CAREER: Fast coherent and incoherent control of atomic ions in scalable platforms

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Individual ions immobilized in vacuum and precisely controlled with lasers constitute a leading platform for quantum computing (QC), simulation, and metrology. Current academic and industrial QC systems operating on up to a few tens of qubits are however far from the millions required for fault-tolerant universal QC, as may be required for practically useful quantum advantage. This scaling represents a challenge that will be met only with innovations in the basic physical techniques used for qubit control, and simultaneously the classical hardware interfacing with qubits. The proposed research will invent and experimentally explore physical methods for ion qubit control capable of overcoming fundamental limitations in speed and error of current approaches. Ion qubit control is generally performed with laser fields, typically assumed to be in spatial profiles essentially uniform over the atom's extent due to conventional implementations with free-space laser beams. This imposes serious limitations on a range of basic functionalities, compromising operation speeds, errors achievable, and physical architectures. Chip-integrated hardware platforms that the PI has pioneered facilitate scaling, and furthermore enable practical and stable delivery of tailored spatial field profiles, where fine spatial variations of the field profile can play a critical role in dynamics. The present work will explore new atom-light interactions enabled in these configurations, thereby opening a new frontier for quantum control in scalable atomic systems. The research immerses PhD and undergraduate researchers in ideas drawing deeply from both classical optics/photonics and quantum science, an intersection of broad and growing importance both in research and for industry workforce. Outreach involving active participation by local middle and high school students is planned. The proposed work explores how structured light fields can address the fundamental challenges in scaling trapped-ion quantum systems -- how can we reduce limiting operation times for both incoherent (laser cooling, readout) and coherent (quantum logic) operations, while further reducing limiting infidelities? Since this work leverages scalable hardware platforms and foundry-fabricated devices to address these questions, achieved advances will directly impact practical large-scale systems in development. Furthermore, the techniques pursued here will inform efforts in precision metrology and searches for new physics based on atomic spectroscopy, in which the PI is also actively involved in collaborations internationally. Key to the concepts proposed are the ability to tailor spatially structured light fields at the atom location with electric field gradients or curvatures along desired directions, but at nulls in the electric field and thus intensify itself. This allows for driving sideband transitions that couple to ion motion with suppressed off-resonant carrier excitation, or driving of particular desired electric quadrupole or octupole transitions with minimal off-resonant couplings. Integrated photonic delivery offers a route to design such delivered beams with high precision, and furthermore deliver the spatially varying profiles to atomic ions with the few nm-level stability required for realization of these concepts. Specific aims within this program include realization of Doppler laser cooling of ion motion 50x faster than current methods allow, fast and broadband cooling to the quantum ground state in novel proposed schemes utilizing tailored optical field profiles, probing of optical quadrupole transitions in higher-order Hermite-Gauss modes, and pursuit of integrated realization of multi-qubit logic with 10^-4 level error, all within a scalable optical platform.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.