Showing papers on "Quantum capacity published in 1968"

Logic, Probability, and Quantum Theory

Abstract: The aim of this paper is to present and discuss a probabilistic framework that is adequate for the formulation of quantum theory and faithful to its applications Contrary to claims, which are examined and rebutted, that quantum theory employs a nonclassical probability theory based on a nonclassical "logic," the probabilistic framework set out here is entirely classical and the "logic" used is Boolean The framework consists of a set of states and a set of quantities that are interrelated in a specified manner Each state induces a classical probability space on the values of each quantity The quantities, so considered, become statistical variables (not random variables) Such variables need not have a "joint distribution" For the quantum theoretic application, there is a uniform procedure that defines and determines the existence of such "joint distributions" for statistical variables A general rule is provided and it is shown to lead to the usual compatibility-commutivity requirements of quantum the

On the orthogonality condition for the excited states of stationary quantum systems

Abstract: A theorem establishing the correct orthogonality condition for the perturbation expansions of the state vectors for the excited states of stationary quantum systems is enunciated. A common misunderstanding on this subject is discussed and corrected. Implications of the theorem to the use of the variation perturbation method for calculating approximate eigenvalues and eigenvectors for excited states is discussed.

Quantum electrodynamics of a communication channel

Abstract: A simple one-dimensional model is taken to illustrate the quantum effects of a narrowband communication system. The system is quantized, and its dynamics are discussed in terms of the Heisenberg equations for field operators. The detection process of a "coherent joint detector," whose compatibility with quantum physics was justified elsewhere, is discussed. The detector, which is capable of measuring the quadrature-modulating components at Nyquist rate with minimum possible uncertainty allowed by quantum theory and which is most suitable for a continuous channel, is used to determine the channel capacity. It is shown that the noise of the channel, due to both thermal and quantum fluctuations, is additive and Gaussian. The classical concepts and expressions for the average mutual information and channel capacity are still valid, provided that the quantum noise of one quantum is included properly. The results obtained approach straightforwardly Shannon's in the classical limit.