In quantum information theory, it is well known that the tripartite entanglement of three qubits is described by the group SL 2; C 3 and that the entanglement measure is given by Cayley's hyperdeterminant. This has provided an analogy with certain N 2 supersymmetric black holes in string theory, whose entropy is also given by the hyperdeterminant. In this paper, we extend the analogy to N 8. We propose that a particular tripartite entanglement of seven qubits, encoded in the Fano plane, is described by the exceptional group E 7 C and that the entanglement measure is given by Cartan's quartic E 7 invariant. For our purposes, the important properties of the hyperdeterminant are that it is a quartic invariant under SL 2 3 and under a triality that interchanges A, B, and D. These properties are valid whether the a ABD are complex, real, or integer.The hyperdeterminant makes its appearance in quantum information theory [2]. Let the three-qubit system ABD (Alice, Bob, and Daisy) be in a pure state j i, and let the components of j i in the standard basis be a ABD :(1.3)Then the three-way entanglement of the three qubits A, B, and D is given by the 3-tangle [3] 3 ABD 4jDeta ABD j:However, one of us recently found another physical application of this hyperdeterminant [4] by associating the eight components of a ABD with the four electric and four magnetic charges of the STU black hole in fourdimensional string theory [5] and showing that its entropy [6] is given byAs far as we can tell [4], the appearance of the Cayley hyperdeterminant in these two different contexts of stringy black hole entropy (where the a ABD are integers and the symmetry is SL 2; Z 3 ) and three-qubit quantum entanglement (where the a ABD are complex numbers and the symmetry is SL 2; C 3 ) is a purely mathematical coincidence. Nevertheless, it has already provided fascinating new insights [7,8] into the connections between strings, black holes, and quantum information. 1 The black holes described by Cayley's hyperdeterminant are those of N 2 supergravity coupled to three vector multiplets, where the symmetry is SL 2; Z 3 . One might therefore ask whether the black hole/information theory correspondence could be generalized. There are three generalizations we might consider:(1) N 2 supergravity coupled to l vector multiplets where the symmetry is SL 2; Z SO l ÿ 1; 2; Z and the black holes carry charges belonging to the 2; l 1 representation (l 1 electric plus l 1 magnetic).(2) N 4 supergravity coupled to m vector multiplets where the symmetry is SL 2; Z SO 6; 6 m; Z where the black holes carry charges belonging to the 2; 12 m representation (m 12 electric plus m 12 magnetic). * m.duff@imperial.ac.uk † Sergio.Ferrara@cern.ch 1 A third application [9], not considered in this paper, is the Nambu-Goto string whose action is also given by jDeta ABD j p in spacetime signature (2, 2).