  There are several important solid-state systems, such as defects in solids,
superconducting circuits and molecular qubits, for attractive candidates of
quantum computations. Molecular qubits, which benefit from the power of
chemistry for the tailored and inexpensive synthesis of new systems, face the
challenge from decoherence effect. The decoherence effect is due to the
molecular qubits' inevitable interactions to their environment. Strategies to
overcome decoherence effect have been developed, such as designing a nuclear
spin free environment and working at atomic clock transitions. These chemical
approaches, however, have some fundamental limitations. For example, chemical
approach restricts the ligand selection and design to ligands with zero nuclear
magnetic dipole moment, such as carbon, oxygen, and sulfur. Herein, a physical
approach, named Dynamical decoupling (DD), is utilized to combat decoherence,
while the limitations of the chemical approaches can be avoided. The phase
memory time $T_2$ for a transition metal complex has been prolonged to exceed
one millisecond ($1.4~$ms) by employing DD. The single qubit figure of merit
$Q_M $ reaches $ 1.4\times 10^5$, which is $40$ times better than that
previously reported value for such system. Our results show that molecular
qubits, with milliseconds $T_2$, are promising candidates for quantum
information processing.
