We propose a new method for detecting entanglement of two qubits and discuss its relation with the Clauser-Horne-Shimony-Holt (CHSH) Bell inequality. Without the need for full quantum tomography for the density matrix we can experimentally detect the entanglement by measuring less than 9 local observables for any given state. We show that this test is stronger than the CHSH-Bell inequality and also gives an estimation for the degree of entanglement. If prior knowledge is available we can further greatly reduce the number of required local observables. The test is convenient and feasible with present experimental technology.
@article{arxiv.quant-ph/0306137,
title = {Detection of entanglement and Bell's inequality violation},
author = {Kai Chen and Ling-An Wu},
journal= {arXiv preprint arXiv:quant-ph/0306137},
year = {2007}
}