Quantum Theory of Message Transmission

The question of the quantity of information transferable by a given ensemble of pure quantal states for a known reception characteristic is considered. The cases are discussed where the sets of states which can be sent by the transmitter and fixed by the receiver are nonorthogonal. The formulas derived are applied for the calculation of the quantity of information transferable by an ensemble of pure radiation states with given values of the field intensity, and receivable by a linear receiver. The density matrices of these states (quantal time functions) are found by the principle of maximum disinformation. In conclusion a comparison is made between a linear and a square law receiver, and a simple calculation is carried out for estimating their efficiencies.