Schematic diagram of the quantum interference of two-mode squeezed states on a 50% BS. (a) left: schematic diagram of the interference of the squeezed state light fields coupled into the 50% beam splitter; right: the error contours of the output states versus the phase difference θ in phase space. (b) left: schematic diagram of the entangled state light fields entering the 50% beam splitter; right: the error contours of the output states versus θ in phase space. (c) Theoretical calculation of the variance of quadrature phase of the output state. Blue line, red line and black line correspond to the two squeezed states, entangled states and SNL, respectively.