  Uhrig's dynamical decoupling pulse sequence has emerged as one universal and
highly promising approach to decoherence suppression. So far both the
theoretical and experimental studies have examined single-qubit decoherence
only. This work extends Uhrig's universal dynamical decoupling from one-qubit
to two-qubit systems and even to general multi-level quantum systems. In
particular, we show that by designing appropriate control Hamiltonians for a
two-qubit or a multi-level system, Uhrig's pulse sequence can also preserve a
generalized quantum coherence measure to the order of $1+O(T^{N+1})$, with only
$N$ pulses. Our results lead to a very useful scheme for efficiently locking
two-qubit entangled states. Future important applications of Uhrig's pulse
sequence in preserving the quantum coherence of multi-level quantum systems can
also be anticipated.
