Entangled webs: Tight bound for symmetric sharing of entanglement - art. no. 050302

Quantum entanglement cannot be unlimitedly shared among an arbitrary number of qubits. The degree of bipartite entanglement decreases as the number of entangled pairs in an N-qubit system increases. We analyze a system of N q ubits in which an arbitrary pair of particles is entangled. We show that th e maximum degree of entanglement (measured in the concurrence) between any pair of qubits is 2/N. This tight bound can be achieved when the qubits are prepared in a pure symmetric (with respect to permutations) state with jus t one qubit in the basis stare \0 > and the others in the basis state \1 >.