We study nonlinear response in quantum spin systems near infinite-randomness critical points. Nonlinear dynamical probes, such as two-dimensional (2D) coherent spectroscopy, can diagnose the nearly localized character of excitations in such systems. We present exact results for nonlinear response in the 1D random transverse-field Ising model, from which we extract information about critical behavior that is absent in linear response. Our analysis yields exact scaling forms for the distribution functions of relaxation times that result from realistic channels for dissipation in random magnets. We argue that our results capture the scaling of relaxation times and nonlinear response in generic random quantum magnets in any spatial dimension.

中文翻译：

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随机量子磁体非线性光谱的渐近精确理论

我们研究了在无限随机临界点附近的量子自旋系统中的非线性响应。非线性动态探针（例如二维（2D）相干光谱）可以诊断此类系统中激发的近乎局部性。我们在1D随机横向场Ising模型中给出非线性响应的精确结果，从中我们提取有关线性响应中不存在的关键行为的信息。我们的分析得出了弛豫时间分布函数的精确缩放形式，这是由随机磁体中的实际耗散通道所产生的。我们认为，我们的结果捕获了任何空间维度上通用随机量子磁体中弛豫时间的比例和非线性响应。