Near extremal black hole entropy as entanglement entropy via AdS2/CFT1

We point out that the entropy of ( near) extremal black holes can be interpreted as the entanglement entropy of dual conformal quantum mechanics via AdS(2)/CFT1. As an explicit example, we study near extremal Banados- Teitelboim- Zanelli black holes and derive this claim from AdS(3)/CFT2. We also analytically compute the entanglement entropy in the two dimensional CFT of a free Dirac fermion compactified on a circle at finite temperature. From this result, we clarify the relation between the thermal entropy and entanglement entropy, which is essential for the entanglement interpretation of black hole entropy.