1202.2798 (Chao-Qian Pang et al.)

Most robust and fragile two-qubit entangled states under depolarizing
channels    [PDF]

Chao-Qian Pang, Fu-Lin Zhang, Yue Jiang, Mai-Lin Liang

In the two-qubit system under the local depolarizing channels, the most
robust and the most fragile states for a given concurrence or negativity are
derived. For the one-sided channel, with the aid of the evolution equation for
entanglement given by Konrad \emph{et al.} [Nat. Phys. 4, 99 (2008)], the pure
states are proved to be the most robust. Based on a generalization of the
evolution equation, we classify the ansatz states in our investigation by the
amount of robustness, and consequently derive the most fragile states. For the
two-sided channel, the pure states are proved to be the most robust for a fixed
concurrence, but is the most fragile with a given negativity when the channel
is uniform. Under the uniform channel, for a given negativity, the most robust
states are the ones with the maximal concurrence, which are also the most
fragile states when the concurrence is given in the region of [1/2,1]. When the
entanglement approaches zero, the most fragile states for a given negativity
become the pure states, but the ones for concurrence turn into the mixture of
two separated pure states.

View original: http://arxiv.org/abs/1202.2798