HAYSTAC Axion Dark Matter Experiment: Phase III

要理解，有三种天文观测需要所谓的暗物质的存在，暗物质是一种几乎完全通过引力与自身和其他物质相互作用的无形物质。首先，束缚在星系(包括银河系)中的恒星的速度太快，无法用可见恒星的总质量来解释。其次，宇宙的膨胀需要引入比我们作为普通原子和粒子所能观察到的更多的物质。第三，星系分布的丝状结构不能建立在星系之间的引力相互作用基础上，而不是基于观测到的质量。暗物质的基本性质是现代科学中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类型的大质量暗物质粒子，这些粒子是基于被称为超对称的粒子物理学的扩展理论而预测的。到目前为止，还没有在加速器或暗物质探测器中看到这样的粒子。另一种可能的理论暗物质粒子是轴子，它的引入是为了使强力或核力与时间方向无关，这已经被实验确定为非常高的精确度。虽然轴子从未被观测到，但它的性质是可以计算的，对于暗物质候选者来说，它是完美的。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，一个微波谐振器被放置在一个非常强的磁场中。在磁场存在的情况下，星系晕中的轴子可以转化为光子或无线电波。使用灵敏的放大器来搜索由这种转换产生的信号，该信号的频率是未知的。这个被称为日光镜的系统必须在频率上缓慢调谐，才能搜索转换信号。该小组已经在4-7 GHz范围内运行了几年的探测器，并正在继续搜索，并计划提高灵敏度。整个合作范围内支持Haystac的努力正在导致许多技术创新，这些创新将在许多研究和技术领域有用，主要结果是有可能使精细的量子状态测量子系统在受振动和非常大磁场影响的真实系统中运行，同时在接近一年的时间尺度上以近100%的可靠性运行。Haystac还为粒子物理、轴子暗物质和量子传感技术的学生和博士后提供了一个极好的培训基地。自2014年夏天首次试运行以来，Haystac(耶鲁大学对Axion冷暗物质敏感的光晕)一直在连续运行，系统升级中断。第一个版本的探测器基于约瑟夫森参数放大器，能够达到保相放大器的量子噪声极限。2019年，该项目成功地将基于不受标准量子限制的压缩态接收器系统的量子增强检测纳入其中。这使频率扫描速度提高了两倍，灵敏度略有提高，这是因为获得了大约4分贝的压缩，但受到微波环行器中的损耗的限制。该系统目前在4.5-5 GHz范围内采集数据，并将持续到2023年夏季，灵敏度为KSVZ模型级别。Haystac从一开始就发展起来的专业技术包括振动抑制、对转换腔频率和耦合的精确控制，以及对需要在转换所用的8特斯拉超导磁体附近运行的量子放大器的高效磁屏蔽。该项目开发了允许低温系统连续运行数月的操作技术。在拟议活动的第一年，该实验将安装一个新的多棒腔，它将允许在更高的频率(宇宙起源的轴子模型所青睐的)下工作，并测试其低温性能。接下来，科罗拉多大学正在开发的一种新的量子使能接收器系统将被集成到Haystac中。该系统消除了有损耗的环行器，并将大幅提高灵敏度。该小组预计，升级后的系统将于2025年年中初完成全面调试，并在7-10 GHz或更高的范围内运行，灵敏度达到KSVZ参数范围。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.