281 research outputs found
Observation of off-diagonal geometric phase in polarized neutron interferometer experiments
Off-diagonal geometric phases acquired in the evolution of a spin-1/2 system
have been investigated by means of a polarized neutron interferometer. Final
counts with and without polarization analysis enable us to observe
simultaneously the off-diagonal and diagonal geometric phases in two detectors.
We have quantitatively measured the off-diagonal geometric phase for noncyclic
evolutions, confirming the theoretical predictions. We discuss the significance
of our experiment in terms of geometric phases (both diagonal and off-diagonal)
and in terms of the quantum erasing phenomenon.Comment: pdf, 22 pages + 8 figures (included in the pdf). In print on Phys.
Rev.
Noncyclic Pancharatnam phase for mixed state SU(2) evolution in neutron polarimetry
We have measured the Pancharatnam relative phase for spin-1/2 states. In a
neutron polarimetry experiment the minima and maxima of intensity modulations,
giving the Pancharatnam phase, were determined. We have also considered general
SU(2) evolution for mixed states. The results are in good agreement with
theory.Comment: 5 pages, 4 figures, to be published in Phys.Lett.
Towards a Modelling of USANSPOL Intensities from Magnetic Ribbons
AbstractAmorphous magnetic ribbons represent both novel technologically relevant complex samples which are currently in the process of material development for use as magnetic sensors and actuators due to their exceptional magnetostriction properties as well as illustrative examples for developing the technique of ultra-small-angle polarised neutron scattering (USANSPOL) for the study of magnetic microstructure. We present the formalism on which the USANSPOL technique is based and highlight a potential route on which USANSPOL data analysis may be performed. Experimentally obtained scattering patterns are the results of a variety of parameters like material composition and production conditions as well as various environmental conditions, including zero-field environment, the influence of external magnetic field, mechan- ically induced stress, or a combination of both effects, and in magnetically saturated state. In the case of non-isotropic structures a two-dimensional record of the scattered neutron intensity is essential and more complexity is added by the special features of magnetic neutron scattering and the USANSPOL technique itself. In this work we concentrate on these peculiarities and describe the current experimental status which is driven by the underlying USANSPOL scat- tering formalism. Recent experimental results are presented to illustrate the phenomenological correspondence to our modelling
Zero-field and Larmor spinor precessions in a neutron polarimeter experiment
We present a neutron polarimetric experiment where two kinds of spinor
precessions are observed: one is induced by different total energy of neutrons
(zero-field precession) and the other is induced by a stationary guide field
(Larmor precession). A characteristic of the former is the dependence of the
energy-difference, which is in practice tuned by the frequency of the
interacting oscillating magnetic field. In contrast the latter completely
depends on the strength of the guide field, namely Larmor frequency. Our
neutron-polarimetric experiment exhibits individual tuning as well as specific
properties of each spinor precession, which assures the use of both spin
precessions for multi-entangled spinor manipulation.Comment: 12 pages, 4 figure
Exact solutions of n-level systems and gauge theories
We find a relationship between unitary transformations of the dynamics of
quantum systems with time-dependent Hamiltonians and gauge theories. In
particular, we show that the nonrelativistic dynamics of spin-
particles in a magnetic field can be formulated in a natural way as
an SU(2) gauge theory, with the magnetic field playing the role of the
gauge potential A^i. The present approach can also be applied to systems of n
levels with time-dependent potentials, U(n) being the gauge group. This
geometric interpretation provides a powerful method to find exact solutions of
the Schr\"odinger equation. The root of the present approach rests in the
Hermiticity property of the Hamiltonian operators involved. In addition, the
relationship with true gauge symmetries of n-level quantum systems is
discussed.Comment: LaTeX file, 5 pages, published versio
Neutron wave packet tomography
A tomographic technique is introduced in order to determine the quantum state
of the center of mass motion of neutrons. An experiment is proposed and
numerically analyzed.Comment: 4 pages, 3 figure
A CVD diamond detector for (n,alpha) cross section measurements
Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike LicenceIn astrophysics, the determination of the optical alpha-nucleus potential for low alpha-particle energies, crucial in understanding the origin of the stable isotopes, has turned out to be a challenge. Theory still cannot predict the optical potentials required for the calculation of the astrophysical reaction rates in the Hauser-Feshbach statistical model and there is scant experimental information on reactions with alpha particles at the relevant astrophysical energies. Measurements of (n,alpha) cross-sections offer a good opportunity to study the alpha channel. At the n_TOF experiment at CERN, a prototype detector, based on the chemical vapor deposition (CVD) diamond technology, has been recently developed for (n,alpha) measurements. A reference measurement of the 10B(n,alpha)7Li reaction was performed in 2011 at n_TOF as a feasibility study for this detector type. The results of this measurement and an outline for future experiments are presented here
Topology, Locality, and Aharonov-Bohm Effect with Neutrons
Recent neutron interferometry experiments have been interpreted as
demonstrating a new topological phenomenon similar in principle to the usual
Aharonov-Bohm (AB) effect, but with the neutron's magnetic moment replacing the
electron's charge. We show that the new phenomenon, called Scalar AB (SAB)
effect, follows from an ordinary local interaction, contrary to the usual AB
effect, and we argue that the SAB effect is not a topological effect by any
useful definition. We find that SAB actually measures an apparently novel spin
autocorrelation whose operator equations of motion contain the local torque in
the magnetic field. We note that the same remarks apply to the Aharonov-Casher
effect.Comment: 9 page
Berry phase in entangled systems: a proposed experiment with single neutrons
The influence of the geometric phase, in particular the Berry phase, on an
entangled spin-1/2 system is studied. We discuss in detail the case, where the
geometric phase is generated only by one part of the Hilbert space. We are able
to cancel the effects of the dynamical phase by using the ``spin-echo'' method.
We analyze how the Berry phase affects the Bell angles and the maximal
violation of a Bell inequality. Furthermore we suggest an experimental
realization of our setup within neutron interferometry.Comment: 10 pages, 6 figures, Introduction extended, References adde
Geometric Phase in Entangled Systems: A Single-Neutron Interferometer Experiment
The influence of the geometric phase on a Bell measurement, as proposed by
Bertlmann et al. in [Phys. Rev. A 69, 032112 (2004)], and expressed by the
Clauser-Horne-Shimony-Holt (CHSH) inequality, has been observed for a spin-path
entangled neutron state in an interferometric setup. It is experimentally
demonstrated that the effect of geometric phase can be balanced by a change in
Bell angles. The geometric phase is acquired during a time dependent
interaction with two radio-frequency (rf) fields. Two schemes, polar and
azimuthal adjustment of the Bell angles, are realized and analyzed in detail.
The former scheme, yields a sinusoidal oscillation of the correlation function
S, dependent on the geometric phase, such that it varies in the range between 2
and 2\sqrt{2} and, therefore, always exceeds the boundary value 2 between
quantum mechanic and noncontextual theories. The latter scheme results in a
constant, maximal violation of the Bell-like-CHSH inequality, where S remains
2\sqrt2 for all settings of the geometric phase.Comment: 10 pages 9 figure
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