Submillihertz magnetic spectroscopy performed with a nanoscale quantum sensor

<jats:title>Enhancing quantum sensing</jats:title> <jats:p> The quantum properties of the nitrogen vacancy (NV) defect in diamond can be used as an atomic compass needle that is sensitive to tiny variations in magnetic field. Schmitt <jats:italic>et al.</jats:italic> and Boss <jats:italic>et al.</jats:italic> successfully enhanced this sensitivity by several orders of magnitude (see the Perspective by Jordan). They applied a sequence of pulses to the NV center, the timing of which was set by and compared with a highly stable oscillator. This allowed them to measure the frequency of an oscillating magnetic field (megahertz bandwidth) with submillihertz resolution. Such enhanced precision measurement could be applied, for example, to improve nuclear magnetic resonance-based imaging protocols of single molecules. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6340" page="832" related-article-type="in-this-issue" vol="356" xlink:href="10.1126/science.aam5532">832</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6340" page="837" related-article-type="in-this-issue" vol="356" xlink:href="10.1126/science.aam7009">837</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6340" page="802" related-article-type="in-this-issue" vol="356" xlink:href="10.1126/science.aan1112">802</jats:related-article> </jats:p>