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

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., Absorption/Transmission Spectroscopy
The broad band absorption spectra reported in the manuscript were collected using the Shimadzu UV-3101PC UV-VIS-NIR scanning spectrophotometer. A high-resolution transmission/absorption spectrum of the sample was measured with a tunable narrow band CW laser (M Squared SolsTis Ti:Sapph laser). The laser beam is split into two paths by a polarizing beam splitter (PBS). One beam measures the absorption of the solvent and the other measures the absorption of the sample. The quarter waveplate is used to change the polarization of the laser beam so that we can measure the absorption of circlarly polaried light. The two permanent magnets create a strong static magnetic field to induce Zeeman splitting. The translational stage allows us to control the distance between the magnet and the sample and to vary the strength of the magnetic field at the sample’s location. The setup is shown in fig. S37.
Fluorescence Spectroscopy
The fluorescence spectra of the room..., , # Toward liquid cell quantum sensing: Ytterbium complexes with ultra-narrow absorption

[https://doi.org/10.5061/dryad.tht76hf6x](https://doi.org/10.5061/dryad.tht76hf6x)

All the spectral data behind the main text figures in the manuscript is provided here. The raw data are provided with their units noted, and manual fitting of those data as described in the main text leads to the reported spectral properties. The fitting is done either by Gaussian, Lorentzian, or linear functions, depending on the data. Combined with descriptions in the manuscript, details provided in the supplemental material, and the data provided here - all figures and conclusions are reproducible. 

## Description of the data and file structure

Data for every plot in each main text figure are provided here. The tabulated data can be found in \"AllFigures.xlsx\". However, we recommend using the provided MATLAB script to visualize the data. The script output is also included under \"AllFigures.pdf\".

The tabulated dat...