Among the known particles, the neutron is special because it provides experimental access to all of the four fundamental forces and a wide range of hypothetical interactions. Despite being unstable, free neutrons live long enough to be used as test particles in interferometric, spectroscopic and scattering experiments probing low-energy scales. Recognized already in the 1970s, fundamental concepts of quantum mechanics can be tested in neutron interferometry using silicon perfect single crystals. Besides enabling tests of uncertainty relations or Bell inequalities, neutrons offer the opportunity to observe the effects of gravity and hypothetical dark forces acting on extended matter wavefunctions. Such tests gained importance in the light of recent discoveries of inconsistencies in the understanding of cosmology and the incompatibility between quantum mechanics and general relativity. Experiments with low-energy neutrons are, thus, indispensable tools for probing fundamental physics and represent a complementary approach to particle colliders. In this Review, we discuss the history and experimental methods used at this low-energy frontier of physics and overview the current bounds and limits on quantum mechanical relations and dark energy interactions.

在已知粒子中，中子是特殊的，因为它提供了对所有四个基本力的实验访问以及广泛的假设相互作用。尽管不稳定，但自由中子的寿命足够长，可以用作探测低能级的干涉，光谱和散射实验中的测试粒子。量子力学的基本概念早在1970年代就已被认可，可以使用硅完美单晶在中子干涉测量中进行测试。中子除了能够进行不确定性关系或贝尔不等式的测试之外，还提供了观察重力和假设的暗力对扩展物质波函数的影响的机会。鉴于最近发现的对宇宙学的理解以及量子力学与广义相对论之间的不相容性，这种测试变得越来越重要。因此，低能中子的实验是探测基础物理学必不可少的工具，是解决粒子对撞机的一种补充方法。在这篇综述中，我们讨论了在这个低能物理学前沿中使用的历史和实验方法，并概述了量子力学关系和暗能量相互作用的当前界限和极限。