and Liu proved that UDD is universal for suppressing single-qubit decoherence [@univUDD]. That is, for a single qubit coupled with an arbitrary bath, UDD works regardless of how the qubit is coupled to its bath.

Given the universality of UDD for suppression of single-qubit decoherence, it becomes urgent to examine whether UDD is useful for preserving quantum coherence of two-qubit states. This extension is necessary and important because many quantum operations involve at least two qubits. Conceptually there is also a big difference between single-qubit coherence and two-qubit coherence: preserving the latter often means the storage of quantum entanglement. Furthermore, because quantum entanglement is a nonlocal property and cannot be affected by local operations, preserving quantum entanglement between two qubits by a control pulse sequence will require the use of nonlocal control Hamiltonians.

In this work, by exploiting a central result in Yang and Liu’s universality proof [@univUDD] for UDD in single-qubit systems and by adopting a generalized coherence measure for two-qubit states, we show that UDD pulse sequence does apply to two-qubit systems, at least for preserving one pre-determined type of quantum coherence. The associated control Hamiltonian is also explicitly constructed. This significant extension from single-qubit to two-qubit systems 