### 3.11 Entanglement entropy as one-loop quantum correction

A natural point of view on the entanglement entropy of a black hole is that this entropy, as was
suggested by Callan and Wilczek [33], is the first quantum correction to the Bekenstein–Hawking
entropy.
Indeed, the Bekenstein–Hawking entropy can be considered as classical, or tree-level, entropy. If we
restore the presence of the Planck constant the Bekenstein–Hawking entropy is proportional to
while the entanglement entropy is an quantity. The total entropy of a black hole is then
the sum
where all particles that exist in nature contribute to the entanglement entropy .