Closed-loop Quantum Optimal Control for High Sensitivity and Robustness in Multi-loop Atom Interferometry

Resonant atom interferometry is a method by which a Mach-Zehnder atom interferometer is given multiple mirror operations, forming loops in the trajectories. Phase shift signatures from gravitational waves and those theorized in ultra-light dark matter models can be coherently amplified by the total loops in the interferometer sequence if the looping frequency approaches the wave frequency. One limiting factor of this technique is imperfect mirror pulse efficiencies that can quickly deplete population from the looping trajectory. Our solution is to engineer the phases of each mirror pulse in the interferometer sequence such that lost atom trajectories are guided back onto the main path. Using this method, we are able to increase the total possible loops by a factor of 50 and amplify phase shifts by a factor of 1000, limited only by spontaneous emission of the atom transition. Naturally, this method makes for a resonant atom interferometer robust to laser intensity, inhomogeneity, and detuning errors, applicable in practical interferometers and those in precision measurement. This talk will focus on our implementation of quantum optimal control to find the most robust phase sequences. We will detail our progress using gradient decent, gaussian process, neural networks, and others in a closed loop system, where real-time experimental data guides the optimization. Lastly, we will present our technique for mitigating collective phases from decohered atoms.