Optimized generalized monogamy relations and upper bounds for N-qubit systems

We present optimized generalized monogamy relations and upper bounds derived from concurrence and concurrence of assistance. We first establish a tighter general upper bound of the ath (0 <= alpha <= 2) power of concurrence for N-qubit states. Then for N-qubit systems ABC(1)... CN-2, the optimized monogamy relations and upper bounds satisfied by the ath (0 <= alpha <= 2) power of concurrence of N-qubit pure states under the partition AB and C-1... CN-2, as well as under the partition ABC(1) and C-2... CN-2 are established, which give rise to restrictions on the entanglement distribution and trade offs among the subsystems. Moreover, the utilization of the W-class states demonstrates that our results are tighter compared with the existing results. Similar results are also obtained for negativity.