Effect of measurement on the decay rate of a quantum system

We investigated the electron tunneling out of a quantum dot in the presence of continuous monitoring by a detector. It is shown that the Schrodinger e quation for the whole system can be reduced to new Bloch-type rate equation s describing the time development of the detector and the measured system a t once. Using these equations we find that the continuous measurement of th e unstable system does not affect its exponential decay, exp(-Gamma t), con trary to expectations based on the quantum Zeno effect. However, the width of the energy distribution of the tunneling electron is no longer Gamma, bu t increases due to the decoherence, generated by the detector.