Engineering effective Hamiltonians is essential for advancing quantum technologies, including quantum simulation, sensing, and computing. This paper presents a general framework for effective Hamiltonian engineering, enabling robust, precise, and efficient quantum control strategies. To achieve efficiency, we focus on creating target zeroth-order effective Hamiltonians while minimizing higher-order contributions and enhancing robustness against systematic errors. The control design identifies the minimal subspace of the toggling-frame Hamiltonian and the full set of achievable, zeroth-order, effective Hamiltonians. The framework also enables robust state transfer and characterization of achievable density matrices, and extends to stochastic fluctuations via a cumulant expansion. Examples are included to illustrate the process flow and resultant precision and robustness.

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.

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.

Quantum technologies are rapidly advancing across multiple research domains, with a growing impact on biomedical imaging and sensing. We examine their emerging role in ophthalmology through four complementary directions: photon-limited retinal imaging, correlation based imaging, nanoscale optical probes, and quantum-limited visual perception. Advances in optical coherence tomography and single-photon detection enable imaging under strict photon budget constraints, reducing phototoxicity while preserving image quality. Correlation-based approaches, including ghost imaging, offer alternative strategies for image formation in low-light and scattering environments, although practical implementation remains limited by detection efficiency and acquisition time. In parallel, nanoscale optical platforms such as quantum dots provide tunable and photostable probes for enhanced contrast and targeted delivery, with ongoing challenges related to biocompatibility and clinical translation. Finally, experiments at the single-photon level and with structured light fields demonstrate how the visual system itself operates near physical detection limits and can be probed using controlled optical states. While many of these approaches remain at an early stage, they collectively illustrate how quantum and quantum-inspired methods may augment current ophthalmic imaging and diagnostic technologies while providing new tools for studying visual function under well-defined physical constraints.

Perfect-crystal neutron interferometry has been a useful tool in measuring nuclear-interactions, probing fundamental physics, and exploring quantum phenomenon. Historically, neutron interferometry experiments have been carried out at room temperature and standard atmospheric pressure. However, neutron interferometry is sensitive to changes in the local environment, especially thermal gradients across the crystal, resulting in phase drifts and systematic uncertainty. A need for measurements performed in different sample environments compound these issues. Fortunately, the use of a vacuum chamber has been shown to be an effective method of environmental isolation for perfect-crystal neutron interferometers. A large volume, highly versatile vacuum chamber has been installed at the Neutron Interferometry and Optics Facility at the NIST Center for Neutron Research to isolate interferometry from local temperature and pressure deviations as well as allowing for the introduction of cryogenically cooled samples. The prospect of incorporating a cryostat within a neutron interferometer opens up new areas of investigation, such as superconductivity. In addition to describing the vacuum chamber, we report on the first measurement of a cryogenic-cooled sample by a neutron interferometer. For this demonstration contrast was measured with a Ni60Cu40 sample between 4 K to 300 K.

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. 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 RT 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. 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. 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.

Spin-orbit beams, in which the orbital angular momentum degree of freedom is coupled to a two-level system such as polarization of light or spin in electrons and neutrons, have gained significant interest for their unique propagation properties and potential applications in imaging, material characterization, optical trapping, and quantum information processing. In this work we introduce a method for generating and engineering two-dimensional lattices of such spin-orbit beams based on coherent averaging in k-space. By programming the angle, amplitude, and polarization of a set of input beams we obtain precise control over lattice geometry and period, as well as the orbital and radial degrees of freedom inside each unit cell. We explore both electromagnetic and matter wave implementations, and we experimentally demonstrate the generation and characterization of a micron-scale optical hexagonal lattice with well defined orbital and radial numbers in each unit cell. The described methods provide a robust and general method of generating and controlling structured waves such as optical skyrmions and matter wave implementations of orbit and spin-orbit beams.

