Creating and detecting micro-macro photon-number entanglement by   amplifying and de-amplifying a single-photon entangled state
  We propose a scheme for the observation of micro-macro entanglement in photon number based on amplifying and de-amplifying a single-photon entangled state in combination with homodyne quantum state tomography. The created micro-macro entangled state, which exists between the amplification and de-amplification steps, is a superposition of two components with mean photon numbers that differ by approximately a factor of three. We show that for reasonable values of photon loss it should be possible to detect micro-macro photon-number entanglement where the macro system has a mean number of one hundred photons or more. 
Roohollah Ghobadi, Alexander Lvovsky, Christoph Simon
quant-ph