T. Titkos: On the strength function of positive semidefinite operators

The aim of this talk is to draw attention to an interesting functional representation of the cone of bounded positive semidefinite operators. The natural and elegant notion of the strength function was introduced by Busch and Gudder in their paper "Effects as functions on projective Hilbert space" (Lett. Math. Phys. 47, 329–337, 1999). While this representation has many appealing properties — most notably, that it turns the Löwner order into the pointwise order — surprisingly little is known about the structure of the set of strength functions. I will talk about the little that I know about this topic.