Quantum Control Noise Spectroscopy with Optimal Suppression of Dephasing

TL;DR

This paper develops an advanced quantum noise spectroscopy method that uses optimal control waveforms to suppress dephasing and detuning errors, enabling more accurate noise spectrum estimation in quantum systems.

Contribution

It introduces a novel optimal control approach with simple analytic waveforms to improve quantum noise spectroscopy under dephasing and detuning errors.

Findings

Waveforms effectively suppress low-frequency noise

Enhanced robustness in spectral estimation

Accurate noise spectrum estimation in simulated experiments

Abstract

We extend quantum noise spectroscopy (QNS) of amplitude control noise to settings where dephasing noise or detuning errors make significant contributions to qubit dynamics. Previous approaches to characterize amplitude noise are limited by their vulnerability to low-frequency dephasing noise and static detuning errors, which can overwhelm the target control noise signal and introduce bias into estimates of the amplitude noise spectrum. To overcome this problem, we leverage optimal control to identify a family of amplitude control waveforms that optimally suppress low-frequency dephasing noise and detuning errors, while maintaining the spectral concentration in the amplitude filter essential for spectral estimation. The waveforms found via numerical optimization have surprisingly simple analytic forms, consisting of oscillating sine waves obeying particular amplitude and frequency constraints. In numerically simulated QNS experiments, these waveforms demonstrate superior robustness, enabling accurate estimation of the amplitude noise spectrum in regimes where existing approaches are biased by low-frequency dephasing noise and detuning errors.