Qubits as spectrometers of dephasing noise

TL;DR

This paper introduces a method for directly characterizing dephasing noise on a single qubit through repeated measurements and control sequences, enabling detailed noise correlation function reconstruction across multiple timescales.

Contribution

It presents a novel procedure combining measurements under control sequences and free evolution to reconstruct noise correlation functions over broad timescales.

Findings

Effective reconstruction of short-time noise correlation functions.

Ability to characterize noise over many orders of magnitude in timescale.

Robustness analysis confirms reliability of the method.

Abstract

We present a procedure for direct characterization of the dephasing noise acting on a single qubit by making repeated measurements of the qubit coherence under suitably chosen sequences of controls. We show that this allows a numerical reconstruction of the short time noise correlation function and that it can be combined with a series of measurements under free evolution to allow a characterization of the noise correlation function over many orders of magnitude range in timescale. We also make an analysis of the robustness and reliability of the estimated correlation functions. Application to a simple model of two uncorrelated noise fluctuators using decoupling pulse sequences shows that the approach provides a useful route for experimental characterization of dephasing noise and its statistical properties in a variety of condensed phase and atomic systems.