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<p>The degeneracy of two or more energy bands at a singular point in the band structure, such as a Dirac point, gives rise to intriguing quantum phenomena as well as unusual material properties. Systems at the Dirac points can possess topological charges and their unique properties can be probed by various methods, such as transport measurement, interferometry and momentum spectroscopy. While the topology of Dirac point in the momentum space is well studied theoretically, observation of topological defects in a many-body quantum system at Dirac point remains an elusive goal. Based on atomic Bose–Einstein condensate in a graphene-like optical honeycomb lattice, we directly observe emergence of quantized vortices induced by the non-commutativity between the harmonic trap and the pseudo-spin–orbit coupling at the Dirac point. By adiabatic control of the honeycomb lattice with an additional harmonic trapping potential, the phase diagram of lattice bosons at the Dirac point is revealed. Our work provides a new way of generating vortices in a quantum gas, and the method is generic and can be applied to different types of optical lattices with topological singularities, including topological flat bands near Dirac points in twisted bilayer optical lattices.</p>

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Observation of quantized vortex in atomic Bose–Einstein condensate at Dirac point with emergent spin–orbit coupling

  • 期刊论文

  • 发表日期：

    2025年9月29日

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  • Yunda Li,
  • Wei Han,
  • Zengming Meng,
  • Wenxin Yang,
  • Cheng Chin,
  • Jing Zhang

摘要

The degeneracy of two or more energy bands at a singular point in the band structure, such as a Dirac point, gives rise to intriguing quantum phenomena as well as unusual material properties. Systems at the Dirac points can possess topological charges and their unique properties can be probed by various methods, such as transport measurement, interferometry and momentum spectroscopy. While the topology of Dirac point in the momentum space is well studied theoretically, observation of topological defects in a many-body quantum system at Dirac point remains an elusive goal. Based on atomic Bose–Einstein condensate in a graphene-like optical honeycomb lattice, we directly observe emergence of quantized vortices induced by the non-commutativity between the harmonic trap and the pseudo-spin–orbit coupling at the Dirac point. By adiabatic control of the honeycomb lattice with an additional harmonic trapping potential, the phase diagram of lattice bosons at the Dirac point is revealed. Our work provides a new way of generating vortices in a quantum gas, and the method is generic and can be applied to different types of optical lattices with topological singularities, including topological flat bands near Dirac points in twisted bilayer optical lattices.