# Jakub Rembielinski

## Unstable particles as open quantum systems

We present the probability preserving description of the decaying particle
within the framework of quantum mechanics of open systems taking into
account the superselection rule prohibiting the superposition of the
particle and vacuum. In our approach the evolution of the system is given by
a family of completely positive trace preserving maps forming one-parameter
dynamical semigroup. We give the operator sum representation (Kraus
representation) for the general evolution of such systems which allows to
write the evolution for systems with two or more particles. We also show
that there are remarkable restrictions on the possible strength of
decoherence.