Exotic physics could emerge from interplay between geometry and correlation. In fractional quantum Hall (FQH) states¹, novel collective excitations called chiral graviton modes (CGMs) are proposed as quanta of fluctuations of an internal quantum metric under a quantum geometry description^2,3,4,5. Such modes are condensed-matter analogues of gravitons that are hypothetical spin-2 bosons. They are characterized by polarized states with chirality^6,7,8 of +2 or −2, and energy gaps coinciding with the fundamental neutral collective excitations (namely, magnetorotons^9,10) in the long-wavelength limit. However, CGMs remain experimentally inaccessible. Here we observe chiral spin-2 long-wavelength magnetorotons using inelastic scattering of circularly polarized lights, providing strong evidence for CGMs in FQH liquids. At filling factor v = 1/3, a gapped mode identified as the long-wavelength magnetoroton emerges under a specific polarization scheme corresponding to angular momentum S = −2, which persists at extremely long wavelength. Remarkably, the mode chirality remains −2 at v = 2/5 but becomes the opposite at v = 2/3 and 3/5. The modes have characteristic energies and sharp peaks with marked temperature and filling-factor dependence, corroborating the assignment of long-wavelength magnetorotons. The observations capture the essentials of CGMs and support the FQH geometrical description, paving the way to unveil rich physics of quantum metric effects in topological correlated systems.

几何学和相关性之间的相互作用可能会产生奇异的物理学。在分数量子霍尔（FQH）态¹中，称为手性引力子模式（CGM）的新型集体激发被提议作为量子几何描述下的内部量子度量的涨落量子^2,3,4,5。这种模式是引力子的凝聚态类似物，即假设的自旋 2 玻色子。它们的特征是具有+2或-2的手性^6,7,8的极化态，以及在长波长极限内与基本中性集体激发（即磁旋子^9,10 ）一致的能隙。然而，CGM 在实验上仍然无法实现。在这里，我们利用圆偏振光的非弹性散射观察了手性自旋 2 长波长磁旋子，为 FQH 液体中的 CGM 提供了强有力的证据。在填充因子v = 1/3 时，在对应于角动量S = -2 的特定偏振方案下出现了被识别为长波长磁旋子的间隙模式 ，该模式在极长波长下持续存在。值得注意的是，模式手性在v = 2/5 时保持为 -2，但在v = 2/3 和 3/5 时变为相反 。这些模式具有特征能量和尖锐的峰值，具有明显的温度和填充因子依赖性，证实了长波长磁转子的分配。这些观察结果捕获了 CGM 的本质并支持 FQH 几何描述，为揭示拓扑相关系统中量子度量效应的丰富物理特性铺平了道路。