The quantum Zeno effect in double well tunnelling

Measurement lies at the heart of quantum theory, and introductory textbooks in quantum mechanics cover the measurement problem in topics such as the Schrodinger's cat thought experiment, the EPR problem, and the quantum Zeno effect (QZE). In this article we present a new treatment of the QZE suitable for undergraduate students, for the case of a particle tunnelling between two wells while being observed in one of the wells. The analysis shows that as the observation rate increases, the tunnelling rate tends towards zero, in accordance with Zeno's maxim 'a watched pot never boils'. The method relies on decoherence theory, which replaces aspects of quantum collapse by the Schrodinger evolution of an open system, and its recently simplified treatment for undergraduates. Our presentation uses concepts familiar to undergraduate students, so that calculations involving many-body theory and the formal properties of the density matrix are avoided.