  Modeling and reasoning about concurrent quantum systems is very important
both for distributed quantum computing and for quantum protocol verification.
As a consequence, a general framework describing formally the communication and
concurrency in complex quantum systems is necessary. For this purpose, we
propose a model qCCS which is a natural quantum extension of classical
value-passing CCS with the input and output of quantum states, and unitary
transformations and measurements on quantum systems. The operational semantics
of qCCS is given based on probabilistic labeled transition system. This
semantics has many different features compared with the proposals in literature
in order to describe input and output of quantum systems which are possibly
correlated with other components. Based on this operational semantics, we
introduce the notions of strong probabilistic bisimilarity and weak
probabilistic bisimilarity between quantum processes and discuss some
properties of them, such as congruence under various combinators.
