Tracking the precession of single nuclear spins by weak measurements

TL;DR

This paper demonstrates tracking of single nuclear spin precession using periodic weak measurements, enabling high-resolution NMR spectroscopy at the atomic scale with potential applications in single-molecule analysis.

Contribution

It introduces a novel method of using periodic weak measurements to monitor single nuclear spins, overcoming quantum back-action effects and enabling high-resolution NMR spectroscopy.

Findings

Successful detection of single nuclear spin precession.

Minimized measurement-induced decoherence.

Achieved high-resolution NMR spectroscopy of multiple spins.

Abstract

Nuclear magnetic resonance (NMR) spectroscopy is a powerful technique for analyzing the structure and function of molecules, and for performing three-dimensional imaging of the spin density. At the heart of NMR spectrometers is the detection of electromagnetic radiation, in the form of a free induction decay (FID) signal, generated by nuclei precessing around an applied magnetic field. While conventional NMR requires signals from 1e12 or more nuclei, recent advances in sensitive magnetometry have dramatically lowered this number to a level where few or even individual nuclear spins can be detected. It is natural to ask whether continuous FID detection can still be applied at the single spin level, or whether quantum back-action modifies or even suppresses the NMR response. Here we report on tracking of single nuclear spin precession using periodic weak measurements. Our experimental system consists of carbon-13 nuclear spins in diamond that are weakly interacting with the electronic spin of a nearby nitrogen-vacancy center, acting as an optically readable meter qubit. We observe and minimize two important effects of quantum back-action: measurement-induced decoherence and frequency synchronization with the sampling clock. We use periodic weak measurements to demonstrate sensitive, high-resolution NMR spectroscopy of multiple nuclear spins with a priori unknown frequencies. Our method may provide the optimum route for performing single-molecule NMR at atomic resolution.