  In quantum information processing, it is vital to protect the coherence of
qubits in noisy environments. Dynamical decoupling (DD), which applies a
sequence of flips on qubits and averages the qubit-environment coupling to
zero, is a promising strategy compatible with other desired functionalities
such as quantum gates. Here we review the recent progresses in theories of
dynamical decoupling and experimental demonstrations. We give both
semiclassical and quantum descriptions of the qubit decoherence due to coupling
to noisy environments. Based on the quantum picture, a geometrical
interpretation of DD is presented. The periodic Carr-Purcell-Meiboom-Gill DD
and the concatenated DD are reviewed, followed by a detailed exploration of the
recently developed Uhrig DD, which employs the least number of pulses in an
unequally spaced sequence to suppress the qubit-environment coupling to a given
order of the evolution time. Some new developments and perspectives are also
discussed.
