Quantum states are not observables like in any wave mechanics but co-observables describing the reality as a possible knowledge about the statistics of all quantum events, like quantum jumps, quantum decays, quantum diffusions, quantum trajectories, etc.
However, as we show, the probabilistic interpretation of the traditional quantum mechanics is inconsistent with the probbilistic causality and leads to the infamous quantum measurement problem. Moreover, we prove that all attempts to solve this problem as suggested by Bohr are doomed in the traditional framework of the reversible interactions.
We explore the only possibility left to resolve the quantum causality problem while keeping the reversibility of Schroedinger mechanics. This is to break the time symmetry of the Heisenberg mechanics using the nonequivalence of the Schroedinger and Heisenberg quantum mechanics on nonsimple operator algebras in infinite dimensional Hilbert spaces. This is the main idea of Eventum Mechanics, which enhances the quantum world of the future by classical events of the past and constructs the reversible Schroedinger evolutions compatible with observable quantm trajectories by irreversible quantum to classicl interfaces in terms of the reversible unitary scatterings. It puts the idea of hidden variables upside down by declaring that what is visible (in the past by now) is not quantum but classical and what is visible (by now in the future) is quantum but not classical. More on the philosophy of Eventum Mechanics can be found in .
We demonstrate these ideas on the toy model of the nontrivial quantum - classical bit interface. The application of these ideas in the continuous time leads to derivation of the quantum stochastic master equations reviewed in  and of my research pages .
V. P. Belavkin: Quantum Causality, Stochastics, Trajectories and Information. Reports on Progress in Physics 65 (3): 353-420 (2002). quant-ph/0208087, PDF.