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<p>Weak transitions between quantum states are of fundamental importance for a broad range of phenomena from analytical biochemistry to precision physics, but generally challenge experimental detection. Due to their small cross sections scaling with the absolute square of their transition matrix elements, spectroscopic measurements often fail in particular in the presence of competing background processes. Here we introduce a general concept to break this scaling law and enhance the transition probability by exploiting a stronger laser-coupled pathway to the same excited state. We demonstrate the concept experimentally by attosecond transient absorption spectroscopy in helium atoms. The quasi-forbidden transitions from the ground state 1<i>s</i><sup>2</sup> to the weakly coupled doubly excited 2<i>p</i>3<i>d</i> and <i>s</i><i>p</i><sub>2,4−</sub> states are boosted by an order of magnitude. Enhancing single-photon-suppressed transitions can find widespread applicability, from spectral diagnostics of complex molecules in life and chemical sciences to precision spectroscopy of weak transitions in metastable atomic nuclei in the search for new physics.</p>

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Bringing weak transitions to light

  • 期刊论文

  • 出版模式：

    开放获取

  • 发表日期：

    2025年6月20日

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  • Yu He,
  • Xiao-Min Tong,
  • Shuyuan Hu,
  • Gergana D. Borisova,
  • Hao Liang,
  • Maximilian Hartmann,
  • Veit Stooß,
  • Chunhai Lyu,
  • Zoltán Harman,
  • Christoph H. Keitel,
  • Kenneth J. Schafer,
  • Mette B. Gaarde,
  • Christian Ott,
  • Thomas Pfeifer

摘要

Weak transitions between quantum states are of fundamental importance for a broad range of phenomena from analytical biochemistry to precision physics, but generally challenge experimental detection. Due to their small cross sections scaling with the absolute square of their transition matrix elements, spectroscopic measurements often fail in particular in the presence of competing background processes. Here we introduce a general concept to break this scaling law and enhance the transition probability by exploiting a stronger laser-coupled pathway to the same excited state. We demonstrate the concept experimentally by attosecond transient absorption spectroscopy in helium atoms. The quasi-forbidden transitions from the ground state 1s2 to the weakly coupled doubly excited 2p3d and sp2,4− states are boosted by an order of magnitude. Enhancing single-photon-suppressed transitions can find widespread applicability, from spectral diagnostics of complex molecules in life and chemical sciences to precision spectroscopy of weak transitions in metastable atomic nuclei in the search for new physics.