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<p>Phase transitions can dramatically alter system dynamics, potentially improving device performance. Exceptional points, in which the eigenvalues and corresponding eigenvectors of a coupled linear system coalesce, are particularly relevant for sensing applications because they can increase sensor response to external perturbations. However, the coalescence of eigenstates at linear exceptional points amplifies noise, negating the signal-to-noise-ratio enhancement. Here we overcame this limitation using nonlinearity that produces an exceptionally high signal-to-noise ratio around a bistable transition point. We coupled a diamond nitrogen-vacancy quantum sensor to a nonlinear van der Pol oscillator, forming a self-oscillating hybrid system that exhibits both single-valued and bistable phases. The boundaries between these phases are marked by both adiabatic and deterministic non-adiabatic transitions that enable chiral state switching and state coalescence at the bistable transition point. Nitrogen-vacancy magnetometry performed near the bistable transition point exhibited a 17-fold enhancement in the signal-to-noise ratio. The demonstrated sensitivity surpassed the limit of an ideal bare electron magnetometer and resolved a long-standing debate regarding exceptional-point-like physics in advanced quantum sensing.</p>

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Exceptional sensitivity near the bistable transition point of a hybrid quantum system

  • 期刊论文

  • 发表日期：

    2026年3月20日

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  • Hanfeng Wang,
  • Kurt Jacobs,
  • Donald Fahey,
  • Yong Hu,
  • Dirk R. Englund,
  • Matthew E. Trusheim

摘要

Phase transitions can dramatically alter system dynamics, potentially improving device performance. Exceptional points, in which the eigenvalues and corresponding eigenvectors of a coupled linear system coalesce, are particularly relevant for sensing applications because they can increase sensor response to external perturbations. However, the coalescence of eigenstates at linear exceptional points amplifies noise, negating the signal-to-noise-ratio enhancement. Here we overcame this limitation using nonlinearity that produces an exceptionally high signal-to-noise ratio around a bistable transition point. We coupled a diamond nitrogen-vacancy quantum sensor to a nonlinear van der Pol oscillator, forming a self-oscillating hybrid system that exhibits both single-valued and bistable phases. The boundaries between these phases are marked by both adiabatic and deterministic non-adiabatic transitions that enable chiral state switching and state coalescence at the bistable transition point. Nitrogen-vacancy magnetometry performed near the bistable transition point exhibited a 17-fold enhancement in the signal-to-noise ratio. The demonstrated sensitivity surpassed the limit of an ideal bare electron magnetometer and resolved a long-standing debate regarding exceptional-point-like physics in advanced quantum sensing.