Structured light (SL)-induced polarization perception presents a promising method for the early detection of macular diseases such as age-related macular degeneration. We investigated the test-retest reliability of a psychophysical task using SL-based stimuli to induce entoptic patterns in individuals with healthy vision. Twenty-eight participants underwent thorough eye examinations to confirm they had healthy eyes and good vision (logMAR BCVA 0.00). Of these, 25 participants (n=50 eyes) aged 21 to 75 completed two identical tasks separated by 1 to 14 days. Using SL-based stimuli that produced a rotating entoptic pattern containing 22 azimuthal brushes, we measured the retinal eccentricity threshold R_T at which participants could reliably identify the direction of rotation by varying the size of a central obstruction. This threshold reflects the visual angle of the pattern for each participant. We calculated the reliability coefficient (intraclass correlation coefficient, ICC) using a two-way mixed-effects model and conducted a Bland-Altman analysis to assess test-retest reliability. The ICC was 0.83 [95

To characterize the optical density of circularly oriented macular pigment (MP) in the human retina, as a quantification of macular health, Psychophysical discrimination tests were performed on human subjects using structured light-induced entoptic phenomena. Central exclusions were used to determine the visual extents of stimuli with varying spatiotemporal frequencies. A model was developed to describe the action of circularly oriented MP, and map stimuli to perceived sizes. The experimental results provided validation for the computational model, showing good agreement between measured data and predictions with a Pearson χ2 fit statistic of 0.06. This article contains a description of a new quantification of macular health and the necessary tools for clinical development. The integration of structured light into vision science has led to the development of more selective and versatile entoptic probes of eye health that provide interpretable thresholds of structured light perception. This work develops a model that maps perceptual thresholds of entoptic phenomena to the underlying MP structure that supports its perception. We selectively characterize the circularly oriented MP optical density, rather than the total MP optical density as typically measured. The presented techniques can be applied in novel early diagnostic tests for a variety of diseases related to macular degeneration such as age-related macular degeneration, macular telangiectasia, and pathological myopia. This work both provides insights into the microstructure of the human retina and uncovers a new quantification of macular health.

We present an experimental arrangement that permits engineering of cavity back-action on a mesoscopic spin ensemble. By coupling a superconducting thin-film Nb microstrip resonator to a Trityl OX63 electron spin sample, we access different regimes of spin-cavity dynamics by designing the ensemble size, effective coupling strength, cavity temperature, and spin saturation. We performed transient spectroscopy measurements under continuous microwave drive in the strong radiation damping regime. These measurements exhibit a long-lived plateau response that distinguishes important features of spin-cavity models, such as the radiation damping Bloch equations and Maxwell-Bloch equations. We demonstrate control of the plateau response through adjustment of temperature, microwave drive power, and variable spin saturation. The presented experimental arrangement serves as a robust system to explore the space of spin-cavity dynamics and develop new quantum devices that harness the complexity of mesoscopic spin ensembles coherently interacting with high quality factor cavities.

Hybrid quantum systems consisting of a collection of N spin-1/2 particles uniformly interacting with an electromagnetic field, such as one confined in a cavity, are important for the development of quantum information processors and will be useful for metrology, as well as tests of collective behavior. Such systems are often modeled by the Tavis-Cummings model, and having an accurate understanding of the thermal behaviors of this system is needed to understand their behavior in realistic environments. We quantitatively show in this work that the Dicke subspace approximation is at times invoked too readily. Specifically, we show that there is a temperature above which the degeneracies in the system become dominant and the Dicke subspace is minimally populated. This transition occurs at a lower temperature than previously considered. In such a temperature regime, the key constants of the motion are the total excitation count between the spin system and cavity and the collective angular momentum of the spin system. These enable perturbative expansions for thermal properties in terms of the energy shifts of dressed states, called Lamb shifts herein. They enable efficient numeric methods that scale in terms of the size of the spin system. Notably the runtime to obtain certain parameters of the system scales as O(root N), and is thus highly efficient. These provide methods for approximating, and bounding, properties of these systems as well as characterizing the dominant population regions, including under perturbative noise. In the regime of stronger spin-spin coupling, the perturbations outweigh the expansion series terms, and inefficient methods must likely be employed, removing the computational efficiency of simulating such systems. The results in this work can also be used for related systems such as coupled-cavity arrays, cavity-mediated coupling of collective spin ensembles, and collective spin systems.

