Indirect measurements in quantum mechanics lead to stochastic evolution equations for the density matrix, the so-called quantum trajectories. par Generically, the measurements themselves favor wave function collapse towards certain states, while the internal evolution, if it does not preserve these states, prevents the collapse. In this talk I'll describe the regime when the time scale of the collapse is very short compared to the typical time scale of the internal evolution. In this regime, which is a strong noise regime, quantum trajectories, though continuous, are closely related to Poisson processes and a strong universality emerges. par The mathematical tools we use have recently attracted the attention of probabilists who are now aiming at a fully rigorous treatment.

IPhT