Information Theory of Quantum-Mechanical Channels

Publisher Summary This chapter discusses the information theory of quantum-mechanical channels. It highlights a formula for the maximum attainable capacity of a continuous channel based on quantum mechanics. The channel may be supposed to consist of a lossless coaxial line operated in the principal mode. Fundamental assumptions are that the system is noiseless, the signal power is limited on the average, and the capacity is considered per unit bandwidth. In a real physical channel, this cannot occur because the quantum effect causes the so-called zero-point fluctuation equivalent to a certain noise. The communication system is supposed to consist of the transmitter, the line, and the receiver. At the transmitter, the information is stored as the numbers of photons belonging to each oscillation mode.