Apoorva G. Wagh

On measuring the Pancharatnam phase. II. SU(2) polarimetry

Abstract We put forth a polarimetric method for determining the Pancharatnam phase in a general non-cyclic SU (2) evolution.

On measuring the Pancharatnam phase. I. Interferometry

Abstract The Pancharatnam connection prescribes the phase acquired by a quantal system in any arbitrary evolution. The correct method of observing the Pancharatnam phase with an interferometer is delineated.

Surfactant-induced protein unfolding as studied by small-angle neutron scattering and dynamic light scattering

The structural changes of protein bovine serum albumin (BSA) during its unfolding on the addition of anionic surfactant sodium dodecyl sulfate (SDS) have been studied using small-angle neutron scattering (SANS) and dynamic light scattering (DLS). It is observed that at small surfactant concentrations, individual surfactant molecules bind to the protein, increasing the size of the protein. On the other hand, surfactant molecules at higher concentrations aggregate to form micelle-like clusters along the unfolded polypeptide chains of the protein. SANS data indicates the formation of a fractal structure representing a necklace model of micelle-like clusters randomly distributed along the polypeptide chain. The overall size of the complex increases and the fractal dimension decreases on increasing the surfactant concentration. The size of the micelle-like clusters does not show any change, while the number of such micelle-like clusters in protein–surfactant complexes increases with the surfactant concentration. The conformation of the unfolded protein has been determined directly using contrast variation SANS measurements by contrast matching the surfactant to the medium. It is found that the protein acquires a random coil Gaussian conformation on unfolding, with its radius of gyration increasing with an increase in surfactant concentration. The results of DLS measurements are found to be in good agreement with those obtained using SANS.

Neutron polarimetric separation of geometric and dynamical phases

Abstract We present a neutron polarimetric experiment clearly demarcating geometric and dynamical phases. Here a relative rotation between two identical π spin flippers produces a pure geometric phase and their relative translation yields a pure dynamical phase. The experiment agrees with theory to within about 1%.

Geometric phase in neutron interferometry

Abstract We revisit a recent proposal by Wagh to test the dependence of spinor phase on the orientation of the precession axis. We identify the spinor phase shift originating from the misalignment between π-flippers in the two branches of a neutron interferometer with a geometric phase. We also interpret quantum beats in polarised neutron interferometry observed by Rauchs group as a manifestation of a time-dependent geometric phase shift.

The new V12 ultra-small-angle neutron scattering and tomography instrument at the Hahn–Meitner Institut

The new V12 instrument at the Hahn–Meitner Institute in Berlin is a multiple setup combining several techniques to investigate the internal structure of bulk samples. It consists of two double-crystal diffractometers (DCDs) and an attenuation tomography device operating with monochromatic neutrons. The three instrument parts can be used independently at the same time. The DCDs are mainly used in the ultra-small-angle neutron scattering (USANS) regime, where they overlap the accessible range of small-angle neutron scattering instruments, while tomographic methods collect real-space information on a macroscopic scale. Together they enable structural investigations over six orders of magnitude (50 nm to 5 cm). Scattering and tomographic methods can even be combined by means of diffraction and scattering-enhanced imaging. The sample environment can be varied over a large range of temperatures and pressures for USANS measurements and a polarized USANS option is available.

Dependence of the spinor phase on the orientation of the precession axis

Abstract We examine the dependence of the phase acquired by a spinor during a precession, on the orientation of the precession axis. We suggest possible neutron interferometric experiments for investigating such a dependence.

Nonadiabatic geometric spinor phase in rotating magnetic fields

Abstract We describe exact cyclic spinor evolutions in cyclic and noncyclic magnetic Hamiltonians, each resulting in a pure geometric phase. These evolutions are realisable in neutron interferometric and polarimetric experiments.

A fresh look at diffraction from a nonabsorbing perfect crystal in the Bragg-Laue configuration

Abstract The Bragg diffraction from a thick, nonabsorbing perfect crystal theory of dynamical diffraction. The intensities of two beams, one in the incident and the other in the diffracted direction, exciting the side face of the crystal are characterised. The implications of such beams for neutron diffraction experiments are indicated.

A polarised SUSANS facility to study magnetic systems

Using a right-angled magnetic air prism, we have achieved a separation of ∼10 arcsec between ∼2 arcsec wide up and down-spin peaks of 5.4 Å neutrons. The polarised neutron option has thus been introduced into the SUSANS instrument. Strongly spindependent SUSANS spectra have been observed over ±1.3 × 10−4 Å−1 range for several magnetic alloy samples. Spatial pair-distribution functions for the up and down-spins as well as the nuclear and magnetic scattering length density distributions in the micrometer domain, have been deduced from these spectra.