Endomorphisms of B(H), extensions of pure states, and a class of representations of O_n

Abstract

Let F_n be the fixed-point algebra of the gauge action of the circle on the Cuntz algebra O_n. For every pure state ρof F_n and every representation θof C(T) we construct a representation of O_n, and we use the resulting class of representations to parameterize the space of all states of O_n which extend ρ. We show that the gauge group acts transitively on the pure extensions of ρand that the action is p-to-1 with p the period of ρunder the usual shift. We then use the above representations of O_n to construct endomorphisms of B(H) which we classify up to conjugacy in terms of the parameters ρand θ. In particular our construction yields every ergodic endomorphism αwhose tail algebra $\bigcap_kα^k(B(H))$ has a minimal projection, and our results classify these ergodic endomorphisms by an equivalence relation on the pure states of F_n. As examples we analyze the ergodic endomorphisms arising from periodic pure product states of F_n, for which we are able to give a geometric complete conjugacy invariant, generalizing results of Stacey, Laca, and Bratteli-Jorgensen-Price on the shifts of Powers.