26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

An Eigenstate Solution for Crystal Field Modelling of Ytterbium Ions

Not scheduled

20m

Belinda Hutchinson Building (The University of Sydney )

Contributed Oral AIP | Quantum Science and Technology (QST)

Speaker

Mr Lasse Sweetland (University of Sydney)

Description

In the global research effort to construct quantum devices, networked devices via distributed entanglement are emerging as a promising method of addressing the problem of scaling up quantum technologies. Rare-earth ions embedded in crystalline hosts are a leading hardware platform for implementing quantum networks, compatible with both microwave-domain quantum computers and the optical links used in the modern internet. Recent demonstrations indicate the long optical and spin transition coherence times in rare-earth ions result in state-of-the-art quantum networking performance (Ruskuc et al., Nature, 639, 2025).

While interactions between rare-earth ions and their crystalline hosts is of fundamental relevance, they are generally poorly understood. The precise nature of these interactions is unclear, ab initio calculations have not yet reached sufficient accuracy, and modelling techniques are phenomenological. This is despite the opportunity to dramatically enhance rare-earth ion device performance through deliberate crystal field design.

Amongst rare-earth ions, ytterbium-based systems such as Yb$^{3+}$:YVO$_4$ are increasingly significant within quantum information research. However, ytterbium systems often defy standard crystal field modelling techniques; the relative simplicity of the Yb$^{3+}$ $4f$ configuration provides insufficient data to reliably fit phenomenological parameters, and strong coupling to phonons hinders interpretation of spectra. We present a new method for approaching ytterbium crystal field analysis, based on Zeeman interaction measurements. Through a set of projection operations, we identify crystal field eigenstates and define a system of equations to calculate crystal field parameters.

Our results solve an important outstanding problem in solid-state rare-earth ion physics. We apply our method to the electronic structure of Yb$^{3+}$:YVO$_4$, improving the model accuracy by two orders of magnitude compared to previous literature. We also apply this model to other outstanding challenges: describing variations and correlations between inhomogeneously broadened transition frequencies, symmetry-lowering phenomena via perturbative treatments, and extensions to other systems such as Yb$^{3+}$:CaWO$_4$.