  For quantum information processing, each physical system has different
advantage for the implementation and so hybrid systems to benefit from several
systems would be able to provide a promising approach. One of the common hybrid
approach is to combine a superconducting qubit as a controllable qubit and the
other quantum system with a long coherence time as a memory qubit. The
superconducting qubit allows us to have an excellent controllability of the
quantum states and the memory qubit is capable of storing the information for a
long time. By tuning the energy splitting between the superconducting qubit and
the memory qubit, it is believed that one can realize a selective coupling
between them. However, we have shown that this approach has a fundamental
drawback concerning energy leakage from the memory qubit. The detuned
superconducting qubit is usually affected by severe decoherence, and this
causes an incoherent energy relaxation from the memory qubit to the
superconducting qubit via the imperfect decoupling. We have also found that
this energy transport can be interpreted as an appearance of anti quantum Zeno
effect induced by the fluctuation in the superconducting qubit. We also discuss
a possible solution to avoid such energy relaxation process, which is feasible
with existing technology.
