  In this paper, we consider double trace deformation to single CFT${}_2$, and
study time evolution after the deformation. The double trace deformation we
consider is nonlocal: composed of two local operators placed at separate
points. We study two types of local operators: one is usual local operator in
CFT, and the other is HKLL bulk local operator, which is still operator in CFT
but has properties as bulk local operator. We compute null energy and averaged
null energy in the bulk in both types of deformations. We confirmed that, with
the suitable choice of couplings, averaged null energies are negative. This
implies causal structure is modified in the bulk, from classical background. We
then calculate time evolution of entanglement entropy and entanglement Renyi
entropy after double trace deformation. We find both quantities are found to
show peculiar shockwave-like time evolution.
