arXiv subjects

H. Ekinci

Publications and source records attributed to H. Ekinci.

5 recordsLinked to original sources

arXiv2026

Probing Single-Particle Spatial Extent With Helical Neutron Wavefronts

Distinguishing transverse coherence length from single-particle wavepacket extent is fundamentally challenging, as both manifest through spatial broadening of observed intensity profiles in conventional experiments. Here we introduce a method based on helical neutron wavefronts that enables this separation. Helical neutron states produce annular intensity profiles whose peak radius depends on the transverse wavepacket extent, while coherence length only contributes to profile broadening. In our experimental geometry we measure a beam divergence of ~1.1 mrad, corresponding to a transverse coherence length of ~180 nm. In contrast, the same measurement places a lower bound of >= 2 um on the spatial extent of the individual neutron wavepackets, more than an order of magnitude larger than the coherence length. These results provide direct experimental evidence that transverse coherence length and single-particle wavepacket extent are distinct physical quantities, resolving a longstanding source of confusion in the neutron literature.

quant-ph↗

arXiv2026

Experimental Limit on Neutron Orbital Angular Momentum Detection Using Polarized 3He

A recent proposal suggested that neutron orbital angular momentum (OAM) states could be detected via spin-polarized absorption in polarized 3He, 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 3He cell. Within statistical precision, no OAM-dependent change in the absorption cross section was observed. This null result places stringent constraints on polarized 3He-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 3He nuclei, while off-axis capture samples only a locally uniform phase and reduces the interaction to the known spin dependence. These results clarify the limits of absorptive nuclear methods for probing neutron OAM and emphasize the necessity of spatially resolved interactions in any viable detection scheme.

physics.app-ph↗

arXiv2023

Phase and contrast moiré signatures in two-dimensional cone beam interferometry

Neutron interferometry has played a distinctive role in fundamental science and characterization of materials. Moiré neutron interferometers are candidate next-generation instruments: they offer microscopy-like magnification of the signal, enabling direct camera recording of interference patterns across the full neutron wavelength spectrum. Here we demonstrate the extension of phase-grating moiré interferometry to two-dimensional geometries. Our fork-dislocation phase gratings reveal phase singularities in the moiré pattern, and we explore orthogonal moiré patterns with two-dimensional phase-gratings. Our measurements of phase topologies and gravitationally induced phase shifts are in good agreement with theory. These techniques can be implemented in existing neutron instruments to advance interferometric analyses of emerging materials and precision measurements of fundamental constants.

physics.app-ph↗

arXiv2023

Cone beam neutron interferometry: from modeling to applications

Phase-grating moire interferometers (PGMIs) have emerged as promising candidates for the next generation of neutron interferometry, enabling the use of a polychromatic beam and manifesting interference patterns that can be directly imaged by existing neutron cameras. However, the modeling of the various PGMI configurations is limited to cumbersome numerical calculations and backward propagation models which often do not enable one to explore the setup parameters. Here we generalize the Fresnel scaling theorem to introduce a k-space model for PGMI setups illuminated by a cone beam, thus enabling an intuitive forward propagation model for a wide range of parameters. The interference manifested by a PGMI is shown to be a special case of the Talbot effect, and the optimal fringe visibility is shown to occur at the moire location of the Talbot distances. We derive analytical expressions for the contrast and the propagating intensity profiles in various conditions, and analyze the behaviour of the dark-field imaging signal when considering sample characterization. The model's predictions are compared to experimental measurements and good agreement is found between them. Lastly, we propose and experimentally verify a method to recover contrast at typically inaccessible PGMI autocorrelation lengths. The presented work provides a toolbox for analyzing and understanding existing PGMI setups and their future applications, for example extensions to two-dimensional PGMIs and characterization of samples with non-trivial structures.

physics.app-ph↗

arXiv2022

Experimental Realization of Neutron Helical Waves

Methods of preparation and analysis of structured waves of light, electrons, and atoms have been advancing rapidly. Despite the proven power of neutrons for material characterization and studies of fundamental physics, neutron science has not been able to fully integrate such techniques due to small transverse coherence lengths, the relatively poor resolution of spatial detectors, and low fluence rates. Here, we demonstrate methods that are practical with the existing technologies, and show the experimental achievement of neutron helical wavefronts that carry well-defined orbital angular momentum (OAM) values. We discuss possible applications and extensions to spin-orbit correlations and material characterization techniques.

physics.app-ph↗