Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On singularities of the mixed state phase   A recent proposal of Sjoqvist et.al. to extend Pancharatnam's criterion for
phase difference between two different pure states to the case of mixed states
in quantum mechanics is analyzed and the existence of phase singularities in
the parameter space of an interference experiment with particles in mixed
states pointed out. In the vicinity of such singular points the phase changes
sharply and precisely at these points it becomes undefined. A closed circuit in
the parameter space around such points results in a measurable phase shift
equal to 2n\pi, where n is an integer. Such effects have earlier been observed
in interference experiments with pure polarization states of light, a system
isomorphic to the spin-1/2 system in quantum mechanics. Implications of phase
singularities for the interpretation of experiments with partially polarized
and unpolarized neutrons are discussed. New kinds of topological phases
involving variables representing decoherence (depolarization) of pure states
are predicted and experiments to verify them suggested.

9
The categories of this paper are: nlin
35
The categories of this paper are: mtrl-th
3
The categories of this paper are: physics
32
The categories of this paper are: atom-ph
12
The categories of this paper are: nucl-th
19
The categories of this paper are: eess
10
The categories of this paper are: q-bio
0
The categories of this paper are: hep-ph
6
The categories of this paper are: astro-ph
22
The categories of this paper are: chao-dyn
14
The categories of this paper are: math-ph
34
The categories of this paper are: chem-ph
26
The categories of this paper are: bayes-an
21
The categories of this paper are: adap-org
33
The categories of this paper are: plasm-ph
1
The categories of this paper are: cs