Department of Electrical and Computer Engineering, University of California San Diego, La Jolla, California 92093-0407, USA.
Nature. 2017 Jan 11;541(7636):196-199. doi: 10.1038/nature20799.
In 1929, only three years after the advent of quantum mechanics, von Neumann and Wigner showed that Schrödinger's equation can have bound states above the continuum threshold. These peculiar states, called bound states in the continuum (BICs), manifest themselves as resonances that do not decay. For several decades afterwards the idea lay dormant, regarded primarily as a mathematical curiosity. In 1977, Herrick and Stillinger revived interest in BICs when they suggested that BICs could be observed in semiconductor superlattices. BICs arise naturally from Feshbach's quantum mechanical theory of resonances, as explained by Friedrich and Wintgen, and are thus more physical than initially realized. Recently, it was realized that BICs are intrinsically a wave phenomenon and are thus not restricted to the realm of quantum mechanics. They have since been shown to occur in many different fields of wave physics including acoustics, microwaves and nanophotonics. However, experimental observations of BICs have been limited to passive systems and the realization of BIC lasers has remained elusive. Here we report, at room temperature, lasing action from an optically pumped BIC cavity. Our results show that the lasing wavelength of the fabricated BIC cavities, each made of an array of cylindrical nanoresonators suspended in air, scales with the radii of the nanoresonators according to the theoretical prediction for the BIC mode. Moreover, lasing action from the designed BIC cavity persists even after scaling down the array to as few as 8-by-8 nanoresonators. BIC lasers open up new avenues in the study of light-matter interaction because they are intrinsically connected to topological charges and represent natural vector beam sources (that is, there are several possible beam shapes), which are highly sought after in the fields of optical trapping, biological sensing and quantum information.
1929 年，即量子力学出现仅三年后，冯·诺依曼（von Neumann）和维格纳（Wigner）就证明了薛定谔方程在连续统阈之上可以具有束缚态。这些奇特的状态，称为连续统中的束缚态（BIC），表现为不衰减的共振。此后的几十年里，这个想法一直处于休眠状态，主要被视为一种数学上的好奇心。1977 年，赫尔里克（Herrick）和斯蒂林格（Stillinger）在建议 BIC 可以在半导体超晶格中观察到时，重新引起了人们对 BIC 的兴趣。BIC 自然地源自 Feshbach 的共振量子力学理论，正如 Friedrich 和 Wintgen 所解释的那样，因此比最初意识到的更具物理意义。最近，人们意识到 BIC 本质上是一种波动现象，因此不受量子力学领域的限制。此后，它们已被证明出现在包括声学、微波和纳米光子学在内的许多不同的波动物理领域。然而，BIC 的实验观测一直局限于被动系统，并且 BIC 激光器的实现仍然难以捉摸。在这里，我们在室温下报告了从光泵浦 BIC 腔中产生激光的情况。我们的结果表明，所制造的 BIC 腔的激光波长，每个腔都是由悬浮在空气中的圆柱形纳米谐振器阵列制成，根据 BIC 模式的理论预测，与纳米谐振器的半径成比例。此外，即使将阵列缩小到只有 8×8 个纳米谐振器，设计的 BIC 腔的激光作用也仍然存在。BIC 激光器为光与物质相互作用的研究开辟了新途径，因为它们与拓扑电荷内在相关，并且代表了自然的矢量光束源（即，存在几种可能的光束形状），在光学捕获、生物传感和量子信息等领域受到高度追捧。
