We define a smooth functional calculus for a noncommuting tuple of (unbounded) operators Aj on a Banach space with real spectra and resolvents with temperate growth, by means of an iterated Cauchy formula. The construction is also extended to tuples of more general operators allowing smooth functional calculii. We also discuss the relation to the case with commuting operators.

In quantum detection theory the optimum detection operators must commute; admitting simultaneous approximate measurement of noncommuting observables cannot yield a lower Bayes cost. The lower bounds on mean square errors of parameter estimates predicted by the quantum-mechanical Cramer-Rao inequality can also not be reduced by such means.

The results presented in this paper extend and complement the corresponding ones of Hussain-Jungck[Common fixed point and invariant approximation results for noncommuting generalized (f,g)-nonexpansive maps, J. Math. Anal. Appl. 321(2006), 851-861], and drop some restricts such as the continuity of f, g and demiclsedness of f − T . Mathematics Subject Classification: 41A50, 47H10, 54H25

We extend some known fixed point results for mappings satisfying Kannan type conditions to the context of K-metric spaces. Firstly, we prove a common fixed point result for noncommuting maps. A generalization of Kannan’s fixed point theorem is given in some class of spaces including K-metric spaces.

We prove that it is possible to remotely prepare an ensemble of noncommuting mixed states using communication equal to the Holevo information for this ensemble. This remote preparation scheme may be used to convert between different ensembles of mixed states in an asymptotically lossless way, analogous to concentration and dilution for entanglement.

Lie algebraic method generalize matrix methods and algebraic rank conditions to smooth nonlinear systems. They capture the essence of noncommuting flows and give rise to noncommutative analogues of Taylor expansions. Lie algebraic rank conditions determine controllability, observability, and optimality. Lie algebraic methods are also employed for statespace realization, control design, and path...