HAYSTAC Axion Dark Matter Experiment: Phase III

有三种天文观测需要所谓的暗物质的存在才能被理解，暗物质是一种不可见的物质，几乎只通过引力与自身和其他物质相互作用。首先，星系（包括银河系）中恒星的速度太快，无法用可见恒星的总质量来解释。第二，宇宙的膨胀需要引入比我们所能观察到的普通原子和粒子更多的物质。第三，星系分布的丝状结构不能基于星系间的引力相互作用，不能基于观测到的质量来建立。暗物质的基本性质是现代科学尚未解决的主要问题之一。人们已经做了很多工作来探测新型的大质量暗物质粒子，这些粒子是根据粒子物理学的一种扩展理论——超对称理论——来预测的。到目前为止，还没有在加速器或暗物质探测器中发现这样的粒子。另一种可能的理论上的暗物质粒子是轴子，它的引入是为了使强作用力或核力与时间的方向无关，这一点已经通过实验得到了非常高的精度。虽然轴子从未被观测到，但它的性质是可以计算出来的，它是暗物质的完美候选者。这样的轴子会在星系周围形成光晕，包括我们自己的星系。为了寻找轴子，微波谐振器被放置在一个非常强的磁场中。在磁场的作用下，星系晕中的轴子可以转化为光子或无线电波。一个灵敏的放大器被用来搜索从这种转换中产生的信号，其频率是未知的。这个系统被称为光镜，必须缓慢地调整频率以寻找转换信号。该小组已经在4-7千兆赫的范围内操作了几年的探测器，并且正在继续搜索，计划增加灵敏度。支持HAYSTAC的合作范围内的努力正在导致许多技术创新，这些技术创新将在许多研究和技术领域有用，主要结果是有可能在现实世界系统中运行一个微妙的量子态测量子系统，该系统受到振动和非常大的磁场的影响，同时以接近100%的可靠性运行，时间尺度接近一年。HAYSTAC还为粒子物理学、轴子暗物质和量子传感技术方面的学生和博士后提供了一个极好的训练基地。HAYSTAC（耶鲁大学敏感轴子冷暗物质光镜）自2014年夏季首次调试以来，一直在持续运行，系统升级中断。第一个版本的探测器是基于约瑟夫森参数放大器，能够达到量子噪声限制的相位保持放大器。2019年，该项目成功地结合了基于不受标准量子限制的压缩状态接收器系统的量子增强探测。由于受到微波环行器损耗的限制，获得了大约4db的压缩，这使得频率扫描速度增加了两倍，灵敏度也有了适度的提高。该系统目前正在采集4.5 - 5 GHz范围内的数据，并将持续到2023年夏季，灵敏度达到KSVZ模型水平。从HAYSTAC开始开发的专业知识包括振动抑制，精确控制转换腔频率和耦合，以及需要在用于转换的8特斯拉超导磁体附近运行的量子放大器的高效磁屏蔽。该项目开发了操作技术，可以使低温系统连续运行数月。在拟议活动的第一年，实验将安装一个新的多棒腔，该腔将允许在更高的频率下运行（受宇宙起源轴子模型的青睐），并且具有良好的体积形状因子，该腔正在加州大学伯克利分校开发，并测试其低温特性。接下来，科罗拉多大学正在开发的一种新的量子接收系统将集成到HAYSTAC中。该系统消除了损耗循环器，并将允许大幅提高灵敏度。该集团预计，升级后的系统的全面调试将在2025年中期开始完成，并在7-10 GHz或更高的范围内工作，灵敏度完全进入KSVZ参数范围。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

There are three astronomical observations that, to be understood, require the presence of so-called Dark Matter, which is invisible matter that almost exclusively interacts with itself and other matter through gravity. First, the velocities of stars bound in galaxies (including the Milky Way) are too fast to be accounted for by the total mass of the visible stars. Second, the expansion of the Universe requires the introduction of more matter than we can observe as ordinary atoms and particles. Third, the filamentary structure of the distribution of galaxies cannot be established based on gravitational interactions between galaxies, based on their observed masses. The fundamental nature of dark matter is one of the leading unsolved problems of modern science. Much work has been done to detect new types of massive dark matter particles that are predicted based on an extended theory of particle physics called supersymmetry. So far, no such particles have been seen in accelerator or dark matter detectors. Another possible theoretical dark matter particle is the axion, which was introduced to make the strong, or nuclear, force independent of the direction of time, as has been experimentally determined to very high precision. Although the axion has never been observed, its properties can be calculated, and it is perfect for a dark matter candidate. Such axions would form halos around galaxies, including our own. To search for axions, a microwave resonator is placed in a very strong magnetic field. The axions in the galactic halo can convert to photons, or radio waves, in the presence of the magnetic field. A sensitive amplifier is used to search for the signal arising from this conversion, the frequency of which is unknown. This system, called a haloscope, must be tuned slowly in frequency to search for the conversion signal. The group has operated the detector in the 4-7 GHz range several years and is continuing the search with a planned increase in sensitivity. The collaboration-wide efforts in support of HAYSTAC are leading to many technical innovations that will be useful in many research and technology fields, with the principal result being that it is possible to have a delicate quantum state measurement subsystem operate in a real-world system that is subject to vibration and very large magnetic fields, while operating with nearly 100% reliability, over times scales approaching a year. HAYSTAC also serves as a fantastic training ground for students and postdocs in particle physics, axion dark matter, and quantum sensing techniques. HAYSTAC (Haloscope at Yale Sensitive to Axion Cold Dark Matter) has been in continuous operation, with interruptions for system upgrades, since the initial commissioning in the Summer of 2014. The first version of the detector was based on a Josephson parametric amplifier that was able to reach the quantum noise limit of the phase-preserving amplifier. In 2019, the project successfully incorporated quantum-enhanced detection based on a squeeze-state receiver system that is not subject to the standard quantum limit. This increased the frequency scan speed by a factor of two with a modest increase in sensitivity, due to the approximately 4 dB of squeezing that was obtained, being limited by losses in the microwave circulators. This system is currently taking data in the 4.5 – 5 GHz range and will continue to do so through Summer 2023, with sensitivity at the KSVZ model level. The expertise that was developed from the beginning of HAYSTAC includes vibration suppression, accurate control of the conversion cavity frequency and coupling, and highly effective magnetic shielding of the quantum amplifiers that need to operate near the 8 Tesla superconducting magnet used for conversion. The project has developed operational techniques that allow continuous operation of the cryogenic system for months. During the first year of the proposed activity, the experiment will install a new multi-rod cavity that will allow operation at higher frequencies (favored by cosmogenic axion models) with a good volume form factor that is being developed at U.C. Berkeley, and test its cryogenic properties. Next, a new quantum enable receiver system being developed at the University of Colorado will be integrated into HAYSTAC. This system eliminates the lossy circulators and will allow a substantial increase in sensitivity. The group anticipates that the full commissioning of the upgraded system will be complete at the beginning in mid-2025, and operate in the 7-10 GHz range or above, with sensitivity well into the KSVZ parameter range.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.