An alternative physical way of communication, communication by the inherent
background noise, is proposed which does not need net energy transfer in the
information channel. The communicator devices do dissipate energy; however,
they do not emit net energy into the channel, instead of that, they modulate
the parameters of inherent spontaneous fluctuations in the channel. The method
can use two different mechanisms, thermal noise (Johnson-Nyquist noise) for
classical communication, and vacuum fluctuations/zero point energy (quantum
uncertainty noise) for quantum communication. The strongest advantage of the
method that this is apparently the most hidden (stealth) way of communication,
because it is using the inherent background noise for communication, therefore
it is extremely difficult or impossible to discover its presence. With proper
wave-based arrangements and specific conditions, the sender and the receiver
can easily detect eavesdropper activities, so that the eavesdropper is detected
as soon as she extracts a single bit of information, thus the security of the
method is comparable to the security of quantum communication/quantum key
distribution schemes. Finally, concerning practical applications, environmental
noise, out of the fundamental/inherent fluctuations, can also be used for this
kind of communication provided that is sufficiently stationary.Comment: Applied Physics Letters, in pres