Quantum noise and quantum communication

We show how the probabilistic interpretation of quantum mechanics leads to unavoidable quantum noise, even for deterministic evolution of the quantum state. Far from being a nuisance, this consequent quantum randomness is at the heart of new concepts in technology. We discuss explicitly the quantum random number generator based on the partitition noise at the beam splitter. Another application of quantum noise is quantum cryptography, where the randomness of the detection event leads to the generation of a random cryptographic key at two locations without the necessity of transporting that key from A to B. Finally, we will show how quantum noise is an intrinsically important part of quantum teleportation, and we conclude with a brief discussion of the possibilities of free-space quantum communication.