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<p>Complex-frequency excitation controls non-Hermitian light-matter interactions by temporally shaping signals to bypass inherent material gain or loss constraints. While virtual loss has enabled coherent perfect absorption, its time-reversed counterpart: virtual gain, remains less explored in optical systems. Here, we theoretically and experimentally demonstrate lasing-like dynamics in a passive whispering-gallery-mode microcavity using complex-frequency excitations. Virtual gain counteracts intrinsic material and radiation losses, producing an instantaneous transmittance that exceeds unity and saturates at a quasi-steady value. Beyond a critical threshold-like point, the system enters a regime of divergent, exponentially growing response, mimicking the transient buildup of a real laser without requiring population inversion or active media. This linear effect allows for the robust coexistence of lasing-like behavior and perfect absorption, with transitions controlled by virtual gain tuning. These results establish a versatile framework for manipulating non-Hermitian interactions in passive platforms, offering remarkable potential for applications in sensing, optical communications, and energy storage.</p>

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Lasing-like dynamics with virtual gain driven by complex-frequency excitations

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年3月3日

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  • Boyi Xue,
  • Ruixiang Zhang,
  • Yicheng Zhu,
  • Yuncong Sun,
  • Xianfeng Chen,
  • Andrea Alù,
  • Wenjie Wan

摘要

Complex-frequency excitation controls non-Hermitian light-matter interactions by temporally shaping signals to bypass inherent material gain or loss constraints. While virtual loss has enabled coherent perfect absorption, its time-reversed counterpart: virtual gain, remains less explored in optical systems. Here, we theoretically and experimentally demonstrate lasing-like dynamics in a passive whispering-gallery-mode microcavity using complex-frequency excitations. Virtual gain counteracts intrinsic material and radiation losses, producing an instantaneous transmittance that exceeds unity and saturates at a quasi-steady value. Beyond a critical threshold-like point, the system enters a regime of divergent, exponentially growing response, mimicking the transient buildup of a real laser without requiring population inversion or active media. This linear effect allows for the robust coexistence of lasing-like behavior and perfect absorption, with transitions controlled by virtual gain tuning. These results establish a versatile framework for manipulating non-Hermitian interactions in passive platforms, offering remarkable potential for applications in sensing, optical communications, and energy storage.