Two-mode heterodyne phase detection

We present an experimental scheme that achieves ideal phase detection on a two-mode field. The two modes a and b are the signal and image band modes of a heterodyne detector, with the field approaching an eigenstate of the photocurrent Z^=a+${\mathit{b}}^{\mathrm{°}}$. The field is obtained by means of a high-gain phase-insensitive amplifier followed by a high-transmissivity beam splitter with a strong local oscillator at the frequency of one of the two modes.