Quantum Metrology in Complex Noise Environments

精确测量物理量的能力，如场的强度、力、温度或时间，在当今世界发挥着关键作用。精密测量对科学和工业研究至关重要，是全球定位系统、蜂窝电话网络和电网等技术的基础。因此，计量学的进步，也就是测量的研究，既有可能推进基础知识的前沿，也有可能改善整个社会。最有前途的发展领域之一是计量学和量子科学的交叉点：量子计量学的目标是利用量子系统(如原子、光子或自旋)对周围环境的非凡敏感性，以提高可实现的精度，使之超过仅使用经典传感器和测量策略所能达到的水平。然而，这种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。这个项目的广泛目标是建立对一般时空相关的非经典噪声环境在量子计量学中的影响的量化理解。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音环境对量子传感器的影响。同时，它将在研究生和本科生水平上纳入强大的教育内容，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学科。最近，主要研究人员在Ramsey干涉计量学的范例环境中研究了时空相关量子噪声集体耦合到两能级(“量子比特”)传感器系统的计量学影响。这项研究证明了一种以前未被认识到的效应，即耦合到量子环境可以调节传感器之间的不可控纠缠，导致额外的测量不确定源。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)通过考虑更广泛的一组初始传感器的状态、测量和非集体耦合，充分量化时空相关量子噪声的影响，并将其应用于囚禁离子设备中的力传感。(2)评估优化噪声协议设计和动态控制以恢复计量优势的潜力。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。通过利用动态修正的量子门和过滤器功能设计的技术，一个关键目标将是设计开环控制，在现实约束下优化这些相互竞争的目标。(Iii)确定非高斯噪声统计可能影响量子估计协议的程度，以及更一般地量化现实噪声源可能引入的估计偏差。在寻求这些问题时，该小组将牢记更大的目标，即在现实的开放量子系统动力学面前，探索量子信息科学是否可以为传感器提供新的模式。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.