Quantum Metrology in Complex Noise Environments

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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.