  We suggest a formalism to illustrate the entanglement of identical particles
in the first quantization language (1QL). Our 1QL formalism enables one to
exploit all the well-established quantum information tools to understand the
indistinguishable ones, including the reduced density matrix and familiar
entanglement measures. The rigorous quantitative relation between the amount of
entanglement and the spatial coherence of particles is possible in this
formalism. Our entanglement detection process is a generalization of the
entanglement extraction protocol for identical particles with mode splitting
proposed by Killoran et al. (2014).
