Engineering Clock Transitions in Molecular Lanthanide Complexes.

Area of Science:

• Quantum technologies
• Molecular magnetism
• Quantum computing

Background:

• Molecular lanthanide (Ln) complexes are key for quantum technologies.
• High-symmetry Ln complexes form quantum two-level systems for magnetic qubits.
• Symmetry lowering in Ln complexes enhances coherence via clock transitions.

Purpose of the Study:

• Investigate nine-coordinate holmium (HoIII) complexes for quantum applications.
• Detail the impact of ligand environment on crystal field properties.
• Demonstrate tunability of clock transitions for improved qubit performance.

Main Methods:

• Single-crystal high-frequency electron paramagnetic resonance (EPR) spectroscopy.
• High-level ab initio quantum chemical calculations.
• Synthesis and characterization of [HoIII L1 L2] complexes with varying L2 ligands (F- or MeCN).

Main Results:

• Pseudo-4-fold symmetry in [HoIII L1 F] creates strong axial anisotropy and an mJ = ±8 ground-state quasi-doublet.
• A giant 116.4 ± 1.0 GHz clock transition was observed in the fluoride complex.
• Replacing F- with MeCN (in [HoIII L1 MeCN]) increased the clock transition frequency by a factor of 2.2.

Conclusions:

• Crystal field engineering offers a route to tune clock transition frequencies in molecular qubits.
• Increased clock transition frequency enhances coherence by reducing sensitivity to magnetic noise.
• These findings pave the way for developing robust molecular qubits for quantum technologies.