Real measurements and the quantum Zeno effect - art. no. 062103

In 1977. Mishra and Sudarshan [J. Math. Phys. 18, 756 (1977)] showed that a n unstable particle would never be found decayed while it was continuously observed. They called this effect the quantum Zeno effect (or paradox). Lat er it was realized that the frequent measurements could also accelerate the decay (quantum anti-Zeno effect). In this paper, we investigate the quantu m Zeno effect using the definite model of the measurement. We take into acc ount the finite duration and the finite accuracy of the measurement. A gene ral equation for the jump probability during the measurement is derived. We find that the measurements can cause inhibition (quantum Zeno effect) or a cceleration (quantum anti-Zeno effect) of the evolution, depending on the s trength of the interaction with the measuring device and on the properties of the system. However, the evolution cannot be fully stopped.