  The effect of a number of mechanisms designed to suppress decoherence in open
quantum systems are studied with respect to their effectiveness at slowing down
the loss of entanglement. The effect of photonic band-gap materials and
frequency modulation of the system-bath coupling are along expected lines in
this regard. However, other control schemes, like resonance fluorescence,
achieve quite the contrary: increasing the strength of the control kills
entanglement off faster. The effect of dynamic decoupling schemes on two
qualitatively different system-bath interactions are studied in depth. Dynamic
decoupling control has the expected effect of slowing down the decay of
entanglement in a two-qubit system coupled to a harmonic oscillator bath under
non-demolition interaction. However, non-trivial phenomena are observed when a
Josephson charge qubit, strongly coupled to a random telegraph noise bath, is
subject to decoupling pulses. The most striking of these reflects the resonance
fluorescence scenario in that an increase in the pulse strength decreases
decoherence but also speeds up the sudden death of entanglement. This
demonstrates that the behaviour of decoherence and entanglement in time can be
qualitatively different in the strong-coupling non-Markovian regime.
