  We find multiple relations between extremal black holes in string theory and
2- and 3-qubit systems in quantum information theory. We show that the entropy
of the axion-dilaton extremal black hole is related to the concurrence of a
2-qubit state, whereas the entropy of the STU black holes, BPS as well as
non-BPS, is related to the 3-tangle of a 3-qubit state. We relate the 3-qubit
states with the string theory states with some number of D-branes. We identify
a set of "large" black holes with the maximally entangled GHZ-class of states
and "small" black holes with separable, bipartite and W states. We sort out the
relation between 3-qubit states, twistors, octonions, and black holes. We give
a simple expression for the entropy and the area of stretched horizon of
"small'' black holes in terms of a norm and 2-tangles of a 3-qubit system.
Finally, we show that the most general expression for the black hole and black
ring entropy in N=8 supergravity/M-theory, which is given by the famous quartic
Cartan E_{7(7)} invariant, can be reduced to Cayley's hyperdeterminant
describing the 3-tangle of a 3-qubit state.
