The Bonn team has developed a measurement scheme that indirectly measures the position of an atom. In essence, one looks where the cesium atom is not. The image clarifies this procedure. Let us assume that two containers are in front of us and a cat is hidden under one of them (a). However, we do not know under which one. We tentatively lift the right jar (b) and we find it empty. We, thus, conclude that the cat must be in the left jar and yet we have not disturbed it. Had we have lifted the left jar instead, we would have disturbed the cat (c), and the measurement must be discarded.
In the macro-realist's world, this measurement scheme would have absolutely no influence on the cat's state, which remains undisturbed all the time. In the quantum world, however, a negative measurement that reveals the cat's position, like in (b), is already sufficient to destroy the quantum superposition and to influence the result of the experiment. The Bonn physicists have exactly observed this effect.