Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On coherence and the transverse spatial extent of a neutron wave packet   In the analysis of neutron scattering measurements of condensed matter
structure, it normally suffices to treat the incident and scattered neutron
beams as if composed of incoherent distributions of plane waves with
wavevectors of different magnitudes and directions which are taken to define an
instrumental resolution. However, despite the wide-ranging applicability of
this conventional treatment, there are cases in which the wave function of an
individual neutron in the beam must be described more accurately by a spatially
localized packet, in particular with respect to its transverse extent normal to
its mean direction of propagation. One such case involves the creation of
orbital angular momentum (OAM) states in a neutron via interaction with a
material device of a given size. It is shown in the work reported here that
there exist two distinct measures of coherence of special significance and
utility for describing neutron beams in scattering studies of materials in
general. One measure corresponds to the coherent superposition of basis
functions and their wavevectors which constitute each individual neutron packet
state function whereas the other measure can be associated with an incoherent
distribution of mean wavevectors of the individual neutron packets in a beam.
Both the distribution of the mean wavevectors of individual packets in the beam
as well as the wavevector components of the superposition of basis functions
within an individual packet can contribute to the conventional notion of
instrumental resolution. However, it is the transverse spatial extent of packet
wavefronts alone that determines the area within which a coherent scattering
process can occur in the first place. This picture is shown to be consistent
with standard quantum theory. It is also demonstrated that these two measures
of coherence can be distinguished from one another experimentally.

9
The categories of this paper are: nlin
10
The categories of this paper are: q-bio
25
The categories of this paper are: patt-sol
27
The categories of this paper are: comp-gas
2
The categories of this paper are: math
0
The categories of this paper are: hep-ph
21
The categories of this paper are: adap-org
6
The categories of this paper are: astro-ph
37
The categories of this paper are: supr-con
12
The categories of this paper are: nucl-th
36
The categories of this paper are: cmp-lg
13
The categories of this paper are: quant-ph
1
The categories of this paper are: cs
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The categories of this paper are: solv-int
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The categories of this paper are: gr-qc
28
The categories of this paper are: alg-geom