Quantum Zeno and anti-Zeno effects in an unstable system with two bound states

We analyze the experimental observations reported by Fischer et al. [M.C. Fischer, B. Gutiérrez-Medina, M.G. Raizen, Phys. Rev. Lett. 87 (2001) 040402] by considering a system of coupled unstable bound quantum states |A〉|A〉 and |B〉|B〉. The state |B〉|B〉 is coupled to a set of continuum states |CΘ(ω)〉|CΘ(ω)〉. We investigate the time evolution of |A〉|A〉 when it decays into |CΘ(ω)〉|CΘ(ω)〉 via |B〉|B〉, and find that frequent measurements on |A〉|A〉 leads to both the quantum Zeno effect and the anti-Zeno effects depending on the frequency of measurements. We show that it is the presence of |B〉|B〉 which allows for the anti-Zeno effect.