Ab initio crystal field splitting of a molecular rare-earth qubit: Er(hfac)<sub>4</sub>
ORAL
Abstract
Rare-earth ions in solid-state hosts have been leading candidates for quantum information science, due to their naturally shielded multilevel 4f manifolds providing long spin coherence times. In particular, Er dopants in crystals such as Er:Y2SiO5 and Er:YVO4 have demonstrated long optical memories and coherent microwave–optical transduction [1,2,3]. Motivated by the restricted tunability of crystalline hosts, we investigate molecular systems such as Er(hfac)4 (hfa = Hexafluoroacetylacetone), which exhibit crystal fields tunable to engineer energy levels desirable for molecular qubits and quantum transducers [4]. When combined with a theoretical framework capable of accurately predicting crystal-field structures, such systems provide a clear pathway to efficient prediction and tuning of novel qubits.
Building on our previous work [5], we develop an improved ab initio framework for crystal-field extraction in rare-earth systems. Crystal field parameters are obtained from density functional calculations using the electronic potential and 4f orbital densities of the doped system, then diagonalized via the effective Hamiltonian approach [6] to yield the full multi-level structure. Compared to earlier methods, our method improve in utilizing a system-dependent extraction of 4f orbital densities, removing the need for empirical fit parameters, and thus resulting in a tranferable method for a wide range of environments. Our work provides an ab intio framework capable of predicting crystal-field structures across a diverse range of rare-earth ions and molecular environments, and lays the groundwork for designing qubits and quantum transducers that bridge optical and microwave ranges.
[1] X. Fernandez-Gonzalvo et al. Phys. Rev. A 100(3), 033807 (2019).
[2] J. G. Bartholomew et al. Nat. commun. 11(1) 3266 (2020).
[3] T. Xie et al. Nat. Phys. 21, 931-937 (2025).
[4] Weiss, Leah R., et al. Science 390(6768) 76-81 (2025).
[5] Y. Limbu et al. arXiv:2501.03353 (2025).
[6] J.-D. Lizarazo-Ferro et al. arXiv:2503.17377 (2025).
Building on our previous work [5], we develop an improved ab initio framework for crystal-field extraction in rare-earth systems. Crystal field parameters are obtained from density functional calculations using the electronic potential and 4f orbital densities of the doped system, then diagonalized via the effective Hamiltonian approach [6] to yield the full multi-level structure. Compared to earlier methods, our method improve in utilizing a system-dependent extraction of 4f orbital densities, removing the need for empirical fit parameters, and thus resulting in a tranferable method for a wide range of environments. Our work provides an ab intio framework capable of predicting crystal-field structures across a diverse range of rare-earth ions and molecular environments, and lays the groundwork for designing qubits and quantum transducers that bridge optical and microwave ranges.
[1] X. Fernandez-Gonzalvo et al. Phys. Rev. A 100(3), 033807 (2019).
[2] J. G. Bartholomew et al. Nat. commun. 11(1) 3266 (2020).
[3] T. Xie et al. Nat. Phys. 21, 931-937 (2025).
[4] Weiss, Leah R., et al. Science 390(6768) 76-81 (2025).
[5] Y. Limbu et al. arXiv:2501.03353 (2025).
[6] J.-D. Lizarazo-Ferro et al. arXiv:2503.17377 (2025).
*This research was supported as part of the Center for Molecular Quantum Transduction (CMQT), an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Basic Energy Sciences, under Award No. DE-SC0021314.
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Presenters
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Yueguang Shi
- University of Iowa