Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Experimental estimation of entanglement at the quantum limit   Entanglement is the central resource of quantum information processing and
the precise characterization of entangled states is a crucial issue for the
development of quantum technologies. This leads to the necessity of a precise,
experimental feasible measure of entanglement. Nevertheless, such measurements
are limited both from experimental uncertainties and intrinsic quantum bounds.
Here we present an experiment where the amount of entanglement of a family of
two-qubit mixed photon states is estimated with the ultimate precision allowed
by quantum mechanics.

7
The categories of this paper are: hep-th
21
The categories of this paper are: adap-org
30
The categories of this paper are: q-alg
9
The categories of this paper are: nlin
19
The categories of this paper are: eess
31
The categories of this paper are: ao-sci
4
The categories of this paper are: cond-mat
12
The categories of this paper are: nucl-th
6
The categories of this paper are: astro-ph
10
The categories of this paper are: q-bio
1
The categories of this paper are: cs
15
The categories of this paper are: nucl-ex
37
The categories of this paper are: supr-con
26
The categories of this paper are: bayes-an
28
The categories of this paper are: alg-geom
16
The categories of this paper are: stat