College of Mathematics and Information Science, Shaanxi Normal University, Xi'an 710062, P. R. China ; College of Mathematics and Information Science, Shaanxi Normal University, Xi'an 710062, P. R. China
Abstract:
In this note, we explore commutativity up to a factor for bounded operators and in a complex Hilbert space. Conditions on possible values of the factor are formulated and shown to depend on spectral properties of the operators. Commutativity up to a unitary factor is considered. In some cases, we obtain some properties of the solution space of the operator equation and explore the structures of and that satisfy for some A quantum effect is an operator on a complex Hilbert space that satisfies The sequential product of quantum effects and is defined by We also obtain properties of the sequential product.