Precise qubit control beyond the rotating wave approximation

Abstract

Fast and accurate quantum operations of a single spin in room-temperature solids are required in many modern scientific areas, for instance in quantum information, quantum metrology, and magnetometry. However, the accuracy is limited if the Rabi frequency of the control is comparable with the transition frequency of the qubit due to the breakdown of the rotating wave approximation (RWA). We report here an experimental implementation of a control method based on quantum optimal control theory which does not suffer from such restriction. We demonstrate the most commonly used single qubit rotations, i.e. $\pi /2$ - and π -pulses, beyond the RWA regime with high fidelity $F_{\pi /2}^{{\rm exp} }=0.95\pm 0.01$ and $F_{\pi }^{{\rm exp} }=0.99\pm 0.016$ , respectively. They are in excellent agreement with the theoretical predictions, $F_{\pi /2}^{{\rm theory}}=0.9545$ and $F_{\pi }^{{\rm theory}}=0.9986$ . Furthermore, we perform two basic magnetic resonance experiments both in the rotating and the laboratory frames, where we are able to deliberately ‘switch’ between the frames, to confirm the robustness of our control method. Our method is general, hence it may immediately find its wide applications in magnetic resonance, quantum computing, quantum optics, and broadband magnetometry.

Keywords

• nitrogen-vacancy (NV)
• optimal control
• strong driving