UCLA

In recent years, there has been significant progress in the field of quantum information processing and quantum sensing. Researchers have been actively exploring new quantum systems that possess high accuracy, scalability, and compatibility with other systems. The focus of this thesis is to examine various molecular systems that hold promise for quantum sensing and information processing applications.

We report a ferrocene-supported ytterbium based complex ((thiolfan)YbCl(THF), thiolfan = 1,1'-bis(2,4-di-tert-butyl-6-thiomethylenephenoxy)ferrocene) that exhibits an isolated ultranarrow absorption linewidth in solution at room temperature with a full width at half maximum (FWHM) of (151 $\pm$ 1) GHz. A detailed absorption spectroscopy analysis from room temperature (RT) to 5 K and emission spectroscopy allow us to assign the narrow near infrared (NIR) transitions to atom-centered \textit{f-f} transitions. Zeeman spectroscopy and electron paramagnetic resonance measurement help us to determine the dominant quantum numbers and Land e g-factors of the ground and excited states. A combination of density functional theory and multireference methods match experimental transition energies and oscillator strengths, providing insights into 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 (Ln) complexes.

We demonstrate that the ultranarrow linewidth of this system allows for magnetic field imaging and magnetic field sensing down to Earth scale, which we term an "atom-like molecular sensor" (ALMS). Furthermore, by optically depleting some population, we are able to selectively address the burned spectral hole with a FHWM of 99 kHz, paving the way for optical state preparation and readout of ground state coherence in this liquid molecular system.

In addition, we also describe our efforts in building surface-based molecular systems for quantum information and we find that the sensitivity is limited by scatters from the substrate.

Overall, our results suggest that molecular systems like ALMS may have great potential for quantum sensing and information applications.