Robust Quantum Control for Bragg Pulse Design in Atom Interferometry

TL;DR

This paper presents a robust optimal control algorithm for designing energy-efficient Bragg pulses in atom interferometry, achieving high fidelity transfers despite parameter variability.

Contribution

It introduces a new control synthesis method that ensures robustness against parameter variations in ultra-cold atom interferometry applications.

Findings

Successfully transfers atoms to high momentum states with 10-40% initial momentum variability.

Achieves high fidelity in multi-photon Bragg diffraction schemes up to | 40 k.

Validated performance through laboratory experiments.

Abstract

We formulate a robust optimal control algorithm to synthesize minimum energy pulses that can transfer a cold atom system into various momentum states. The algorithm uses adaptive linearization of the evolution operator and sequential quadratic programming to iterate the control towards a minimum energy pulse that achieves optimal target state fidelity. Robustness to parameter variation is achieved using Legendre polynomial approximation over the domain of variation. The method is applied to optimize the Bragg beamsplitting operation in ultra-cold atom interferometry. Even in the presence of 10-40% variability in the initial momentum dispersion of the atomic cloud and the intensity of the optical pulse, the algorithm reliably converges to a control protocol that robustly achieves unprecedented momentum levels with high fidelity for a single-frequency multi-photon Bragg diffraction scheme (e.g. $|\pm 40\hbar k\rangle$). We show the advantages of our method by comparison to stochastic optimization using sampled parameter values, provide detailed sensitivity analyses, and performance of the designed pulses is verified in laboratory experiments.