Protecting quantum correlations of two qubits in independent   non-Markovian environments by bang-bang pulses
  We investigate how to protect quantum correlations for two qubits each locally interacting with its own non-Markovian environment by making use of bang-bang pulses. It is shown that the quantum discord dynamics presents the phenomenon of sudden change for some certain initial states. We also find that the amount of quantum correlation between two qubits can be improved by applying a train of pulses and protected more effectively with shorter interval pulses or longer reservoir correlation time. 
Hang-Shi Xu, Jing-Bo Xu
quant-ph