Optical nanoantennas can convert propagating light to local fields. The local-field responses can be engineered to exhibit nontrivial features in spatial, spectral and temporal domains, where local-field interferences play a key role. Here, we design nearly fully controllable local-field interferences in the nanogap of a nanoantenna, and experimentally demonstrate that in the nanogap, the spectral dispersion of the local-field response can exhibit tuneable Fano lineshapes with nearly vanishing Fano dips. A single quantum dot is precisely positioned in the nanogap to probe the spectral dispersions of the local-field responses. By controlling the excitation polarization, the asymmetry parameter q of the probed Fano lineshapes can be tuned from negative to positive values, and correspondingly, the Fano dips can be tuned across a broad spectral range. Notably, at the Fano dips, the local-field intensity is strongly suppressed by up to ~50-fold, implying that the hot spot in the nanogap can be turned into a cold spot. The results may inspire diverse designs of local-field responses with novel spatial distributions, spectral dispersions and temporal dynamics, and expand the available toolbox for nanoscopy, spectroscopy, nano-optical quantum control and nanolithography.

光学纳米天线可以将传播光转换为局部场。局部场响应可以设计为在空间、频谱和时间域中表现出重要的特征，其中局部场干扰起着关键作用。在这里，我们在纳米天线的纳米间隙中设计了几乎完全可控的局域场干扰，并通过实验证明，在纳米间隙中，局域场响应的光谱色散可以表现出可调谐的法诺线形，且法诺倾角几乎消失。单个量子点精确定位在纳米间隙中，以探测局部场响应的光谱色散。通过控制激发偏振，所探测的 Fano 线型的不对称参数q可以从负值调整到正值，相应地，Fano 倾角可以在较宽的光谱范围内调整。值得注意的是，在 Fano 倾角处，局部场强度被强烈抑制高达约 50 倍，这意味着纳米间隙中的热点可以变成冷点。研究结果可能会激发具有新颖空间分布、光谱色散和时间动力学的局部场响应的多种设计，并扩展纳米显微镜、光谱学、纳米光学量子控制和纳米光刻的可用工具箱。