The sensing of magnetic field with ultra-high sensitivity can be achieved using quantum magnetometers, which are based on the quantum natures of micro-particles. These quantum natures, namely, discreteness and quantum coherences (including quantum entanglement), are dominant factors that equip quantum magnetometers with properties, e.g., ultra-high sensitivity, which are otherwise hardly achievable with classical sensors. Quantum magnetometers have found broad applications in fundamental physics, non-invasive biomedical diagnostics, and remote sensing.
In quantum magnetometry, two fundamental questions have garnered broad attention: First, is there a fundamental limit for the capability of magnetometers? Second, to what degree can we conclude that the magnetometer is essentially quantum?
Recently, Professor Hong Guo's team from Peking University gives a perspective for these two questions by focusing on the evaluation methods of sensitivity limits. Sensitivity, reflecting the smallest detectable variation in magnetic field for a given time duration, is a critical performance metric for quantum magnetometer. There are typically three perspectives for evaluating the sensitivity limits of quantum magnetometers: noise, quantum parameter estimation, and energy resolution limit. The researchers explore these methods and their intrinsic connections, emphasizing that they follow the same basic principles, such as the uncertainty principle, statistical estimation theory, and thermodynamics of information. Additionally, the researchers analyze the relationships between the limits of quantum magnetometers and their quantum characteristics, providing a basis for determining whether a magnetometer is quantum. This study advances the theoretical development in quantum magnetometry and the experimental optimization of quantum magnetometers.
