Quantum Magnetometers for Rapid Identification of Resonance Frequencies in Explosives, Pharmaceuticals, and Other Substances

晶体固体，如炸药和药品，具有固有的共振，为材料提供独特的射频指纹。简单地用共振频率的磁波刺激样品，就会产生一个信号。然而，微弱的信号强度和对未研究材料中共振的长达数月的搜索阻碍了这种廉价而简单的技术的采用，这种技术被称为核四极共振。灵敏度高于标准线圈探测器的量子磁力计有助于解决前一个问题，但随着这个项目的发展，它将提高搜索速度，可能比传统方法快五个数量级。尽管发现新的共振线很困难，但研究人员已经在一些对安全和社会至关重要的应用中追求使用四极共振进行物质检测；特别是在检查站侦测爆炸物和辨别假药和真药。如果能够快速识别新材料的共振线，那么在检查点和标准应用中采用四极共振将大大扩展。除了国家安全利益外，该项目还将通过振兴实验室课程，在电气工程和物理系之间建立牢固的联系，从而改善乔治梅森大学的科学、技术、工程和数学教育。此外，通过创建以K-12教育经验为重点的本科实习项目，将培养初入行的科学教师，并为培养多样化和有竞争力的技术和工程劳动力埋下种子。原子磁强计与线圈磁强计本质上是不同的传感器。使用光学排列的原子作为检测介质和光学读出的传感器与激光提供了更好的检测灵敏度比线圈；磁力计中的噪声基本上受量子涨落的限制。此外，可以很容易地改变磁强计的工作频率，使其与小的静态磁场的激励频率相匹配。鉴于这些优点，激励频率可以连续扫描，而不是单一工作频率的脉冲激励，从而避免了逐点搜索的需要。在脉冲激励下，在获得另一个信号之前，材料必须返回到平衡状态；数据获取之间通常需要很长的等待时间。然而，通过扫过更高的频率，然后回到原来的频率，材料自动恢复平衡。这样，就避免了影响标准脉冲技术有效性的漫长等待时间。作为该项目的一部分，将实现以下目标：1)将设计和建造活性体积为2 cm3的磁力计单元。由此产生的磁力计将具有亚飞特斯拉的灵敏度。小体积对于在有限材料条件下实现共振搜索是至关重要的。不断地调整磁力计到一个变化的频率不会改变它的灵敏度。3)在几厘米外的样品上施加100微特斯拉量级的谐振激励，可以保持磁力计的灵敏度。线圈几何和共模抑制方案使用第二个磁力计将被采用。4)如果实现以上三个目标，共振频率的搜索速度可以比传统技术提高多达五个数量级。

Crystalline solids, such as explosives and pharmaceuticals, have intrinsic resonances that provide a unique radio-frequency fingerprint for the material. Simply exciting the sample with a magnetic wave at its resonance frequency, yields a signal. However, weak signal strength and months-long searches for resonances in unstudied materials prevent ready adoption of this inexpensive and simple technique, known as nuclear quadrupole resonance. Quantum magnetometers, with sensitivities better than standard coil detectors, help with the former problem, but will, with this project, be developed to increase the search speed, potentially five orders of magnitude faster than the conventional method. Despite the difficulty of discovering new resonance lines, researchers have pursued the use of quadrupole resonance for substance detection in a few applications of critical importance for security and society; in particular, the detection of explosives and the identification of counterfeit from real medicine at checkpoints. The adoption of quadrupole resonance for checkpoint and standards applications would greatly expand if resonance lines could be quickly identified for new materials. In addition to national security benefits, the project will improve science, technology, engineering and mathematics education within George Mason by forging strong ties between the Electrical Engineering and Physics Departments through revitalized laboratory courses. Furthermore, by creating undergraduate internship projects focused on K-12 educational experiences, fledgling science teachers will be nurtured and seeds of a diverse and competitive technology and engineering workforce will be planted.Atomic magnetometers are fundamentally different sensors than coils. The use of optically aligned atoms as the detection medium and optical read-out of the sensor with a laser gives a better detection sensitivity than coils; noise in the magnetometer is fundamentally limited by quantum fluctuations. Moreover, the operating frequency of the magnetometer can easily be changed to match the frequency of the excitation with a small static magnetic field. In light of these advantages, the excitation frequency can be swept continuously, as opposed to pulsed excitation at a single operating frequency, obviating the need for a point by point search. With pulsed excitation the material must return to an equilibrium condition before another signal is acquired; often long wait times are required between data acquisitions. However by sweeping up through higher frequencies, then back down to the original frequency, the material is automatically returned to equilibrium. In this way, the long wait times that compromise the effectiveness of standard pulse techniques is avoided. As part of the project, the following goals will be met: 1) Magnetometer cells with an active volume of 2 cm3 will be designed and constructed. The resulting magnetometer will have sub-femtoTesla sensitivity. The small volume is critical for the practical implementation of the resonance search with a limited quantity of material.2) Continuously tuning the magnetometer to a changing frequency will not alter its sensitivity.3) The sensitivity of the magnetometer can be retained while resonant excitation on the order of a 100 micro Tesla is applied to a sample a couple centimeters away. Coil geometry and common mode rejection schemes using a second magnetometer will be employed.4) If the above three goals are achieved, the search speed for resonance frequencies can be improved by as much as five orders of magnitude over conventional techniques.