Pulsed Electron Paramagnetic Resonance at Millikelvin Temperatures

电子顺磁共振光谱在材料科学和生物学应用中的技术改进是优先计划1601的核心。这一目标基于两个主要的创新分支：第一，通过采用超灵敏微波分析技术以及优化的低损耗和小型化微波检测电路来提高检测灵敏度。第二，通过开发优化的脉冲序列来改进对自旋系综的控制，因为集成的亚波长微波电路以增加的微波磁场不均匀性为代价。利用这些新的发展可以提高检测灵敏度，提高信噪比，缩短采集时间，并能够研究更小的样品体积，这反过来又将允许高度空间分辨的研究。为此，我们将促进最初为量子信息应用开发的超灵敏微波光谱技术，该技术能够在单光子水平上检测信号幅度。我们将这些方法转移到超灵敏的微波分析工具的EPR光谱。在这种情况下，低温设置将提供一个关键的开发平台，因为它们提供了一个具有良好特性和理解的噪声环境的实验环境，旨在抑制微波频段的热噪声。此外，这种检测灵敏度允许进行单次EPR实验，其中可以原位研究激发脉冲和所产生的自旋系综响应。结合超导微波谐振器的微波磁场不均匀性、低的可用激发功率、长的自旋寿命和退相干时间，这些系统为最佳控制脉冲提供了一个新的平台，因此，我们期望这种极低噪声的环境将成为发展EPR超灵敏微波探测技术的理想平台。

The technological improvement of electron paramagnetic resonance spectroscopy for material science and biological applications is at the heart of the Priority Program 1601. This objective is based on two main innovation branches: First, the improvement of the detection sensitivity by employing ultra-sensitive microwave analysis techniques as well as optimized low-loss and downsized microwave detection circuits. Second, an improved control over the spin ensembles by the development of optimized pulse sequences, because integrated sub-wavelength microwave circuits come with the cost of an increased microwave magnetic field inhomogeneity. Harnessing these new developments gives access to increased detection sensitivity, higher signal-to-noise ratio corresponding to shorter acquisition times, and the ability to investigate smaller sample volumes, which in turn will allow for highly spatially resolved studies.The current project aims at the improvement of the microwave signal techniques. To this end, we will facilitate the ultra-sensitive microwave spectroscopy techniques originally developed for quantum information applications, which are capable to detect signal amplitudes on the single photon level. We will transfer these approaches to ultra-sensitive microwave analysis tools for EPR spectroscopy. In this context, low-temperature setups will provide a key development platform, as they offer an experimental environment with a well-characterized and understood noise environment, designed to suppress thermal noise in the microwave frequency band. Furthermore, this detection sensitivity allows for performing single-shot EPR experiments, where the excitation pulse and the resulting response of the spin ensemble can be studied in-situ. Combined with the microwave magnetic field inhomogeneity of the employed superconducing microwave resonators, the low available excitation powers, and the long spin life and decoherence times, these systems provide a new playground for optimal control pulses.Thus, we expect that this extremely low-noise environment will be the ideal platform for the development of ultra-sensitive microwave detection techniques for EPR.