Push-pull optimization of quantum controls

Optimization of quantum controls to achieve a target process is centered around an objective function comparing the realized process with the target. We propose an objective function that incorporates not only the target operator but also a set of its orthogonal operators whose combined influence leads to an efficient exploration of the parameter space, faster convergence, and extraction of superior solutions. The push-pull optimization, as we call it, can be adopted in various quantum control scenarios. We describe adopting it for gradient based and variational-principle based approaches. Numerical analysis of quantum registers with up to seven qubits reveals significant benefits of the push-pull optimization. We describe applying the push-pull optimization to prepare a long-lived singlet order in a two-qubit system using NMR techniques.