Magneto-optical trapping and sympathetic cooling of molecules

在磁光阱（MOT）中，精确调谐的激光和磁场的组合被用来将原子冷却到1毫开尔文以下的温度，并一次捕获它们几分钟。25年来，MOT一直是使用超冷原子的所有应用的核心。其中包括最先进的仪器，如原子钟、磁力计、重力仪和加速度计、常数测量，以及对物质在量子状态下的性质和行为的广泛研究。超冷分子的潜在应用甚至更远。它们可以用作敏感的场传感器，并用于进行极其精确的测量，以测试我们最基本的物理模型。因为分子的相互作用比原子更强烈，所以可以用来研究当每个粒子相互作用时量子物质的行为。这对于理解和设计新材料和化学工艺非常重要。超冷分子还可以用于研究量子水平上的基本化学过程，以及制造量子处理器的组件。为了实现这些应用，我们首先需要学习如何为分子制作MOT。这比原子更困难，因为激光往往会使分子旋转和振动，使它们升温而不是降温。我们之前的工作已经展示了如何克服这些困难，现在我们准备制作MOT，这是本提案的主要主题。我们将重点讨论氟化钙（CaF）分子。这些将被减慢到静止，然后在MOT中被捕获，在MOT中，多个激光频率将被用来冷却和捕获它们。我们的模拟显示，CaF会冷却到大约1毫开尔文。对于许多应用程序来说，这是一个很好的起点，但对于其他应用程序来说仍然不够冷。为了达到更低的温度，CaF将与Rb原子混合，后者很容易冷却到微开尔文的温度。我们将研究这两种物质在磁场和微波场中的碰撞。在最佳条件下，CaF会与Rb一起升温，使我们能够将它们的温度降低到1微开尔文左右。

In a magneto-optical trap (MOT), a combination of precisely-tuned laser light and a magnetic field is used to cool atoms to temperatures below 1 milli-Kelvin and trap them for minutes at a time. For over 25 years the MOT has been at the heart of all applications that use ultracold atoms. These include state-of-the-art instruments such as atomic clocks, magnetometers, gravimeters and accelerometers, measurements of constants, and a wide range of studies into the properties and behaviour of matter in the quantum regime. The potential applications of ultracold molecules go even further. They can be used as sensitive field sensors, and for making extremely precise measurements that test our most fundamental models of physics. Because molecules interact more strongly than atoms they can be used to study how quantum matter behaves when every particle is interacting with every other. This is important for understanding and designing new materials and chemical processes. Ultracold molecules can also be used to study fundamental processes in chemistry at the quantum level, and to make components of a quantum processor. To realize these applications, we first need to learn how to make a MOT for molecules. This is more difficult than for atoms because the laser light tends to set molecules rotating and vibrating, heating them up instead of cooling them down. Our previous work has shown how to overcome these difficulties, and we are now ready to make the MOT, which is the main subject of this proposal.We will focus on calcium fluoride (CaF) molecules. These will be slowed to rest and then captured in the MOT where multiple laser frequencies will be used to cool and trap them. Our simulations show that the CaF will cool to about 1 milli-Kelvin. This is an excellent starting point for many applications, but still not cold enough for others. To reach even colder temperatures, the CaF will be mixed with Rb atoms which are easy to cool to micro-Kelvin temperatures. We will investigate the collisions between these two species in a magnetic field and in a microwave field. Under optimum conditions, the CaF will thermalize with the Rb, allowing us to reduce their temperature to about 1 micro-Kelvin.