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<p>Single atomic adsorbates on ultrathin insulating films provide a promising route towards building bottom-up quantum architectures based on atomically identical yet individually addressable spin qubits on solid surfaces. A key challenge in engineering quantum-coherent spin nanostructures lies in understanding and controlling the spin state of individual adsorbates. In this work, we investigate single titanium (Ti) atoms adsorbed on MgO/Ag(100) surfaces using a combined scanning tunneling microscopy and electron spin resonance. Our measurements reveal two distinct spin states, <i>S</i>&#xa0;=&#xa0;1/2 and <i>S</i>&#xa0;=&#xa0;1, depending on the local adsorption site and the thickness of the MgO film. Density functional theory calculations suggest a Ti<sup>+</sup> configuration for the Ti adsorbates with approximately 3 electrons in the 4<i>s</i> and 3<i>d</i> valence shells. Using multi-orbital magnetic multiplet calculations the site dependence of the spin can be rationalized as a charge redistribution between spin-polarizing and depolarizing orbitals. These findings underscore the potential of surface-supported single atoms as spin qubits with tunable spin and charge states, enabling atom-by-atom control in the realization of a versatile quantum platform on surfaces.</p>

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Spin-state engineering of single titanium adsorbates on ultrathin magnesium oxide

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年1月16日

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  • Soo-hyon Phark,
  • Hong Thi Bui,
  • We-hyo Seo,
  • Yaowu Liu,
  • Valeria Sheina,
  • Curie Lee,
  • Christoph Wolf,
  • Andreas J. Heinrich,
  • Roberto Robles,
  • Nicolás Lorente

摘要

Single atomic adsorbates on ultrathin insulating films provide a promising route towards building bottom-up quantum architectures based on atomically identical yet individually addressable spin qubits on solid surfaces. A key challenge in engineering quantum-coherent spin nanostructures lies in understanding and controlling the spin state of individual adsorbates. In this work, we investigate single titanium (Ti) atoms adsorbed on MgO/Ag(100) surfaces using a combined scanning tunneling microscopy and electron spin resonance. Our measurements reveal two distinct spin states, S = 1/2 and S = 1, depending on the local adsorption site and the thickness of the MgO film. Density functional theory calculations suggest a Ti+ configuration for the Ti adsorbates with approximately 3 electrons in the 4s and 3d valence shells. Using multi-orbital magnetic multiplet calculations the site dependence of the spin can be rationalized as a charge redistribution between spin-polarizing and depolarizing orbitals. These findings underscore the potential of surface-supported single atoms as spin qubits with tunable spin and charge states, enabling atom-by-atom control in the realization of a versatile quantum platform on surfaces.