  Quantum steganography is a powerful method for information security where
communications between a sender and receiver are disguised as naturally
occurring noise in a channel. We encoded the phase and amplitude of weak
coherent laser states such that a third party monitoring the communications
channel, measuring the flow of optical states through the channel, would see an
amalgamation of states indistinguishable from thermal noise light. Using
quantum state tomography, we experimentally reconstructed the density matrices
for artificially engineered thermal states and spontaneous emission from an
optical amplifier and verified a state fidelity F>0.98 when compared with
theoretical thermal states.
