  We suppose that a structure working as a quantum switch will be a significant
element of future networks realizing transmissions of quantum information. In
this chapter we analyze a process of switch's operating -- especially in
systems with a noise presence. The noise is caused by a phenomenon of quantum
decoherence, i.e. distorting of quantum states because of an environmental
influence, and also by some imperfections of quantum gates' implementation. In
the face of mentioned problems, the possibility of tracing the switch's
behavior during its operating seems very important. To realize that we propose
to utilize a Coherence measure which, as we present in this chapter, is
sufficient to describe operating of the quantum switch and to verify
correctness of this process. It should be also stressed that the value of
Coherence measure may be estimated by a quantum circuit, designed especially
for this purpose.
