Continuous and pulsed observations in the quantum Zeno effect

The usual formulation of the quantum Zeno effect (QZE) uses a sequence of rapid observations to prevent change. The same effect can be achieved with continuous observation. For partial inhibition of change we provide a quantitative relation between pulsed (at intervals delta t) and continuous (with response time tau(o)) observations: the slowdown is the same for delta t=4 tau(o). Including the continuous observer in the Hamiltonian gives an alternative view of the QZE, showing the appropriateness of the name "dominated time evolution." Finally, the variation on the QZE in which a nonconstant sequence of projections can force change is also shown to be achievable by time-varying continuous observation. [S1050-2947(98)01303-1].