Optical squeezing degradation by loss ($V_{\mathrm{out}}=\eta V_{\mathrm{in}}+(1-\eta )/4$)

Mixing a mode with independent vacuum on a beam splitter of intensity transmission $\eta$ gives the displayed optical quadrature variance when vacuum variance is $1/4$. It approaches vacuum noise as transmission falls. Phase noise instead mixes squeezed and anti-squeezed axes, and cannot in general be represented by the same efficiency alone.