Enhancing atomic dark matter and gravitational wave detectors with quantum optimal control*

Large scale atom interferometers using strontium atoms are promising for searching for ultralight dark matter and gravitational waves in a currently unexplored frequency range. In atom interferometry, the atomic superposition states are created and controlled by transferring momentum from laser pulses. The interferometer sensitivity can be enhanced by implementing large momentum transfer (LMT) atomic beam splitters with hundreds or even thousands of pulses which drives atomic transitions between ground and excited states. Deviation from ideal transitions limit the control efficiency and lead to significant atom loss after numerous pulses. During the driving process, deviations can be induced by various factors such as location deviation of atoms in the cloud, non-zero initial velocity spread of atoms respective to the rest-frame, intensity, phase fluctuations and polarization aberration in the laser pulses, and non-zero environmental electromagnetic fields. We manage to drive transitions of the 87Sr atoms in simulation with high fidelity and shorter pulse duration by employing the quantum optimal control techniques which increase the robustness and efficiency of driving pulses against nonideal factors by detuning the amplitude and phase instantaneously and constantly in the pulse duration timescale. As a result, in our full interferometer simulation, the optimized pulse reveals big advantages over primitive and other composite pulses.