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，为材料提供了独特的射频指纹。简单地用磁波以样品的共振频率激励样品，就会产生一个信号。然而，微弱的信号强度和对未研究材料的共振的长达数月的搜索阻碍了这种廉价而简单的技术的迅速采用，这种技术被称为核四极共振。具有比标准线圈探测器更高灵敏度的量子磁强计，有助于解决前一个问题，但通过这个项目，将被开发来提高搜索速度，可能比传统方法快五个数量级。尽管很难发现新的共振线，但研究人员在一些对安全和社会至关重要的应用中继续使用四极共振进行物质检测；特别是在检查站检测爆炸物和识别伪劣药品和真品。如果能迅速确定新材料的共振线，则在检查点和标准应用中采用四极共振将大大扩大应用范围。除了国家安全方面的好处，该项目还将通过振兴实验室课程，在电气工程系和物理系之间建立牢固的联系，从而改善乔治·梅森内部的科学、技术、工程和数学教育。此外，通过创建专注于K-12教育经验的本科生实习项目，将培养初出茅庐的科学教师，并将种植多样化和具有竞争力的技术和工程劳动力的种子。原子磁强计是与线圈根本不同的传感器。使用光学排列的原子作为检测介质，并使用激光光学读出传感器，比使用线圈提供更好的检测灵敏度；磁强计中的噪声从根本上受到量子涨落的限制。此外，磁力计的工作频率可以很容易地改变，以与小静磁场的励磁频率相匹配。鉴于这些优点，激励频率可以连续扫描，而不是在单一工作频率下的脉冲激励，从而消除了逐点搜索的需要。使用脉冲激励时，材料必须在采集另一个信号之前返回到平衡状态；数据采集之间通常需要很长的等待时间。然而，通过向上扫描更高的频率，然后向下返回到原始频率，材料会自动恢复到平衡。通过这种方式，避免了危及标准脉冲技术有效性的长等待时间。作为该项目的一部分，将实现以下目标：1)设计和建造有效体积为2立方米的磁强计单元。由此产生的磁强计将具有亚飞特斯拉的灵敏度。小体积对于使用有限数量的材料进行共振搜索的实际实施至关重要。2)连续将磁强计调整到改变频率不会改变其灵敏度。3)在对几厘米外的样品施加约100微特斯拉的共振激励时，磁强计的灵敏度可以保持。将采用线圈几何结构和使用第二个磁强计的共模抑制方案。4)如果实现上述三个目标，对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.