Nano-Optics, sometimes also called nanophotonics, aims to understand and tame the interaction of light and matter at the nanometer scale. The field, as such, emerged at about the same time as Nano Letters in the wake of the rapidly flourishing activities in nanoscience and nanotechnology. While in the year 1995 the term “nano-optics” (N-O) would have been considered an oxymoron,(1) by the year 2000, the terminology had found its way to the description of conference topics(2,3) and shortly after to the title of textbooks.(4) I first heard the word “nano-optics” in 1996 from Prof. Franz Aussenegg of University of Graz in Austria. At the end of that year, we used this term to name our new group at the University of Konstanz in Germany because it captured a wide range of science that we had in mind. Since then, N-O has become an overarching research field that unites scientists from very different academic areas such as molecular spectroscopy, semiconductor physics, quantum optics, physical chemistry, biophysics, material science, and engineering. The story of this vibrant field is nicely captured in a series of interviews with pioneers from various areas from which N-O evolved, such as scanning near-field optical microscopy, single-molecule spectroscopy, high-resolution microscopy, photonic crystals, plasmonics, semiconductor quantum physics, and quantum optics.(5) The videos were recorded at a workshop that celebrated 20 years of N-O in 2017.(6) The origins and properties of light and matter have fascinated human beings for thousands of years, and although we believe to understand their underlying physics in the post quantum physics era of the 21st century, there remain many fundamental questions and even more technological challenges ahead. One of the central difficulties of N-O in dealing with light is the richness of Maxwell’s equations. Although simple to formulate and despite the impressive progress of numerical packages for solving these three-dimensional vectorial partial differential equations, handling light fields in complex nanoscopic geometries remains nontrivial. In the future, these electromagnetic calculations will also be coupled to theoretical techniques from quantum chemistry and solid-state physics to help us understand, model, and design novel light and matter interactions at the nanoscale. The central challenge of N-O from the materials side is the defect-free fabrication and structuring of matter with atomic control, somewhat along the lines of what Richard Feynman dreamt about in his famous 1959 speech.(7) Furthermore, arrangements of hybrid materials, e.g., on a chip, would be required in order to optimally exploit the electronic, spin, and mechanical degrees of freedom for achieving different functionalities. These developments would allow us to control bulk parameters such as the dielectric function (ε) and magnetic permeability (μ) at the level of their quantum mechanical graininess, which becomes important at very small scales and at interfaces. Although phenomena such as quantum confinement and tunneling are already exploited in everyday devices, general access and control of quantum features such as coherence and entanglement remain elusive, especially in the condensed phase. Higher degrees of control over quantum emitters such as molecules, color centers, ions, or semiconductor nanostructures will make it possible to create quantum metamaterials, in which individual unit cells consist of single quantum emitters (see Figure 1a), but now in arrangements that do not appear in nature.(8) Figure 1. Sketches of some nano-optical future scenarios. (a) Man-made three-dimensional arrangements of natural quantum emitters: h and Λ could cover distances ranging from atomic to supra-wavelength scales. The lines connecting individual emitters indicate phononic or photonic interactions. (b) Controlled hybridization of many photons and quantum emitters. (c) Quantum engineered states of light. The spring-like structures indicate entanglement or quantum correlations. (d) A nanophotonic circuit made of subwavelength waveguides, quantum emitters, microresonators, and nanoantennas. (e) Efficient interaction of a photon with a protein. Indeed, one of the most fruitful areas of N-O has been the realization of single-photon sources based on single quantum emitters,(9) recently also extended to new two-dimensional materials.(10) Controlled fabrication of many individual emitters and their efficient coupling to photonic modes via optical antennas(11) will allow us to sculpt light with single-photon precision and thus tune its properties such as the number of photons, polarization state, or angular momentum (see Figure 1b).(12) The combination of such “nano-light” with quantum tailor-made matter will open the door to the realization of novel hybrid states of light and matter (see Figure 1c).(13,14) Furthermore, a controlled number of single-emitter transistors and memories will be connected and actuated via linear and nonlinear interactions mediated by subwavelength waveguides, microresonators, and nanoantennas to realize integrated quantum optical nanocircuits (see Figure 1d).(15) These endeavors will inevitably also demand a better understanding of the phononic couplings of quantum emitters with their environment. Paramount to the future of N-O is the efficiency of interaction between individual photons and quantum emitters. Recent progress has demonstrated that the fundamental optical cross section of matter is sufficiently large to allow visualization of single dye molecules and proteins via interferometric detection of Rayleigh scattering, or otherwise-stated extinction measurements.(16,17) Further enhancement of this exquisite sensitivity in optical detection will allow optical measurements to detect nano-objects at the single-digit kDa level in a label-free fashion (see Figure 1e). Access to better detectors and cameras (critical features: spectral range, sensitivity, dynamic range, speed, affordability) as well as light sources (critical features: spectral range, temporal bandwidth, frequency bandwidth, power, compactness, affordability) will usher in sensitive spectroscopy beyond the visible range and allow us to record absorption and vibrational spectra of the nanomatter. These developments will further advance the ongoing revolution in optical microscopy to imaging modalities with higher spatial and temporal resolution as well as new fluorescence-free contrast mechanisms.(18) The combination of spectroscopy and microscopy holds enormous promise for applications in biomedicine, astrochemistry, and environmental science, among others. Although these applications do not necessarily involve quantum phenomena, they all aspire to analyze matter with atomic and molecular sensitivity. A crucial future challenge for reaching the above-mentioned goals will be an efficient implementation of the already existing physical concepts into more complex architectures, be it quantum or classical. Indeed, a great many of the recent breakthroughs in N-O have resulted from the combinations of well-known light phenomena such as interference, diffraction, polarization, and angular momentum with available material features such as dispersion, morphology, and chirality.

