  Quantum channels can be activated by a kind of channels whose quantum
capacity is zero. This activation effect might be useful to overcome noise of
channels by attaching other channels which can enhance the capacity of a given
channel. In this work, we show that such an activation is possible by specific
positive-partial-transpose channels for Gaussian lossy channels whose quantum
capacities are known. We also test more general case involving Gaussian thermal
attenuator whose the exact value of quantum capacity has been unknown so far.
For a recently suggested narrow upper bound on quantum capacity of the thermal
attenuator, we confirm the fact that an activation of quantum capacity occurs
as well. This result is applicable for realistic situations in which Gaussian
channels describe the noises of communication systems.