The Airy wave packet is a solution to the potential-free Schrödinger equation that exhibits remarkable properties such as self-acceleration, nondiffraction, and self-healing. Although Airy beams are now routinely realized with electromagnetic waves and electrons, the implementation with neutrons has remained elusive due to small transverse coherence lengths, low fluence rates, and the absence of neutron lenses. In this Letter, we overcome these challenges through a holographic approach and present the first experimental demonstration of neutron Airy beams. The presented techniques pave the way for fundamental physics studies with Airy beams of nonelementary particles, the development of novel neutron optics components, and the realization of neutron Airy-vortex beams.

The experimental manipulation of neutrons with orbital angular momentum (OAM) has paved the way for significant advancements in both fundamental physics and materials science. This study introduces novel applications, including the interference of neutron states with different OAM to enhance Small Angle Neutron Scattering (SANS) interferometry. This technique allows for the extraction of previously inaccessible phase information from diffraction patterns of complex samples. Additionally, we have successfully engineered neutron Airy beams, demonstrating the capability to tailor neutron wavefunctions for unique propagation behaviors. Here, we detail our methodologies for generating and controlling these tailored wavefronts, exploring their potential applications in the study of bulk quantum materials, particularly in the context of skyrmion-based spintronic devices.

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.

Bipartite entangled states between a qubit and macroscopically distinct states of a mesoscopic system, known as micro-macro entangled states, are emerging resources for quantum information processing. One main challenge in generating such states in the lab is their fragility to environmental noise. We analyze this fragility in detail for single particle noise by identifying what factors play a role in the robustness and quantifying their effect. There is a trade-off between the macroscopicity of a micro-macro entangled state and the robustness of its bipartite entanglement to environmental noise. We identify symmetric micro-macro entangled states as the most robust states to single particle noise. We show that the robustness of bipartite entanglement of such states to single particle noise decreases as the second order of macroscopicity, which identifies a regime where the bipartite entangled state is both robust and macroscopic. Our result is a step towards retaining quantum characteristics on large scales and experimental realization of micro-macro entangled spin states and their use for connecting separated qubits. Moreover, it advances our understanding of quantum to classical transition.

Perfect-crystal neutron interferometry, which is analogous to Mach-Zehnder interferometry, uses Bragg diffraction to form interfering neutron paths. The measured phase shifts can be used to probe many types of interactions whether it be nuclear, electromagnetic, gravitational, or topological in nature. For a perfect-crystal interferometer to preserve coherence, the crystal must possess a high degree of dimensional tolerance as well as being relatively defect-free with minimal internal stresses. In the past, perfect-crystal neutron interferometers have been produced by a two-step process. First, a resin diamond wheel would be used to remove excess material and shape the interferometer. Afterword, the crystal would be etched to remove surface defects and elevate strains. This process has had limitations in terms of repeatability and in maximizing the final contrast, or fringe visibility, of the interferometer. We have tested various fabrication and post-fabrication techniques on a single perfect-crystal neutron interferometer and measured the interferometer's performance at each step. Here we report a robust, nonetching fabrication process with high final contrast. For the interferometer used in this work, we achieved contrasts of greater than 90% several times and ultimately finished with an interferometer that has 92% contrast and a uniform phase distribution.

The ability to perceive polarization-related entoptic phenomena arises from the dichroism of macular pigments held in Henle's fiber layer of the retina and can be inhibited by retinal diseases, such as age-related macular degeneration, which alters the structure of the macula. Structured light tools enable the direct probing of macular pigment density and retinal structure through the perception of polarization-dependent entoptic patterns. Here, we directly measure the visual angle of an entoptic pattern created through the illumination of the retina with a structured state of light and a perception task that is insensitive to corneal birefringence. The central region of the structured light stimuli was obstructed, with the size of the obstruction varying according to a psychophysical staircase. Two stimuli, one producing 11 azimuthal fringes and the other three azimuthal fringes, were presented to 24 healthy participants. The pattern with 11 azimuthal fringes produced an average visual angle threshold of 10° ± 1° and a 95% confidence interval (C.I.) of [6°, 14°]. For the pattern with three azimuthal fringes, a threshold extent of 3.6° ± 0.3° C.I. = [1.3°, 5.8°] was measured, a value similar to the published extent of Haidinger's brush (4°). The increase in apparent size and clarity of entoptic phenomena produced by the presented structured light stimuli offers the potential to detect the early signs of macular disease over perception tasks using uniform polarization stimuli.