Measuring environmental quantum noise exhibiting a non-monotonous spectral shape

TL;DR

This paper compares and evaluates various quantum noise spectroscopy methods, especially for non-monotonous broadband spectra, demonstrating the superior performance of a modified DYSCO sequence through theoretical analysis and experimental validation with NV centers.

Contribution

It introduces a modified DYSCO sequence with a Gaussian envelope and compares its effectiveness against existing methods for complex noise spectra in quantum systems.

Findings

gDYSCO outperforms other sequences in reconstructing non-trivial spectral features

The methods are validated experimentally using NV centers in diamond

The study enhances the ability to characterize complex quantum noise environments

Abstract

Understanding the physical origin of noise affecting quantum systems is important for nearly every quantum application. Quantum noise spectroscopy has been employed in various quantum systems, such as superconducting qubits, NV centers and trapped ions. Traditional spectroscopy methods are usually efficient in measuring noise spectra with mostly monotonically decaying contributions. However, there are important scenarios in which the noise spectrum is broadband and non-monotonous, thus posing a challenge to existing noise spectroscopy schemes. Here, we compare several methods for noise spectroscopy: spectral decomposition based on the Carr-Purcell-Meiboom-Gill (CPMG) sequence, the recently presented DYnamic Sensitivity COntrol (DYSCO) sequence and a modified DYSCO sequence with a Gaussian envelope (gDYSCO). The performance of the sequences is quantified by analytic and numeric determination of the frequency resolution, bandwidth and sensitivity, revealing a supremacy of gDYSCO to reconstruct non-trivial features. Utilizing an ensemble of nitrogen-vacancy centers in diamond coupled to a high density $^{13}$C nuclear spin environment, we experimentally confirm our findings. The combination of the presented schemes offers potential to record high quality noise spectra as a prerequisite to generate quantum systems unlimited by their spin-bath environment.