A Quantum Jump Sensor for Dark Matter Detection

值得注意的是，在宇宙的尺度上，我们不知道什么构成了宇宙中84%的物质。这种暗物质对恒星的运动、星系的形成和大爆炸余辉中的模式都有深远的影响，但我们只能假设它的真实性质可能是什么。我们将建造一种新型的量子传感器，它使用一个孤立的电子，它将足够灵敏，以判断暗物质是否由某些类型的新粒子组成。似乎大多数缺失的物质是某种新类型的物质，这种物质几乎不会与普通物质发生电磁相互作用。强核力和弱核力的不同对称性，使粒子物理学家提出了一种新的粒子--轴子，这可能是一个线索。预测轴子的理论并没有预测它的质量，但比电子质量小10^9-10^12的光轴粒子可能在早期宇宙中被创造出来，今天仍然以暗物质的形式存在。除了粒子物理学的暗示外，宇宙学也有暗物质的性质的迹象。对早期宇宙被称为宇宙黎明时期氢的微波跃迁频率的观察表明，宇宙比预期的要冷。这也是暗物质可能与普通物质碰撞并降低其温度的时期。带有微小电荷的奇异粒子--也就是所谓的微充电粒子--可以解释这种观测结果。已经进行了许多实验来探测轴子和毫升粒子，但还没有发现任何实验。探测轴子最灵敏的实验使用强磁场来鼓励轴子衰变成频率与轴子质量直接相关的微波光子。然后，他们探测到这些微波。不幸的是，对于一个重要的轴子质量范围，最先进的微波探测器有一个基本的和不可避免的噪声源，它使轴子信号相形见绌。这种被称为标准量子极限的最小噪声可以通过计算组成电磁场的光子数来克服。在30-60 GHz范围内没有合适的单光子计数器，所以我们将发明一个。我们选择的技术是单电子，被困在电场和磁场的组合中。当电子吸收微波光子时，它的量子轨道会发生明显的变化。被俘获的电子对任何毫升充电的暗物质的碰撞也很敏感，碰撞后也会改变其轨道。这种轨道变化可以用量子跳跃光谱学来测量，这种光谱学以前是用来测量电子的磁矩的。如果我们能揭示暗物质的本质，我们最终就会了解宇宙中最丰富的物质，并表征其精确的性质，这将对天体物理学的许多方面产生影响。轴子或毫升粒子的发现只会是粒子物理学新纪元的开始，因为预计这两个粒子都会伴随着其他粒子。在轴子的情况下，这些粒子可能是更重的希格斯粒子，这为在欧洲核子研究中心建造未来的环形对撞机来发现它们提供了额外的强有力的论据。最后，该装置是一种最弱可检测微波信号的传感器，可应用于改进的微波天文、分子光谱学等化学物质的识别和传感。

It is remarkable that on a cosmic scale, we do not know what makes up 84% of the matter in the universe. This dark matter has a profound impact on the movement of stars, the formation of galaxies and the patterns in the afterglow of the Big Bang, but we can only hypothesise what its true nature might be. We will build a new type of quantum sensor using a single isolated electron that will be sensitive enough to tell if dark matter is made from certain types of new particles.It seems likely that most of the missing matter is some new type of substance which barely interacts with ordinary matter electromagnetically. One hint for what this might be comes from the differing symmetries of the strong and weak nuclear forces, which led particle physicists to propose a new particle, the axion. The theory which predicted the axion does not predict its mass, but light axions around 10^9-10^12 times less than the mass of an electron would have been created in the early universe and still be present today as dark matter.As well as hints from particle physics, there are also indications from cosmology as to the properties of dark matter. Observations of the microwave transition frequencies of hydrogen in the period of the early universe known as the cosmic dawn suggest that it was colder than expected. This was also the period where dark matter could collide with ordinary mater and reduce its temperature. Exotic particles with tiny charges - known as millicharged particles - would account for this observation. Many experiments have been carried out to detect axions and millicharged particles, but none have been discovered. The most sensitive experiments to detect axions use a strong magnetic field to encourage the axions to decay into microwave photons with a frequency directly related to the axion mass. They then detect those microwaves. Unfortunately, for an important axion mass range, state-of-the art microwave detectors have a fundamental and unavoidable noise source which dwarfs the axion signal. This minimum noise, referred to as the Standard Quantum Limit can be overcome by counting the number of photons which make up the electromagnetic field. No suitable single photon counter exists in the range 30-60 GHz, so we will invent one. The technology we have chosen is a single electron, trapped in a combination of electric and magnetic fields. As the electron absorbs a microwave photon, its quantum orbit changes detectably. A trapped electron is also sensitive to collisions with any millicharged dark matter, also changing its orbit after a collision. This change in orbit can be measured using quantum jump spectroscopy, which was previously used to measure the electron's magnetic moment.If we could uncover the nature of dark matter, we would finally have understood the most abundant substance in the universe and characterising its precise properties would have implications for many aspects of astrophysics. A discovery of the axion or millicharged particle would only be the start of a new era of particle physics since both particles would be expected to be accompanied by others. In the case of the axion, these could be much heavier Higgs particles, giving an additional strong argument for the construction of a Future Circular Collider at CERN to discover them. Finally, this device is a sensor for the weakest detectable microwave signals, which could be applied to improved microwave astronomy, molecular spectroscopy for the identification of chemical substances and sensing.