Experiments on quantum materials have uncovered many interesting quantum phases ranging from superconductivity to a variety of topological quantum matter including the recently observed fractional quantum anomalous Hall insulators. The findings have come in parallel with the development of approaches to probe the rich excitations inherent in such systems. In contrast to observing electrically charged excitations, the detection of charge-neutral electronic excitations in condensed matter remains difficult, although they are essential to understanding a large class of strongly correlated phases. Low-energy neutral excitations are especially important in characterizing unconventional phases featuring electron fractionalization, such as quantum spin liquids, spin ices and insulators with neutral Fermi surfaces. In this Perspective, we discuss searches for neutral fermionic, bosonic or anyonic excitations in unconventional insulators, highlighting theoretical and experimental progress in probing excitonic insulators, new quantum spin liquid candidates and emergent correlated insulators based on two-dimensional layered crystals and moiré materials. We outline the promises and challenges in probing and using quantum insulators, and discuss exciting new opportunities for future advancements offered by ideas rooted in next-generation quantum materials, devices and experimental schemes.

对量子材料的实验发现了许多有趣的量子相，从超导性到各种拓扑量子物质，包括最近观察到的分数量子异常霍尔绝缘体。这些发现与探测此类系统中固有的丰富激发的方法的发展并行。与观察带电激发相比，检测凝聚态物质中的电荷中性电子激发仍然很困难，尽管它们对于理解一大类强相关相至关重要。低能中性激发在表征具有电子分馏的非常规相时尤为重要，例如量子自旋液体、自旋冰和具有中性费米表面的绝缘体。在这个视角中，我们讨论了在非常规绝缘子中寻找中性费米子、玻色子或任意子激发，强调了探测激子绝缘子、新的量子自旋候选液体和基于二维层状晶体和莫尔材料的新兴相关绝缘子的理论和实验进展。我们概述了探测和使用量子绝缘体的前景和挑战，并讨论了植根于下一代量子材料、设备和实验方案的思想为未来进步提供的令人兴奋的新机会。