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


In quantum technology (such as atomic vapor cells used in precision magnetometry), the energetic disorder induced by a fluctuating liquid environment acts in direct 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. Herein, we report a ferrocene-supported ytterbium complex ((thiolfan)YbCl(THF), thiolfan = 1,1′-bis(2,4-di-tert-butyl-6-thiomethylenephenoxy)ferrocene) that exhibits an extraordinarily narrow absorption linewidth in solution at room temperature with a full-width at half-maximum of 0.625 ± 0.006 meV. A detailed spectroscopic analysis allows us to assign all near infrared (NIR) transitions to atom-centered f-f transitions, protected from the solvent environment. A combination of density functional theory and multireference methods match experimental transition energies and oscillator strengths, illustrating the role of spin-orbit coupling and asymmetric ligand field in enhancing absorption and pointing toward molecular design principles that create well-protected yet observable electronic transitions in lanthanide complexes. Narrow linewidths allow for a demonstration of extremely low-field magnetic circular dichroism at room temperature, employed to sense and image magnetic fields, down to Earth scale. We term this system an ‘atom-like molecular sensor’ (ALMS), and propose approaches to improve its performance.


Supplementary material

Supporting Information for Toward liquid cell quantum sensing: Ytterbium complexes with ultra-narrow absorption
Materials and characterization of ytterbium complexes studied are shown, including the synthesis process, crystal structure, NMR, SQUID, and EPR spectra. Details of the electronic and MCD spectroscopy are included, laying out the spectroscopic setups used and relevant background information. Further information about the theoretical calculations are included, elaborating on magnetic dipole, electronic, and g-factor calculations.
MCD Imaging of External Magnetic Field
Dynamic intensity mapping of the external magnetic field around the atom-like molecular sensor (ALMS).