A Gromov-Hausdorff Distance between von Neumann Algebras and an Application to Free Quantum Fields

A distance between von Neumann algebras is introduced, depending on a further norm inducing the $w^{\ast }$-topology on bounded sets. Such notion is related both with the Gromov-Hausdorff distance for quantum metric spaces of Rieffel and with the Effros-Marechal topology on the von Neumann algebras acting on a Hilbert space. This construction is tested on the local algebras of free quantum fields endowed with norms related with the Buchholz-Wichmann nuclearity condition, showing the continuity of such algebras w.r.t. the mass parameter.