Error-correcting transition pulses for co-located spin ensembles without frequency selectivity
We present a new class of control pulses designed to transfer co-located ensembles without relying on frequency selectivity, thereby allowing much faster state-transitions. A geometric approach allows us to construct sequences which are robust to changes in the background magnetic field along multiple axes, and errors in the pulse area. \red{These pulses are extremely fast, with robustness to pulse area shown at half the quantum speed limit.} We demonstrate these sequences on nuclear-dipole states, showing milliradian precision over several hours, 30-fold beyond the previous state of the art. This provides a path for extending the coherent integration time of ultra-long-lived nuclear-spin states to the fundamental limit set by their $>$10000 second lifetimes, as the limiting self-interactions of the nuclei are suppressed in the symmetric superposition. The state-preparation quality demonstrated here directly opens up 30-fold improvements in next generation tests of the standard model, especially tests of the symmetries of QCD and searches for dark matter; it is also crucial for the development of nuclear-spin based quantum memories and may be useful in other scenarios demanding extremely fast but robust transitions.