Robust entangled qutrit states in atmospheric turbulence
  The entangled quantum state of a photon pair propagating through atmospheric turbulence suffers decay of entanglement due to the scintillation it experiences. Here we investigate the robustness against this decay for different qutrit states. We use an infinitesimal-propagation equation to obtain the density matrix as a function of the propagation distance and we use the tangle to quantify the entanglement between a pair of qutrits. The evolution of various initial states as they propagate through turbulence is considered. Using optimization of the initial parameters, we obtain expressions for bipartite qutrit states that retain their initial entanglement longer than the initially maximally entangled states. 
Tobias Bruenner and Filippus S Roux
physics.optics quant-ph