Universal entanglement decay in atmospheric turbulence
  We consider the propagation of two photonic qubits, initially maximally entangled in their orbital angular momenta (OAM), across a turbulent atmosphere. By introducing the {\it phase correlation length} of an OAM beam, we show that the entanglement of OAM photons exhibits a universal exponential decay under turbulence. 
Nina D. Leonhard, Vyacheslav N. Shatokhin, Andreas Buchleitner
quant-ph