  Full formal descriptions of algorithms making use of quantum principles must
take into account both quantum and classical computing components, as well as
communications between these components. Moreover, to model concurrent and
distributed quantum computations and quantum communication protocols,
communications over quantum channels which move qubits physically from one
place to another must also be taken into account.
  Inspired by classical process algebras, which provide a framework for
modeling cooperating computations, a process algebraic notation is defined.
This notation provides a homogeneous style to formal descriptions of concurrent
and distributed computations comprising both quantum and classical parts. Based
upon an operational semantics which makes sure that quantum objects, operations
and communications operate according to the postulates of quantum mechanics, an
equivalence is defined among process states considered as having the same
behavior. This equivalence is a probabilistic branching bisimulation. From this
relation, an equivalence on processes is defined. However, it is not a
congruence because it is not preserved by parallel composition.
