Dipolar Decoupling in Magnetic Resonance Force Microscopy using Optimal Control Pulses

We present data showing how a modified gradient ascent pulse engineering method can be used to design nuclear magnetic resonance pulses that perform a single unitary transformation over a large range of maximum Rabi field strengths $(B_1)$, while decoupling the secular dipolar interactions between spins. We designed dipolar-decoupling $\pi$-pulses that perform well over spins feeling maximum $B_1$ fields from $131-274G$. By combining these $\pi$-pulses into a simple multiple pulse sequence, with fields produced by a silver microwire, we have increased $T2^*$ in a polystyrene sample attached to the tip of a silicon nanowire from $11\mu s$ to $\sim250ms$. This dipolar decoupling could be used to improve the spatial resolution of nano-MRI experiments and to allow spectroscopy of chemical shifts in nanoscale samples.