  The entanglement between Gaussian entangled states can be increased by
non-Gaussian operations. We design a new scheme named coherent photon addition,
which can coherently add one photon generated by spontaneous parametric down
conversation process to Gaussian quadrature-entangled light pulses created by a
non-degenerate optical parametric amplifier. This operation can increase the
entanglement of input two-mode Gaussian states as an entanglement distillation,
and provides us a new method of non-Gaussian operation. This scheme can also
help us to study the decoherence of adding one to two-mode Gaussian states from
coherent photon addition to normal photon addition.
