Measuring Environmental Quantum Noise Exhibiting a Nonmonotonic Spectral Shape

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.arXiv:1803.07390v3 [quant-ph]

The dynamical-decoupling-based spatiotemporal noise spectroscopy

“…Although the idea is rather simple and appealing, using such a spectrometer to obtain quantitative data on the spatiotemporal spectrum of the noise field requires more caution than when a single qubit is used to reconstruct the spectrum of temporal fluctuations of the local noise affecting it (note that the latter task, while routinely performed in recent years, is not entirely trivial either, especially in case of temporal spectra having peaks at finite frequencies [63,65]). Large part of the paper has been devoted to detailed explanation of methods allowing for reliable extraction of 'spectroscopic' information (spectroscopic formulas defined in section 4.1) from raw measured data.…”

Characterizing spin-bath parameters using conventional and time-asymmetric Hahn-echo sequences

“…The numerically extracted curve can be fitted to various functional forms to obtain the best-fitting spectral distribution and the corresponding physical parameters. This method, which is referred to as "spectral decomposition" [22,27], has been recently used to characterize the noise surrounding NV centers in diamond with the Carr-Purcell-Meiboom-Gill [29] and DYSCO [30] sequences serving as the control schemes. Beyond the long experiment times (several hours up to days) involved in its experimental realization, such an analysis results in significant vulnerability to experimental drifts, pulse imperfections and numerical inaccuracies.…”

All-optical noise spectroscopy of a solid-state spin

“…Noise spectroscopy elucidates the fundamental noise sources in spin systems, which is essential for developing spin qubits with long coherence times for quantum information processing [1], communication [2], and sensing [3]. But noise spectroscopy typically relies on microwave coherent spin control to extract the noise spectrum [4][5][6][7][8][9], which becomes infeasible when there are highfrequency noise components stronger than the available microwave power. Here, we demonstrate an alternative all-optical approach to performing noise spectroscopy.…”

“…The coherent control of spin qubits can be used to conduct noise spectroscopy of their surrounding environment [4][5][6][7][8][9], in which the spin is used to probe the frequencies of the fluctuating fields generated by neighbouring nuclear and electronic spins as well as the strength of their interaction with the spin (i.e., the spectral density). Such noise spectroscopy using microwave fields has shed light on the fundamental noise processes of spin systems such as superconducting qubits [4,5], nitrogen-vacancy centres in diamond [6,7], and gate-defined quantum dots [8,9]. However, the bandwidth of noise spectroscopy utilising microwave fields is limited by the rate of the spin rotation (i.e., the Rabi frequency), which must exceed the frequencies of the noise.…”

“…These low power rotations could then enable multi-pulse sequences prolonging spin coherence times. Furthermore, the application of hundreds of pulses could enable the realisation of advanced pulse sequences for high resolution quantum sensing (e.g., "DYSCO" [7] sequences), and for the preservation of arbitrary spin states (e.g., XY8-based sequences [28]) for quantum information processing.…”