An _open quantum system_ is any [quantum system](Quantum%20systems.md) that interacts with one or more quantum systems such that there is a transfer [information.](Quantum%20Information%20(index).md) ^e00545 [Quantum measurement](Quantum%20measurement%20(index).md#Basic%20Concepts) may be modeled as the interaction of an open quantum system with an _observer_ where we postulate the following attributes pertaining to quantum measurement.   %%They are introduced in terms of quantum noise in Nielsen and Chuang pg. 353 - here there's the notion of quantum operators. Though, careful, this notion is not completely general.%% #QuantumMechanics/FoundationsOfQuantumMechanics