BELL INEQUALITY, BELL STATES AND MAXIMALLY ENTANGLED STATES FOR N QUBITS

First, we present a Bell-type inequality for n qubits, assuming that m out of the n qubits are independent. Quantum mechanics violates this inequality by a ratio that increases exponentially with m. Hence an ex periment on n qubits violating this inequality sets a lower bound on t he number m of entangled qubits. Next, we propose a definition of maxi mally entangled states of n qubits. For this purpose we study five dif ferent criteria. Four of these criteria are found compatible. For any number n of qubits, they determine an orthogonal basis consisting of m aximally entangled states generalizing the Bell states. (C) 1998 Elsev ier Science B.V.