  We revisit the entanglement of a Schwinger pair created by external fields of
arbitrary strength, using a holographic dual description of QCD. When external
fields are strong in comparison to the string tension, the entanglement is
geometrically tied to the Einstein-Rosen (ER) bridge in the bulk, and
disappears when the pair production is not exponentially suppressed at the
boundary. For moderate external fields, the entanglement is shown to follow
from the geometrical interplay between the position of the ER bridge and the
confining wall in the bulk. We clarify the physical nature of quantum
entanglement in pair production, and connect it to the entropy of entanglement
between the left- and right-moving fermions. In particular, we clarify the
effect of real radiation off the produced particles on quantum entanglement of
the pair.
