连续谱中的双光子束缚态：一个禁则定理与长寿命准束缚态
Two-Photon Bound States in the Continuum: A No-Go Theorem and Long-Lived Quasi-Bound States
AI总结：
该研究证明了双光子束缚态的禁则定理，发现长寿命双光子准束缚态仍可实现，明确了精确多光子限域极限并为工程化长寿命少光子态提供了途径。
AI中文摘要：
连续谱中的双光子束缚态提供了一个严格的场景，在该场景中，尽管存在光子-光子相互作用，量子干涉仍必须抑制辐射衰减。在此，我们证明了一个禁则定理：若局部谱密度仅在孤立能量处消失，则与无相互作用玻色型连续谱线性耦合的单个非线性模式无法支持相互作用活性型双光子束缚态。除该正则条件外，该结果与连续谱色散及频率相关耦合无关。尽管此类精确束缚态被禁止，但长寿命双光子准束缚态仍可能存在。对于非局域耦合到波导的巨克尔腔，我们推导了双光子衰减率随耦合点间距从弱非线性到硬核极限的渐近标度关系。我们进一步确定了双光子共振寿命显著长于单光子激发的区域。本研究明确了精确多光子限域的极限，同时为工程化长寿命相互作用少光子态开辟了途径。
英文摘要：
Two-photon bound states in the continuum provide a stringent setting in which quantum interference must suppress radiative decay despite photon--photon interactions. Here, we prove a no-go theorem showing that a single nonlinear mode linearly coupled to a noninteracting bosonic continuum cannot support an interaction-active two-photon bound state in the continuum, provided the local spectral density vanishes only at isolated energies. Apart from this regularity condition, the result is independent of the continuum dispersion and the frequency-dependent coupling. Although such an exact bound state is forbidden, long-lived two-photon quasi-bound states remain possible. For a giant Kerr cavity nonlocally coupled to a waveguide, we derive the asymptotic scaling of the two-photon decay rate with the coupling-point separation from weak nonlinearity to the hard-core limit. We further identify a regime in which the two-photon resonance is substantially longer lived than the single-photon excitation. Our work establishes the limits of exact multiphoton confinement while opening a route to engineering long-lived interacting few-photon states.