While the development of N-O over the past 20 years presents a true success story in interdisciplinarity, progress in the next 20 years will require a still much more cohesive and well-informed effort to ensure optimal use of the existing expertise and to avoid unnecessary reinventions of concepts known in other disciplines.

To achieve this, I propose new university study and research programs in photonic engineering and quantum engineering as umbrella structures for pulling together and hosting experimental and theoretical competences from solid-state physics, quantum optics, chemistry, material science, and biophysics. We can be sure that such an extensive and inclusive undertaking will turn many isolated nanophenomena into monumental scientific and technological breakthroughs. While the development of N-O over the past 20 years presents a true success story in interdisciplinarity, progress in the next 20 years will require a still much more cohesive and well-informed effort to ensure optimal use of the existing expertise and to avoid unnecessary reinventions of concepts known in other disciplines. The author declares no competing financial interest. I am grateful to the Max Planck Society for generous support of our research activities. This article references 18 other publications. How could light, which is diffraction limited to about 0.5 μm, be “nano”?

中文翻译：

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2020年的纳米光学±20。

纳米光学有时也称为纳米光子学，旨在理解和驯服纳米尺度的光与物质的相互作用。如此，该领域与纳米字母同时出现随着纳米科学和纳米技术的迅猛发展。1995年，术语“纳米光学”（NO）曾被认为是一种矛盾现象，（1）到2000年，该术语已用于描述会议主题（2,3），此后不久（4）我是1996年从奥地利格拉茨大学的弗朗兹·奥斯森格教授那里首次听到“纳米光学”一词的。那年年底，我们用这个术语来命名我们在德国康斯坦茨大学的新小组，因为它涵盖了我们所考虑的广泛科学领域。从那时起，NO成为一个综合的研究领域，它将来自非常不同的学术领域的科学家团结在一起，例如分子光谱学，半导体物理学，量子光学，物理化学，生物物理学，材料科学和工程学。在来自NO演变的各个领域的先驱者进行的一系列采访中，很好地捕捉了这个充满生机领域的故事，例如扫描近场光学显微镜，单分子光谱，高分辨率显微镜，光子晶体，等离子体，半导体量子物理和量子光学。（5）这些视频是在2017年庆祝20周年纪念的研讨会上录制的。（6）光和物质的起源和性质使人类着迷了数千年，尽管我们相信了解21世纪后量子物理学时代的基础物理学，仍然存在许多基本问题，甚至还有更多技术挑战。NO处理光线的主要困难之一是 单分子光谱学，高分辨率显微镜，光子晶体，等离子体，半导体量子物理学和量子光学。（5）该视频是在2017年庆祝20周年的研讨会上录制的。（6）光和物质已经使人类着迷了数千年，尽管我们相信了解21世纪后量子物理学时代的人类基础物理学，但仍然存在许多基本问题，甚至还有更多技术挑战。