Editing Bell state (section)

=== Properties of Bell states ===
The result of a measurement of a single qubit in a Bell state is indeterminate, but upon measuring the first qubit in the ''z''-basis, the result of measuring the second qubit is guaranteed to yield the same value (for the <math>\Phi</math> Bell states) or the opposite value (for the <math>\Psi</math> Bell states). This implies that the measurement outcomes are correlated.  [[John Stewart Bell|John Bell]] was the first to prove that the measurement correlations in the Bell State are stronger than could ever exist between classical systems. This hints that quantum mechanics allows information processing beyond what is possible with classical mechanics.  In addition, the Bell states form an orthonormal basis and can therefore be defined with an appropriate measurement. Because Bell states are entangled states, information on the entire system may be known, while withholding information on the individual subsystems.  For example, the Bell state is a [[Quantum state|pure state]], but the reduced density operator of the first qubit is a [[Quantum state|mixed state]]. The mixed state implies that not all the information on this first qubit is known.<ref name="Nielsen-2010" /> Bell States are either symmetric or antisymmetric with respect to the subsystems.<ref name="Sych-2009" /> Bell states are maximally entangled in the sense that its reduced density operators are maximally mixed, the multipartite generalization of Bell states in this spirit is called the [[Absolutely maximally entangled state|absolutely maximally entangled (AME) state]].