Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Quantum discord of two-qubit rank-two states   Among various definitions of quantum correlations, quantum discord has
attracted considerable attention. To find analytical expression of quantum
discord is an intractable task. In this paper, we discuss thoroughly the case
of two-qubit rank-two states. An analytical expression for the quantum discord
is obtained by means of Koashi-Winter relation. A geometric picture is
demonstrated by means of quantum steering ellipsoid. We point out that in this
case the optimal measurement is indeed the von Neumann measurement, which is
usually used in the study of quantum discord. However, for some two-qubit
states with the rank larger than two, we find that three-element POVM
measurement is more optimal. It means that more careful attention should be
paid in the discussion of quantum discord.

18
The categories of this paper are: econ
34
The categories of this paper are: chem-ph
37
The categories of this paper are: supr-con
3
The categories of this paper are: physics
0
The categories of this paper are: hep-ph
21
The categories of this paper are: adap-org
1
The categories of this paper are: cs
17
The categories of this paper are: q-fin
10
The categories of this paper are: q-bio
4
The categories of this paper are: cond-mat
28
The categories of this paper are: alg-geom
22
The categories of this paper are: chao-dyn
31
The categories of this paper are: ao-sci
11
The categories of this paper are: hep-lat
16
The categories of this paper are: stat
33
The categories of this paper are: plasm-ph