NO处理光线的主要困难之一是 单分子光谱学，高分辨率显微镜，光子晶体，等离子体，半导体量子物理学和量子光学。（5）该视频是在2017年庆祝20周年的研讨会上录制的。（6）光和物质已经使人类着迷了数千年，尽管我们相信了解21世纪后量子物理学时代的人类基础物理学，但仍然存在许多基本问题，甚至还有更多技术挑战。NO处理光线的主要困难之一是 （6）光和物质的起源和性质使人类着迷了数千年，尽管我们相信了解21世纪后量子物理学时代的基本物理学，但仍然存在许多基本问题，甚至还有更多技术挑战先。NO处理光线的主要困难之一是 （6）光和物质的起源和性质使人类着迷了数千年，尽管我们相信了解21世纪后量子物理学时代的基本物理学，但仍然存在许多基本问题，甚至还有更多技术挑战先。NO处理光线的主要困难之一是麦克斯韦方程的丰富性。尽管公式简单，尽管用于解决这些三维矢量偏微分方程的数值软件包取得了令人瞩目的进步，但在复杂的纳米几何中处理光场仍然是不平凡的。将来，这些电磁计算还将与量子化学和固态物理学的理论技术相结合，以帮助我们理解，建模和设计纳米级的新型光和物质相互作用。从材料方面来看，NO的主要挑战是采用原子控制的无缺陷制造和结构化，这有点类似于理查德·费曼（Richard Feynman）在1959年发表的著名演讲中所梦dream以求的路线。（7）此外，将需要混合材料（例如在芯片上）的排列，以便最佳地利用电子，自旋和机械度。实现不同功能的自由。这些发展将使我们能够在其量子力学粒度上控制整体参数，例如介电函数（ε）和磁导率（μ），这在非常小的规模和界面上变得非常重要。尽管在日常设备中已经利用了诸如量子限制和隧穿之类的现象，但是对量子特征（如相干和纠缠）的一般访问和控制仍然难以捉摸，尤其是在凝聚阶段。对量子发射器（例如分子，量子超材料，其中单个晶胞由单个量子发射器组成（请参见图1a），但现在其排列方式在自然界中是不存在的。（8）图1.一些纳米光学未来场景的草图。（a）天然量子发射器的人造三维排列：h和Λ可以覆盖从原子到超波长范围的距离。连接各个发射器的线表示声子或光子相互作用。（b）许多光子和量子发射器的受控杂交。（c）量子工程光。弹簧状结构表示纠缠或量子相关性。（d）由亚波长波导，量子发射器，微谐振器和纳米天线构成的纳米光子电路。（e）光子与蛋白质的有效相互作用。的确，一氧化氮最富有成果的领域之一是基于单量子发射器的单光子源的实现，（9）最近还扩展到了新的二维材料。（10）许多单个发射器的受控制造及其高效通过光学天线耦合到光子模式（11）将使我们能够以单光子精度雕刻光，从而调整其特性，例如光子数，偏振态或角动量（请参见图1b）。（12）这种“纳米光”与量子定制物质的结合将为实现光和物质的新型混合态打开了大门（见图1c）。（13,14）此外，通过亚波长介导的线性和非线性相互作用，将连接并控制一定数量的单发射极晶体管和存储器。波导，微谐振器和纳米天线，以实现集成的量子光学纳米电路（参见图1d）。（15）这些努力不可避免地也需要更好地理解量子发射器与其环境之间的声子耦合。。NO的未来最重要的是各个光子与量子发射器之间相互作用的效率。最近的进展已经表明，物质的基本光学截面是足够大以允许通过瑞利散射，或以其它方式态消光测量的干涉检测单个染料分子和蛋白质的可视化。（16,17）这进一步增强精美灵敏度在光学检测它将允许光学测量以无标签的方式检测单位kDa级别的纳米物体（参见图1e）。使用更好的检测器和摄像机（关键特性：光谱范围，灵敏度，动态范围，速度，可承受性）以及光源（关键特性：光谱范围，时间带宽，频率带宽，功率，紧凑性，可承受性）将带来敏感光谱超出可见光范围，使我们能够记录纳米物质的吸收光谱和振动光谱。这些发展将进一步推动正在进行中的光学显微镜革命（18）光谱学和显微术的结合为生物医学，天体化学和环境科学等方面的应用提供了广阔的前景。尽管这些应用程序不一定涉及量子现象，但它们都渴望以原子和分子敏感性来分析物质。为了实现上述目标，未来面临的关键挑战将是将已经存在的物理概念有效地实施到更复杂的体系结构中，无论是量子体系还是经典体系。的确，NO的许多最新突破都是由众所周知的光现象（例如干涉，衍射，偏振和角动量）与可用的材料特征（例如色散，形态和手性）的组合产生的。

尽管过去20年中NO的发展代表了跨学科的成功案例，但未来20年的进步将需要更加凝聚和灵通的努力，以确保最佳地利用现有专业知识并避免不必要的创新其他学科中已知的概念。

为此，我提出了新的大学研究计划，将光子工程和量子工程作为伞形结构，以汇集并容纳来自固态物理学，量子光学，化学，材料科学和生物物理学的实验和理论能力。我们可以肯定，如此广泛和包容的工作将把许多孤立的纳米现象变成重大的科学和技术突破。虽然过去20年中NO的发展代表了跨学科的成功案例，但未来20年的进步仍需要更加凝聚和灵通的努力，以确保最佳地利用现有专业知识并避免不必要的创新其他学科中已知的概念。作者声明没有竞争性的经济利益。感谢马克斯·普朗克学会对我们的研究活动的大力支持。本文引用了其他18个出版物。衍射限制在约0.5μm的光怎么会变成“纳米”？