Zeeman Sisyphus Deceleration of Molecules

分子的量子力学特性可以用来揭示我们宇宙的基本性质。相互作用的分子阵列可以用来模拟材料和探测量子系统。分子的内部结构可以作为灵敏的探针来测量基本常数。冷控制分子之间的反应和碰撞可以用来研究量子化学。通过这些应用，分子提供了一条很有前途的途径来推进我们对自然的理解。为了实现这些机会，我们必须将分子冷却到非常低的温度。这可以通过应用从超冷原子实验中获得的知识来实现。冷却和控制原子的工作始于上个世纪，并在激光发明后迅速发展。这项工作导致了;物质的新相的实现（例如，玻色-爱因斯坦凝聚），单个原子的捕获，最精确的时钟，等等。由于分子具有强大的长程相互作用、丰富的内部结构（即振动和旋转自由度）以及与外部场的有效耦合，分子有望使我们走得更远。分子的复杂结构使它们从根本上难以冷却，因为用于原子的激光减速需要封闭的跃迁，这可能会散射数万个光子。为了克服这一点，开发了两种创造超冷分子的互补途径。第一种是间接技术，使用超冷原子样品并将它们结合形成分子。这些技术需要由激光冷却原子组成的分子，通常形成双碱分子。这些分子具有非常复杂的内部结构。第二种途径是直接冷却：分子首先被创造出来，然后被减速。已经开发了各种减速技术，包括斯塔克、塞曼和离心减速器。在过去的十年中，分子的一个子集已被激光冷却，随后被困在磁光阱。这些物种有一个小的质量，显着封闭的冷却转变，和简单的内部结构。将激光冷却扩展到重分子将需要更多的光子被散射。即使这些分子具有同样的闭合跃迁，减慢的效率也会降低，需要更多的激光。这增加了实验的复杂性和成本。在这个项目中，我们将测试一种新型的减速器，它只需要几百个光子。一个分子穿过一个空间变化的磁场，当它接近一个高场区域时，它被光学泵浦到一个弱场寻求状态，然后当它接近一个低场时，它被光学泵浦到一个强场寻求状态。因此，分子不断地失去能量并减慢速度。由于这种减速器使用磁场来去除能量，而不是光子反冲，因此分子的质量无关紧要。因此，这种技术适用于更大类别的分子，它们所需要的只是磁矩。我们将使用一氟化钙分子的低温束来演示减速器。该项目的结果将直接与激光冷却数据相比较，并且很容易用不同的分子实现。

The quantum mechanical characteristics of molecules can be used to reveal fundamental properties of our universe. Arrays of interacting molecules can be used to mimic materials and probe quantum systems. The internal structure of molecules can be used as sensitive probes to measure fundamental constants. Reactions and collisions between cold controlled molecules can be used to investigate quantum chemistry. With these applications molecules offer a promising route to advancing our understanding of nature. To realise these opportunities, we must cool molecules down to very low temperatures. This can be done by applying the knowledge gained from ultracold atomic experiments. Work on cooling and controlling atoms started in the last century and advanced rapidly following the invention of the laser. This work led to; the realisation of novel phases of matter (e.g., Bose-Einstein condensates), the trapping of individual atoms, the most precise clocks, and much more. Molecules promise to take us even further due to their strong, long-range interactions, rich internal structure (namely vibrational and rotational degrees of freedom) and efficient coupling to external fields. The complex structure of molecules makes them fundamentally harder to cool as laser slowing, used for atoms, requires closed transitions which can scatter tens of thousands of photons. To overcome this, two complimentary routes to creating ultracold molecules developed. The first is indirect techniques using samples of ultracold atoms and associating them to form molecules. These techniques require molecules made up of laser-coolable atoms, generally forming bialkali molecules. These molecules have a very complicated internal structure. The second route is direct cooling: molecules are created first and then decelerated. Various deceleration techniques have been developed including Stark, Zeeman and centrifuge decelerators. Over the last decade, a subset of molecules has been laser cooled and subsequently trapped in a magneto-optical trap. These species have a small mass, remarkably closed cooling transitions, and simple internal structure. Extending laser cooling to heavy molecules would require many more photons to be scattered. Even if those molecules have equally closed transitions, the slowing will be less efficient and require more lasers. This both increases the complexity and the cost of an experiment. In this project we will test a new type of decelerator which requires only a couple of hundred photons. A molecule travels through a spatially varying magnetic field, it is optically pumped into a weak-field seeking state each time it approaches a high field region and then into a strong-field seeking state as it approaches a low field. The molecule therefore constantly loses energy and slows down. As this decelerator uses magnetic fields to remove energy as opposed to photon recoil, the mass of the molecule irrelevant. This technique is therefore applicable to a much larger class of molecules, all they need is a magnetic moment. We will demonstrate the decelerator using a cryogenic beam of calcium monofluoride molecules. The results of this project will be directly comparable to laser cooling data and would be readily implemented with different molecules.