Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Optimal measurements for quantum fidelity between Gaussian states and
  its relevance to quantum metrology   Quantum fidelity is a measure to quantify the closeness of two quantum
states. In an operational sense, it is defined as the minimal overlap between
the probability distributions of measurement outcomes and the minimum is taken
over all possible positive-operator valued measures (POVMs). Quantum fidelity
has been investigated in various scientific fields, but the identification of
associated optimal measurements has often been overlooked despite its great
importance for practical purposes. We find here the optimal POVMs for quantum
fidelity between multi-mode Gaussian states in a closed analytical form. Our
general finding is specified for selected single-mode Gaussian states of
particular interest and we identify three types of optimal measurements: a
number-resolving detection, a projection on the eigenbasis of operator
$\hat{x}\hat{p}+\hat{p}\hat{x}$, and a quadrature detection, each of which is
applied to distinct types of single-mode Gaussian states. We also show the
equivalence between optimal measurements for quantum fidelity and those for
quantum parameter estimation, enabling one to easily find the optimal
measurements for displacement, phase, squeezing, and loss parameter estimations
using Gaussian states.

7
The categories of this paper are: hep-th
35
The categories of this paper are: mtrl-th
5
The categories of this paper are: gr-qc
15
The categories of this paper are: nucl-ex
16
The categories of this paper are: stat
29
The categories of this paper are: funct-an
12
The categories of this paper are: nucl-th
14
The categories of this paper are: math-ph
3
The categories of this paper are: physics
21
The categories of this paper are: adap-org
22
The categories of this paper are: chao-dyn
27
The categories of this paper are: comp-gas
0
The categories of this paper are: hep-ph
37
The categories of this paper are: supr-con
2
The categories of this paper are: math
32
The categories of this paper are: atom-ph