Quantum Zeno and anti-Zeno effects: without the rotating-wave approximation.

We show that the counterrotating, neglected in the previous studies of the quantum Zeno effect (QZE) in atomic decay, can have a large impact on the short-time evolution. We calculate the electron self-energy, the Lamb shift, and the QZE without making the rotating-wave approximation (RWA) and show that, for hydrogen in free space, the Zeno time is longer by 2 orders of magnitude than that obtained from the RWA. We also show that there is no anti-Zeno effect as the counterrotating terms and rotating terms represent the opposite processes in the higher frequency region. Consequently, the experimental measurement of the QZE may be much easier than what was determined with the RWA results.