Field-squared quadrature
= Field-squared quadrature
{title2=$K_1=(a^{\dagger2}+a^2)/2,\quad K_2=(a^{\dagger2}-a^2)/(2i)$}
Hermitian combinations of pair creation and <annihilation operators>. With $K_3=(N+1/2)/2$, their <commutators> are $[K_1,K_2]=-4iK_3$, $[K_2,K_3]=iK_1$ and $[K_3,K_1]=iK_2$. A <coherent state> has both <variances> $\langle N\rangle+1/2$, saturating the corresponding uncertainty product.