  We experimentally demonstrate phase-insensitive linear optical amplification
which preserves the idler at the output. Since our amplification operation is
unitary up to small excess noise, it is reversible beyond the classical limit.
The entanglement between the two output modes is the resource for the
reversibility. The amplification gain of 2.0 is demonstrated. In addition,
combining this amplifier with a beamsplitter, we also demonstrate approximate
cloning of coherent states where an anticlone is present. We investigate the
reversibility by reconstructing the initial state from the output correlations,
and the results are slightly beyond the cloning limit. Furthermore, full
characterization of the amplifier and cloner is given by using coherent states
with several different mean values as inputs. Our amplifier is based on linear
optics, offline preparation of nonclassical ancillas, and homodyne measurements
followed by feedforward. Squeezed states are used as the ancillas, and
nonlinear optical effects are exploited only for their generation. The ancillas
introduce nonclassicality into the amplifying operation, making entanglement at
the output.
