  The bosonic quantum channels have recently attracted a growing interest,
motivated by the hope that they open a tractable approach to the generally hard
problem of evaluating quantum channel capacities. These studies, however, have
always been restricted to memoryless channels. Here, it is shown that the
classical capacity of a bosonic Gaussian channel with memory can be
significantly enhanced if entangled symbols are used instead of product
symbols. For example, the capacity of a photonic channel with 70%-correlated
thermal noise of one third the shot noise is enhanced by about 11% when using
3.8-dB entangled light with a modulation variance equal to the shot noise.
