= Two-qubit state
{title2=$|\psi\rangle=\alpha|00\rangle+\beta|01\rangle+\gamma|10\rangle+\delta|11\rangle$}
A <quantum state> on the <tensor product> of two two-dimensional complex state spaces. A normalized pure state has squared coefficient moduli summing to one. It is a <product state> exactly when $\alpha\delta=\beta\gamma$, by the <two-qubit product-state determinant criterion>. The weaker equality of moduli only characterizes <independence> of the computational-basis outcomes; phases can preserve <quantum entanglement> despite those independent statistics.
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