Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2023)

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.

    Cover page: Exploring Potential Molecular Platforms for Quantum Technology
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2024)
    Achieving ultranarrow absorption linewidths in the condensed phase enables optical state preparation of specific non-thermal states, a prerequisite for quantum-enabled technologies. The 4f orbitals of lanthanide(iii) complexes are often referred to as atom-like, reflecting their isolated nature, and are promising substrates for the optical preparation of specific quantum states. To better understand the photophysical properties of 4f states and assess their potential for quantum applications, theoretical building blocks are required for rapid screening. In this study, an atomic-level perturbative calculation (i.e., spin-orbit crystal field, SOCF) is applied to various Yb(iii) complexes to investigate their linear absorption and emission through a fitting mechanism of their experimentally determined transition energies and oscillator strengths. In particular, the optical properties of (thiolfan)YbCl(THF) (thiolfan = 1,1-bis(2,4-di-tert-butyl-6-thiomethylenephenoxy)ferrocene), a recently reported complex with an ultranarrow optical linewidth, are computed and compared to those of other Yb(iii) compounds. Through a transition energy sampling study, major contributors to the optical linewidth are identified. We observe particularly isolated f-f transitions and narrow linewidths, which we attribute to two distinct factors. Firstly, the ultra-high atomic similarity of the orbitals involved in the optical transition, along with the presence of an anisotropic crystal field, collectively contribute to the observed narrow transitions. Secondly, we note highly correlated excited-ground energy fluctuations that serve to greatly suppress inhomogeneous line-broadening. This article illustrates how SOCF can be used as a low-cost method to probe the influence of crystal field environment on the optical properties of Yb(iii) complexes to assist the development of novel lanthanide series quantum materials.
      Cover page: Elucidating ultranarrow 2F7/2 to 2F5/2 absorption in ytterbium(iii) complexes.
      • Article
      • Peer Reviewed
      UCLA Previously Published Works (2021)
      Quantum information processors based on trapped atoms utilize laser-induced optical cycling transitions for state preparation and measurement. These transitions consist of an electronic excitation from the ground to an excited state and a decay back to the initial ground state, associated with a photon emission. While this technique has been used primarily with atoms, it has also recently been shown to work for some divalent metal hydroxides (e.g. SrOH) and alkoxides (e.g. SrOCH3). This extension to molecules is possible because these molecules feature nearly isolated, atomic-like ground and first-excited electronic states centered on the radical metal atom. We theoretically investigate the extension of this idea to a larger scale by growing the alkyl group, R, beyond the initial methyl group, CH3, while preserving the isolated and highly vertical character of the electronic excitation on the radical metal atom, M. Theory suggests that in the limit as the size of the ligand carbon chain increases, it can be considered a functionalized diamond (or cubic boron nitride) surface. Several requirements must be observed for the cycling centers to function when bound to the surface. First, the surface must have a significant band gap that fully encapsulates both the ground and excited states of the cycling center. Second, while the surface lattice imposes strict limits on the achievable spacing between the SrO- groups, at high coverage, SrO- centers can interact, and show geometric changes and/or electronic state mixing. We show that the coverage of the diamond surface with SrO- cycling centers needs to be significantly sub-monolayer for the functionality of the cycling center to be preserved. Having the lattice-imposed spatial control of SrO- placements will allow nanometer-scale proximity between qubits and will eliminate the need for atom traps for localized cycling emitters. Our results also imply that a functionalization could be done on a scanning microscope tip for local quantum sensing or on photonic structures for optically-mediated quantum information processing.
        Cover page: Surface chemical trapping of optical cycling centers.
        Top