标题： 宇宙中微子背景、轴子、暗物质和反应堆中微子的超辐射相互作用 显示英文标题

标题： Superradiant Interactions of the Cosmic Neutrino Background, Axions, Dark Matter, and Reactor Neutrinos

摘要： 本文我们做了三件事。 首先，我们概述了非弹性过程中导致$N$目标系统内部状态改变的相互作用速率按$N^2$比例缩放的条件。这是一种与相干弹性散射不同的效应，但具有相同的尺度。 其次，我们计算了各种弱相互作用粒子的此类过程的速率。 最后，我们指出了这些过程除了能量交换之外的潜在量子可观测量。 当目标处于基态和激发态的叠加态时，非弹性过程中可以实现最大相干性。 这些相干的非弹性过程类似于Dicke超辐射，因此我们将它们称为超辐射相互作用。 我们计算了宇宙中微子背景（C$\nu$B）、暗物质散射和吸收以及晚期宇宙中的粒子（如核磁共振反应堆产生的中微子）的超辐射相互作用速率，此时的两能级系统由磁场中的核自旋或电子自旋构成。 这些速率在宏观上但尺寸较小的目标上可能较大。 例如，C$\nu$B以$\mathcal{O}(\text{Hz})$的速率散射在一个10 cm液体或固态密度自旋极化的球体上，比非相干贡献增强了$\mathcal{O}(10^{21})$倍。 对于QCD轴子暗物质，可以用小得多的样本实现相似的速率，即$N \sim \mathcal{O}(10^{15})\left(\frac{m}{2\times 10^{-8}~\text{eV}}\right)^{-1/2}$，其中$m$是轴子质量。 使用林德布拉德形式主义，我们表明这些超辐射相互作用可以表现为系统上的噪声源。 这指向了新的可观测量，对激发和去激发速率之和敏感，可以看作是在系统中引入扩散和退相干。 本文所述的效果可能指向一类新的超低阈值探测器。 显示英文摘要

摘要： In this paper we do three things. First, we outline the conditions under which the interaction rate of inelastic processes that change the internal state of a system of $N$ targets scales as $N^2$. This is an effect distinct from coherent elastic scattering, but with the same scaling. Second, we compute rates for such processes for various weakly interacting particles. Finally, we point to potential quantum observables for these processes, beyond energy exchange. Maximal coherence in inelastic processes is achieved when the targets are placed in an equal superposition of the ground and excited states. These coherent inelastic processes are analogous to Dicke superradiance, and we thus refer to them as superradiant interactions. We compute the superradiant interaction rates for the Cosmic Neutrino Background (C$\nu$B), dark matter scattering and absorption, and late-universe particles, such as reactor neutrinos, when the two-level system is realized by nuclear or electron spins in a magnetic field. The rates can be sizeable on macroscopic yet small targets. For example, the C$\nu$B interacts with a rate of $\mathcal{O}(\text{Hz})$ when scattering off a 10~cm liquid or solid-state density spin-polarized sphere, a $\mathcal{O}(10^{21})$ enhancement compared to the incoherent contribution. For QCD axion dark matter, similar rates can be achieved with much smaller samples, $N \sim \mathcal{O}(10^{15})\left(\frac{m}{2\times 10^{-8}~\text{eV}}\right)^{-1/2}$, where $m$ is the axion mass. Using the Lindblad formalism, we show that these superradiant interactions can manifest as a source of noise on the system. This points to new observables, sensitive to the sum of the excitation and de-excitation rates, and can be viewed as introducing diffusion and decoherence to the system. The effects presented in this paper may point to a new class of ultra-low threshold detectors.