A generalization of Ando's dilation, and isometric dilations for a class of tuples of $q$-commuting contractions

TL;DR

This paper extends Ando's dilation theorem to pairs of $Q$-commuting contractions with unitary $Q$, and constructs explicit isometric dilations for certain classes of $q$-commuting and $q$-commuting $n$-tuples, broadening the understanding of operator dilations.

Contribution

The paper provides explicit constructions of isometric dilations for $Q$-commuting contractions with unitary $Q$, generalizing Ando's theorem and addressing cases for $q$-commuting and $q$-commuting $n$-tuples.

Findings

Explicit dilation for pairs of $Q$-commuting contractions with unitary $Q$.

Construction of dilations for $q$-commuting contractions with $|q|=1$.

Extension to certain classes of $q$-commuting $n$-tuples.

Abstract

Given a bounded operator $Q$ on a Hilbert space $\mathcal{H}$, a pair of bounded operators $(T_1, T_2)$ on $\mathcal{H}$ is said to be $Q$-commuting if one of the following holds: \[ T_1T_2=QT_2T_1 \text{ or }T_1T_2=T_2QT_1 \text{ or }T_1T_2=T_2T_1Q. \] We give an explicit construction of isometric dilations for pairs of $Q$-commuting contractions for unitary $Q$, which generalizes the isometric dilation of Ando [2] for pairs of commuting contractions. In particular, for $Q=qI_{\mathcal{H}}$, where $q$ is a complex number of modulus $1$, this gives, as a corollary, an explicit construction of isometric dilations for pairs of $q$-commuting contractions which are well studied. There is an extended notion of $q$-commutativity for general tuples of operators and it is known that isometric dilation does not hold, in general, for an $n$-tuple of $q$-commuting contractions, where $n\geq 3$. Generalizing the class of commuting contractions considered by Brehmer [8], we construct a class of $n$-tuples of $q$-commuting contractions and find isometric dilations explicitly for the class.