We study the long time non-exponential decay in an open quantum system in which a bound state approaches the energy continuum as the system parameters are varied. We find that at least two regions exist yielding different power law decay behaviors; we term these the long-time near zone and the long-time far zone . In the near zone the survival probability falls off according to a t -1 power law, while in the far zone it falls off as t -3 . The timescale T Q separating these two regions is inversely related to the gap between the bound state energy and the continuum threshold, hence when the bound state is absorbed into the continuum for special parameter values, this time scale diverges and the survival probability follows the enhanced t -1 power law even on asymptotic scales.
 S. Garmon, T. Petrosky, L. Simine, and D. Segal, Fortschr. Phys. 61 , 261 (2013)
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