured neutron beams that enable simultaneous access to multiple, well-defined OAM modes, and to hybrid combinations of OAM and Airy states. This multimode approach, analogous to wavelength- or OAM-multiplexing in optics, facilitates the efficient investigation of material scattering properties and nuclear interactions with a neutron source composed of a discretized OAM spectrum.

Amyloidosis is a protein misfolding disease caused by the deposition of large, insoluble aggregates (amyloid fibrils) of protein in a tissue, which has been associated with various conditions, such as lymphoid disorders, Alzheimer’s disease, diabetes mellitus type 2, chronic inflammatory processes, and cancers. Amyloid fibrils are commonly diagnosed by qualitative observation of green birefringence from Congo red-stained biopsy tissue samples under polarized light, a technique that is limited by lack of specificity, dependence on subjective interpretation, and technical constraints. Studies emphasize the utility of quantitative polarized light microscopy (PLM) methodology to diagnose amyloid fibrils in Congo red-stained tissues. However, while Congo red enhances the intrinsic birefringence of amyloid fibrillar structures, there are significant disadvantages, such as the appearance of multiple non-green colors under polarized light and binding to other structures, which may result in misdiagnoses with Congo red dye and inconclusive explanations. In this work, we present an improved PLM methodology for the quantitative detection of amyloid fibrils without requiring Congo red staining. We perform PLM measurements on four tissues: abdominal subcutaneous tissue biopsy, duodenal biopsy, thyroid biopsy, and breast biopsy, both with Congo red stain and hematoxylin and eosin (H&E) stain, and through Fourier analysis, quantify birefringence, birefringent axis orientation, dichroism, optical activity, and relative amyloid density. These results emphasize a quantitative analysis for amyloid diagnosis rooted in Fourier signal harmonics that does not require Congo red dye and paves the way for rapid, simple, and accurate diagnosis of amyloid fibrils.