CANISIUS The Austrian Neutron Spin Echo Interferometer

TL;DR

CANISIUS introduces a versatile neutron spin-echo interferometer that operates in both continuous broad-band and Time-of-Flight modes to support SESANS, NRSE, MIEZE, and coherent averaging. By integrating adiabatic RF flippers, v-coils, and modular polarizers, the instrument enables both polychromatic SESANS and the generation of structured neutron waves, including orbital angular momentum states. The authors demonstrate ToF performance, white-beam SESANS, and coherent averaging to produce vortex-like neutron states, illustrating potential applications in quantum information, foundational tests, and OAM-dependent scattering. Overall, CANISIUS offers high flux, modularity, and flexible modes that open new avenues for studying quantum phenomena and material structure with neutron beams.

Abstract

The broad band resonant spin echo interferometer, CANISIUS, is presented. CANISIUS is built in a versatile way, such that it can be operated in both a continuous broad band beam or a pulsed Time of Flight beam. This versatility also extends to the modes available to the instrument, such as Neutron Resonant Spin Echo, Spin Echo (Modulated) Small Angle Neutron Scattering and coherent averaging to produce structured wavefunctions for scattering. The instrument may also be used as an interferometer, to probe fundamental questions in quantum mechanics. In this paper we detail both the continuous and Time of Flight options of the instruments. In addition we demonstrate the applicability of our interferometer to ultra small angle scattering in a white beam. Finally we demonstrate a new spin echo interferometry tool, which uses incomplete recombination of the two path states to generate composite wavefunctions with special structure. In particular we show that this method produces neutron wavefunctions that exist in a superposition of two quantum mechanical OAM modes, l =+1 or -1 We illustrate that just as this method can be used to generate certain structured waves, it may also be used to characterize the structure of the input wavefunction.

Figures (10)

• Figure 1: Render of the CANISIUS instrument configured for white beam SESANS. The beam propagates from right to left. First the beam is polarised by double reflection from two single substrate m=4 polarising supermirrors (1). Next the polarisation is adiabatically rotated by 90 degrees by a v-coil (2). The beam then passes through a pair (arm 1) of adiabatic RF flippers with parallelogram shaped poleshoes, which act as the first beam splitter and mirror (3). A field stepper is positioned between the first and second pair (arm 2) of RF flippers, to facilitate a fast non-adiabatic field transition from arm 1 to arm 2 (4). Samples of various types may be inserted right before the field stepper. The second arm of RF flippers serve effectively as a mirror and beam splitter to recombine the split beams. Between the last two RF flippers the beam is passed through a precession coil (5), which manipulates the spin phase to measure the spin echo curve. Finally before the spin is selected by the last polarising supermirror (7) the neutrons pass through a final v-coil facilitating another adiabatic 90 degree rotation (6). Neutrons passing the polarising supermirror are detected by a high-efficency $^3\textrm{He}$ counting tube. In addition to the usual continuous mode of operation the CANISIUS instrument can also be operated in ToF mode. For this purpose two chopper device are available: a conventional mechanical chopper (10) as well as a spin-chopper system (9), consisting of an RF flipper in combination with the pre-polarizer, that is the very first supermirrors (1). The length of the instrument, given by the distance between chopper (9,10) and detector (8) is 3 meters.
• Figure 2: Render of the adiabatic RF spin flippers with parallelogram shaped poleshoes at 45 deg (a), 45 $\pm$ 5 deg (b), and 90 deg in (c). The photo in (d) shows a top-view of one RF coil partly taken out of the parallelogram shaped poleshoes for demonstration purposes to see the water cooled RF coil, the gradient field coil, as well as the inlet of the coolant and the electrical conducting.
• Figure 3: Flipping efficiency of one adiabatic RF flipper against wavelength measured using the ToF technique. This is calculated using ToF spectrums with the flipper on and off, the result is finally normalised by the instrument efficiency of 0.904. The weighted average of the flipping effiency over the entire spectrum is 0.977.
• Figure 4: Normalized Time of Flight spectra produced using the RF spin chopping device (blue circular data points) and the mechanical chopper (red cross shaped data points).
• Figure 5: Schematic representation of Spin-Echo Small Angle Neutron Scattering. Two inclined magnetic field regions of opposite polarization (represented in light blue and red) are used to induce a transverse separation between the two neutron spin states, also indicated in blue and red. The SESANS configuration shown here also induces a longitudinal separation between the wavepackets indicated by $v\tau_{SE}$. The sample indicated in gray causes the beam to be scattered by a small angle $\alpha$. As a result the path length through the second field region is changed $L_2'$ (as opposed to the non-scattered path $L_2$), resulting in a net phase shift between the two spin states upon recombination.