Monitoring of the Process of System Information Broadcasting in Time.

One of the problems of quantum physics is how a measurement turns quantum, noncopyable data, towards copyable classical knowledge. We use the quantum state discrimination in a central system model to show how its evolution leads to the broadcasting of the information, and how orthogonalization and decoherence factors allow us to monitor the distance of the state in question to the one perfectly broadcasting information, in any moment of time not just asymptotically. We illustrate this in the spin-spin model where the distance is shown to be typically small and provide the related time scales.