通过量子干涉工程一个连续谱中的束缚态
Engineering a Bound State in the Continuum via Quantum Interference
AI总结：
通过量子干涉工程实现超冷原子碰撞中连续谱中的束缚态，揭示了非厄米特哈密顿量的调控机制。
摘要：
量子力学相互作用势通常支持在解离阈值以下的局域化束缚态或在以上处的非局域化散射态。虽然束缚态在能量上是孤立的，散射态将量子系统嵌入环境模式的连续体中，使耗散和损失成为开放量子系统的固有特征。一个显著的例外是连续谱中的束缚态（BICs），它们尽管位于散射连续体中，仍能保持局域化，这是由于破坏性干涉。曾预测这样的状态可以由两个连接到共同连续体的费舍巴赫共振的干涉产生，但这种机制在真正的量子系统中仍无法实验验证。在此，我们通过利用Floquet工程相干耦合两个可调费舍巴赫共振，在超冷${}^6$Li原子碰撞中展示了这种干涉稳定态的形成。在临界参数点，弹性与非弹性耦合到连续体均消失，产生一个位于解离阈值以上的分子态。损失光谱、淬火动力学和rf-光关联直接揭示了由此产生的与散射态的解耦。我们的观测被完整的耦合通道计算和一个最小的非厄米特模型定量捕捉，识别出一个弗里德里希-文廷格BIC。我们的结果确立了量子干涉作为控制量子物质开放性的强大机制，以及工程非厄米特哈密顿量的手段。
英文摘要：
Quantum mechanical interaction potentials typically support either localized bound states below the dissociation threshold or delocalized scattering states above it. While bound states are energetically isolated, scattering states embed a quantum system in a continuum of environmental modes, making dissipation and loss intrisic features of open quantum systems. A striking exception are bound states in the continuum (BICs), which remain localized despite lying within the scattering continuum due to destructive interference. It was predicted that such states can arise from the interference of two Feshbach resonances coupled to a common continuum, yet this mechanism has remained experimentally inaccessible in genuine quantum systems. Here we demonstrate the formation of such an interference-stabilized state in ultracold collisions of ${}^6$Li atoms by coherently coupling two tunable Feshbach resonances using Floquet engineering. At a critical parameter point, both elastic and inelastic coupling to the continuum vanish, yielding a molecular state above the dissociation threshold. Loss spectroscopy, quench dynamics, and rf-photoassociation directly reveal the resulting decoupling from scattering states. Our observations are quantitatively captured by full coupled-channel calculations and a minimal non-Hermitian model, identifying a Friedrich-Wintgen BIC. Our results establish quantum interference as a powerful mechanism for controlling openness in quantum matter and for engineering non-Hermitian Hamiltonians.
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