  Quantum entanglement plays a fundamental role in quantum computation and
quantum communication. Feedback control has been widely used in stochastic
quantum systems to generate given entangled states since it has good
robustness, where the time required to compute filter states and conduct filter
based control usually cannot be ignored in many practical applications. This
paper designed two control strategies based on the Lyapunov method to prepare a
class of entangled states for qubit systems with a constant delay time. The
first one is bang bang like control strategy, which has a simple form with
switching between a constant value and zero, the stability of which is proved.
Another control strategy is switching Lyapunov control, where a constant delay
time is introduced in the filter-based feedback control law to compensate for
the computation time. Numerical results on a two qubit system illustrate the
effectiveness of these two proposed control strategies.
