Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: When is an input state always better than the others ?: universally
  optimal input states for statistical inference of quantum channels   Statistical estimation and test of unknown channels have attracted interest
of many researchers. In optimizing the process of inference, an important step
is optimization of the input state, which in general do depend on the kind of
inference (estimation or test, etc.), on the error measure, and so on. But
sometimes, there is a universally optimal input state, or an input state best
for all the statistical inferences and for all the risk functions. In the
paper, the existence of a universally optimal state is shown for group
covariant/contravariant channels, unital qubit channels and some measurement
families. To prove these results, theory of "comparison of state families" are
used. We also discuss about effectiveness of entanglement and adaptation of
input states.

26
The categories of this paper are: bayes-an
8
The categories of this paper are: hep-ex
2
The categories of this paper are: math
30
The categories of this paper are: q-alg
29
The categories of this paper are: funct-an
4
The categories of this paper are: cond-mat
35
The categories of this paper are: mtrl-th
9
The categories of this paper are: nlin
15
The categories of this paper are: nucl-ex
22
The categories of this paper are: chao-dyn
5
The categories of this paper are: gr-qc
12
The categories of this paper are: nucl-th
19
The categories of this paper are: eess
37
The categories of this paper are: supr-con
21
The categories of this paper are: adap-org
20
The categories of this paper are: acc-phys