  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 an heterodyne detector, with the field approaching an eigenstate of the
photocurrent $\hat{Z}=a+b^{\dag}$. 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.
