1,165 research outputs found
Generation of a spin-polarized electron beam by multipoles magnetic fields
The propagation of an electron beam in the presence of transverse magnetic
fields possessing integer topological charges is presented. The spin--magnetic
interaction introduces a nonuniform spin precession of the electrons that gains
a space-variant geometrical phase in the transverse plane proportional to the
field's topological charge, whose handedness depends on the input electron's
spin state. A combination of our proposed device with an electron orbital
angular momentum sorter can be utilized as a spin-filter of electron beams in a
mid-energy range. We examine these two different configurations of a partial
spin-filter generator numerically. The results of these analysis could prove
useful in the design of improved electron microscope.Comment: 7 pages, 7 figure
Quantum simulation of a spin polarization device in an electron microscope
A proposal for an electron-beam device that can act as an efficient
spin-polarization filter has been recently put forward [E. Karimi et al., Phys.
Rev. Lett. 108, 044801 (2012)]. It is based on combining the recently developed
diffraction technology for imposing orbital angular momentum to the beam with a
multipolar Wien filter inducing a sort of artificial non-relativistic
spin-orbit coupling. Here we reconsider the proposed device with a fully
quantum-mechanical simulation of the electron beam propagation, based on the
well established multi-slice method, supplemented with a Pauli term for taking
into account the spin degree of freedom. Using this upgraded numerical tool, we
study the feasibility and practical limitations of the proposed method for
spin-polarizing a free electron bea
Full-field mode sorter using two optimized phase transformations for high-dimensional quantum cryptography
High-dimensional encoding schemes have emerged as a novel way to perform
quantum information tasks. For high dimensionality, temporal and transverse
spatial modes of photons are the two paradigmatic degrees of freedom commonly
used in such experiments. Nevertheless, general devices for multi-outcome
measurements are still needed to take full advantage of the high-dimensional
nature of encoding schemes. We propose a general full-field mode sorting scheme
consisting only of up to two optimized phase elements based on evolutionary
algorithms that allows for joint sorting of azimuthal and radial modes in a
wide range of bases. We further study the performance of our scheme through
simulations in the context of high-dimensional quantum cryptography, where
high-fidelity measurement schemes are crucial
Holographic generation of highly twisted electron beams
Free electrons can possess an intrinsic orbital angular momentum, similar to
those in an electron cloud, upon free-space propagation. The wavefront
corresponding to the electron's wavefunction forms a helical structure with a
number of twists given by the \emph{angular speed}. Beams with a high number of
twists are of particular interest because they carry a high magnetic moment
about the propagation axis. Among several different techniques, electron
holography seems to be a promising approach to shape a \emph{conventional}
electron beam into a helical form with large values of angular momentum. Here,
we propose and manufacture a nano-fabricated phase hologram for generating a
beam of this kind with an orbital angular momentum up to 200. Based on a
novel technique the value of orbital angular momentum of the generated beam are
measured, then compared with simulations. Our work, apart from the
technological achievements, may lead to a way of generating electron beams with
a high quanta of magnetic moment along the propagation direction, and thus may
be used in the study of the magnetic properties of materials and for
manipulating nano-particles.Comment: 4 pages, 4 figures - Supplementary Material (3 pages and 2 figures)
accompanies this manuscrip
Spin-to-Orbital Angular Momentum Conversion and Spin-Polarization Filtering in Electron Beams
We propose the design of a space-variant Wien filter for electron beams that
induces a spin half-turn and converts the corresponding spin angular momentum
variation into orbital angular momentum of the beam itself by exploiting a
geometrical phase arising in the spin manipulation. When applied to a spatially
coherent input spin-polarized electron beam, such a device can generate an
electron vortex beam, carrying orbital angular momentum. When applied to an
unpolarized input beam, the proposed device, in combination with a suitable
diffraction element, can act as a very effective spin-polarization filter. The
same approach can also be applied to neutron or atom beams.Comment: 9 pages, 5 figure
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