  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.
