  Quantum entanglement and its paradoxical properties hold the key to an
information processing revolution. Much attention has focused recently on the
challenging problem of characterizing entanglement. Entanglement for a two
qubit system is reasonably well understood, however, the nature and properties
of multiple qubit systems are largely unexplored. Motivated by the importance
of such systems in quantum computing, we show that typical pure states of N
qubits are highly entangled but have decreasing amounts of pairwise
entanglement (measured using the Wootter's concurrence formula) as N increases.
Above six qubits very few states have any pairwise entanglement, and generally,
for a typical pure state of N qubits there is a sharp cut-off where its
subsystems of size m become PPT (positive partial transpose i.e., separable or
only bound entangled) around N >~ 2m + 3, based on numerical analysis up to
N=13.
