Universal Characterization of Classical Qubit Noise

TL;DR

This paper introduces a universal method for fully characterizing classical noise affecting qubits using Ramsey interferometry, capable of detecting arbitrary correlation functions without complex pulse sequences.

Contribution

The authors develop a direct sampling technique for noise correlation functions via Ramsey measurements, avoiding the need for dynamical decoupling pulses.

Findings

Method works for Gaussian and non-Gaussian noise models.

It is robust against qubit decoherence and measurement errors.

Numerical simulations validate the approach for Ornstein-Uhlenbeck and TLF noise.

Abstract

We propose a general method to fully characterize a classical stochastic noise process causing qubit dephasing through repetitive Ramsey interferometry measurements (RIMs) on the qubit. Compared to filter-function-based spectroscopy, our method does not require complicated dynamical decoupling pulses and can directly detect arbitrary-order correlation functions of such noise processes. We show that each RIM with a short evolution time and suitably chosen control pulses can perform a direct sampling of the noise field and the $n$-point correlations of the RIM outcomes are proportional to the $n$-point correlation functions of the noise processes. Then we numerically demonstrate this method for characterizing two typical examples of classical noises, including the Ornstein-Uhlenbeck processes producing Gaussian noises and an ensemble of TLFs producing non-Gaussian noises. Our method is independent of qubit lifetime and robust against qubit decoherence and measurement errors, thus offering a universal and efficient protocol for qubit noise spectroscopy across diverse platforms.