Uncertainty, entropy, and mutual information for quantum states

Abstract

The quantity mutual information is introduced as a good measure of the quantum-mechanical uncertainty of a state. The mutual information is the measured value of entropy for both discrete and continuous variables, with the resolution of the measuring device as a constraint. The mutual information is calculated for coherent states and squeezed states; the values of the variables before and after the measurement are assumed to be correlated Gaussian, with correlation coefficient γ. It is found that the information increases or decreases from the corresponding coherent state value, depending on γ.