In a strange dream, Henry is coherently transported towards his bride down the aisle. But just as a small portion of him arrives next to her, that portion disappears in a flash of light caused by a snapshot! Henry keeps trying to be united with his bride, but repeated snapshots cause Henry’s collapse to being far away from her. This dream illustrates the quantum Zeno effect (QZE): if a measurement collapses the quantum state with high probability to the initial state, then frequent repeated measurements can almost stop the change of the quantum state. Yet less frequent measurements cause the opposite, anti-Zeno effect (AZE), whereby change or decay increases. Thus, decay is controllable. These effects confirm Zeno’s argument that change is an illusion, as it is up to the observer to prevent or induce it by appropriate observation. The appendix to this chapter explains the QZE for coherent and decay processes.
Evolution of an Atom Impeded by Measurement: The Quantum Zeno Effect
