Quantum optimal control using phase-modulated driving fields

TL;DR

This paper introduces a phase-modulated control method for quantum systems that improves optimization efficiency and robustness against noise and inhomogeneities, enhancing quantum gate performance and coherence times.

Contribution

A novel phase-modulated optimal control technique that reduces computational overhead and increases robustness in quantum control tasks.

Findings

Outperforms Fourier-basis methods in control efficiency

Enhances robustness against inhomogeneities and noise

Prolongs quantum coherence time by 50% with optimized sequences

Abstract

Quantum optimal control represents a powerful technique to enhance the performance of quantum experiments by engineering the controllable parameters of the Hamiltonian. However, the computational overhead for the necessary optimization of these control parameters drastically increases as their number grows. We devise a novel variant of a gradient-free optimal-control method by introducing the idea of phase-modulated driving fields, which allows us to find optimal control fields efficiently. We numerically evaluate its performance and demonstrate the advantages over standard Fourier-basis methods in controlling an ensemble of two-level systems showing an inhomogeneous broadening. The control fields optimized with the phase-modulated method provide an increased robustness against such ensemble inhomogeneities as well as control-field fluctuations and environmental noise, with one order of magnitude less of average search time. Robustness enhancement of single quantum gates is also achieved by the phase-modulated method. Under environmental noise, an XY-8 sequence constituted by optimized gates prolongs the coherence time by $50\%$ compared with standard rectangular pulses in our numerical simulations, showing the application potential of our phase-modulated method in improving the precision of signal detection in the field of quantum sensing.