Continuously Measured Systems,Path Integrals and Information

A continuously measured quantum system may be described by restricted path integrals (RPI) or equivalently by non-Hermitian Hamiltonians. The measured system is then considered as an open system, the influence of the environment being taken into account by restricting the path integral or by inclusion of an imaginary part in the Hamiltonian. This way of description of measurements naturally follows from the Feynman form of quantum mechanics without any additional postulates and may be interpreted as an information approach to continuous quantum measurements. This reveals deep features of quantum physics concerning relations between quantum world and its classical appearance.