  We study how conditional photon operations can affect multipartite quantum
correlations, specifically nonlocality and entanglement, of the continuous
variable GHZ states. We find that the violation of the Mermin-Klyshko
inequality revealing the multipartite nonlocality can be made stronger with
photon subtraction applied on each mode of the original GHZ states,
particularly in a weak squeezing regime. Photon addition applied on local modes
also turns out to enhance the degree of multipartite nonlocality in a broad
range of parameters. We further investigate the effects of the photon
operations on the degree of multipartite entanglement by looking into the
Gaussian tangle, the fidelity of teleportation network, and the quadrature
correlations. We find that photon subtraction applied on two modes enhances
those entanglement characteristics in a practical squeezing regime while there
is no improvement made by photon addition.
