Yb (III) Single Molecule Magnet as a Liquid Quantum Cell for Magnetic Sensing

Atomic vapor cells (AVCs) are widely used for many commercial and scientific applications in sensing, computing, navigating, and precise frequency/time referencing (e.g. atomic clocks). They provide one of the most sensitive methods of measuring magnetic fields, able to detect magnetic fields ten times smaller than that of the Earth’s intrinsic field. Resonant light excites electrons in atomic vapors, creating long-lived magnetic dipole moments that are responsive to small fluctuations in the external environment. However, in all AVCs, the sensitivity limit lies with low particle density and achieving higher densities of atomic vapors will dramatically increase the sensitivity of AVCs. To address this issue, the development of liquid quantum cells (LQCs) will be a transformative step toward miniaturization of quantum sensing technology due to the relatively high concentration of identical, controllable spins that can be achieved in condensed phase environments. A “molecular AVC” will allow specific advantages over atomic vapor cells, where more particles can be packed into a set volume and ligand design can provide local protection of the atomic center from collisions.<br/>Our target systems have narrow optical features with long coherent lifetimes, but also accessible chemical handles for solubility and functionalization. A key feature of trivalent Yb complexes is a surprisingly narrow absorption peak near the gas phase 980 nm transition. Specifically, our (thiolfan)YbCl complex demonstrates one of the narrowest absorption peaks (FWHM= 0.6 meV) ever seen in a solution sample at room temperature. With a joint experimental and computational approach, we characterize and investigate the molecular design principles responsible for this narrow linewidth. We present single crystal XRD, high resolution absorption, temperature dependence, emission, polarization, magnetic response, and pump-probe measurements, which altogether point to a well-defined system that can be applied to quantum sensing of magnetic fields.