Thousandfold Phase Amplification in a Robust Resonant Atom Interferometer via Applying Quantum Control to Multipath interference*

Resonant atom interferometers amplify the interferometer phase response to signals oscillating at a particular target frequency, making them a promising candidate for quantum sensing. We propose and demonstrate a novel type of robust resonant light-pulse atom interferometer that leverages multipath interference of different spatial trajectories to overcome limitations from pulse infidelities and coherently amplify the readout signal. In these interferometers, the phase amplification and fringe visibility are optimized using the framework of quantum control by adjusting relative phases between pulses. This method allows us to demonstrate resonant phase amplification factors in excess of 1000, arising from the sequential application of in excess of 500 mirror pulses, despite individual pulse transfer efficiencies being limited to approximately 90%. In this context, we will discuss and compare the results of several different approaches to quantum control, including open-loop and closed-loop quantum optimal control. We anticipate that this technique will benefit dark matter and gravitational wave detectors based on atom interferometers, as well as having applications in quantum sensing with matter wave interferometry more broadly.