Toward liquid cell quantum sensing: Ytterbium complexes with ultra-narrow absorption

<p>The energetic disorder induced by fluctuating liquid environments acts in opposition to the precise control required for coherence-based sensing. Overcoming fluctuations requires a protected quantum subspace that only weakly interacts with the local environment. We reported a ytterbium complex that exhibited an ultra-narrow absorption linewidth in solution at room temperature with a full-width at half-maximum of 0.625 meV. Using spectral hole-burning, we measured an even narrower linewidth of 410 peV at 77 K. Narrow linewidths allowed low-field magnetic circular dichroism at room temperature, used to sense Earth-scale magnetic fields. These results demonstrated that ligand protection in lanthanide complexes could significantly diminish electronic state fluctuations. We termed this system an 'atom-like molecular sensor' (ALMS) and proposed approaches to improve its performance.</p>