Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Unitary-Only Quantum Theory Cannot Consistently Describe the Use of
  Itself: On the Frauchiger-Renner Paradox   The Frauchiger-Renner Paradox is an extension of paradoxes based on the
'Problem of Measurement,' such as Schrodinger's Cat and Wigner's Friend. All of
these paradoxes stem from assuming that quantum theory has only unitary
(linear) physical dynamics, and the attendant ambiguity about what counts as a
'measurement'--i.e., the inability to account for the observation of
determinate measurement outcomes from within the theory itself. This paper
discusses a basic inconsistency arising in the FR scenario at a much earlier
point than the derived contradiction: namely, the inconsistency inherent in
treating an improper mixture (reduced density operator) as a proper, epistemic
mixture. This is an illegitimate procedure that is nevertheless endemic if
quantum theory is assumed to be always unitary. In contrast, under a
non-unitary account of quantum state reduction yielding determinate outcomes,
the use of a proper mixture for measurement results becomes legitimate, and
this entire class of paradoxes cannot be mounted. The conclusion is that the
real lesson of the FR paradox is that it is the unitary-only assumption that
needs to be critically reassessed.

31
The categories of this paper are: ao-sci
32
The categories of this paper are: atom-ph
37
The categories of this paper are: supr-con
23
The categories of this paper are: solv-int
26
The categories of this paper are: bayes-an
7
The categories of this paper are: hep-th
10
The categories of this paper are: q-bio
15
The categories of this paper are: nucl-ex
2
The categories of this paper are: math
17
The categories of this paper are: q-fin
22
The categories of this paper are: chao-dyn
4
The categories of this paper are: cond-mat
18
The categories of this paper are: econ
11
The categories of this paper are: hep-lat
30
The categories of this paper are: q-alg
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The categories of this paper are: hep-ex