Virtual quantum subsystems - art. no. 077901

The physical resources available to access and manipulate the degrees of fr eedom of a quantum system define the set A of operationally relevant observ ables. The algebraic structure of A selects a preferred tensor product stru cture, i.e., a partition into subsystems. The notion of compoundness for qu antum systems is accordingly relativized. Universal control over virtual su bsystems can be achieved by using quantum noncommutative holonomies.