Precise ultra fast single qubit control using optimal control pulses

TL;DR

This paper demonstrates an optimal control method for ultra fast, precise single-qubit operations that surpass the limitations of the rotating wave approximation, achieving high fidelities in quantum gate implementation.

Contribution

The authors experimentally implement an optimal control approach for quantum gates that maintains high fidelity at high Rabi frequencies, overcoming RWA restrictions.

Findings

Achieved high-fidelity Hadamard and NOT gates using optimal control.

Demonstrated switching between rotating and lab frames in magnetic resonance.

Validated the method's general applicability across quantum technologies.

Abstract

Ultra fast and accurate quantum operations are required in many modern scientific areas - for instance quantum information, quantum metrology and magnetometry. However the accuracy is limited if the Rabi frequency is comparable with the transition frequency due to the breakdown of the rotating wave approximation (RWA). Here we report the experimental implementation of a method based on optimal control theory, which does not suffer these restrictions. We realised the most commonly used quantum gates - the Hadamard (\pi/2 pulse) and NOT (\pi pulse) gates with fidelities ($F^{\mathrm{exp}}_{\pi/2}=0.9472\pm0.01$ and $F^{\mathrm{exp}}_{\pi}=0.993\pm0.016$), in an excellent agreement with the theoretical predictions ($F^{\mathrm{theory}}_{\pi/2}=0.9545$ and $F^{\mathrm{theory}}_{\pi}=0.9986$). Moreover, we demonstrate magnetic resonance experiments both in the rotating and lab frames and we can deliberately "switch" between these two frames. Since our technique is general, it could find a wide application in magnetic resonance, quantum computing, quantum optics and broadband magnetometry.