MPS/CHE-EPSRC: Exploring Molecular Lanthanides as Optical Qubits using Coherent Optical Spectroscopies

Researchers from the University of California, Los Angeles, along with their collaborator at the University of Oxford in the United Kingdom, are supported to develop new design principles to control the optical and quantum properties of rare earth containing molecules for use in quantum information science. Rare earth ions, particularly lanthanides (elements at the bottom of the periodic table), have narrow optical transitions linked to magnetic states that make them attractive building blocks for quantum technologies. Quantum information science (QIS) practitioners largely focus on lanthanides embedded in salt-like crystals, which limit their operation to extraordinarily low temperatures as molecules in solution are thought to be too strongly disturbed by their surroundings to preserve these delicate quantum properties. Preliminary results suggest that careful chemical design of the molecules surrounding a lanthanide ion can overcome this limitation, opening the possibility of controlling coherent optical behavior even in liquid solutions. The research team will combine synthesis of lanthanide containing molecules with a suite of specialized optical and microwave spectroscopy techniques adapted from the quantum information science community to measure and manipulate the electronic states of these systems. Their discoveries could establish molecular based quantum bits that can be produced and manipulated in large quantities for future quantum sensing, communication, and information storage technologies. The project will also train graduate and undergraduate students at the intersection of chemistry, physics, and quantum information science, and will build connections between the United States and United Kingdom research communities through student exchange and jointly organized scientific meetings. This award is made under the NSF-UKRI lead agency opportunity. The project focuses on lanthanide coordination complexes whose f-to-f electronic transitions are shielded from the surrounding environment by filled outer orbitals, giving rise to unusually narrow linewidths even outside a solid host. The first aim examines how ligand symmetry, denticity, and electronic structure influence linewidths and oscillator strengths, with initial emphasis on ytterbium complexes. The second aim applies coherent optical spectroscopy methods, coupled with microwave spectroscopy, to probe dephasing mechanisms and demonstrate qubit like manipulation of lanthanide optical transitions in solution. The third aim tests whether the resulting design principles extend to europium, whose ground state lacks orbital angular momentum. Throughout, electronic structure theory and computation guide hypothesis generation and are validated against spectroscopic and structural measurements. The collaboration draws on coherent spectroscopy expertise at UCLA, computational and theoretical chemistry at UCLA, and lanthanide synthesis and spectroscopy expertise at Oxford. The outcome will be a set of transferable chemical design rules for engineering molecular lanthanide emitters for optically addressed quantum information applications. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.