Bell inequality for qubits based on the Cauchy-Schwarz inequality

Jing-Ling Chen, Dong-Ling Deng

Published 2008-08-17, updated 2009-01-14Version 2

We develop a systematic approach to establish Bell inequalities for qubits based on the Cauchy-Schwarz inequality. We also use the concept of distinct "roots" of Bell function to classify some well-known Bell inequalities for qubits. As applications of the approach, we present three new and tight Bell inequalities for four and three qubits, respectively.