Cavity-assisted Quantum Sensing

第一代原子量子传感器是众多现代技术的基础。例如，全球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接近所谓的标准量子灵敏度极限。目前，英国和世界各地都在积极开发“量子2.0”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极限。这项工作的一部分侧重于对成熟技术的技术改进，着眼于商业化和在现实环境中的部署。第二部分旨在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用冷原子蒸汽进行腔辅助量子传感的新技术。通过将原子捕获在光学环形谐振器中——这里是一个高质量镜面的三角形排列——信号光将通过传感介质多次，极大地提高了测量的灵敏度。我们将利用低于绝对零度千分之一度的原子气体作为增益介质，制造一种冷原子激光器，它可以向一个或两个反向传播方向发射光。这将使我们能够研究之前在我们的实验中观察到的时间反转对称性的明显破坏（光学“非互易性”）。据预测，非互易效应可以提高对小信号的灵敏度，但实验证明很少且不完整，并且这种系统的噪声特性尚未得到很好的理解。在项目的最后阶段，我们将展示腔辅助磁强计的新方案。原子磁力计用于各种超越标准模型的新物理学的搜索，并应用于医学和生物物理学，航海，考古学和土木工程。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状态的能力将使我们能够探测到原子蒸气折射率的非常小的变化，这将对透射光施加与磁场强度成比例的频率的幅度调制。通过结合如上所述的激光，可以增加信号功率，从而相应地提高灵敏度。该项目将补充国家量子技术计划的工作，并有助于扩大英国在量子科学和技术领域的全球领导者地位。

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.