Entanglement propagation of a quantum optical vortex state
  We study the entanglement evolution of a quantum optical vortex state propagating through coupled lossless waveguides. We consider states generated by coupling two squeezed modes using a sequence of beam splitters and also by subtracting photons from the signal in spontaneous parametric down conversion. We reconstruct the Wigner function at a later time to study the correlation and quantify the entanglement after propagation using \emph{logarithmic negativity}. 
Anindya Banerji, Ravindra Pratap Singh, Dhruba Banerjee and Abir   Bandyopadhyay
quant-ph physics.optics