  Even if a logical network consists of thermodynamically reversible gate
operations, the computation process may have high dissipation rate if the gate
implementation is controlled by external clock signals. It is an open question
whether the global clocking mechanism necessarily envolves irreversible
processes. However, one can show that it is not possible to extract any timing
information from a micro-physical clock without disturbing it. Applying recent
results of quantum information theory we can show a hardware-independent lower
bound on the timing information that is necessarily destroyed if one tries to
copy the signal. The bound becomes tighter for low energy signals, i.e., the
timing information gets more and more quantum.
