  During recent years, dynamical decoupling (DD) has gained relevance as a tool
for manipulating quantum systems and extracting information from them. This is
particularly relevant for spins involved in nuclear magnetic resonance (NMR),
where DD sequences can be used to prolong quantum coherences, or for
selectively couple/decouple the effects imposed by random environmental
fluctuations. In this Letter, we show that one can exploit these concepts in
order to selectively recouple diffusion processes in restricted spaces. The
ensuing method provides a novel tool to measure restriction lengths in confined
systems such as capillaries, pores or cells. The principles of this method for
selectively recoupling diffusion-driven decoherence, its standing within the
context of diffusion NMR, and corroborating experiments, are presented.
