Quantification of Continuous Variable Entanglement with only Two Types   of Simple Measurements
  Here we propose an experimental set-up in which it is possible to measure the entanglement of a two-mode Gaussian state, be it pure or mixed, using only simple linear optical devices. After a proper unitary manipulation of the two-mode Gaussian state only number and purity measurements of just one of the modes suffice to give us a complete and exact knowledge of the state's entanglement. 
Gustavo Rigolin and Marcos C. de Oliveira