As with classical information, error-correcting codes enable reliable transmission of quantum information through noisy or lossy channels. In contrast to classical theory, imperfect quantum channels exhibit a strong kind of synergy: pairs of discrete memoryless quantum channels exist, each of zero quantum capacity, which acquire positive quantum capacity when used together. Here, we show that this - superactivationg phenomenon also occurs in the more realistic setting of optical channels with attenuation and Gaussian noise. This paves the way for its experimental realization and application in real-world communications systems. © 2011 Macmillan Publishers Limited. All rights reserved.