Quadrature squeezing
= Quadrature squeezing
{title2=$\operatorname{Var}X_\vartheta<1/4$}
With $X_\vartheta=(ae^{-i\vartheta}+a^\dagger e^{i\vartheta})/2$, the coherent-state and vacuum <variances> are $1/4$. A state is squeezed in the chosen quadrature when its <variance> about its own mean is smaller. A second moment about zero is not the <variance> when that mean is nonzero. <balanced homodyne detection> measures a phase-selected quadrature distribution.