The short-time behavior of quantum decay of an unstable state initially located within an interaction region of finite range is investigated using a resonant expansion of the survival amplitude. It is shown that in general the short-time behavior of the survival probability $S\left(t\right)$ has a dependence on the initial state and may behave as either $S\left(t\right)=1-O\left(t^{3/2}\right)$ or $1-O\left(t^2\right)$. These cases are illustrated by solvable models. The experiment reported by Wilkinson et al. [Nature (London) 387, 575 (1997)] does not distinguish between the above short-time behaviors.

• Received 6 March 2012

DOI:https://doi.org/10.1103/PhysRevA.86.062116