The maximally entangled symmetric state in terms of the geometric measure

The geometric measure of entanglement is investigated for permutation symmetric pure states of multipartite qubit systems, in particular the question of maximum entanglement. This is done with the help of the Majorana representation, which maps an n qubit symmetric state to n points on the unit sphere. It is shown how symmetries of the point distribution can be exploited to simplify the calculation of entanglement and also help find the maximally entangled symmetric state. Using a combination of analytical and numerical results, the most entangled symmetric states for up to 12 qubits are explored and discussed. The optimization problem on the sphere presented here is then compared with two classical optimization problems on the S2 sphere, namely Tóth’s problem and Thomson’s problem, and it is observed that, in general, they are different problems. 6 Author to whom any correspondence should be addressed. New Journal of Physics 12 (2010) 073025 1367-2630/10/073025+34$30.00 © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft