新一代量子传感器：强关联多体探针

量子传感是量子系统在资源效率方面优于经典系统的一个很好的例子。有两种量子传感器能实现量子增强的精度：(1)具有特殊量子纠缠形式的非相互作用粒子 (2)临界多体系统。非相互作用的纠缠传感器在工程实现上是十分困难的，并且对退相干高度敏感。多体传感器，将是本提案的主题，可以以更鲁棒的方式实现量子增强的精度。然而，这种传感器也存在着一些挑战，例如需要全局可访问性，可操作区域十分狭窄和需要复杂的测量策略。.为了应对这些挑战，申请人采取全新的方法，通过多个项目以开发出全新一代的多体传感器。新一代的多体探针将提供量子增强的精度，即使是在只有局部可访问性的前提下。这是通过利用新的相变来实现的，例如动态、周期性驱动和测量诱导的量子相变。此外，将设计在机器学习的基础上，实际可用的测量策略和新的估计算法。.该提案与时俱进、跨学科、有抱负，旨在填补中国在量子模拟与量子通信领域的宏大成就与量子传感领域之间的空白。

Every person in the world carries several sensors in their pocket as an inseparable part of their mobile phones. Sensors shape all aspects of humans’ life, from daily activities to the most advanced technologies. Environmental protection, geological prospection, mining, climate monitoring, space exploration and security heavily rely on various types of sensors for constantly monitoring the values of several quantities, such as temperature, pressure, speed, electric and magnetic fields. By the advancements of technology, the demand for better sensing precisions is escalating. Therefore, a huge effort is dedicated to the development of better sensors...Quantum systems are very delicate and show extreme sensitivity to tiny variations in the environment. This makes them excellent candidates for being exploited as sensors. Indeed, quantum sensing is now one of the pillars of quantum technologies and thanks to their huge economic impacts they receive a lot of support for their development from governments and private sectors all over the world. This is exemplified by the investment of Quantum Flagship program in Europe (with €1b investment) and Quantum Hubs (with £270m investment) in the United Kingdom. .Quantum sensing represent an excellent example of the superiority of quantum systems over their classical counterparts with respect to resource efficiency. So far, three different types of quantum sensors have been explored: (i) single particle sensors; (ii) non-interacting particles with a special form of entanglement in their quantum states; and (iii) critical many-body systems. The last two types are specially interesting as they are the ones which provide resource efficiency in comparison with classical sensors. For the case of non-interacting entangled sensors, it is very difficult to generate such form of entangled states and even after creation they are highly sensitive to decoherence and particle loss making them notoriously difficult in practice. The third form of sensors are more robust and can provide quantum enhanced precision in many-body systems. This type of sensors will be the subject of this proposal. However, these sensors have several challenges too which the applicant tries to address them in this proposal. For instance, they demand global accessibility on the entire system and provide quantum enhanced sensing in a very narrow region around their criticality where a 2nd order quantum phase transition happens. In addition, they demand measurement setups which are complex and usually depend on the unknown parameter itself. .In order to address these challenges, the applicant has defined three objectives. They aim for developing entirely new generation of many-body sensors and explore their properties in the main three aspects: (i) computing the ultimate bound for the achievable precision; (ii) investigating the optimal measurement setup which can saturate the precision bound; and (iii) designing new estimation algorithms which use the measurement data and process them for inferring the unknown parameter. To achieve the objectives several projects have been designed. The major problems which will be addressed include the development of a new generation of many-body sensors which provide quantum enhanced sensing beyond the critical region without demanding global accessibility. A series of novel phase transitions, e.g. dynamical, periodically driven and measurement induced quantum phase transitions, will be explored carefully. Moreover, practically available measurement setups and new estimation algorithms, based on machine learning, will be designed to fulfil the capacity of such sensors. .The proposal is timely, ambitious and large scale and is designed to fill the gap between the magnificent achievements of China in developing quantum simulators and the lack of development of quantum sensors. The excellent track record of the applicant guarantees the success of the proposal.