Quantum Metrology in Complex Noise Environments

精确测量诸如磁场强度、力、温度或时间等物理量的能力在当今世界发挥着关键作用。精确测量对科学和工业研究至关重要，也是全球定位系统、移动电话网络和电网等技术的基础。由此可见，计量学的进步，即对测量的研究，具有推进基础知识前沿和改善整个社会的潜力。最有前途的进步领域之一在于计量学和量子科学的交叉点：量子计量学旨在利用量子系统（如原子，光子或自旋）对周围环境的非凡灵敏度，以提高可实现的精度，超出仅使用经典传感器和测量策略的可能性。然而，灵敏度的提高是一把双刃剑，因为它也使量子传感器更容易受到实践中不可避免地存在的“噪声”的影响。该项目的主要目标是建立对量子计量中一般时空相关、非经典噪声环境影响的定量理解。这项跨学科的努力将确定精度界限，并开发新的方法来对抗现实噪声环境对量子传感器的影响。与此同时，它将在研究生和本科阶段纳入强大的教育组成部分，涉及开放和多体量子系统，量子估计和量子控制理论之间的边界主题。最近，主要研究人员在拉姆齐干涉测量的范例设置中研究了时空相关量子噪声集体耦合到双电平（“量子位”）传感器系统的计量影响。这项研究证明了一种以前未被认识到的效应，即与量子环境的耦合可以介导传感器之间不受控制的纠缠，从而导致测量不确定性的额外来源。在这些发现的基础上，本项目将探索几个相互关联的研究方向，包括：(i)通过考虑更广泛的初始传感器状态、测量和非集体耦合，充分量化时空相关量子噪声的影响，并将其应用于困离子器件的力传感。（ii）评估噪音优化方案设计和动态控制的潜力，以恢复计量优势。虽然标准的开环控制和纠错策略可以抑制噪声，但它们通常也会去除感兴趣的信号或不适用于相关噪声。通过利用动态校正量子门和滤波函数设计的技术，一个关键目标将是设计开环控制，在现实约束下优化这些竞争目标。（iii）确定非高斯噪声统计可能影响量子估计协议的程度，以及更普遍地量化现实噪声源可能引入的估计偏差。在追求这些问题的过程中，该小组将牢记更大的目标，即探索量子信息科学是否可以在面对现实的开放量子系统动力学时为传感器提供新的模式。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。

The ability to precisely measure physical quantities such as the strength of a field, a force, temperature or time plays a pivotal role in today’s world. Precision measurement is essential for scientific and industrial research, and underpins technologies like the Global Positioning System, cellular phone networks and power grids. It follows that progress in metrology, the study of measurement, has the potential to both advance fundamental knowledge frontiers and improve society at large. One of the most promising areas for advancement lies at the intersection of metrology and quantum science: quantum metrology aims to harness the extraordinary sensitivity of quantum systems (such as atoms, photons, or spins) to their surrounding environment to increase the achievable precision beyond what is possible by using only classical sensors and measurement strategies. This boost in sensitivity is a double-edged sword, however, in that it also makes quantum sensors more susceptible to “noise” that is inevitably present in practice. The broad aim of this project is to build a quantitative understanding of the impact of general – spatiotemporally correlated, non-classical – noise environments in quantum metrology. This cross-disciplinary endeavor will determine precision bounds and develop new methods to counter the effects of realistic noise environments on quantum sensors. In parallel, it will incorporate a strong educational component at the graduate and undergraduate level, on subjects at the boundary between open and many-body quantum systems, quantum estimation, and quantum control theory. The metrological impact of spatiotemporally correlated quantum noise collectively coupled to a system of two-level (“qubit’’) sensors was recently examined by the principal investigators in the paradigmatic setting of Ramsey interferometry. This study demonstrated a previously unrecognized effect, namely, that coupling to a quantum environment can mediate uncontrolled entanglement between the sensors, resulting in an additional source of measurement uncertainty. Building on these findings, the present project will explore several interrelated research directions – including: (i) Fully quantifying the effects of spatiotemporally correlated quantum noise, by considering a broader set of initial sensors’ states, measurements, and non-collective couplings, with application to force sensing in trapped-ion devices. (ii) Assessing the potential for noise-optimized protocol design and dynamical control to restore metrological advantage. While standard open-loop control and error-correction strategies can suppress noise, they often also remove the signal of interest or are inapplicable to correlated noise. By leveraging techniques from dynamically corrected quantum gates and filter-function design, a key objective will be devising open-loop controls that optimize these competing objectives under realistic constraints. (iii) Determining the extent to which non-Gaussian noise statistics may impact quantum estimation protocols, along with more generally quantifying estimation bias that realistic noise sources may introduce. In pursuing these questions, the group will keep in mind the bigger goal of exploring whether quantum information science may inform yet new modalities for sensors in the face of realistic open quantum system dynamics.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.