Cavity-assisted Quantum Sensing

第一代原子量子传感器支撑着广泛的现代技术。例如，全球范围内的“原子钟”网络构成了全球卫星定位系统的时基，使我们的通信网络和导航服务同步。这些技术中的许多都在所谓的标准量子灵敏度极限附近运行。目前，英国和世界各地都在积极努力开发“量子2.0”技术，这种技术利用量子系统的一些更奇特的方面，使这些设备超越目前的限制。这项工作的一个重点是对经过验证的技术进行技术改进，着眼于在现实世界中进行商业化和部署。第二个目标是确定能够提供超越下一代能力的新系统和技术。这里提出的研究计划将展示利用冷原子蒸气进行腔辅助量子传感的新技术。通过将原子捕获到光学环形谐振器中--这里是由极高质量的镜片组成的三角形排列--信号光将大量穿过传感介质，从而极大地提高测量的灵敏度。使用绝对零度以上不到千分之一度的原子气体作为增益介质，我们将建立一个冷原子激光器，它可以向两个反传播方向之一或两个方向发射光。这将使我们能够研究之前在我们的实验中观察到的明显的时间反转对称性的破坏(光学“非互易”)。有人预测，非互易效应可以提高对小信号的灵敏度，但实验演示很少，而且不完整，而且对这类系统的噪声特性还没有很好的了解。在项目的最后阶段，我们将演示空腔辅助磁测量的新方案。原子磁强计被用于研究超越标准模型的新物理，以及在医学和生物物理、航海、考古和土木工程中的应用。我们的方法将再次集中在利用光学腔内冷原子和光之间增强的相互作用。我们达到光-物质相互作用的集体强耦合区域的能力将使我们能够探测到原子蒸气折射率的非常微小的变化，这将以与磁场强度成正比的频率对透射光施加幅度调制。通过如上所述地结合激光，可以增加信号功率，从而在灵敏度上给出相应的改进。该项目将补充国家量子技术计划的工作，并有助于扩大英国作为量子科学和技术全球领导者的角色。

First generation atomic quantum sensors underpin a vast range of modern technologies. For example, a worldwide network of 'atomic clocks' forms the time-base for the global satellite positioning systems which synchronise our communications networks and navigation services. Many of these technologies operate near the so-called standard quantum limit of sensitivity. Currently there is an active effort in the UK and around the world to develop 'Quantum 2.0' technologies, which leverage some of the more exotic aspects of quantum systems to take these devices beyond their current limits. One strand of this effort focuses on technological refinement of proven techniques, with an eye towards commercialisation and deployment in real-world settings. A second strand aims to identify new systems and techniques which could offer beyond-next-generation capabilities.The research programme proposed here will demonstrate novel techniques for cavity-assisted quantum sensing with cold atomic vapours. By trapping the atoms within an optical ring resonator -- here a triangular arrangement of extremely high-quality mirrors -- the signal light will pass through the sensing medium a large number of times, vastly improving the sensitivity of the measurement. Using a gas of atoms less than one thousandth of a degree above absolute zero as a gain medium, we will build a cold-atom laser which can be made to emit light into one or both of two counterpropagating directions. This will allow us to investigate the apparent breaking of time-reversal symmetry (optical 'non-reciprocity') previously observed in our experiment. It has been predicted that non-reciprocal effects can lead to enhanced sensitivity for small signals, but experimental demonstrations are few and incomplete, and the noise properties of such systems are not well understood. In the final phase of the project, we will demonstrate new schemes for cavity-assisted magnetometry. Atomic magnetometers are used in a variety of searches for new physics beyond the Standard Model and applications in medical and bio-physics, navigation, archaeology, and civil engineering. Our approach will again be focused on exploiting the enhanced interaction between cold atoms and light within the optical cavity. Our ability to reach the collective strong coupling regime of light-matter interactions will allow us to detect very small changes in the refractive index of the atomic vapour, which will impose an amplitude modulation on the transmitted light at a frequency proportional to the magnetic field strength. By incorporating lasing as described above, the signal power can be increased, giving a corresponding improvement in the sensitivity. This project will complement the work of the National Quantum Technologies programme and help extend the UK's role as a worldwide leader in quantum science and technology.