  In this paper, we discuss how effective environments incorporating periodic
measurements can be used to prepare a two-level system (TLS) in almost
arbitrary thermal states: Concretely, we study a TLS coupled to a spin
environment, the magnetization of which is measured periodically. In ensemble
average these measurements cause a relaxation of the TLS into a thermal
(diagonal) state. By adjusting the time between the measurements and the
detuning of the environmental spins, the creation of very low temperatures as
well as inversion becomes possible. Our analytical results derived for large
environments are numerically shown to be valid even for quite small
environments, down to only a few spins.
