QUANTUM ZENON EFFECTS IN COMPOSITE SYSTEMS

Quantum Zenon effects are discussed in terms of a specific class of qu antum trajectories? which are conditioned by continuous, mutually excl usive measurement signals. Such a conditioning is not restricted to si mple systems but can be generalized to composite networks. In any case , the characteristic features of these trajectories tend to be washed out in the ensemble limit and thus require single system analysis. Onl y on a sufficiently small time-scale and for a coherent initial state, also the ensemble exhibits some Zenon effect. In this case, ironicall y, actual measurements are not required: a closed single composite sys tem can emulate this behavior. Such a kind of quantum parallelism unde rlies also recent proposals for quantum computation.