Existence and examples of quantum isometry group for a class of compact metric spaces

We formulate a definition of isometric action of a compact quantum group (CQG) on a compact metric space, generalizing Banica’s definition for finite metric spaces. For metric spaces $(X,d)$ which can be isometrically embedded in some Euclidean space, we prove the existence of a universal object in the category of the compact quantum groups acting isometrically on $(X,d)$. In fact, our existence theorem applies to a larger class, namely for any compact metric space $(X,d)$ which admits a one-to-one continuous map $f : X \raro \IR^n$forsome$n$suchthat$d_0(f(x),f(y))=\phi(d(x,y))$(where$d_0$ is the Euclidean metric) for some homeomorphism $\varphi$ of ${\text{IR}}^{+}$. As concrete examples, we obtain Wang’s quantum permutation group ${\text{cls}}_n^{+}$ and also the free wreath product of ${\text{IZ}}_2$ by ${\text{cls}}_n^{+}$ as the quantum isometry groups for certain compact connected metric spaces constructed by taking topological joins of intervals in \cite{huang1}.