CAREER: Optomechanical Sensors Leveraging Quantum Noise

具有前所未有灵敏度的机械传感器将提供一种方法来寻找目前方法无法检测到的极其微小的力。这种微小的信号可能来自宇宙学的起源，比如某些假设的暗物质类型，它们必须大量存在才能使我们的星系保持在一起，但不能用普通的天文观测直接看到。另一个尚未被探测到的信号来源来自于被提议的效应，这些效应会破坏奇异的量子力学行为，比如一个物体同时存在于两个地方。观察或限制这两种信号的存在将有助于我们对宇宙本质的基本理解。在更小的尺度上，超灵敏的机械探测器可以感受到来自单个原子和原子核的磁力，对生物上重要的分子或半导体电子器件进行纳米级磁共振成像（MRI），这些是传统技术无法成像的。随着机械传感器的设计噪音越来越低，设备正在挑战基本的量子噪声极限。该项目将开发绕过这些量子限制的方法，并改进对代表新物理现象的小机械信号的搜索。为此，将开发具有新型光学探测技术的超低噪声机械传感器，以提高面对量子噪声的测量灵敏度。该项目还将为本科生提供教育研究培训，为下一代科学家和工程师解决现实问题做好准备。学生将在光学和机械传感器方面进行一个真正的开放式研究项目，从概念和设计一直到制造和测试，在足够快的连续时间内，允许通过现代计算机辅助设计、仿真和制造工具进行多次迭代。理解光学探测机械系统中的量子噪声限制可以追溯到量子力学的出现，海森堡的显微镜思想实验说明了位置灵敏度和反作用力之间的基本权衡（即由反冲光子产生的随机动量踢模糊了被光观察到的物体的运动）。已经提出了许多方法来逃避这种量子逆作用的有害影响，其中大多数需要复杂的光学或机械配置，并对经典噪声，损耗和稳定性有严格的限制。在这里，我们的目标是在一种更简单和普遍的精密光学测量技术中展示类似的量子优势——光学杠杆，测量从倾斜表面反射的光的角偏差。对标准设置进行简单的修改，可以增加来自测量的量子信息，降低对反作用力引起的运动的灵敏度，否则会掩盖小信号。该技术将应用于超低机械耗散，高张力振动弦机械谐振器，可用于感应应变，重力和超越标准量子极限的磁场。此外，该串光机械传感器将锚定在宏观测试质量上，并将研究测试质量运动引起的测量应变的量子极限。该系统的测量将对包括奇异量子退相干模型和超轻标量暗物质在内的超标准模型相互作用施加有意义的约束。从长远来看，这里开发的技术将在引力波的量子增强探测、纳米级力显微镜以及量子信息处理中量子态的机械介导存储和转导中得到应用。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。

Mechanical sensors with unprecedented sensitivity will provide a means to look for extremely tiny forces that are undetectable by current methods. Such small signals can arise from cosmological origins, such as certain hypothetical types of dark matter which must exist in great abundance to hold our galaxy together but cannot be seen directly with normal astronomical observation. Another source as-of-yet undetected signals is from proposed effects which act to spoil exotic quantum mechanical behaviors such as an object existing simultaneously in two places at once. Observing or putting limits on the existence of either of these signals will add to the fundamental understanding of the nature of our universe. At much smaller scales, ultrasensitive mechanical detectors could feel the magnetic forces from individual atoms and nuclei, performing nanoscale magnetic resonance imaging (MRI) for biologically important molecules or semiconductor electronic devices that cannot be imaged via conventional techniques. As mechanical sensors are devised with lower and lower noise, devices are running up against fundamental quantum noise limits. This project will develop methods to side-step these quantum limits and improve searches for small mechanical signals representing new physical phenomena. To this end, ultralow noise mechanical sensors with new optical probing techniques will be developed to enhance measurement sensitivity in the face of quantum noise. This project will also provide educational research training for undergraduate students, preparing the next generation of scientists and engineers to tackle real-world problems. Students will take a real open-ended research project in optical and mechanical sensors from concept and design all the way through fabrication and testing in rapid enough succession to allow for multiple iterations facilitated by modern computer-aided design, simulation, and manufacturing tools.Understanding quantum noise limits in optically probed mechanical systems goes back to the advent of quantum mechanics, with Heisenberg’s microscope thought experiment illustrating a fundamental trade-off between position sensitivity and backaction (i.e. random momentum kicks from recoiling photons obscuring the motion of an object being observed with light). Many methods to evade the deleterious effects of this quantum backaction have been proposed, most of which require complex optical or mechanical configurations with demanding constraints on classical noise, loss, and stability. Here, the goal is to demonstrate a similar quantum advantage in a much simpler and ubiquitous precision optical measurement technique – the optical lever, measuring the angular deviation of light reflecting off a tilting surface. Simple modifications to the standard setup yield an increase in the quantum information from the measurement and a reduction in the sensitivity to backaction-induced motion that would otherwise mask small signals. This technique will be applied to ultralow mechanical dissipation, high-tension vibrating string mechanical resonators that can be functionalized for sensing strain, gravity, and magnetic fields beyond standard quantum limits. Further, this string optomechanical sensor will be anchored to a macroscopic test mass and the quantum limits of measuring strain induced by test mass motion will be investigated. Measurements of this system will put meaningful constraints on beyond-standard-model interactions including exotic quantum decoherence models and ultralight scalar dark matter. In the longer term, the techniques developed here will find applications in the quantum-enhanced detection of gravitational waves, nanoscale force microscopy, and in mechanically mediated storage and transduction of quantum states for quantum information processing.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.