Quantum Control over Highly-Coherent Nuclear Spins

Some of the most coherent quantum states ever produced, with N >10¹⁸ and lifetimes of 10,000 seconds, are ensembles of optically-pumped noble gas spins. We are working to maximize their sensing potential with quantum control techniques such as adaptive feedback optimal control and dynamical decoupling. Already, certain implementations provide the most sensitive absolute measurements of the energy splitting between quantum states, and have been used to measure fundamental physics. Such implementations are additionally being studied for advanced navigation and sensing purposes. Currently, these measurements are limited by non-linear interactions among the spins. The associated decoherence be overcome by application of decoupling pulses that suppress the time-average of the unwanted interactions, or by careful preparation of specific superposition states that are insensitive to problematic non-linearities. The complexity of the quantum control challenge is increased by the need to control multiple, spatially overlapping, spin ensembles. I will discuss our strategies, simulations and (possibly) experimental demonstrations of quantum control over these highly-coherent, spatially overlapped, systems.